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Motor Unit

A motor neuron and all of the skeletal muscle cells it stimulates

Axon Terminals

The axon of each motor neuron has numerous endings

Synaptic cleft

The actual gap between an axonal ending and the muscle cell


within the axonal endings are many small vesicles containing a neurotransmitter substance

Action potential

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.


A continuous contraction that shows no evidence of relaxation

Isotonic concentration

A contraction in which the muscle shortens and work is done

Many Motor Units

To accomplish a strong contraction, these are stimulated at a rapid rate

few motor units

when a weak but smooth muscle contraction is desired, these are stimulated at a rapid rate


when muscle is being stimulated but is not able to respond due to oxygen debt

Isometric Contraction

The muscle does not shorten but the tension in the muscle keeps increasing


connective tissue surrounding a fascicle


connective tissue ensheathing the entire muscle


contractile unit of muscle


a muscle cell


thin connective tissue investing each muscle cell


plasma membrane of the muscle cell


a long, filamentous organelle found within muscle cells that has a banded appearance


actib or myosin containing structure


cord-like extension of connective tissue beyond the muscle, serving to attach it to the bone


a discrete bundle of muscle cells

Smooth muscle tissue

cardiac muscle tissue

functions of the muscular system

movement,posture,stabilize joints, generate heat

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


sheet-like structure connecting muscle to bone

transverse tubules

transmit electircal impulses deep into cell

sarcoplasmic reticulum

specialized smooth endoplasmic reticulum stores and releases calcium

thick filament

with protein myosin, with atp enzymes

thin filament

with protein actin


ability to receieve and respond to a stimulus


ability to shorten when a stimulus is received

skeletal muscles must be stimulated by a nerve to contract


neuromuscular junction

where nerve and muscle associate

synaptic cleft

gap between nerve and muscle- they do not make contact
(area between nerve and muscle is filled with interstitial fluid)

Action potential

(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)


(not normal) single, brief contraction


(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


incomplete tetanus some relaxation occurs between contractions


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

Direct phosphorylation

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

Anaerobic glycolysis

.) glucose is broken down to pyruvic acis to produce 2 ATP (no oxygen needed)
.)pyruvic acid is converted to lactic acid
.) fast but innefficient (needs lots of glucose, and lactic acid causes muscle fatigue) 2 BATTERIES

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