Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
A&P Chp. 6
The Muscular System
| Question | Answer |
|---|---|
| The Muscular System | the muscles are responsible for all types of body movement |
| 3 Basic Muscle Types | -skeletal muscle -cardiac muscle -smooth muscle |
| General Characteristics of Muscle Tissue | -skeletal and smooth muscle cells are elongated -contraction and shortening of muscles is due to the movement of myofilaments -all muscles share some terminology (myo + sarco) |
| Charactersitics of Skeletal Muscle | -attached to bones and skin -striated -voluntary -powerful -each muscle is served by 1 artery, 1 nerve, and one or more veins |
| Characteristics of Cardiac Muscle | -only in heart -striated -involuntary |
| Characteristics of Smooth Muscle | -in the walls of hollow organs -no striated -involuntary |
| Special Characteristics of Muscle Tissue | -excitability -contractility -extensibility -elasticity |
| Excitability | ability to receive and respond to stimuli |
| Contractility | ability to shorten when stimulated |
| Extensibility | ability to be stretched |
| Elasticity | ability to recoil to resting length |
| 4 Muscle Functions | -movement of bones or fluids -maintaining posture and body position -stabilizing joints -heat generation |
| Connective Tissue Sheaths of Skeletal Muscle | -endomysium -perimysium -epimysium |
| Endomysium | fine areolar connective tissue surrounding each muscle fiber |
| Perimysium | fibrous connective tissue surrounding fascicles (groups of muscle fibers) |
| Epimysium | dense regular connective tissue surrounding entire muscle |
| Direct Muscle Attachment | epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage |
| Indirect Muscle Attachment | connective tissue wrappings extend beyond the muscle as a rope-like tendon or sheet-like aponeurosis (more common attachment) |
| Microscopic Anatomy of a Skeletal Muscle Fiber | -cylindrical cell 10 to 100um in diameter, up to 30cm long -multible peripheral nuclei -many mitochondria -glycosomes for glycogen storage, myoglobin for O2 storage -also contain myofibrils, sarcoplasmic reticulum, and T tubules |
| Myofibrils Characteristics | -densely packed, rod-like elements -~80% of cell volume -exhibit striations (A bands, I bands) |
| Sarcomeres Charactersitics | -smallest contractile unit of a muscle fiber -the region of a myofibril between two successive Z discs -composed of thick and thin myofilaments made of contractile proteins |
| Features of Sarcomeres | -thick filaments -thin filaments -Z disc -H zone -M line |
| Thick Filaments | run the entire length of an A band |
| Think Filaments | run the length of the I band and partway into the A band |
| Z Disc | coin-shaped sheet of proteins that anchors the think filaments and connects myofibrils to one another |
| H Zone | lighter midregion where filaments do not overlap |
| M Line | line of protein myomesin that holds adjacent thick filaments together |
| Sarcoplasmic Reticulum Characteristics | -network of smooth endoplasmic reticulum surrounding each myofibril -pairs of terminal cisternae form perpendicular cross channels -functions in the regulation of intracellular Ca2+ levels |
| T Tubules Characteristics | -continuous with the sarcolemma -penetrate the cell's interior at each A band-I band junction -associate with the paired terminal cisternae to form triads that encircle each sarcomere |
| Triad Relationship | -T tubules conduct impulses deep into muscle fiber -integral proteins protrude into the intermembrane space from T tubule and SR cisternae membranes -T tubule proteins -SR foot proteins |
| What is T Tubule? | voltage sensors |
| What is SR Foot Proteins? | gated channels that regulate Ca2+ release from the SR cisternae |
| Contraction | -the generation of force -does not necessarily cause shortening of the fiber |
| When Does Shortening Occurs? | shortening occurs when tension generated by cross bridges on the thin filaments exceeds forces opposing shortening |
| Sliding Filament Model of Contraction | -in the relaxed state, thin and thick filaments overlap only slightly -during contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filaments toward the M line -as H zone shorten & disappear, sarcomeres, whole muscle shorte |
| Requirements for Skeletal Muscle Contraction | -activation -excitation |
| Activation | -neural stimulation at a neuromuscular junction |
| Excitation | -contraction coupling -generation and propagation of an action potential along with sarcolemma -final trigger (a brief rise in intracellular Ca 2+ levels) |
| The Neuromuscular Junction and the Nerve Stimulus 1 | -skeletal muscles are stimulated by somatic motor neurons -axons of motor meurons travel from the central nervous system via nerves to skeletal muscles |
