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A&P
Test 4
| Question | Answer |
|---|---|
| Know the 5 characteristics of skeletal muscle. | Contractility Contractility Excitability Extensibility Elasticity |
| Contractility | ability of the muscle to shorten. |
| Excitability | can be stimulated by chemical signals, nerves and stretch. |
| Conductivity | the signal for a muscle to contract is spread from the point of stimulation throughout the entire muscle. |
| Extensibility | ability of a muscle and muscle cell to be stretched. |
| Elasticity | ability to return to normal size & shape after being stretched. |
| Know the two structures that meet at the neuromuscular junction. | the motor neuron meets muscular material at an axion terminal |
| Know which structures make up the presynaptic? | axon terminal of motor neuron |
| Know which structures make up the postsynaptic membranes? | sacrolemma of muscle fiber/motor end plate |
| functions of tropomyosin. | is a protein involved in skeletal muscle contraction and that wraps around actin and prevents myosin from grabbing it |
| functions of troponin | tropomyosin blocks the attachment site for the myosin crossbridge, thus preventing contraction. |
| Know the function of myoglobin | is a protein found in muscles that binds oxygen with its heme group like hemoglobin. |
| Know the function of creatine phosphate | which is a source of ATP which in turn provides your body with energy. |
| Define motor unit. | motor neuron and the skeletal muscle fibers innervated by that motor neuron's axonal terminals. |
| Define isometric | relating to or denoting muscular action in which tension is developed without contraction of the muscle. |
| Define isotonic contractions | generate force by changing the length of the muscle and can be concentric contractions or eccentric contractions |
| Know the steps in muscle contraction. 1/2 | 1. Neuron action potential arrives at end of motor neuron 2. ACH is released |
| Know the steps in muscle contraction. 3/4 | 3. ACh binds to receptors on motor end plate 4. Permeability of sarcolemma changes (Na rushes in)(an action potential is produced) |
| Know the steps in muscle contraction. 5/6 | 5.Muscle action potential sweeps into the T tubules triggering 6. release of Ca from the cisternae of the sarcoplasmic reticulum |
| Know the steps in muscle contraction. 7/8 | 7. CA binds to troponin 8. Troponin changes shape and shifts tropomyosin to expose binding sites of actin |
| Know the steps in muscle contraction. 9/10 | 9. myosin binds to actin (cross bridge is formend)(ADP released from myosin) 10. Myosin head pivots (pulling actin) |
| Know the steps in muscle contraction. 11/12 | 11. Myosin releases from actin (cross bridge is broken)(another ATP binds to myosin) 12. Myosin re-extends into "ready" position (ATP->ADP+Pi)(ADP is bound to myosin) |
| latent period | the delay between the receipt of a stimulus by a sensory nerve and the response to it. |
| contraction | the action of a functioning muscle or muscle fiber in which force is generated accompanied especially by shortening and thickening of the muscle or muscle fiber or sometimes by its lengthening isometric contraction isotonic contraction |
| relaxation during muscle contraction | |
| stimulus | is a detectable change in the internal or external environment. |
| muscle twitch | is a single contraction resulting from a threshold stimulus, where a threshold stimulus is the smallest stimulus strength that actually results in a contraction. |
| summation | in physiology, the additive effect of several electrical impulses on a neuromuscular junction, the junction between a nerve cell and a muscle cell. |
| incomplete tetanus | in which each stimulus causes a contraction to be initiated when the muscle has only partly relaxed from the previous contraction. |
| tetany | A condition that is due usually to low blood calcium (hypocalcemia) and is characterized by spasms of the hands and feet, cramps, spasm of the voice box (larynx), and overactive neurological reflexes |
| complete tetanus. | in which stimuli to a particular muscle are repeated so rapidly that decrease of tension between stimuli cannot be detected. |
| muscle tone | is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It helps maintain posture and declines during REM sleep. |
| muscle fatigue | is the decline in ability of a muscle to generate force |
| oxygen debt. | a cumulative deficit of oxygen available for oxidative metabolism that develops during periods of intense bodily activity and must be made good when the body returns to rest |
| Know 3 ways to make ATP | Cellular respiration ,Creatine phosphate breakdown, Fermentation |
| Cellular respiration | aerobic, converts glucose to 36 ATP+co2+H2O |
| Creatine phosphate breakdown | anaerobic, recharges ADP to ATP |
| Fermentation | anaerobic, converts glucose to 2 ATP + lactic acid |
| Know what causes rigor | The phenomenon is caused by the skeletal muscles partially contractin |
| Know structures found in cardiac muscle: | junctions and desmosomes |
| intercalated discs | are microscopic identifying features of cardiac muscle |
| pacemaker | This device uses low-energy electrical pulses to prompt the heart to beat at a normal rate |
| Know the term used to name the area where two neurons communicate. | SYNAPSE |
| Know what causes release of neurotransmitter from the axon terminals. | The process occurring at the axon terminal is exocytosis, which a cell uses to exude secretory vesicles out of the cell membrane. |
| neurotransmitters | are excitatory or inhibitory, and that this is due to both the neurotransmitter itself and the receptor it binds to |
| chemical synapses | specialized junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands |
| electrical synapses | mechanical and electrically conductive link between two neighboring neurons that is formed at a narrow gap between the pre- and postsynaptic neurons known as a gap junction. |
| Know the ways the effects of neurotransmitters are terminated. | enzyme binds to the neurotransmitter and breaks it apart so that the neurotransmitter can no longer fit into a receptor on the receiving cell. |
| Know the polarity of the resting membrane potential. | a potential difference between the inside of the cell( intracellular) and the outside of the cell (extracellular) across the membrane. |
| (Where is the membrane negative, where is it positive?) | negative inside positive outside |
| leakage | an occurrence in which something (such as a liquid or gas) passes through a hole in a surface |
| , chemically gated | permitting or blocking passage through a cell membrane in response to an electrical stimulus |
| Skeletal muscles make up | 40–50% of an adult’s weight |
| One function of skeletal muscle is | body movement that occurs from contraction of muscles attached to skeletal bones. |
| A second function of skeletal muscle is | maintenance of posture, which occurs by skeletal muscle contracting and thus stabilizing joints, holding the head and trunk erect, and contracting continuously during waking periods to prevent bodily collapse |
| A third function of skeletal muscle is | protection and support of internal organs within the abdominopelvic cavity by muscle layering along walls of the abdominal and pelvic cavities. |
| A fourth function of skeletal muscle is | A fourth function of skeletal muscle is storage and movement of materials via the contraction and relaxation of circular muscle bands, or sphincters, which allow the passage of materials through openings, or orifices. |
| A fifth function of skeletal muscle is. | heat production which occurs when muscles use energy to contract, noted in the second law of thermodynamics |
| Excitability | is the process of muscles responding to nervous system stimulation where neurotransmitters released by neurons bind to muscle receptors |
| Conductivity | is the process whereby an electrical change travels along the plasma membrane due to neurotransmitter molecule binding |
| Contractility | occurs when contractile proteins slide past one another causing muscle shortening and tension pulls on skeletal bones causing movement |
| Elasticity | occurs when muscles contract like coils until tension is released causing them to return back to original length |
| Extensibility | is muscle lengthening upon contraction, such as elbow flexion |
| Bundles | muscle fibers are called fascicles. |
| Dense irregular connective tissue surrounding the entire skeletal muscle is | epimysium. |
| Dense irregular connective tissue containing an extensive network of blood vessels and nerves surrounding the fascicles | perimysium. |
| The innermost areolar connective tissue layer that insulates each muscle fiber | endomysium. |
| Cordlike structures composed of three layers of dense regular connective tissue which attach muscle to bone, skin, or another muscle are | tendons |
| Thin, flattened sheets of dense irregular tissue are | aponeuroses |
| A sheet of dense irregular connective tissue external to the epimysium that separates individual muscles is | deep fascia or visceral fascia |
| Fascia composed of areolar connective tissue and adipose tissue separating muscle from skin | superficial fascia. |
| Skeletal muscle composed of a network of blood vessels delivering both oxygen and a nutrient to muscle fibers while eliminating waste products | vascularized |
| Skeletal muscle is innervated or connected to and controlled | by motor neurons. |
| Extending from the brain and spinal cord to muscle fibers are motor neurons, each having a long branched extension at its terminal end | called an axon, or nerve fiber |
| Skeletal muscle contains neuromuscular junctions which exist between axons and muscle fibers and is considered voluntary muscle, as it is consciously | controlled by the nervous system. |
| Cytoplasm of muscle fibers containing typical cellular structures is | sarcoplasm |
