Human Physiology, Vander Ch.9
Terms
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- skeletal muscle
- Striated muscle attached to bone or skin and responsible for skeletal movements and facial expression; controlled by somatic nervous system
- smooth muscle
- Nonstriated muscle that surrounds hollow organs and tubes; see also multiunit smooth muscle, single-unit smooth muscle
- cardiac muscle
- Heart muscle
- muscle fiber
- Muscle cell
- myoblasts
- Embryological cell that gives rise to muscle fibers
- satellite cells
- Undifferentiated cells found within skeletal muscle tissue that can fuse and develop into new muscle fibers following muscle injury.
- hypertrophy
- Enlargement of a tissue or organ due to increased cell size rather than increased cell number.
- muscle
- Number of muscle fibers bound together by connective tissue
- tendons
- Collagen fibre bundle that connects skeletal muscle to bone and transmits muscle contraction force to the bone.
- striated muscle
- Muscle having transverse banding pattern due to repeating sarcomere structure; see also cardiac muscle, skeletal muscle
- myofibrils
- Bundle of thick or thin contractile filaments in cytoplasm of striated muscle; myofibrils exhibit a repeating sarcomere pattern along longitudinal axis of muscle.
- sarcomere
- Repeating structural unit of myofibril; composed of thick and thin filaments; extends between two adjacent Z lines
- thick filaments
- Myosin filament in muscle cell
- thin filaments
- Actin filament in muscle cell
- actin
- Globular contractile protein to which myosin cross-bridges bind; located in muscle thin filaments and in microfilaments of cytoskeleton.
- A band
- One of the transverse bands making up repeated striations of cardiac and skeletal muscle; region of aligned myosin-containing thick filaments.
- Z line
- Structure running across myofibril at each end of striated muscle sarcomere; anchors one end of thin filaments and titin
- I band
- One of transverse bands making up repeating striations of cardiac and skeletal muscle; located between A bands of adjacent sarcomeres and bisected by Z line.
- H zone
- One of the transverse bands making up striated pattern of cardiac and skeletal muscle; light region that bisects A band.
- M line
- Transverse stripe occurring at the center of the A band in cardiac and skeletal muscle; location of energy-generating enzymes and proteins connecting adjacent thick filaments.
- titin
- Protein that extends from the Z line to the thick filaments and M line of skeletal muscle.
- contraction
- Operation of the force-generating process in a muscle cell.
- relaxation
- Return of muscle to a low force-generating state, caused by detachment of cross-bridges.
- sliding-filament mechanism
- Process of muscle contraction in which shortening occurs by thick and thin filaments sliding past each other.
- heavy chains
- Painrs of large, coiled polypeptides that make up the rod and globular head of a myosin molecule.
- light chains
- Pair of small polypeotides bound to each globular head of a myosin molecule; function is to modulate contraction.
- cross-bridge cycle
- Sequence of events between binding of cross-bridge to actin, its release, and reattachment during muscle contraction.
- power stroke
- The step of a cross-bridge cycle involving physical rotation of the globular head.
- rigor mortis
- Stiffness of skeletal muscles after death due to failure of cross-bridges to dissociate from actin because of loss of ATP.
- troponin
- Regulatory protein bound to actin and tropomyosin of striated muscle thin filaments; site of calcium binding that initiates contractile activity
- tropomyosin
- Regulatory protein capable of reversibly converting binding sites on actin; associated with muscle thin filaments.
- excitation-contraction coupling
- In muscle fibers, mechanism linking plasma membrane
- sarcoplasmic reticulum
- Endoplasmic reticulum in muscle fiber; site of storage and release of calcium ions.
- lateral sacs
- Enlarged region at end of each sarcoplasmic reticulum segment; adjacent to transverse tubule.
- transverse tubule (T-tubule)
- Tubule extending from striated-muscle plasma membrane into the fiber, passing between opposed sarcoplasmic reticulum segments; conducts muscle action potential into muscle fiber.
- junctional feet “foot proteins”
- Large extension of sarcoplasmic reticulum calcium channels (ryanodine receptors), which connect them to the T-tubule membrane and mediate excitation-contraction coupling in skeletal muscle; also known as junctional feet
- dihydropyridine (DHP) receptor
- Nonconducting calcium channels in the T-tubule membranes of skeletal muscle cells, which act as voltage sensors in excitation-contraction coupling
- ryanodine receptor
- Calcium-release channel found in the lateral sas of the carcoplasmic reticulum in skeletal muscle cells.
- motor neurons
- Somatic efferent neuron, which innervates skeletal muscle.
- motor unit
- Motor neuron plus the muscle fibers it innervates.
- acetylcholine (ACh)
- A neurotransmitter released by pre- and post-ganglionic parasympathetic neurons, preganglionic sympathetic neurons, somatic neurons, and some CNS neurons.
- motor end plate
- Specialized region of muscle cell plasma membrane that lies directly under axon terminal of a motor neuron
- neuromuscular junction
- Synapse-like junction between an axon terminal of an efferent nerve fiber and a skeletal muscle fiber.