| The Neuromuscular Junction and the Nerve Stimulus 2 | -each axon forms several branches as it enters a muscle -each axon ending forms a neuromuscular junction with a single muscle fiber. |
| Neuromuscular Junction Characteristics 1 | -situated midway along the length of a muscle fiber -axon terminal and muscle fibers are separated by a gel-filled space called the synaptic cleft |
| Neuromuscular Junction Characteristics 2 | -synaptic vesicles of axon terminal contain the neurotransmitter acetylcholine (ACh) -junctional folds of the sarcolemma contain ACh receptors |
| Events at the Neuromuscular Junction | -nerve impulse arrives at axon terminal -ACh is released and binds with receptors on the sarcolemma -electrical events lead to the generation of an action potential |
| Excitation | -contraction (E-C) coupling -sequence of events by which transmission of an AP along the sarcolemma leads to sliding of the myofilaments -latent period -AP is propagated along sarcomere to T tubules -voltage |
| Latent Period | -time when E-C coupling events occur -time between AP initiation and the beginning of contraction |
| Voltage | -sensitive proteins stimulate Ca2+ release from SR -Ca2+ is necessary for contraction |
| At Low Intracellular Ca2+ Concentration | -tropomyosin blocks the active site on actin -myosin heads cannot attach to actin -muscle fiber relaxes |
| At High Intracellular Ca2+ Concentration | -Ca2+ binds to troponin -troponin changes shape and moves tropomyosin away from active sites -events of the cross bridge cycle occur -when nervous stimulation ceases, Ca2+ is pumped back into the SR and contraction ends |
| Cross Bridge Cycle | 1. cross bridge formation 2. working stroke 3. cross bridge detachment 4. "cocking" of the myosin head *continues as long as the Ca2+ signal and adequate ATP are present* |
| Motor Unit | -the nerve-muscle functional unit -a motor neuron and all muscle fibers it supplies |
| Muscle Twitch | -response of a muscle to a single, brief threshold stimulus -simplest contraction observable in the lab |
| Three Phases of a Twitch | -Latent Period: events of excitation-contraction coupling -Period of Contraction: cross bridge formation; tension increases -period of relaxation: Ca2+ reentry into the SR; tension declines to zero |
| Muscle Twitch Comparisons | Different strength and duration of twitches are due to variations in metabolic properties and enzymes between muscles |
| Graded Muscle Responses | -variations in the degree of muscle contraction -required for proper control of skeletal movement |
| Responses are Graded By | -changing the frequency of stimulation -changing the strength of the stimulus |
| Muscle Tone | -constant, slightly contracted state of all muscles -due to spinal reflexes that activate groups of motor units alternately in response to input from stretch receptors in muscles -keeps muscles firm, healthy, and ready to respond |
| Isotonic Contractions | -muscle changes in length and moves the load -isotonic contractions are either concentric or eccentric |
| Concentric Contractions | the muscle shortens and does work |
| Eccentric Contractions | the muscle contract as it lengthens |
| Isomeric Contractions | -the load is greater than the tension the muscle is able to develop -tension increases to the muscle's capacity, but the muscle neither shortens or lengthens |
| Muscle Metabolism | -energy for contraction -ATP is the only source used directly for contractile activities -available stores of ATP are depleted in 4-6 seconds |
| ATP is Regenerated By... | -direct phosphorylation of ADP by creatine phosphate (cp) -anaerobic pathway (glycolysis) -aerobic respiration |
| Anaerobic Pathway at 70% of Maximum Contractile Activity | -bulging muscles compress blood vessels -oxygen delivery is impaired -pyruvic acid is converted into lactic acid |
| Lactic Acid | -diffuses into the bloodstream -used as fuel by the liver, kidney, and heart -converted back into pyruvic acid by the liver |
| Anaerobic Pathway | -produces 95% of ATP during rest and light to moderate exercise |
| Fuels | -stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids |
| Muscle Fatigue | -physiological inability to contract -total lack of ATP occurs rarely, during states of continuous contraction, and causes contractures |
| Muscle Fatigue Occurs When | -ionic imbalances interfere with E-C coupling -prolonged exercise damages the SR and interferes with Ca2+ regulation and release |
| Oxygen Deficit; Extra O2 Needed After Exercise for | -replenishment of oxygen reserves, glycogen stores, ATP and CP reserves -conversion of lactic acid to pyruvic acid, glucose and glycogen |
