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chapter 10
anatomy
| Question | Answer |
|---|---|
| What are the functions of the skeletal muscles? | body movement, maintenance of posture, protection and support, regulating elimination of materials, heat production, |
| What are the characteristics of skeletal muscle tissue? | excitability, conductivity, contractility, elasticity, and extensibility |
| What is excitability? | the ability of a cell to respond to a stimulus (e.g., chemical, stretch) |
| What is conductivity? | involves an electrical change that travels along the plasma membrane as voltage-gated channels open sequentially during an action potential |
| What is contractility? | is exhibited when contractile proteins within the skeletal muscle cells slide past one another |
| What is elasticity? | is the ability of a muscle to return to its original length following either shortening or lengthening of the muscle |
| What is extensibility? | the lengthening of a muscle cell |
| Why are skeletal muscle cells often referred to as muscle fibers? | because of their potentially extraordinary length |
| What is a skeletal muscle? | an organ composed of skeletal muscle fibers, connective tissue layers, blood vessels, and nerves |
| What three layers of connective tissue occur within muscles? | the epimysium, the perimysium, and the endomysium |
| What are the functions of the layers of connective tissue? | provide protection, sites for distribution of blood vessels and nerves, and a means of attachment to the skeleton or other structures within the body |
| What is the epimysium? | layer of dense irregular connective tissue that surrounds the whole skeletal muscle |
| What is the perimysium? | surrounds the fascicles, dense irregular tissue sheath of the perimysium contains extensive arrays of blood vessels and nerves that branch to supply muscle fibers within each individual fascicle |
| What is the endomysium? | the innermost connective tissue layer, a delicate, areolar connective tissue layer that surrounds and electrically insulates each muscle fiber, it contains reticular protein fibers to help bind muscle fibers together and support capillaries |
| What is a tendon? | a thick, cordlike structure composed of dense regular connective tissue |
| Tendons attach to what? | bones |
| What is an aponeurosis? | thin, flattened sheet of dense irregular tissue |
| What is deep fascia or visceral muscular fascia? | additional expansive sheet of dense irregular connective tissue that is external to the epimysium |
| What is the function of deep fascia? | separates individual muscles, binds together muscles with similar functions, contains nerves, blood vessels, and lymph vessels and serves to fill spaces between muscles |
| What is the superficial fascia layer composed of? | areolar connective tissue and adipose connective tissue that separates muscle from skin |
| What is the function of blood vessels in skeletal muscle? | deliver both oxygen and nutrients to the muscle fibers, they also remove waste products produced by the muscle fibers |
| Is skeletal muscle vascularized or avascularized? | vascularized |
| What is skeletal muscle innervated by? | motor neurons |
| What does innervated mean? | functionally connected to and controlled by |
| What is an axon? | a long extension of a motor neuron |
| What is the neuromuscular junction? | the junction between the axon and the muscle fiber itself |
| Skeletal muscle is classified as what kind of muscle, because the muscle fibers can be consciously controlled by the nervous system? | voluntary muscle |
| What are skeletal muscle fibers? | the cells forming a muscle |
| What is the sarcoplasm? | the cytoplasm in skeletal muscle fibers |
| How big is a skeletal muscle fiber typically in diameter? | 10 and 500 micrometers (um) |
| What are myoblasts? | groups of embryonic cells |
| Skeletal muscle fibers (are, are not) multinucleated? | are |
| What does multinucleated mean? | they have numerous nuclei |
| What are satellite cells? | the myoblasts that do not fuse with muscle fibers during development and instead remain in adult skeletal muscle tissue |
| What is the sarcolemma? | the plasma membrane of a skeletal muscle fiber |
| What are T-tubules? | deep invaginations of the sarcolemma |
| What are myofibrils? | 80% of the volume of a skeletal muscle fiber, long cylindrical structures |
| How many myofibrils does a skeletal muscle fiber contain? | hundreds to thousands |
| What is the sarcoplasmic reticulum? | an internal membrane complex that is similar to the smooth endoplasmic reticulum of other cells |