| Skeletal muscle fibers are approximately 10–500 micrometers in length, multinucleated, and contain. | myoblasts, or groups of embryonic cells |
| Satellite cells do not fuse with muscle fibers during development, but instead remain in the tissue until triggered | to differentiate due to muscular injury. |
| The skeletal muscle fiber, plasma membrane, is | sarcolemma |
| T-tubules, or transverse tubules, are a network of | membranous tubules or deep invaginations of the sarcolemma. |
| Sodium/potassium pumps are located along the length of the | sarcolemma and establish the resting membrane potential based on the unequal distribution of sodium and potassium ions, since sodium concentration is greater outside and potassium is greater inside. |
| Resting membrane potential accounts for the | excitability of muscle fibers |
| Voltage-gated sodium channels and voltage-gated potassium channels are located | along the sarcolemma and establish the conductivity or electrical charge of that fiber |
| The sarcoplasmic reticulum is an | internal membrane complex which encases groups of myofibrils, or contractile proteins |
| Blind sacs located at each end of individual segments of the sarcoplasmic reticulum are | terminal cisternae |
| Terminal cisternae lie adjacent to each | T-tubule and serve as calcium ion reservoirs |
| A triad, the combination of two | terminal cisternae and a central T-tubule, participates in muscle contraction |
| Two types of transport proteins and location? | calmodulin and calsequestrin are located in the sarcoplasmic reticulum and control the release of calcium ions, and thus muscle contraction |
| what percent of muscle fiber volume is made up of myofibrils, long cylindrical structures, approximately one to two micrometers in diameter that extend the length of each fiber | 80% |
| Each myofibril contains bundles of protein filaments | myofilaments |
| Two types of myofilaments exist | thick and thin. |
| Thick filaments are comprised of bundles of | 200 to 500 myosin protein molecules and are approximately 11 nanometers in diameter |
| Myosin consists of two strands, with each strand having | head and a tail. |
| Myosin heads serve as binding sites for actin or thin filaments and sites where | ATP attaches and splits into ADP and phosphate by ATPase to generate the energy for contraction |
| Thin filaments are composed of | two strands of actin protein and are approximately five to six nanometers in diameter |
| F-actin, filamentous actin, | two beaded necklaces intertwined, while |
| G-actin, globular actin, | resembles individual beads and contains a feature called a myosin binding site, where the myosin head attaches during muscle contraction. |
| Troponin and tropomyosin are regulatory proteins and make up the troponin-tropomyosin complex. | are regulatory proteins and make up the troponin-tropomyosin complex. |
| Tropomyosin | is a short, thin twisted filament that covers actin strands and myosin binding sites of non-contracting muscle. |
| Troponin | is a globular protein and binding site for Ca2+. |
| Sarcomeres are myofilaments within myofibrils, arranged | in repeating cylindrical units approximately two micrometers in length and composed of overlapping thick and thin filaments. |
| Each end of a sarcomere is delineated by | Z discs, or Z lines, positioned perpendicular to myofilaments and anchor thin filaments |
| I bands are bisected by the | Z disc, contain only thin filaments, and are pulled past thick filaments during maximal muscle contraction, at which point they disappear. |
| A bands | the central region of the sarcomere, contains the entire thick filament; thin filaments only partially overlap the thick filaments |
| H zones, or H bands, | the most central portion of the A band in a resting sarcomere, consists of only thick filaments and lack any thin filament overlap |
| M lines | thin transverse protein networks in the center of the H zone, where thick and thin filaments attach and are kept aligned during contraction and relaxation |
| Overlapping myofilaments form | light and dark regions, thus appearing striated due to size and density differences of the thin and thick filaments. |
| Nebulin is the actin-binding | protein part of the I band that is proportional in length to thin filaments and thus is responsible for thin filament length during sarcomere construction. |
| Dystrophin | anchors myofibrils adjacent to the sarcolemma to proteins in the sarcolemma, as well as internal myofilament proteins to external proteins. |
| Skeletal muscles have approximately | 300 mitochondria performing aerobic cellular respiration, myoglobin serving as an oxygen-binding molecule that also aids mitochondria in the production of ATP and phosphate, which supplies ATP anaerobically |
| Motor units are composed of a | single motor neuron and the muscle fibers it controls. |
| Motor unit size has an inverse relationship with degree of control | such that the smaller the motor neurons the greater the degree of control, as seen in eye muscles. |
| Motor unit muscle fibers are dispersed throughout the | muscle rather than clustered and produce a strong contraction in a localized area and weak contraction over a wide area. |
| Each muscle fiber has one | neuromuscular junction, or specific location, in the mid-region of a fiber where it is innervated by a motor neuron |
| The expanded tip of an axon is called the | synaptic knob, which enlarges and flattens, covering a large area of sarcolemma as well as housing synaptic vesicles containing the neurotransmitter acetylcholine within its cytosol. |
| The synaptic knob contains | calcium ion pumps that establish a concentration gradient, maintaining more calcium ions outside the neuron than inside, and voltage-gated calcium ion channels that allow calcium ions to flow down its concentration gradient. |
| The synaptic knob, due to its negative charge | based on the presence of phosphate groups, repels negatively charged vesicles. |
| A specialized region of the sarcolemma, containing numerous indentations and junction folds which increase the membrane surface area covered by the synaptic knob, is called. | motor end plate |
| The motor end plate has multiple Ach receptors, or plasma membrane protein channels, that provide for the | binding of Ach and thus the opening of these channels, allowing the entry of sodium and exit of potassium |
| A narrow, fluid-filled space separating the synaptic knob and motor end plate is called the | synaptic cleft |
| The synaptic cleft houses the enzyme acetylcholinesterase, which breaks down Ach molecules released into | the synaptic cleft |
| At rest, the skeletal muscle cell’s membrane voltage is | 90mV; this is the skeletal muscle cell’s resting membrane potential |
| Since no acetylcholine is being delivered to the muscle, the voltage-gated Na+ channels and voltage-gated K+ channels in the | sarcolemma and T-tubules are closed |
| Calcium ion is stored within the | terminal cisternae of the sarcoplasmic reticulum. |
| The contractile proteins (myofilaments) within the sarcomeres are in their | relaxed position. |
| During muscle contraction, muscle fiber decreases in | length as thick and thin filaments cause sarcomeres to shorten |
| Tension exerted on the skeleton where muscle is | attached generates movement of the body |
| Anatomy of Skeletal Muscle: | A single muscle is composed of thousands of muscle cells, also termed muscle fibers. |
| Physiology of Skeletal Muscle Contraction: | A contracting muscle decreases in length as thick and thin protein filaments within sarcomeres interact to cause sarcomeres to shorten |
| Two events occur at the neuromuscular junction | Acetylcholine from a synaptic vesicle is released and Ach binds to Ach receptors, which causes muscle fiber contraction. |
| Excitation-contraction coupling involves | propagation of an action potential triggered by the binding of Ach along the sarcolemma and T-tubules to the sarcoplasmic reticulum, stimulating the release of calcium ions |
| Crossbridge cycling involves | calcium ion binding to troponin, which triggers the sliding of thin filaments past thick and thus the shortening of sarcomeres and muscle contraction. |
| A nerve signal is passed down a motor axon, triggering the entry of | calcium ions into the synaptic knob, calcium ions then bind to proteins in the synaptic membrane, and this binding of calcium ions with synaptic vesicles triggers the release of Ach into the synaptic cleft. |
| Once Ach is released from the | synaptic knob, Ach diffuses across the synaptic cleft in the motor end plate and is available to bind with Ach receptors. |
| Myasthenia Gravis is an | autoimmune disease that occurs in about 1 in 10,000 people, primarily women between 20 and 40 years of age |
| Myasthenia Gravis is an | Antibodies attach acetylcholine receptors on the muscle, causing them to cluster together, which results in them being carried into the muscle cell by endocytosis; |
| Myasthenia Gravis is an | this loss of receptors leads to muscle weakness due to insufficient stimulation by acetylcholine. |
| Myasthenia Gravis is an | Some patients die quickly due to overall loss of physical stamina and some have a normal life span |
| Sarcolemma, T-tubules, and Sarcoplasmic Reticulum: | Excitation-Contraction Coupling |
| Binding of Ach to Ach receptors in the motor end plate triggers the opening of channels that allow | for the rapid diffusion of sodium into the muscle fiber and slow diffusion of potassium out. |
| End-plate potential is a reversal | in polarity, whereby there is a reversal in electrical charge difference at the motor end plate |
| Action potential involves two events: | depolarization, where an influx of sodium causes the sarcolemma to become more positive, and repolarization, where the flow of potassium of the sarcolemma returns the sarcolemma back to its original negative resting membrane potential of −95 millivolts. |
| Repolarization allows the muscle fiber to | generate a new action potential time and time again when stimulated by a motor neuron. |
