bio chap 9

force of contraction is affected by:

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)