- end-plate potential (EPP)
- Depolarization of motor end plate of skeletal muscle fiber in response to acetylcholine; initiates action potential in muscle plasma membrane
- acetylcholinesterase
- Enzyme that breaks down acetylcholine into acetic acid and choline.
- tension
- Force; see also muscle tension
- load
- External force acting on muscle.
- Isometric contraction
- Contraction of muscle under conditions in which it develops tension but does not change length
- isotonic
- Containing the same number of effectively nonpenetrating solute particles as normal extracellular fluid
- Isotonic contraction
- Contraction of muscle under conditions in which load on the muscle remains constant but muscle shortens
- concentric contraction
- Muscle activity that involves shortening of muscle length.
- Lengthening contraction (eccentric contraction)
- Contraction as an external force pulls a muscle to a longer length despite opposing forces generated by the active cross-bridges.
- twitch
- Mechanical response of muscle to single action potential
- latent period
- Period lasting several milliseconds between action potential initiation in a muscle fiber and beginning of mechanical activity
- contraction time
- Time between beginning of force development and peak twitch tension by the muscle.
- summation
- Increase in muscle tension or shortening in response to rapid, repetitive stimulation relative to single twitch
- tetanus
- Maintained mechanical response of muscle to high-frequency stimulation; also the disease lockjaw
- unfused tetanus
- Stimulation of skeletal muscle at a low-to-moderate action potential frequency that results in oscillating, submaximal force
- fused tetanus
- Skeletal muscle activation in which action potential frequency is sufficiently high to cause a smooth, sustained, maximal strength contraction.
- creatine phosphate (CP)
- Molecule that transfers phosphate and energy to ADP to generate ATP.
- oxygen debt
- Decrease in energy reserves during exercise that results in an increase in oxygen consumption and an increased production of ATP by oxidative phosphorylation following the exercise.
- muscle fatigue
- Decrease in muscle tension with prolonged activity
- Fatigue from high-intensity, short duration exercise is thought to involve at least three different mechanisms
- Conduction failure, lactic acid buildup, inhibition of cross-bridge cycling
- lactic acid
- Three-carbon molecule formed by glycolytic pathway in absence of oxygen; dissociates to form lactate and hydrogen ions.
- central command fatigue
- Muscle fatigue due to failure of appropriate regions of cerebral cortex to excite motor neurons.
- fast fibers
- Skeletal muscle fiber that contains myosin having high ATPase activity.
- slow fibers
- Muscle fiber whose myosin has low ATPase activity.
- oxidative fibers
- Muscle fiber that has numerous mitochondria and therefore a high capacity for exidative phosphorylation; red muscle fiber
- myoglobin
- Muscle fiber protein that binds oxygen.
- red muscle
- Muscle having high oxidative capacity and large amount of myoglobin.
- glycolytic fibers
- Skeletal muscle fiber that has a high concentration of glycolytic enzymes and large glycogen stores; white muscle fiber.
- white muscle
- Muscle lacking appreciable amounts of myoglobin
- slow-oxidative fibers
- Type of skeletal muscle fiber that has slow intrinsic contraction speed but fatigues very slowly due to abundant capacity for production of ATP by aerobic oxidative phosphorylation.
- fast-oxidative fiber
- Type of skeletal muscle fiber that has high intrinsic contraction speed and abundant capacity for production of ATP by aerobic oxidative phosphorylation.
- fast-glycolytic fiber
- Type of skeletal muscle fiber that has high intrinsic contraction speed and abundant capacity for production of ATP by anaerobic glycolysis.
- recruitment
- Activation of additional cells in response to increased stimulus strength; increasing the number of active motor units in a muscle.
- flexion
- Bending a joint
- extension
- Straightening a joint
- antagonists
- (muscle) muscle whose action opposes intended movement; (drug) molecule that competes with another for a receptor and binds to the receptor but does not trigger the cellÂ’s response.
- hypocalcemia
- The condition of low blood (and interstitial) calcium concentration.
- dense bodies
- Cytoplasmic structure to which thin filaments of a smooth muscle fiber are anchored.
- myosin light-chain kinase
- Smooth-muscle protein kinase; when activated by Ca-calmodulin, phosphorylates myosin light chain.
- myosin light-chain phosphatase
- Enzyme that removes high-energy phosphate from myosin; important in the relaxation of smooth muscle.
- latch state
- Contractile state of some smooth muscles in which force can be maintained for prolonged periods with very little energy use; cross-bridge cycling slows to the point where thick and thin filaments are effectively “latched” together.
- smooth muscle tone
- Smooth-muscle tension due to low-level cross-bridge activity.
- pacemaker potential
- Spontaneous gradual depolarization to threshold of some nerve and muscle cellsÂ’ plasma membrane
- Varicosity
- Swollen region of axon; contains neurotransmitter-filled vesicles; analogous to presynaptic ending
- single-unit smooth muscles
- Smooth muscle that responds to stimulation as single unit because gap junctions join muscle fibers.
- multiunit smooth muscles
- Smooth muscle that little, if any propagation of electrical activity from fiber to fiber and whose contractile activity is closely coupled to its neural input.