| The period of time between depolarization and repolarization when a muscle cannot be restimulated is | refractory period. |
| When calcium is released from the sarcoplasmic reticulum and binds to globular troponin, troponin | changes shape, and the troponin-tropomyosin complex moves, exposing the myosin binding sites of actin and thus crossbridge cycling is initiated. |
| Crossbridge cycling occurs in four steps: | crossbridge formation, power stroke, release of myosin heads, and reset of myosin heads. |
| Step one in crossbridge cycling | the process of myosin heads attaching to myosin binding sites and forming a crossbridge between thick and thin filaments, is called crossbridge formation. |
| Step two in crossbridge cycling, | the process of myosin heads swiveling and pulling thin filaments past thick filaments toward the center of the sarcomere, is called a power stroke. |
| During the power stroke process | ADP and phosphate are released and the ATP binding site once again is available. |
| .Step three in crossbridge | cycling involves the binding of ATP to the ATP binding site of a myosin head, resulting in the release of the myosin head from the actin binding site. |
| Step four in crossbridge cycling | involves the enzyme ATPase splitting ATP into ADP and phosphate, resulting in a release of energy which will serve to reset the myosin head in a cocked position. |
| Changes that occur in contracted muscle are: | H zone disappearance, I band narrowing, and Z discs in one sarcomere moving closer to one another. |
| The repetitive sliding movement of thin filaments past thick is | called the sliding filament theory. |
| Relaxation involves the returning of all muscle fibers to resting state when | stimulation ceases |
| Muscle relaxation starts with | nerve signal termination, therefore preventing further release of Ach, while acetylcholinesterase continually hydrolyzes Ach in the synaptic cleft, thus dissociating it from its receptor and terminating stimulation. |
| The closing of Ach receptors at the end plate, motor end plate, action potential along the sarcolemma and T-tubules causes . | cessation |
| Following cessation | remaining calcium ions in the sarcoplasm are transported back into the sarcoplasmic reticulum’s storage, troponin reverts back to its original shape following the removal of calcium ions, and tropomyosin moves over the myosin binding sites on actin |
| Muscular Paralysis and Neurotoxins | a. Muscular paralysis may occur due to either dysfunction at the neuromuscular junction or a problem with excitation-contraction coupling. |
| Muscular Paralysis and Neurotoxins - B pt 1 | There are two types of paralysis, a spastic paralysis or a flaccid paralysis; a spastic paralysis is a paralysis where the muscles become excessively tight and motionless |
| Muscular Paralysis and Neurotoxins - B pt 2 | whereas a flaccid paralysis is where the muscles are motionless due to no muscle tension. |
| Muscular Paralysis and Neurotoxins - C pt 1 | Tetanus is a condition caused by a toxin produced by the bacterium Clostridium tetani; |
| Muscular Paralysis and Neurotoxins - C pt 2 | the toxin inhibits the release of the inhibitory neurotransmitter glycine from neurons in the spinal cord, thus leading to a spastic paralysis due to overstimulation of the muscle |
| Muscular Paralysis and Neurotoxins - D pt 1 | a. Botulism is a condition caused by a toxin produced by the bacterium Clostridium botulinum; the toxin inhibits the release of acetylcholine from the synaptic knobs, |
| Muscular Paralysis and Neurotoxins - D pt 2 | thus leading to a flaccid paralysis due to inadequate stimulation of the skeletal muscle. |
| Rigor Mortis - A | Rigor mortis is a condition that occurs at death when skeletal muscles become excessively tight and hard due to a sustained contraction |
| Rigor Mortis - B | The condition is caused by nonproduction of ATP that occurs at death. |
| Rigor Mortis - C | a. Without ATP, calcium ions cannot be pumped back into the sarcoplasmic reticulum, thus they stay attached to troponin C, which prevents tropomyosin from covering the myosin binding sites on actin. |
| Rigor Mortis - D | a. Without ATP, the actin binding site on myosin also remains open, thus the actin and myosin can lock together. |
| Rigor Mortis -E | a. Though the actin and myosin are locked together there can be no contraction, because there is no ATP to energize the contraction. |
| Rigor Mortis - F | a. Rigor mortis only lasts for a certain amount of time because lysosomal enzymes in the muscle open and cause destruction of the muscle. |
| Rigor Mortis - G | a. Forensic pathologists can use the timing of rigor mortis and its resolution to estimate the time of death of an individual. |
| Skeletal Muscle Metabolism: | The energy for skeletal muscle contraction is provided by ATP; the supply of ATP can be classified into an immediate supply, short-term supply, and long-term supply |
| The phosphagen system is an | anaerobic system which generates ATP by use of high-energy phosphate molecules. |
| ATPase hydrolyzes ATP into | ADP and phosphate, providing the muscle fiber with approximately five to six seconds of energy at maximum exertion. |
| Myokinase causes a yielding of | ATP and AMP by transferring a phosphate from one ADP to another. |
| Additional energy, ATP and creatine, | are generated by creatine kinase transfer of phosphate from creatine phosphate |
| The oxygen deficient metabolic process of generating two ATP molecules from the enzymatic break down of glucose into two pyruvate molecules | anaerobic cellular respiration, or glycolysis. |
| Insufficient oxygen during aerobic cellular respiration causes buildup of pyruvate and thus a buildup of lactic acid which will either be used by the heart as fuel to generate ATP or by the liver to produce glucose . | by gluconeogenesis |
| Aerobic cellular respiration occurs within | the mitochondria, requires oxygen, and is fueled by the pyruvate generated from anaerobic cellular respiration |
| Aerobic cellular respiration involves | the oxidation of pyruvate into carbon dioxide through metabolic pathways and the citric acid cycle |
| Pyruvate oxidation causes energy transfer to NADH and FADH2 as well as the generation of ATP in the electron transport system, a process called | oxidative phosphorylation. |
| Aerobic cellular respiration also generates | ATP from fatty acids, its preferred fuel molecule; the longer the fatty acid chain, the more ATP is generated. |
| Immediate ATP supply comes from the phosphagen system while short-term ATP supply comes from anaerobic cellular respiration, and long-term ATP supply comes from | aerobic cellular respiration. |
| Exercise intensity and duration dictate which . | ATP supply will accessed |
| Creatinine Kinase - A | a. Creatine phosphokinase is the enzyme that helps transfer a phosphate between creatine and ATP. |
| Creatinine Kinase - B | Two different forms of this enzyme are found in cardiac muscle and skeletal muscle. |
| Creatinine Kinase - C | If a person suffers a heart attack (myocardial infarction), they will release an increased amount of the cardiac form of the enzyme into the bloodstream, thus assisting the diagnosis of a myocardial infarction |
| Creatinine Kinase - D | a. If a person suffers significant damage to skeletal muscle or a degenerative muscle disease, the skeletal muscle form of this enzyme will be released into the bloodstream, thus assisting in the diagnosis of the disorder. |
| Oxygen debt occurs when | oxygen demand exceeds oxygen availability |
| Oxygen debt requires that additional oxygen be inhaled post-exercise | to restore pre-exercise oxygen. |
| Skeletal Muscle Fiber Types: | Skeletal muscle fiber types are organized into three primary categories. |
| Skeletal muscle fibers that compose a muscle are differentiated into three categories based upon two criteria: | (1) the type of contraction generated, and (2) the primary means used to for supplying ATP |
| Skeletal muscle fibers differ in | power, speed, and duration of the muscle contraction. |
| Muscle contraction power relates to | fiber diameter in that the larger the fiber, the more powerful. |
| Muscle contraction | speed depends on the number of fast-twitch and slow-twitch fibers the muscle has. |
| Higher numbers of fast-twitch fibers result in | increased muscle contraction speed. |
| Fast-twitch fibers contain fast a genetic variant of myosin ATPase, produce | a powerful contraction, initiate contraction quicker, and produce shorter contraction duration. |
| Oxidative fibers use | aerobic cellular respiration and contain an extensive capillary network, abundant mitochondria, and myoglobin |
| The ability of fibers to continue contracting for long periods of time without wearing out is called | fatigue-resistance |
| Glycolytic fibers use . | anaerobic cellular respiration; they have a limited capillary network, few mitochondria, and minimal myoglobin |
| Slow oxidative fibers contain | slow ATPase and large amounts of myoglobin, producing slower, less powerful contractions. |
| Fast oxidative fibers contain | fast ATPase and produce fast, powerful contractions |
| Fast glycolytic fibers contain | fast ATPase and produce both powerful and speedy contractions, but can only contract for short bursts. |
| Measurement of Skeletal Muscle Tension: | Muscle tension is the force generated when a skeletal muscle is stimulated to contract. |
| A single, brief muscle contraction and relaxation period in response to a single stimulus is called a twitch | a twitch |
| Threshold | is the minimum voltage required to cause a muscle twitch. |
| The delay period in a twitch after the stimulation, but before muscle contraction when there is no fiber length change, is called . | the latent period |
| The period where consecutive power strokes pull thin filaments past thick filaments and sarcomeres are shortened is called | the contraction period |
