Skeletal Muscle Physiology: A & P Exam 3

characteristics of muscles

excitability, conductivity, contractility, extensibility, elasticity

skeletal muscle

voluntary, striated muscle usually attached to bones

striations

alternating light and dark transverse bands

voluntary

usually subject to conscious control

endomysium

connective tissue around muscle cell

perimysium

connective tissue around muscle fascicle

fascicle

group of muscle fibers

epimysium

connective tissue surrounding entire muscle

tendons

attachments between muscle and bone matrix

collagen

somewhat extensible and elastic, stretches slightly under tension and recoils when released

sarcolemma

plasma membrane of a muscle fiber

sarcoplasm

cytoplasm of a muscle fiber

myofibrils

long protein cords occupying most of sacroplasm

glycogen

carbohydrate stored to provide energy for exercise, store sugar

myoglobin

red pigment, provides some oxygen needed for muscle activity

multiple nuclei

flattened nuclei pressed against the inside of the sarcolemma

myoblasts

stem cells that fused to form each muscle fiber early in development

satellite cells

unspecialized myoblasts remaining between the muscle fiber and endomysium

sarcoplasmic reticulum

smooth ER that forms a network around each myofibril

t tubules

tubular infolding of the sacrolemma which penetrate through the cell and emerge on the other side

thick filaments

two chains intertwined to form a shaft-like tail, made of several hundred myosin molecules

troponin molecule

small, calcium-binding protein on each tropomyosin molecule

elastic filaments

run through core of thick filament and anchor it to Z disc and M line, prevent overstretching and provide recoil

titin

huge, springy protein tat makes elastic filament

contractile proteins

myosin and actin do the work of contraction, more overlap between thick and thin filaments

regulatory proteins

tropomyosin and troponin, less overlap between thick and thin filaments, act like a switch that determines when fiber can and cannot contract,

dusstronin

links actin in outermost myofilaments to membrane proteins that link to endomysium, muscular dystrophy

striations

alternating A-bands (dark) and I-bands (light)

A-band

dark,

H-band

not as dark, middle of A-band, thick filaments only

M-band

middle of H-band

I-band

light

Z-disc

provides anchorage for thin filaments and elastic filaments, bisects I band and “zig-zags”

sarcomere

segment from Z-disc to Z-disc,

denervation atrophy

shrinkage of paralyzed muscle then nerve remains disconnected, myofiber shrinkage to myofiber death

somatice motor neurons

nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles

somatic motor fibers

their axons lead to the skeletal muscle, each nerve fiber branches out to a number of muscle fibers, 1 motor neuron= 1 motor neuron

motor unit

one nerve fiber and all the muscle fiber innervated by it

small motor units

fine degree of control, 3-6 fibers per neuron, fingers

large motor neurons

more strength than control, 1,000 muscle fibers per neuron, thigh or lower back

synapse

point where a nerve fiber meets its target cell, where two electrically contact cells come together

neuromuscular junction

when a target cell is a muscle fiber

axon terminal

swollen end of the nerve fiber, contains synaptic vesicles with acetylcholine

synaptic cleft

gap between axon terminal and sacrolemma

Schwann cell

envelops and isolates NMJ

acetylcholine

chemical carries signal from one electrically active cell to another

voltage

a difference in electrical charge from one point to another

resting membrane potential

about -90 mV, seen in a waiting excitable cell

electricity

movement of charged particles

depolarization

inside of the plasma membrane becomes positive

repolarization

loss of positive potassium ions turns the membrane negative again

spastic paralysis

a state of continual contraction of the muscles

tetanus

lockjaw, form of spastic paralysis caused by toxin clostridium tetani

flaccid paralysis

a state in which the muscles are limp and cannot contract

curare

competes with Ash for receptor sites, but does not stimulate the muscles

length-tension relationship

the amount of tension generated by a muscle depends on how stretched or shortened It was before it was stimulated

threshold

minimum voltage necessary to generate an action poteintal in the muscle fiber and produce a contraction

twitch

a quick cycle of contraction and relaxation when stimulus is at threshold or higher

latent period

very brief delay between stimulus and contraction

contraction phase

time when muscle generates external tension

relaxation phase

time when the tension decides to baseline

isometric muscle contraction

“same length”, muscles produce internal tension but external resistance causes it to stay the same length

isotonic muscle contraction

“same tension”, muscle changes in length with no change in tension

concentric contraction

muscle shortens as it maintains tension

eccentric contraction

muscle lengthens as it maintains tension

isometric phase

at the beginning of contraction, muscle tension rises but muscle does not shorten

isotonic phase

muscle begins to shorten and move the load

anaerobic fermentation

enables cells to produce ATP in the ABSCENCE of oxygen, yields little ATP and lactate

aerobic respiration

produces far more ATP, does NOT generate lactate, requires a continual supply of oxygen

myokinase

enzyme that moves phosphate around, transfers P_i from one ADP to another, converting the latter to ATP

creatine kinase

obtains P_i from a phosphate-storage molecule creatine phosphate (CP) and gives it to ADP

prosphagen system

the combination of ATP and CP which provides nearly all energy for short bursts of activity

anaerobic threshold

point at which lactate becomes detectable in the blood, lactate threshold

glycogen-lactate system

the pathway from glycogen to lactate

muscle fatigue

progressive weakness from prolonged use of muscles

central fatigue

when less motor signals are issued from brain

VO₂ max

the point at which the rate of oxygen consumption plateaus and does not increase further with added workload

temporal summation

the greater the frequency of stimulation, the more strongly a muscle contracts

length-tension relationship

a muscle resting at optimal length is prepared to contract more forcefully than a muscle that is excessively contracted or stretched

resistance training

contraction of a muscle against a load that resists movement

endurance training

improves fatigue-resistant muscles, enhances the function of the cardiovascular, respiratory and nervous systems

peristalsis

waves of contraction brought by food distending the esophagus or feces distending the colon

plasticity

the ability to adjust its tension to the degree of stretch

muscular dystrophy

group of hereditary diseases in which skeletal muscles degenerate and weaken and are replaced with fat and fibrous scar tissue

duchenne muscular dystrophy

caused by a sex-linked recess trait, mutation in gene for muscle protein dystrophin