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chap nine muscle


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basic types of muscle tissue
skeletal- striated, voluntairy, multinucleated
cardiac- striated, involuntary- uninucleated
smooth- nonstraited, involuntary, may be multinucleated
4 important functions of muscle tissue
heat generation
maintaining posture
stabilizing joints
gross atatomy
myofibers, vv, nn, connective tissue
connective tissue
endomysium- covers each individual muscle fiber
perimysium- covers fasicles
epimysium covers entire muscle
microscopic structure of myofibers
sarcolemma- cell membrane
sarcoplasm which has gycosomes and myoglobin
myofibrils- contain the contractile elements
a band
i band
h zone
a band is the dark striation
the lighter stipe in the middle of the A band is the H zone and the dark line in the middle of the H Zone is the Z- Disc
I band
m line
I band is the light striation and the m line is a dark line through the light striation
function role of myofibrils
once triggered, they bind and cause contraction of sarcomere
function role of sarcoplasmic reticulum
storage of Calcium ion
transverse tubules
allows action potential to run throughout the entire fascicle
sliding filament mechanism of skeletal muscle contraction
myosin heads attach to the exposed actin binding site and "hook and pull" them. the result is a sliding motion of the 2 proteins
define motor unit
a motorneuron and the muscle fibers it supplies.
how does the cell become polarized?
1. nerve impulse opens Calcium channels allowing Calcium ions to flow into neurotransmitter from extracellular fluid.
The presence of calcium causes neurotransmitter to be released into synaptic cleft. once there, the aCh fuses with receptors in the motor end plate and aCh is broken down. aCh receptors allow sodium ion and potassium ions to pass, more sodium is let in than potassium is let out. interior becomes slightly less negative
how does depolarization pass on action potential
action potential moves along the length of the sarcolemma, opening voltage gated sodium channels. sodium diffuses into cell
restores sarcolemma to polarized state. sodium channels closeing and potassium opening, potassium diffuses out of cell.
how does action potential stimulate muscle to contract?
action potential moves along the SR and down T Tubules. once it passes the triads, it triggers the terminal cisternae to dump an assload of calcium into sarcoplasm. Calcium ions bind to troponin, removing the blocking action of tropomyosin. the myosin heads attach to center of sarcomere. ATP hydrolysis allows the myosin to "pull"
3 phases of muscle twitch
latent period- when excitation-contraction coupling is occurring
period of contraction-period of contraction when cross-bridges are active
period of relaxation-initiated by calium ions going back into SR, contractile force no longer being generated
what is muscle twitch
the responce of a motor unit to a single action potential of its motor neuron
what is the muscles response to changes in stimulation frequency
the second twitch will be stronger than the first, but the refractory period is always honored. if the stimulus strength is held constant and the muscle is stimulated at a faster rate, the relaxation time becomes shorter. but if the muscle did not repolarize, nothing happens.

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