| The passive process depending on the elasticity of connectin, in which crossbridges are released and muscle tension decreases, is called | the relaxation period |
| Voltage increases cause a greater number of motor units to contract due to their | variance in sensitivity. |
| Recruitment, or multiple motor unit summation, | involves the increase in muscle tension occurring with an increase in stimulus intensity until maximum contraction is reached |
| The all-or-none law states that, if and only if a stimulus is sufficient, | will a muscle contract, otherwise no contraction will take place. |
| An increase in stimulus frequency causes greater muscle tension due to an | an insufficient time for removal of all calcium ions from the sarcoplasm. |
| Increased stimulus frequency results in the formation of more crossbridges, stronger contractions, and heat elevation, and | and thus more efficient molecular interactions such as the activity of ATPase. |
| Treppe, or the ‘warming-up’ effect, | is a stepwise increase in contraction strength |
| Wave summation, or temporal summation, occurs when | stimulation occurs so rapidly that relaxation cannot take place before the next stimulation and, therefore, contraction waves are added together |
| Incomplete tetany occurs when | tension increases and distance between waves decreases, resulting in less time for relaxation between contractions. |
| Tetany occurs when muscle fibers | ‘fuse’ and contractions become continuous without any relaxation period |
| Muscle fatigue occurs when | repetitive stimulation eventually causes a decrease in muscle tension. |
| Factors Affecting Skeletal Muscle Tension Within the Body | resting tension in the muscle, the relationship between muscle tension and resistance, how contraction force generated is dependent upon myofilament overlap, and the factors that influence muscle fatigue |
| Muscle resting tension generated by involuntary nervous muscle stimulation is | called muscle tone |
| Resting muscle tone is the | random contraction of small numbers of motor units that do not produce enough tension for movement |
| Isometric contraction occurs when | muscle tension cannot overcome resistance, therefore, muscles do not shorten and movement cannot take place |
| Isotonic contraction occurs when muscle tension overcomes resistance, | allowing for either the shortening of muscles, called concentric contraction, or the lengthening of muscles, called eccentric contraction, and thus movement |
| Sustained isometric contractions can lead | to an increase in blood pressure. |
| Individuals with hypertension should be very careful | when excessively performing isometric exercises. |
| The length-tension relationship is the degree of overlap between thick and thin filaments at the | start of contraction. |
| The length-tension curve is a graphical representation of the muscle tension related to . | its pre-contraction resting length |
| Reduced ability or inability of a muscle to produce tension due to excessive or sustained exercise and decreased glycogen stores is | called muscle fatigue. |
| Insufficient calcium ions at the neuromuscular junction and decreased synaptic vesicle numbers available for release of neurotransmitters | cause a decrease in the ability of motor neuron stimulation |
| Crossbridge cycling causes | fatigue as increased phosphate concentration of the sarcoplasm interferes with the release of phosphate from the myosin head. |
| The buildup of lactic acid in muscle has generally been accepted with the cause for muscle pain after sustained exercise; this concept is changing. | muscle pain after sustained exercise; this concept is changing. |
| Studies show that muscle pain after exercise is, in part, due to minor | muscle tearing and inflammation. |
| Exercise involving repetitive stimulation causes muscle hypertrophy, or an | increase in muscle size, mitochondria numbers, glycogen reserves, and myofibrils, and thus ATP production |
| An increase in the number of muscle fibers is termed | hyperplasia. |
| Atrophy is a decrease in muscle size | due to a lack of exercise. |
| Fibrosis occurs when muscle mass is | replaced by dense regular connective tissue, decreasing flexibility and increasing collagen fibers. |
| Anabolic steroids are | synthetic substances that mimic the actions of testosterone. |
| Over 100 different anabolic steroid preparations have been developed, | but they all require a prescription for legal use in the United States |
| Anabolic steroids only have a few accepted medical uses—among them, | the treatment of delayed puberty, certain types of impotence, and the wasting condition associated with HIV infection and other diseases |
| Because anabolic steroids stimulate the manufacture of muscle proteins, these compounds have become popular with some athletes as performance enhancers; this form of usage is detrimental to an individual’s health for numerous reasons | this form of usage is detrimental to an individual’s health for numerous reasons |
| Cardiac muscle cells: | are striated, longer than skeletal muscle cells, contain sarcomeres and multiple mitochondria, are used for aerobic respiration, and are arranged in thick bundles within the heart walls |
| Intercalated discs are comprised of | desmosomes, gap junctions, and one or two nuclei |
| Cardiac muscle is controlled by the | autonomic nervous system and stimulated by an auto rhythmic pacemaker responsible for repetitious and rhythmic heartbeat |
| Smooth Muscle Tissue: | Smooth muscle is located throughout the body, typically composing 2% of the body weight of an adult |
| Smooth muscle is located in the: | vessels of the cardiovascular system, bronchioles of the respiratory system, stomach, small intestines, large intestines of the digestive system, ureters of the urinary system, and uterus of the female reproductive system. |
| Smooth muscle is capable of | hypertrophy, increase in muscle size; and hyperplasia, increase in number via mitosis. |
| Smooth muscle cells are | small with a diameter of approximately five to ten micrometers and length of 50–200 micrometers, and are surrounded by an endomysium. |
| Smooth muscle sarcolemma contains | multiple types of calcium ion voltage-gated channels and chemically gated channels. |
| Intermediate filaments extend across the | cell along with dense bodies, and anchor to the plasma membrane. |
| The latchbridge mechanism allows | myosin heads to ‘latch on’ to actin of thin filaments and remain attached without additional ATP usage. |
| Two additional proteins are necessary for smooth muscle contraction, | Ca2+-calmodulin complex, and myosin light-chain kinase. |
| Calmodulin protein binds | Ca2+, forming Ca2+-calmodulin complex, and MLCK enzyme is activated by Ca2+-calmodulin complex to phosphorylate the myosin head of smooth muscle. |
| Smooth muscle contraction is initiated by | Ca2+, requires ATP, and involves thin filaments sliding past thick filaments. |
| Smooth muscle contraction has a | maximum tension of approximately 500 milliseconds post stimulation. |
| Smooth muscle must maintain a | contracted state for extended periods of time to maintain continuous tone in visceral walls such as the GI tract and blood vessels. |
| Smooth muscle is more | fatigue-resistant than skeletal muscle in that it has low energy requirements, and employs the use of the latchbridge mechanism, thus maintaining contraction without the need for additional ATP usage |
| Smooth muscle has a | broader length-tension curve due to the fact that it is not limited by Z discs preventing additional shortening, nor by a lack of myosin heads within its thick filaments |
| Smooth muscle contraction and relaxation is not controlled | voluntarily, but rather is controlled by the autonomic nervous system in response to the release of a specific neurotransmitter. |
| The stress-relaxation response occurs when smooth muscle is | stressed’ by being stretched for extended periods of time, eventually inducing relaxation. |
| Multiunit smooth muscle contracts | individually, whereas single-unit smooth muscle contracts in unison, or syncytium. |
| Multiunit smooth muscle contraction is controlled by the | number of motor units activated, thus the more motor units stimulated, the more tension generated. |
| Single-unit smooth muscle, or visceral smooth muscle, is typically comprised of two to three sheets, found in the walls of viscera, linked by gap junctions | two to three sheets, found in the walls of viscera, linked by gap junctions |
| Single-unit smooth muscle stimulation by the | autonomic nervous system occurs through swellings, or varicosities, of the ANS neurons that pass close in proximity to smooth muscle cells. |
| Diffuse junctions of single-unit smooth muscle | are scattered and loosely arranged receptors. |
| Presynaptic neuron | releases neurotransmitter from vesicles into synaptic cleft |
| Synaptic vesicles | contain neurotransmitter |
| Synaptic cleft | fluid filled space between pre and post synaptic membranes |
| Synaptic delay | time it takes for neurotransmitter to be released, diffuse across synaptic cleft and bind to receptors on the postsynaptic membrane |
| Postsynaptic neuron | has receptors that bind to neurotransmitter produces postsynaptic potential [PSP] (graded potential) |
| Electrical | gap junctions between cells; allows ions to flow from one neuron to the next Action potential goes directly from presynaptic neuron to postsynaptic neuron; no delay |
| In PNS | myelin is beneath neurilemma |
| In CNS | no neurilemma |
| Some axons | are not myelinated |
| PNS axons | can regenerate assuming the damage is not too severe and the damage is not too far away from the structure it innervates |
| CNS axons | regeneration limited; oligodendrocytes inhibit axon growth; lack of space in CNS; astrocytes form scar tissue that prevents axon regrowth. |
| Na+/K+ pumps | entire neuron (remember, important in change of polarity for action potential) Ca+2 pumps – axon terminals (remember, calcium is needed for release of neurotransmitters) |
