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within the axonal endings are many small vesicles containing a neurotransmitter substance
when it reaches the ends of the axon. the neurotransmitter is released, and it diffuses to the muscle cell membrane to combine with receptors there.
few motor units
when a weak but smooth muscle contraction is desired, these are stimulated at a rapid rate
cord-like extension of connective tissue beyond the muscle, serving to attach it to the bone
Characteristics of skeletal muscle
1)most attached by tendons to bones
4)cells are surrounded and bundled by connective tissue
characteristics of Smooth Muscle
1) no striations
2) spindle shaped cells
3) involuntary- no conscious control
4) found mainly in the walls of hollow organs
Characteristics of Cardiac Muscle
1) has striations
2)usually has a single nucleus
3) joined to another muscle cell at an intercalated disc
5)found only in the heart
gap between nerve and muscle- they do not make contact
(area between nerve and muscle is filled with interstitial fluid)
(electrical impulse) triggers release of acetylcholine (a neurotransmitter) from the neuron
sodium rushing into the muscle fiber generates another action potential(electrical current) and the release of calcium from sarcoplasmic reticulum
contraction of a muscle cell
1)a single muscle fiber concentration is "all or none"
2)muscles have thousands of fibers, not all fibers may be stimulated at the same time
3)allows graded responses- different degrees of skeletal muscle shortening
3a)frequency of stimulation
3b)number of cells stimulated (more cells=greater force)
(summing of contractions)
1)one contraction is immediately followed by another
2) the muscle does not completely return to a resting state
3) the effects are added
complete tetanus no evidence of relaxation before the following contractions and the result is a sustained muscle contraction
energy for muscle contraction
muscles contract until they run out of energy. initially, muscles use stored ATP
breaking ATP bonds release energy
only 4-6 seconds worth of ATP is stored by muscles
after this initial time, other pathways must be utilized to produce ATP
muscle cells contain creatine phosphate(CP)
.) CP is a high energy molecule
.)Cp transfers energy to ADP, to regenerate ATP
.)1 CP yeilds 1 ATP
CP supplies are exhausted in about 20 seconds
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