| What are terminal cisternae? | blind sacs at either end of individual sections of the sarcoplasmic reticulum |
| What are myofilaments? | are contractile proteins that are bundled within myofibrils |
| Myofibril bundles contain how many types of myofilaments? what are they? | 2, thick filaments and thin filaments |
| What are thick filaments? | assembled from bundles of 200 to 500 myosin protein molecules |
| What are thin filaments? | approximately half of the diameter of thick filaments, they are composed of two strands of atin protein that are twisted around each other to form a helical shape |
| What two proteins are regularly associated with thin filaments? | tropomyosin and troponin |
| When tropomyosin and troponin are together, what are they called? | troponin-tropomyosin complex |
| What is tropomyosin | a short, thin, twisted filament that is a "stringlike" protein |
| What is troponin? | a globular or "ball-like" protein attached to tropomyosin |
| Troponin contains the binding site for what? | Ca2+ |
| Tropomyosin contains the binding site for what? | myosin |
| What are sarcomeres? | repeating microscopic cylindrical units |
| What are Z-discs? | composed of specialized proteins that are positioned perpendicular to the myofilaments and serve as anchors for the thin filaments |
| What is Connectin or titin? | a "cablelike" protein that extends from the Z discs to the M line through the ore of each thick filament |
| What is the function of Connectin? | stabilizes the position of the thick filament and maintain thick filament alignment within a sarcomere |
| What is dystrophin? | part of a protein complex that anchors myofibrils that are adjacent to the sarcolemma to proteins within the sarcolemma |
| What is the genetic disorder of muscular dystrophy caused by? | abnormal structure, or amounts, of dystrophin protein |
| How many mitochondria is in a typical skeletal muscle fiber? | approximately 300 mitochondria |
| What is myoglobin? | a molecule unique to muscle tissue, it is reddish, globular protein that is somewhat similar to hemoglobin, it binds oxygen when the muscle is at rest and releases it for use during muscular contraction |
| What is the function of creatine phosphate? | provides muscle fibers with a very rapid means of supplying ATP |
| What is a motor unit? | a single motor neuron and the muscle fibers it controls |
| The number of skeletal muscle fibers a single motor neuron innervates and the size of the motor unit vary and can range from small motor units that have ____ to large motor units that have _____ muscle fibers. | less than five to several thousand muscle fibers |
| What determines the degree of control of the motor unit? | the size of the motor unit |
| How many neuromuscular junction does each skeletal muscle fiber have? | one |
| What is a neuromuscular junction? | the specific location, usually in the mid-region of the skeletal muscle fiber where it is innervated by a motor neuron |
| What parts does the neuromuscular junction have? | the synaptic knob, motor end plate, and synaptic cleft |
| What is the synaptic knob? | an expanded tip of an axon |
| What does the synaptic knob cytosol house? | numerous synaptic vesicles filled with molecules of the neurotransmitter ACh |
| What are synaptic vesicles? | small membrane sacs |
| What is the motor end plate? | specialized region of the sarcolemma of a muscle fiber, it has numerous folds and indentions to increase the membrane surface area covered by the synaptic knob |
| What is the synaptic cleft? | an extremely narrow (30 nanometers) fluid-filled space separating the synaptic knob and the motor end plate |
| What enzyme resides in the synaptic cleft? | acetylcholinesterase |
| What is the function of the enzyme acetylcholinesterase? | to quickly bread down ACh molecules following their release into the synaptic cleft. |
| What is myasthenia gravis? | an autoimmune disease that occur in about 1 in 10,000 people, primarily women between 20 and 40 years of age in which antibodies attack the neuromuscular junctions, binding ACh receptors into clusters |
| What stimulates skeletal muscle fiber? | motor neuron |
| What is the first physiologic event of skeletal muscle contraction? | muscle fiber excitation by a somatic motor neuron - an event that occurs at the neuromuscular junction and results in release of ACh and its subsequent binding to ACh receptros |
| A nerve signal is propagated (down, up) a motor axon. | down |
| What is the second physiologic event of skeletal muscle contraction? | excitation-contraction coupling- an event that involves the sarcolemma, t-tubules, and sarcoplasmic reticulum in which this event "couples" or links the events of skeletal muscle stimulation at the neuromuscular junction to the events of the third step |