| Leakage | Na+ and K+ - ions move due to a concentration gradient entire neuron |
| Chemically gated | K+ and Cl- - open in response to neurotransmitter binding to receptor; dendrites |
| Voltage gated | Na+, K+- open in response to change in polarity of membrane; axon hillock and axon |
| Voltage gated Ca+2 | open in response to change in polarity of membrane; axon terminals |
| In cytosol of neuron | K+, PO4-3, protein anions |
| In interstitial fluid | Na+ and Cl- |
| Na+, K+, and Cl | cross the membrane; protein anions and phosphate do not cross membrane. |
| Electrical gradient | difference in charge across the membrane; ions move toward oppositely charged membrane |
| Resting membrane potential | inside of membrane is negative, outside is positive |
| Chemical gradient | due to number of ions on each side of the membrane; - ions move from high to low concentration |
| Na+ | higher outside of neuron |
| K+ | higher inside of neuron |
| more excite than inhibitor hitting threshold do you get action potential | yes |
| Voltage | measurement of difference in charge across membrane |
| Resistance | due to phospholipid bilayer – no movement of charged particles |
| Resistance decreased | ion channels are open |
| Resistance increased | ion channels are closed |
| Current | movement of ions across membrane through open channels |
| Ohm’s law | current = voltage/resistance |
| increased voltage and decreased resistance | larger current |
| Resting membrane potential | polarized; negative inside and positive outside |
| Na+ moves into cell | - inside becomes positive and outside becomes negative |
| K+ moves out of cell | inside becomes more negative and outside becomes more positive |
| DEPOLARIZATION | Movement of Na+ into cell causes inside to become more positive |
| Likelihood of generating action potential | depends on whether or not the stimulus is strong enough to reach threshold |
| HYPERPOLARIZATION | Movement of K+ out of cell or Cl- into cell causes inside to become more negative |
| Likelihood of generating action potential | none; charge is moving away from threshold |
| “graded” | short distance communication; depends on strength of stimulus |
| ACTION POTENTIALS | long distance communication |
| Resting state | both Na+ and K+ channels are closed |
| Depolarization | Na+ channels open and ions move into cell |
| Threshold | if stimulus reaches threshold, an action potential occurs if stimulus does not reach threshold, nerve does not fire; no action potential |
| one neuron stimulates if threshold is reached | yes |
| Strong stimulus | – frequent depolarization of membrane and stronger action potentials Propagation through positive feedback mechanism |
| domino effect | as membrane potential is depolarized, more Na+ channels open and depolarization continues |
| One-way transmission | of nerve action potential (long distance) – down axon |
| Repolarization | Na+ channels close; K+ channels open and K+ moves out of cell- restores membrane potential to negative |
| Hyperpolarization | membrane potential becomes even more negative because K+ channels close slower than Na+ channel, so more K+ exits cell |
| Na+/K+ pump | – restore resting membrane potential by pumping 3 Na+ out and 2 K+ in (against their concentration gradients |
| RECEPTIVE SEGMENT | dendrites on postsynaptic neuron receives action potentials from presynaptic neuron |
| Excitatory postsynaptic potential (EPSP) | binding of neurotransmitter depolarizes postsynaptic |
| POSTSYNAPTIC POTENTIALS | graded potentials in postsynaptic neurons |
| Membrane polarity | becomes less negative |
| Movement of ions | through a Na+/K+ channel at the same time in opposite directions, but movement of Na+ into cell is greater than movement of K+ out of cell. membrane potential becomes more positive (closer to threshold) |
| Result | local graded depolarization |
| Function | helps trigger action potential at axon hillock of postsynaptic neuron |
| Membrane polarity | becomes more negative |
| Movement of ions | K+ diffuses out of cell or Cl- moves into cell; |
| Na+ permeability is not affected | membrane potential becomes more negative (further from threshold) |
| Result | local graded hyperpolarization |
| Function | reduces postsynaptic neuron’s ability to generate an action potential |
| Both excitatory and inhibitory | postsynaptic potentials occur at same time on neurons |
| Many EPSPs on same membrane – additive effect; | increases possibility of depolarization to threshold |
| Many IPSPs on same membrane – additive effect; | decreases possibility of depolarization to threshold |
| Sum of excitatory signals | > sum of inhibitory signals |
| Threshold reached | – get an action potential |
| Threshold not reached | – do not get an action potential |
| Sum of inhibitory signals > sum of excitatory signals | – do not get an action potential |
| Spatial summation of EPSPs | several presynaptic neurons transmit action potentials at the same time |
| Neurotransmitter is released from several neurons causing more EPSPs in a short time | Result: greater depolarization of postsynaptic membrane; action potential occurs |
| Temporal summation of EPSPs | one presynaptic neuron transmits action potentials quickly |
| More neurotransmitter released from that neuron causing more EPSPs in a short time | Result: greater depolarization of postsynaptic membrane; action potential occurs |
| Depolarization | Na+ channels open |
| Repolarization | K+ channels open |
| Hyperpolarization | K+ channels stay open longer |
| Effect of alcohol, local anesthetics and neurotoxins | – prevent opening of Na+ channels, No depolarization, no action potential |
| Effect of cooling or pressure | – blocks circulation and delivery of molecules for cell function; Slows nerve impulses, dereases pain sensation |
| Absolute refractory period | during depolarization; Na+ gates open- guarantees that action potential is all or none event and transmission one way |
| Relative refractory period | during repolarization; Na+ gates closed; K+ gates open - second action potential can occur if stimulus is larger than normal |
| Action potential reaches synaptic knob, Ca+2 moves | into axon terminal causing synaptic vesicles to release neurotransmitter |
| Diameter of axon | large diameter conducts action potentials faster because there is less resistance to flow of ions (current) |
| Unmyelinated | continuous conduction; slow |
| Myelinated | saltatory conduction; fast |
| Nodes of Ranvier/neurofibril nodes | many voltage gated Na+ and K+ channels |
| Multiple sclerosis | autoimmune demyelinating disease that affects CNS neurons - cause unknown- varied symptoms depending on nerve fibers involved |
| Guillain-Barré | autoimmune demyelinating disease that affects PNS neurons- associated with bacterial and viral infections- begins in lower extremities and progresses upward |
| Nerve impulse reaches axon terminals of | presynaptic membrane |
| Voltage | -gated calcium channels open and calcium enters axon terminal |
| Calcium binds to vesicles. | Neurotransmitter released by exocytosis |
| Neurotransmitter binds to receptors in | postsynaptic membrane |
| Neurotransmitter binding opens | ion channels in postsynaptic membrane |
| Excitation (Na+ moves into cell) | depolarization |
| Inhibition (K+ moves out of cell or Cl- moves into cell) | hyperpolarization |
| Introduction to the Nervous System: | The nervous system is composed of the brain, spinal cord, nerves, and ganglia |
| The nervous system is the body’s primary communication and control system; | it integrates and regulates body functions through electrical activity |
| Specialized nervous system cells are called | neurons |
| Receptors are specialized nervous system structures that monitor changes called | stimuli |
| After processing sensory input, | the brain and spinal cord determine what response is required. |
| The brain and spinal cord initiate a response | as motor output via nerves to effectors, including all types of muscle tissue and glands. |
| The two anatomic divisions of the nervous system are the | central nervous system and the peripheral nervous system |
| The peripheral nervous system (PNS) includes | nerves, which are bundles of neuron processes (axons), and ganglia, which are clusters of neuron cell bodies located along nerves. |
| The two functional divisions of the nervous system are the | sensory nervous system and the motor nervous system |
| The sensory nervous system is further subdivided based on | whether we are consciously aware of the stimuli that are detected |
| The somatic sensory components detect | stimuli that we consciously perceive |
| Somatic sensory receptors include | the eyes, nose, tongue, ears, skin, and proprioceptors |
| The visceral sensory components detect | stimuli that we do not consciously perceive |
| Visceral sensory receptors are located | within blood vessels and internal organs |
| The motor nervous system is responsible | for initiating and transmitting motor output from the CNS to effectors |
| The motor nervous system is further divided into | somatic motor and autonomic motor systems. |
| The somatic motor component | initiates and transmits motor output from the CNS to voluntary skeletal muscles |
| The autonomic motor component innervates and regulates | cardiac muscle, smooth muscle, and glands without our conscious control |
| The autonomic motor system is still further subdivided into | sympathetic and parasympathetic components |
| Neurons: | Neurons are excitable cells that initiate and transmit electrical signals |
| General Characteristics of Neurons - 1 | The neuron is the basic structural unit of the nervous system. |
| General Characteristics of Neurons - 2 | Neurons exhibit excitability (responsiveness to stimulation), conductivity (electrical changes that are quickly propagated along the plasma membrane), and secretion (the release of neurotransmitters). |
