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75 terms

Chapter 11

<p>&lt;p&gt;Physiology of the Muscular System&lt;/p&gt;</p>
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excitability
the ability to be stimulated
contractility
the ability to contract or shorten
extensibility
the ability to extend or stretch
sarcolemma
cell membrane of muscle fiber
sarcoplasm
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
triad
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
myofibrils
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
sarcomere
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
Myosin
makes up almost all the thick filament, "heads" are chemically attratcted to actin molecules, "heads" are known as cross bridges when attached to actin
actin
globular protein that forms two fibrous strands twisted around each other to form the bulk of the thin filament
tropomyosin
protein that blocks the active sites on actin molecules
troponin
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
acetycholine
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
synapse
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
hemoglobin
transports oxygen in the body
myoglobin
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
electromyography
process of recording the strength of muscle contraction as a result of electrical stimulation
myography
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
treppe
gradual, steplike increase in the strength of contraction, the muscle responds with less forceful contractions and relaxations phase becomes shorter
tetanus
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
flaccid
muscles with less tone than normal
spastic
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
hypertrophy
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