| What is an end-plate potential? | minimum voltage change in the motor end plate that can trigger opening of voltage-gated channels in the sarcolemma to initiate an action potential |
| What are the four steps of crossbridge cycling? | (1) crossbridge formation, (2) power stroke, (3) release of myosin head from actin, (4) resetting of myosin head |
| What is creatine kinase? | the enzyme that helps transfer a phosphate between creatine and ATP |
| The short-term means of supplying ATP is through what? | glycolysis |
| The long-term means of supplying ATP is through what? | aerobic cellular respiration that occurs within mitochondria |
| Aerobic cellular respiration requires what ? | the presence of oxygen |
| The amount of ATP generated is dependent upon what? | the length of the fatty acid chain |
| The longer the chain, the (less, more) ATP produced. | more |
| Glycolysis does not require what? | oxygen |
| What are the preferential fuel molecule for generating ATP in most skeletal muscle tissues? | fatty acids |
| What must be present when using fatty acids? | oxygen |
| The use of immediate, short-term, and long-term sources for supplying ATP is dependent upon what? | both the intensity and duration of an activity |
| What is oxygen debt? | the amount of additional oxygen that is consumed following exercise to restore pre-exercise conditions |
| Skeletal muscle fibers that compose a muscle are differentiated into three categories based on two criteria, what are the criteria? | (1) the type of contraction generated and (2) the primary means used for supplying ATP |
| How do skeletal muscle fibers differ? | power, speed, and duration of the muscle contraction generated |
| Power is what? | related to the diameter of a muscle fiber; large muscle fibers have a larger number of myofibrils in parallel, allowing them to produce a more powerful contraction |
| What are the characteristics of a fast-twitch fiber? | they produce a strong contraction, initiate a contraction more quickly following stimulation, and produce a contraction of shorter duration |
| What do oxidative fibers specialize in? | providing ATP through aerobic cellular respiration and have several feature that support these processes, including an extensive capillary network, large numbers of mitochondria, and a large supply of the red pigment myoglobin |
| What are red fibers? | the presence of both myoglobin and mitochondria gives these fibers a red appearance |
| What are fatigue-resistant? | higher levels of ATP generated provide energy for oxidative fibers to continue contracting for extended periods of time without tiring or fatiguing |
| What do glycolytic fibers specialize in ? | providing ATP through glycolysis, they have fewer structures needed for aerobic cellular respiration - they have less extensive cappliary networks, fewer mitochondria, and smaller amounts of myoblogin |
| What are white fiber? | the relatively small amount of myoglobin and mitochondria is why these fibers have a white appearance |
| What is fatigable? | glycolytic fibers generally tire easily after a short time of sustained muscular acidity |
| What are the three subtypes of contraction? | slow oxidative fibers, fast oxidative fibers, and fast glycolytic fibers |
| What is muscle tension? | the force generated when a skeletal muscle is stimulated to contract |
| What is a twitch? | a single, brief contraction period and then relaxation period of a skeletal muscle in response to a single stimulation |
| What is a threshold? | the minimum voltage needed to stimulate the skeletal muscle to generate a twitch |
| What is the voltage below the threshold? | subthreshold stimulus |
| What is a latent period? | a delay that occurs after the stimulus is applied and before the contraction of the muscle fiber begins |
| What kind of change in fiber length is there during the latent period? | none |
| When does the contraction period begin? | |
| When does the relaxation period begin? | begins with release of crossbridges resulting from return of Ca2+ back into the sarcoplasmic reticulum; muscle tension decreases during muscle relaxation |
| What does relaxation depend on? | the elasticity of Connectin within muscle tissue to return to its original length following shortening of a muscle |
| Skeletal muscles (do, do not) completely relax even when at rest. | do not |
| What is muscle tone? | the resting tension in a muscle generated by involuntary nervous stimulation of the muscle |
| What is resting muscle tone? | this random contraction of small numbers of motor units causes the muscle to develop tension |