| General Characteristics of Neurons - 3 | Neurons have extreme longevity and are amitotic. |
| Neuron Structure - 1/2 | 1. The basic structural features of a neuron include a cell body, dendrites, and an axon. 2. The cell body, or soma, is the neuron’s control center and conducts electrical signals to the axon. |
| Neuron Structure - 3/4 | 3. The cytoplasm within the cell body is called the perikaryon. 4. Free and bound ribosomes are called the chromatophilic substance or Nissl bodies |
| Neuron Structure - 5/6 | 5. Dendrites tend to be relatively short, small processes that branch off the cell body; they conduct electrical signals toward the cell body. |
| Neuron Structure - 7/8 | 7. The axon hillock is a triangular region where the axon emanates from the cell body. 8. The cytoplasm within an axon is called axoplasm, and the plasma membrane of an axon is called an axolemma |
| Neuron Structure - 9/10 | 9. Axon collaterals are side branches of the axon. 10. Most axons and their collaterals branch extensively at their distal end into an array of fine terminal extensions called telodendria |
| Neuron Structure - 11/12 | 11. Synaptic knobs are the extreme tips of the telodendria. 12. In the synaptic knobs are numerous synaptic vesicles which contain neurotransmitter. |
| Neuron Structure- 13/14 | 13. The cytoskeleton in a neuron is composed of microfilaments, intermediate filaments, and microtubules. 14. Neurofilaments aggregate to form bundles called neurofibrils, which extend as a complex network through the neuron |
| Neuron Structure 6 | 6. The axon is typically a longer process emanating from the cell body to make contact with other neurons, muscle cells, or gland cells |
| Neuron Transport - 1/2 | 1. Axons are dependent on the cell body to provide them with and break down materials. 2. Anterograde transport is the movement of materials from the cell body to synaptic knobs |
| Neuron Transport 3/4 | 3. Retrograde transport is the movement of materials from the synaptic knobs to the cell body. 4. Fast axonal transport involves movement along microtubules by motor proteins; transport can be either anterograde or retrograde |
| Neuron Transport 5/6 | 5. Slow axonal transport results from the flow of the axoplasm and can only be moved from the cell body toward the synaptic knob. 6. Clinical View: Pathogenic Agents and Fast Axonal Transport |
| Several pathogenic agents, including herpes virus, rabies virus, polio virus, and the tetanus toxin, enter a neuron at . | the synaptic knob |
| Once inside, these pathogens | “hitch a ride” to the cell body by fast axonal transport |
| The pathogenic agents ultimately cause destruction of these neurons. | destruction of these neurons. |
| Neurons are classified structurally according to | the number of neuron processes emanating directly from the cell body |
| Structural classifications of neurons include | multipolar, bipolar, unipolar, and anaxonic neurons |
| Multipolar neurons have many dendrites and a single axon that | extends from the cell body; they are the most common type of neuron. |
| Bipolar neurons have two processes that extend from the cell body: | one dendrite and one axon |
| Unipolar neurons have a single, short neuron process that emerges from the | cell body and branches into a T |
| Unipolar neurons are also called . | pseudounipolar because they start out as bipolar neurons, but their two processes fuse into a single process |
| Unipolar neurons are composed of the combined | peripheral process and central process (from the cell body into the CNS). |
| Anaxonic neurons have only dendrites and no axon; | they do not produce axon potentials |
| Neurons are classified functionally according to the | direction the action potential travels relative to the CNS. |
| Sensory neurons are the neurons of the sensory nervous system and are responsible for | conducting sensory input from somatic and visceral sensory receptors. |
| Sensory neurons are mostly | unipolar and lie outside the CNS in posterior root ganglia |
| All motor neurons are | multipolar and lie inside the CNS. |
| Motor neurons are the neurons of the | motor nervous system, conducting motor output to the somatic and visceral effectors |
| Interneurons receive stimulation from many other neurons; | they receive, process, and store information, and “decide” how the body responds to stimuli. |
| An estimated 99% of our neurons are interneurons; | they are generally multipolar and lie entirely within the CNS |
| A nerve is a cablelike bundle of parallel axons that are components of the | peripheral nervous system |
| A nerve has three successive connective tissue wrappings | the epineurium, the perineurium, and the endoneurium |
| The epineurium is a thick layer of dense irregular connective tissue that encloses the entire nerve and | provides both support and protection |
| The perineurium is a layer of | dense irregular connective tissue that supports blood vessels and wraps fascicles (bundles of axons). |
| The endoneurium is a delicate layer of | areolar connective tissue that separates and electrically insulates each axon; it also contains capillaries that supply each axon |
| Structural classification of nerves is based upon the | CNS component from which the nerve extends |
| Cranial nerves | extend from the brain, and spinal nerves extend from the spinal cord. |
| The functional classification of nerves | is based upon the functional type of neuron a nerve contains |
| Sensory nerves contain only sensory neurons, | motor nerves contain primarily motor neurons, and mixed nerves contain both sensory and motor neurons |
| Synapses: | Two types of synapses include the chemical synapse and the electrical synapse |
| A synapse is the specific location where a | neuron is functionally connected to either another neuron or an effector |
| A chemical synapse is composed of a | presynaptic neuron, which is the signal producer, and a postsynaptic neuron, which is the signal receiver or target |
| Chemical synapses are the most common | synapses found in the human body. |
| The narrow fluid-filled gap between two neurons is called | the synaptic cleft |
| Transmission between a presynaptic and postsynaptic neuron occurs when | neurotransmitter molecules are released from the synaptic knob of the presynaptic neuron into the synaptic cleft and bind to receptors on the postsynaptic neuron |
| The synaptic delay is the time between the | neurotransmitter release from the presynaptic cell, its diffusion across the synaptic cleft, and neurotransmitter binding to receptors in the postsynaptic plasma membrane. |
| An electrical synapse is composed of a | presynaptic neuron and a postsynaptic neuron physically bound together by gap junctions that allow ion flow; there is synaptic delay in electrical synapses. |
| Nervous Tissue: | Glial Cells: Glial cells are nonexcitable and serve primarily to support and protect neurons. |
| Glial cells are found in both the CNS and PNS | the CNS and PNS |
| Glial cells are smaller | than neurons, are capable of mitosis, and do not transmit nerve signals. |
| Glial cells protect | nourish neurons, as well as provide scaffolding for nervous tissue. |
| Glial cells are critical | for the structure and normal functioning of synapses |
| There are many more glial cells | than neurons in nervous tissue. |
| Four types of glial cells are found in the central nervous system: | astrocytes, ependymal cells, microglia, and oligodendrocytes |
| Astrocytes have projections from their | surface that touch both capillary walls and neurons. |
| Astrocytes are the most abundant. | glial cell in the CNS |
| The ends of astrocyte processes are called | perivascular feet, which cover and wrap around capillaries in the brain, forming a blood-brain barrier (BBB). |
| Astrocytes regulate chemical composition of. | interstitial fluid in the brain |
| The cytoskeleton in astrocytes | strengthens and organizes nervous tissue in the CNS. |
| Astrocytes help direct the development of neurons by | secreting chemicals that regulate the formation of connections between neurons |
| When neurons are damaged and die, the space they formerly occupied is often | filled by cells produced by astrocyte division, or astrocytosis |
| Ependymal cells are ciliated simple cuboidal or simple columnar epithelial cells | that line the internal cavities of the brain and spinal cord. |
| Ependymal cells and nearby blood capillaries together form a choroid plexus, | which produces cerebrospinal fluid (CSF), a clear liquid that bathes the external surfaces of the CNS and fills its cavities |
| Microglia are typically small cells | that have slender branches extending from the main portion of the cell. |
| Microglia are phagocytic cells of the | immune system and wander through the CNS engulfing infectious agents and removing debris from dead or damaged nervous tissue. |
| Oligodendrocytes are large cells with a bulbous body and slender cytoplasmic extensions | that ensheathe portions of axons of many different neurons, forming a myelin sheath |
| Two types of glial cells are found | in the PNS: satellite cells and neurolemmocytes |
| Satellite cells are flattened cells arranged around neuronal cell bodies in a ganglion that | regulate the exchange of nutrients and waste products between neurons and their environment |
| Neurolemmocytes are flattened cells that | ensheathe PNS axons to form a myelin sheath |
| Central Nervous System - A | Neoplasms, or tumors, result from unregulated cell growth; a primary tumor originates within the organ where it is found |
| Central Nervous System - B | Primary tumors in the central nervous system typically originate in supporting tissues within the brain or spinal cord that have retained the capacity to undergo mitosis: the meninges and glial cells |
| Central Nervous System - C | Glial cell tumors are called gliomas. |
| Myelination is the process by | which part of an axon is wrapped with myelin. |
