Studied by 10 peopleforce of contraction is affected by:
number of muscle fibers stimulated to contract
relative size of muscle
degree of prestretch
muscle tissue is one of the _____ primary body tissues
four
muscle tissue accounts for almost _____ the body’s weight
half
muscle tissue is the dominant tissue of the _______________
heart and other visceral organs
muscle functions:
maintain posture
stabilize joints
generate heat
produce movement
smooth muscle tissue:
found in walls of visceral organs (other than the heart)
spindle-shaped fibers
single, centrally located nucleus
no striations
involuntary
cardiac muscle tissue:
makes up the walls of the heart
fibers are branched and striated
single, centrally located nucleus
intercalated disks - fusion of adjacent membranes
involuntary
bifurcated
skeletal muscle tissue:
comprises muscles that are attached to bones
fibers are long cylinders w/ tapered ends
multinucleated
dark striations
voluntary
sarcoplasmic reticulum:
consists of a network of interlocking tubules that form a network over the sarcomere
near the i-bands tubules fuse to form cisternae which occur in pairs
function- to store calcium
t-tubules
calcium triad
sliding filament hypothesis:
myosin cross bridges attach to actin
cross bridges pull actin over myosin and the sarcomere shortens
muscles grow by:
stretching as bones grow in length
increasing in diameter due to the addition of actin and myosin filaments in already existing fibers
tension develops when:
actin and myosin filaments interact and attempt to slide past one another within the sarcomeres
slow twitch:
slow speed of contraction
thin with a rich blood supply (gives red color)
aka: red fibers
contracts for long time but generates little power
less actin/myosin
fast twitch:
fast contracting fibers
large diameter
pale in color
aka: white fibers
contract powerfully but “poop out” quickly
a lot of actin/myosin
how is muscle tissue irritated?
stimulus provided by a motor neuron
single twitch contraction:
simple contraction resulted from a single electric shock
most basic form of a muscle contraction
phases: latent period, contraction phase, relaxation phase
summation contraction:
contraction of great magnitude
results from a second stimulus before end of a contraction
phases: absolute refractory period, relative refractory period
tetanus contraction:
results from a series of stimuli in rapid succession
muscle remains in constant contraction
types: incomplete, complete
all muscle contractions that move body parts are __________
complete tetanus contractions
steps of muscle contraction:
nerve impulses travel down motorneurons to a neuromuscular junction
acteylcholine is released from the motor neuron, crosses the synaptic cleft, and bands to sarcolemma
the binding stimulates the release of calcium from the SR inside the muscle fiber
released Ca binds with troponin, a protein associated with actin
this causes tropomyosin (a ribbon-like protein around actin) to shift and expose myosin binding sites
myosin heads bind to these sites, forming cross-bridges
cross bridges pull actin over the myosin and the sarcomere shortens
events at the neuromuscular junction:
action potential reaches axon terminal of motor neuron
calcium channels open and ca enters the axon terminal
ca entry causes some synaptic vessels to release their contents (acetylcholine, a neurotransmitter) by exocytosis
acetylcholine diffuses across the synaptic cleft and binds to the receptors in the sarcolemma
ach binds and channels open that allow simultaneous passage of na into the muscle fiber. more na ions enter than k ions leave and this produces a local change in the electrical conditions of the membrane (depolarization), which eventually leads to an action potential
ach effects are ended by its breakdown in the synaptic cleft by the enzyme acetylcholinesterase
creatine phosphate cycle:
CP → muscle contraction → free creatine → stimulates production of RNA → myosin/actin → added to muscle → stronger contraction → more CP → (repeat)
Note
Flashcard