| Heat Production During Muscle Activity | - ~40% of the energy released in muscle activity is useful as work -remaining energy (60%) given off as heat -dangerous heat levels are prevented by radiation of heat from the skin and sweating |
| Velocity and Duration of Contraction are Influenced by | 1. Muscle Fiber Type 2. Load 3. Recruitment |
| Muscle Fiber Type is Classified According to Two Characteristics | 1. speed of contraction 2. metabolic pathways for ATP synthesis |
| Speed of Contraction | -speed at which myosin ATPases split ATP -pattern of electrical activity of the motor neurons |
| Metalolic Pathways for ATP Synthesis | -oxidative fibers (aerobic pathways) -glycolytic fibers (anaerobic pathways) |
| Three Types of Muscle Fiber Type | 1. slow oxidative fibers 2. fast oxidative fibers 3. fast glycolytic fibers |
| The Overload Principle | -forcing a muscle to work hard promotes increased muscle strength and endurance -muscles adapt to increased demands -muscles must be overloaded to produce further gains |
| Smooth Muscle | -found in walls of most hollow organs except heart -usually in two layers (longitudinal and circular) |
| Peristalsis | -alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through the lumen of hollow organs |
| Longitudinal Layer of Peristalsis Contracts | organ dilates and shortens |
| Circular Layer of Peristalsis Contracts | organ constricts and elongates |
| Microscopic Structure | -spindle-shaped fibers -connective tissue (endomysium only) -SR -pouchlike infoldings of sarcolemma sequester Ca2+ -no sarcomeres, myofibrils, or T tubules |
| Spindle-Shaped Fibers | thin and short compared with skeletal muscle fibers |
| Innervation of Smooth Musae | -autonomic nerve fibers innervate smooth muscle at diffuse junctions -varicosities (bulbous swellings) of nerve fibers store and release neurotransmitters |
| Myofilaments in Smooth Muscle 1 | -ratio of thich to thin filaments (1:13) is much lower than in skeletal musche (1:2) -thick filaments have heads along their entire length -no troponin complex; protein calmodulin binds Ca2+ |
| Myofilaments in Smooth Muscle 2 | -myofilaments are spirally arranged, causing smooth muscle to contract in a corkscrew manner -dense bodies: proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals |
| Contraction of Smooth Muscle 1 | -slow, synchronized contractions -cells are electrically coupled by gap junctions -some cells are self-excitatory (depolarize w/out external stimuli); act as pacemakers for sheets of muscle |
| Contraction of Smooth Muscle 2 | -rate and intensity of contraction may be modified by neural and chemical stimuli -sliding filament mechanism -final trigger is increase intracellular Ca2+ -Ca2+ is obtained from the SR and extracellular space |
| Role of Calcium Ions | -Ca2+ binds to and activates calmodulin -activated calmodulin activates myosin kinase -activated kinase phosphorylates and activates myosin -cross bridges interact with actin |
| Contraction of Smooth Muscle 3 | -very energy efficient -myofilaments may maintain a latch state for prolonged contractions |
| Relaxation of Smooth Muscle Requires | -Ca2+ detachment from calmodulin -active transport of Ca2+ into SR and ECF -dephosphorylation of myosin to reduce myosin ATPase activity |
| Neural Regulation | -neurotransmitter --> increase Ca2+ in sarcoplasm; either graded (local) potential or action potential -response depends on neurotransmitter released and type of receptor molecules |
| Hormones and Local Chemicals | -may bind to G protein-linked receptors -may either enhance or inhibit Ca2+ entry |
| Stress-Relaxation Response | -responds to stretch only briefly, then adapts to new length -retains ability to contract on demand -enables organs such as the stomach and bladder to temporarily store contents |
| Length and Tension Changes | -can contract when between half and twice its resting length |
| Hyperplasia | -smooth muscle cells can divide and increase their numbers -i.e. pregnancy |
| Types of Smooth Muscle | -single-unit (visceral) smooth muscle -multiunit smooth muscle |
| Single-Unit Smooth Muscle | -sheets contract rhythmically as a unit (gap junction) -often exhibit spontaneous action potentials -arranged in opposing sheets and exhibit stress-relaxation response |
| Multiunit Smooth Muscle | -located in large airways, large arteries, arrector pili muscles, and iris of eye -gap junctions are rare -arranged in motor units -graded contractions occur in response to neural stimuli |
| Motor Unit 1 | -small motor units in muscles that control fine movements -large motor units in large weight-bearing muscles |
| Motor Unit 2 | -muscle fibers from a motor unit are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle -motor units in a muscle usually contract asynchronously; helps prevent fatigue |
Created by:
PRO Teacher
lsearls
Popular Biology sets