| Myelin is the | insulating covering around the axon that consists of repeating concentric layers of plasma membrane of glial cells |
| Myelination is completed by | neurolemmocytes in the PNS and by oligodendrocytes in the CNS. |
| The overlapping inner layers of the plasma membrane of a neurolemmocyte form the myelin sheath, while the periphery of the neurolemmocyte contains the cytoplasm and nucleus, and is called the | neurilemma |
| A neurolemmocyte can myelinate only a 1-millimeter portion of a single axon, and the gaps between the neurolemmocytes are called | neurofibril nodes, or nodes of Ranvier. |
| An oligodendrocyte in the CNS can | myelinate a 1-millimeter portion of many axons at once. |
| Oligodendrocytes do not form neurilemmas, | but they do have neurofibril nodes |
| Unmyelinated axons in the PNS rest in a | depressed portion of a neurolemmocyte |
| Nervous System Disorders Affecting Myelin - 1 | Multiple sclerosis is progressive demyelination of neurons in the central nervous system, accompanied by the destruction of oligodendrocytes; some function is permanently lost |
| Nervous System Disorders Affecting Myelin - 2 | . Guillain-Barré syndrome is a disorder in which inflammation causes loss of myelin from the peripheral nerves and spinal nerve roots; most people recover almost all neurologic function with little medical intervention. |
| Axon Regeneration: | A damaged axon can regenerate if the cell body remains intact and a critical amount of neurilemma remains |
| The success of PNS axon regeneration depends upon two primary factors: | the amount of damage, and the distance between the site of the damaged axon and the structure it innervates. |
| After an axon is severed, the portion proximal to the trauma | seals off and swells due to xoplasmic flow |
| The severed axon and its myelin sheath break down through Wallerian degeneration; | however, the neurilemma in the distal region survives |
| The neurilemma, in conjunction with the remaining endoneurium, forms a regeneration tube in which the axon regenerates and remyelination occurs, | under the influence of nerve growth factors released by the neurolemmocytes |
| Innervation is restored as the | axon reestablishes contact with its original structure |
| Potential regeneration of neurons within the CNS is | very limited. |
| Plasma Membrane of Neurons: | Pumps and channels in the plasma membrane, and the relative concentrations of substances between the inside and outside of neurons make transmitting electrical activity possible |
| Pumps move substances up (against) a concentration gradient, which requires | ENERGY |
| The plasma membrane of neurons contains | sodium-potassium pumps and calcium pumps |
| Channels provide the means to move a substance | down (with) a concentration gradient |
| Neurons contain passive leak channels, | chemically gated channels, and voltage-gated channels |
| Passive leak channels are always open and allow continuous. | diffusion of ions |
| Chemically gated channels are normally closed, but they open in response to | binding of a neurotransmitter |
| Voltage-gated channels are normally closed, but they open in response to | changes in electrical charge across the plasma membrane |
| There are two voltage-gated Na+ channels; | inactivation gate and an activation gate |
| There are three states of voltage-gated Na+ channels: | resting state, activation state, and inactivation state |
| In the resting state, the inactivation gate is | open and the activation gate is closed; entry of Na+ is prevented |
| In the activation state, both the inactivation gate and activation | gate are open; Na+ moves into the cell through the open gates. |
| In the inactivation state, the activation gate is | open, but the inactivation gate is temporarily closed; Na+ can no longer enter into the cell at this time. |
| Some pumps and channels are located throughout the entire neuron plasma membrane | whereas others are primarily located only in specific segments of a neuron’s plasma membrane |
| Sodium leak channels, K+ leak channels, and Na+/K+ pumps are located | throughout the entire neuron plasma membrane; these are important in establishing and maintaining the resting membrane potential |
| A typical neuron is functionally organized into four segments: | receptive segment, initial segment, conductive segment, and transmissive segment; each region differs in the primary types of channels and pumps located within its plasma membrane |
| The receptive segment includes both dendrites and the cell body, which are the regions of the neuron that | receive stimuli to excite the neuron; chemically gated cation channels and chloride channels are present and no significant number of voltage-gated channels |
| The initial segment is conventionally considered to be composed of the axon hillock; this segment contains | both voltage-gated Na+ channels and voltage-gated K+ channels |
| The conductive segment is equivalent to the length of the axon and its branches; it contains both | voltage-gated Na+ channels and voltage-gated K+ channels |
| Introduction to Neuron Physiology: | Establishing and maintaining a resting membrane potential that can be changed from its resting value is critical to neuron function |
| Voltage is the measure of the amount of difference in electrical charge; it is measured in | volts or millivolts |
| Current is the movement of charged particles across the barrier that separates the charge difference; | the greater the movement of charged particles, the greater the current |
| Resistance is the opposition to the movement of charged particles; | the larger the resistance, the lower the current. |
| Ohm’s law shows that current is directly related | to voltage and inversely related to resistance |
| In neurons, charged particles are ions; the difference in charge distribution is the | membrane potential |
| the plasma membrane phospholipid bilayer offers | resistance |
| resistance | is decreased when ion channels are open, and increased when ion channels are closed |
| current | is generated when ions diffuse across the plasma membrane |
| Potassium ions are more prevalent within a neuron’s cytosol; | Na+ and Cl- are in higher concentration in the interstitial fluid |
| A Ca2+ concentration gradient exists at | the synaptic knob |
| Gated channels are closed, including | the chemically gated channels in the receptive segment, the voltage-gated Na+ channels and voltage-gated K+ channels in both the initial segment and conductive segment, and voltage-gated Ca2+ channels in the transmissive segment. |
| plasma membrane calcium pumps constantly | pump calcium outside the synaptic knob ,thus keeping the calcium concentration outside the synaptic knob higher than that inside the knob. |
| An electrical gradient is a | difference in electrical charge between two areas; the inside of the plasma membrane is relatively negative, and the outside is relatively positive. |
| A membrane potential is the difference | in charge on either side of a plasma membrane |
| The membrane potential in a resting, excitable cell like a neuron is called a | resting membrane potential. |
| The resting membrane potential of a typical neuron is | 70 mV |
| A voltmeter is used to measure | voltage difference across the plasma membrane |
| One microelectrode is placed inside the cell and another outside the cell; the voltmeter measures | the voltage difference across the membrane; the resultant value is negative in that the inside of the cell is relatively more negative |
| Establishing and maintaining the RMP is dependent upon | the distribution of Na+, K+, and Cl-ions along with other substances, such as charged phosphate ions and components of organic molecules and negatively charged proteins |
| The RMP is chiefly a consequence of the movement of | ions across the plasma membrane through the leak channels (both K+ leak channels and Na+ leak channels). |
| Potassium diffusion is the most important factor in establishing | resting potential |
| The loss of K+ into the interstitial fluid leaves relatively more negatively charged structures inside the cell; | this movement is with the chemical gradient but opposed to the electrical gradient |
| Na+ enters the cell through Na+ leak channels, | down its chemical concentration gradient and down the electrical gradient |
| The Na+/K+ pump has a relatively small role in maintaining resting membrane potential; for every turn of the pump, | three Na+ are pumped out of the cell, and two K+ are pumped in, accounting for about −3 mV of the resting membrane potential |
| The Na+/K+ pumps have a more significant role in maintaining | the chemical concentration gradients of Na+ and K+. |
| Physiologic Events in the Neuron Segments: | Excitatory and inhibitory postsynaptic potentials in the receptive segment govern the activity of the neuron. |
| Graded potentials in postsynaptic neurons are called | postsynaptic potentials |
| Numerous postsynaptic potentials are typically generated in a single neuron because many neurotransmitters stimulate it simultaneously; | the type of neurotransmitter determines whether depolarization or hyperpolarization occurs |
| Excitatory neurotransmitters bind to and open chemically gated cation channels, causing the inside of the plasma membrane to be more positive than outside; | this more positive state is called an excitatory postsynaptic potential. |
| The degree of change in the resting membrane potential is dependent on the | amount of neurotransmitter bound per unit of time |
| Inhibitory neurotransmitters bind to and open chemically gated K+ or Cl− channels, causing the inside of the plasma membrane to be more | negative than outside this more negative state is called an inhibitory postsynaptic potential |
| Summation of EPSPs and IPSPs occurs at the initial segment (axon hillock); by adding together all postsynaptic potentials, | it determines if threshold membrane potential, or −55 mV, is reached. |
