ch 11 pt w

Question 1

what causes skeletal muscle to contract

Answer 1

skeletal muscle contracts unless stimulated by a nerve

Question 2

how does a muscle become paralyzed

Answer 2

if nerve connections are severed or posioned

denervation atrophy
shrinkage of paralyzed muscle when nerve remains disconnected

Question 3

somatic motor neurons

Answer 3

Nerve cells whose cell bodies are in the brainstem and spinal cord that serve skeletal muscles

Each nerve fiber branches out to a number of muscle fibers

Each muscle fiber is supplied by only one motor neuron

Question 4

what is a motor unit

Answer 4

one nerve fiber and all the muscle fibers innervated by it

Question 5

muscle fibers of one motor unit

Answer 5

Dispersed throughout muscle

Contract in unison

Produce weak contraction over wide area

Provide ability to sustain long-term contraction as motor units take turns contracting

Effective contraction usually requires contraction of several motor units at once

Question 6

how many muscle fibers does the average motor unit contain

Answer 6

200

Question 7

small motor units

Answer 7

fine degree of control

Three to six muscle fibers per neuron

Eye and hand muscles

Question 8

large motor unit

Answer 8

more strength than control

Powerful contractions supplied by large motor units with hundreds of fibers

Gastrocnemius of calf has 1,000 muscle fibers per neuron

Question 9

synapse

Answer 9

point where a nerve fiber meets its target cell

Question 10

neuromuscular junction (NMJ)

Answer 10

when target cell is a muscle fiber

each terminal branch within form a separate synapse with the muscle fiber

one nerve fiber stimulates the muscle fiber at several points within the NMJ

Question 11

axon terminal

Answer 11

swollen end of nerve fiber

Question 12

synaptic cleft

Answer 12

gap between axon terminal and sarcolemma

Question 13

schwann cell

Answer 13

envelops and isolates NMJ