Muscle Contractions

Nerve-Muscle relationship

skeletal muscle never contacts UNLESS nerve stimulation occurs.

somatic motor neurons

type of neuron that controls muscles.

somatic motor fibers

type of fiber that contain somatic motor neurons that lead to the skeletal muscle

motor unit

A motor neuron and all of the muscle fibers it innervates

small motor units

used for fine degree of control, have 3-6 muscle fibers per neuron

large motor units

used for more strength than control, powerful contraction supplied by large motor units with hundreds of fibers. up to 1,000 muscle fibers per neuron (calf muscle)

Neuromuscular Junctions (NMJ)

synapse point where a nerve fiber meets its target cell

synaptic knob

swollen end of the nerve fiber. Contains synaptic vesicles storing ACh (neurotransmitter)

synaptic cleft

gap between synaptic knob and sarcolemma

excitation

first phase of contraction/relaxation, in which nerve signals opens voltage-gated calcium channels, allowing calcium to enter knob

excitation-contraction coupling

second phase of contraction/relaxation , in which action potentials spread across sarcolemma down T-tubules.

contraction

third phase of contraction/relaxation, myosin head rests bound to ATP, ATPase in myosin head hydrolyzes and ATP molecule. recovery stroke

relaxation

final phase of contraction/relaxation, nerve stimulation and ACh release stop, muscle fiber returns to its resting length.

rigor mortis

hardening of muscles and stiffening of body beginning 3-4 hours after death (muscle relaxation requires ATP, ATP is no longer being produced after death).