| Often excitatory and inhibitory neurotransmitters are released from numerous | presynaptic neurons simultaneously |
| When threshold membrane potential is reached, | it initiates an action potential along the axon. |
| Typically, thousands of EPSPs must be generated at once to | trigger an action potential |
| Spatial summation occurs when | multiple presynaptic neurons release neurotransmitter at various locations onto the receptive segment; if sufficient numbers of EPSPs are generated, an action potential is initiated |
| Temporal summation | occurs when a single presynaptic neuron releases excitatory neurotransmitter at the same location repeatedly, resulting in enough EPSPs to initiate an action potential. |
| The all or none law states that | if threshold is reached, an action potential is propagated, whereas if threshold is not reached, no action potential will be initiated. |
| The main activity of the conductive segment, or the axon, is action potential propagation; this propagation is called | a nerve signal or nerve impulse |
| The propagation of depolarization involves the sequential opening | of voltage-gated Na+ channels along the length of the axon; with the down flow of Na+ from adjacent channels bringing each successive channel to threshold |
| The propagation of repolarization occurs as | voltage-gated K+ channels in adjacent regions open sequentially along the length of the axon, returning the regions to resting membrane potential. |
| Hyperpolarization occurs when | voltage-gated K+ channels remain open longer than the time needed to reestablish the resting membrane potential, causing the inside of the neuron to be more negative than resting membrane potential. |
| A refractory period | is the brief time period after an action potential has been initiated during which an axon is either incapable of generating another action potential or a greater than normal amount of stimulation is required to generate another action potential. |
| The absolute refractory period is the | time after an action potential onset when no amount of stimulus can initiate a second action potential; the voltage-gated Na+ channels are in the inactivated state |
| The relative refractory period occurs | immediately after the absolute refractory period, and another action potential may be initiated if the stimulation of the membrane is greater than the initial stimulus; the voltage-gated Na+ channels are in the resting state |
| Local anethetics, such as lidocaine, inhibit the action of voltage-gated Na+ channels | effectively blocking the nerve signal |
| Even applying ice to a painful area can help reduce pain sensation by slowing | transmission of sensory action potentials |
| Neurotoxicity | is the damage causes to nervous tissue (neurons or glial cells) by neurotoxins |
| A toxin is a | harmful substance synthesized by an organism; neurotoxins change the normal activity of neurons |
| A neurotoxin | interacts with receptor proteins in neuron plasma membranes, disrupting the activity of voltage-dependent channels |
| Examples of neurotoxins include | Na+ channel effectors, such as tetrodotoxin, and K+ channel effectors, such as agitoxin from scorpions |
| The main activity of the transmissive segment, or the postsynaptic knobs, | is the release of neurotransmitter from synaptic vesicles |
| Prior to the arrival of an action potential, Ca2+ is in higher concentration in the interstitial fluid than in the postsynaptic knobs | due to Ca2+ pump activity. |
| When the propagated action potential reaches the synaptic knob - 1 | voltage-gated Ca2+ channels are triggered to open; Ca2+ ions flood into the cells, binding to proteins of synaptic vesicles, |
| When the propagated action potential reaches the synaptic knob - 2 | resulting in the fusion of synaptic vesicles with the plasma membrane and the release of neurotransmitter into the synaptic cleft. |
| There are two types of electrical signals associated with neurons: | graded potentials and action potentials |
| Graded potentials occur in the | receptive segment of a neuron (dendrites and cell bodies) and are due to opening of chemically gated channels; this potential establishes a local current. |
| Action potentials are generated within the | initial segment and propagated along the conductive segment of a neuron. |
| Propagation of an action potential along an axon plasma membrane varies in velocity and is influenced | primarily by two factors; one is the diameter of the axon and the other is the myelination of the axon |
| The larger the diameter of the axon, | the faster the velocity of the nerve signal |
| Myelinated axons conduct nerve signals more | rapidly than unmyelinated axons |
| Nerve fibers are classified into three groups based on their conduction velocity: | group A, group B, and group C. |
| Group A | has a conduction velocity as fast as 150 meters per second, has a large diameter, and is myelinated; this group includes most somatic sensory neurons, and all somatic motor neurons. |
| Group B | conducts at about 15 meters per second |
| Group C | conducts at 1 meter per second. |
| Sensory and motor visceral neurons, as well as some small somatic sensory neurons, are included in | groups B and C. |
| Action potentials are always propagated along an axon at the same amplitude, however their frequencies | can vary. |
| The frequency is dependent on the | stimulus strength; the stronger the stimulus strength, the faster the frequency. |
| Neurotransmitters and Neuromodulation: | Neurotransmitters are released at the synaptic cleft and their action is modified by neuromodulation |
| Neurotransmitters are various | small organic compounds, and following their release are quickly removed from the synaptic cleft |
| Neurotransmitters are classified into four groups: | acetylcholine, biogenic amines, amino acids, and neuropeptides. |
| Acetylcholine has a structure significantly different from the other | neurotransmitters |
| Biogenic amines, also called monoamines, | are derived from certain amino acids; these include catecholamines and indolamines. |
| The catecholamines are derived from | tyrosine and include dopamine, norepinephrine, and epinephrine |
| The indolamines (histamine and serotonin) are derived from | histidine and tryptophan, respectively |
| Neurotransmitters are considered excitatory if they induce | an EPSP and inhibitory if they induce an IPSP |
| Direct neurotransmitters bind to receptors on the target cell and cause the | opening of an ion channel; indirect neurotransmitters activate a second messenger pathway. |
| All features of neurotransmitters can be exemplified by the actions of | acetylcholine |
| Three features can be discussed: | synthesis, removal from synaptic cleft, and interaction with target receptors |
| Acetylcholine is enzymatically synthesized from | acetate and choline. |
| Acetylcholine is removed in the synaptic cleft primarily by the | action of the enzyme acetylcholinesterase; this breaks it down into acetate and choline |
| Some acetylcholine molecules are able to | cross the synaptic cleft to interact with the acetylcholine receptors of the target cell |
| Other actions leading to removal of a neurotransmitter substance are | reuptake into the synaptic knob and diffusion from the synaptic cleft |
| Certain prescription drugs were developed based upon their ability to | influence the amount of neurotransmitter in a synaptic cleft. |
| Neuromodulation is the | release of chemicals (called neuromodulators) from cells that locally regulate or alter the response of neurons to neurotransmitters |
| Neuromodulation generally results in either | facilitation or inhibition |
| Facilitation occurs when there | is greater response from a postsynaptic neuron, and can result from either an increased amount of neurotransmitter or an increased number of receptors on the postsynaptic neuron. |
| Inhibition occurs when there | is less response from a postsynaptic neuron, and can result from either a decreased amount of neurotransmitter or a decreased number of receptors on postsynaptic neurons. |
| Nitric oxide is an unusual | neurotransmitter, and is classified by some experts as a neuromodulator. |
| Nitric oxide is synthesized from | amino acid arginine on an ‘as needed basis’ |
| .Nitric oxide enters into presynaptic neurons to provide a retrograde means of communication | it also functions within the brain to develop memories by stimulating presynaptic neurons to increase release of neurotransmitter substa |
| Nitric oxide is released from | motor neurons that innervate blood vessels; this causes vasodilation. |
| Endocannabinoids are molecules that bind with the same receptors as the active ingredient | tetrahydrocannabitol |
| Binding of endocannabinoids decreases | neurotransmitter release from presynaptic neurons, altering learning and memory, affecting appetite, and suppressing nausea |
| Neural Integration and Neuronal Pools of the CNS: | The nervous system coordinates and integrates neuronal activity because billions of interneurons are grouped in complex patterns called neuronal pools. |
| Neuronal pools are identified based upon function into four types of circuits: | converging, diverging, reverberating, and parallel-after-discharge. |
| The converging circuit involves input that comes together at a single | postsynaptic neuron, which receives input from several presynaptic neurons |
| A diverging circuit | spreads information from one presynaptic neuron to several postsynaptic neurons, or from one pool to multiple pools |
| Reverberating | circuits utilize feedback to produce a repeated, cyclical stimulation; once activated, a reverberating circuit may continue to function until the cycle is broken by inhibitory stimuli or synaptic fatigue |
| In a parallel-after-discharge circuit, | input is transmitted simultaneously along several neuron pathways to a common postsynaptic cell. |
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zachflemings