bio chap 9

force 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)