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<p>&lt;p&gt;Physiology of the Muscular System&lt;/p&gt;</p>


the ability to be stimulated


the ability to contract or shorten


the ability to extend or stretch


cell membrane of muscle fiber


cytoplasm of the muscle fiber

sarcoplasmic reticulum (SR)

the muscle fiber's version of smooth endoplasmic reticulum; function is to temporarily store calcium

T tubules

transverse tubules, formed by inward extensions of the sarcolema; main function is to allow electrical signals to move deeper into the cell


a T tubule sandwiched between two sacs of sarcoplasmic reticulum; allows electrical impulse traveling along T tubule to stimulate the membranes of adjacent sacs of the sarcoplasmic reticulum


bundles of very fine cytoskeletal filaments that extend lengthwise along skeletal muscle fiber and almost fill the sarcoplasm

Muscle fibers contain many

mitochondria and several nuclei


segment of myofibril between two successive Z disks; contractile unit of muscle fibers

striated muscle

dark strips called "A bands", light H zone runs across the midsection of each dark A band; light stripes called "I bands", dark Z disk extends across the center of each light I band

Each myofibril

contains thousands of thick and thin myofilaments

Protein molecules that make up myofilaments

Myosin, Actin, Tropomyosin, and Toponin


makes up almost all the thick filament, "heads" are chemically attratcted to actin molecules, "heads" are known as cross bridges when attached to actin


globular protein that forms two fibrous strands twisted around each other to form the bulk of the thin filament


protein that blocks the active sites on actin molecules


protein that holds tropomyosin molecules in place

thin filaments attach to

both Z disks of a sacromere and extend part way toward the center

thick filaments do not

attach to the Z disk

neuromuscular junction

motor neurons connect to the sarcolemma at the motor endplate; is a synapse where neurotransmitter molecules transmit signals


the neurotransmitter released into the synaptic cleft that diffuses across the gap, stimulates the receptors, and initiates an impulse in the sarcolemma

M line

thick (myosin) filaments are held together and stabilized by protein molecules that form a middle line (proteins built up)

A band

the segment that runs the entire length of the thick filaments (dark)

I band

the segment that includes the Z disk and the ends of the thin filaments where they do not overlap the thick filaments (light, and only acton)

H zone

the middle region of the thick filaments where they do not overlap the thin filaments (only myosin)

elastic filaments

composed of a protein called titin, they anchor the ends of the thick filaments to the Z disk

protein molecules that make up myofilaments

myosin, actin, tropomyosin, and troponin

thin filament made of

actin, troponin, and tropomyosin

thick filament made of

myosin and their heads

cross bridges

myosin heads when attached to actin

motor endplate

motor neurons connected to the sarcolemma of a muscle fiber

motor neuron

nerve cell that carries signals from the central nervous system to muscle or gland cells

neuromuscular junction

point of contact between a motor neuron and a skeletal muscle cell


location at which a neuron can transfer an impulse to another cell

acetylcholine (Ach)

a neurotransmitter that triggers muscle contraction

sliding-filament model

The theory explaining how muscle contracts, based on change within a sarcomere, the basic unit of muscle organization, stating that thin (actin) filaments slide across thick (myosin) filaments, shortening the sarcomere; the shortening of all sarcomeres in a myofibril shortens the entire myofibril

creatine phosphate (CP)

a unique high energy molecule stored in muscles, is tapped to regenerate ATP while the metabolic pathways are adjusting to the suddenly higher demands for ATP

aerobic respiration

cellular respiration that uses oxygen, sequentially releasing energy and storing it in ATP


transports oxygen in the body


a hemoprotein that receives oxygen from hemoglobin and stores it in the tissues until needed

red fibers

muscle fibers with high levels of myoglobin, have deep red appearance

white fibers

muscle fibers that have a low content of myoglobin, light pink appearance

slow fibers

red muscle fibers that are slow to contract but have the ability to continue contracting for long periods of time

fast fibers

muscle fibers that contract rapidly and forcefully but fatigue quickly

intermediate fibers

very similar to fast fibers, although they have a greater resistance to fatigue.

lactic acid

product of anaerobic respiration that accumulates in muscle tissue during exercise and causes a burning sensation

motor unit

a motor neuron and all the muscle cells it stimulates

motor nerve

a nerve that passes toward or to muscles or glands

somatic motor neuron

Stimulate skeletal muscle to contract, one neuron sends branches to multiple muscle fibers


process of recording the strength of muscle contraction as a result of electrical stimulation


method of graphing the changing tension of a muscle as it contracts

twitch contraction

single, brief threshold stimulus produces a quick jerk of the muscle

threshold stimulus

The minimal strength required to cause a contraction

the latent period

during which phase of the twitch contraction, is there a triggering of the release of calcium ions into the sarcoplasm

contraction phase

calcium binds to troponin and sliding of filaments occurs

relaxation phase

calcium levels fall, active sties are covered, tension falls to resting levels


gradual, steplike increase in the strength of contraction, the muscle responds with less forceful contractions and relaxations phase becomes shorter


smooth sustained contractions

multiple wave summation

if a series of stimuli come in rapid enough succession, the muscle does not have time to relax completely before the next contraction phase

incomplete tetanus

the tension is not sustained at a completely constant level

complete tetanus

if stimuli are given quickly enough, smooth sustained contraction occurs

tonic contraction

is muscle tone, helps maintain posture and position


muscles with less tone than normal


muscles with more tone than normal

spinal reflex

A simple automatic action of the spinal cord not requiring involvement of the brain, such as the knee-jerk reflex

graded strength principle

skeletal muscles contract with varying degrees of strength at different times

disuse atrophy

when prolonged inactivity results in the muscles getting smaller in size


abnormal enlargement of a body part or organ

length-tension relationship

the maximal strength that a muscle can develop is directly related to the initial length of its fibers

stretch reflex

a response in which the body tries to maintain constancy of muscle length

isotonic contraction

a contraction in which the tone or tension within a muscle remains the same as the length of the muscle changes, aka dynamic tension

concentric contractions

shortening of muscle (pick up book)

eccentric contractions

lengthening of muscle (slowly lower book)

isometric contraction

Muscle contracts but there is no movement, muscle stays the same length, aka static tension

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