| The random contractions of resting muscle tone (do, do not) generate enough tension to cause movement. | do not |
| Muscle tone (increases, decreases) during deep sleep. | decreases |
| What two factors should be considered when describing the consequences of consciously initiating muscle contraction? | (1) force generated by the muscle (2) resistance (load) that must be overcome |
| When muscle tension is insufficient to overcome the resistance, what happens? | there is no movement of the muscle |
| What is isometric contraction? | when the muscle tension is insufficient to overcome the resistance in which there is no movement of the muscle |
| Ex of isometric contraction? | pushing on a wall, holding a very heavy weight in the gym while your arm does not move |
| What is isotonic contraction? | when muscle tension results in movement of the muscle |
| Ex of isotonic contraction? | lifting a baby, swinging a tennis racket |
| What is concentric contraction? | shortening of muscle because the muscle tension is greater than the resistance |
| Ex of concentric contraction? | lifting a baby |
| What is eccentric contraction? | lengthening of a muscle because the muscle exerts less force than that needed to move the load, and the muscle lengthens |
| Ex of eccentric contraction? | placing a baby in a crib |
| What is the length-tension relationship? | a factor that influence the amount of tension a muscle can generate when stimulated is the amount of overlap of thick and thin filaments when the muscle begins its contraction |
| What is the length-tension curve? | a muscle generates different amounts of tension dependent its length at the time of stimulation |
| What is muscle fatigue? | the reduced ability or inability of the muscle to produce muscle tension |
| What is the primary cause of muscle fatigue? | decrease in glycogen stores in excessive or sustained exercise ex running a marathon |
| What is hypertrophy? | increase in muscle size |
| What is atrophy? | lack of exercise or muscle use results primarily in decreasing the muscle fiber size which causes a decrease in muscle fiber size, tone, and power, and the muscle becomes flaccid |
| What is hyperplasia? | limited increase in the number of muscle fibers |
| When does a slow, progressive loss of skeletal muscle mass typically occur? | in a person's mid 30s |
| What is fibrosis? | the process by which muscle mass is often replaced by dense regular connective tissue |
| What are cardiac muscle cells? | individual muscle cells arranged in thick bundles within the heart wall, they branch and are both shorter and thicker than skeletal muscle fibers |
| What is the diameter and length of cardiac muscle cells? | diameter of about 15um and range in length from 50 to 100 um |
| What are intercalated discs? | unique to cardiac muscles; they are composed of desmosomes and gap junction, have only one or two nuclei |
| Characteristics of cardiac muscle cells | striated because they contain sarcomeres |
| What are cardiac muscle cells stimulated by? | specialized autorhythmic pacemaker |
| What is the autorhythmic pacemaker responsible for? | repetitious, rhythmic heartbeat |
| What is the function of the autonomic nervous system? | controls the rate and force of contraction of cardiac muscle |
| What is the function of smooth muscle in the cardiovascular system? | blood vessels regulate blood pressure and the distribution of blood flow |
| What is the function of smooth muscle in the respiratory system? | bronchioles control the resistance to airflow that enters and exits the air sacs of the lungs |
| What is the function of smooth muscle in the digestive system? | the stomach, small intestine, and large intestine mix and propel ingested material as it is moved along the gastrointestinal tract. |
| What is the function of smooth muscle in the urinary system? | ureters propel urine from the kidney to the urinary bladder, which eliminates urine from the body. |
| What is the function of smooth muscle in the female reproductive system? | the uterus helps expel the baby during delivery |
| Characteristics of smooth muscle cells: | they are small and fusiform shaped with a centrally located nucleus, they have a diameter of 5 to 10um and a length of 50 to 200 um |
| What is the myogenic response? | the response to being stretched |
| What is stress-relaxation response? | this happens when the smooth muscle is "stressed" by being stretched and the stretching is prolonged |
| Where is multiunit smooth muscle found? | within the eye in both the iris and ciliary muscles, composing the arrector pili muscles in the skin |
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