Neuromuscular Junction, excitation-contraction coupling

excitable membranes

membrane found in skeletal muscle fiber and neurons that respond to stimuli by rapidly changing its membrane potential. depolarization and repolarization events produce action potentials

neuromuscular junction (NMJ)

synapse between a neuron and a skeletal muscle fiber

Sequence of events at NMJ

• AP arrives at axon terminal

• Ca diffuses into axon terminal

• Ca causes synaptic vesicles to fuse with cell membrane of axon terminal

• NT is released via exocytosis into synaptic cleft

• NT diffuses across to the post-synaptic cell

• NT binds with receptor at post-synaptic membrane

• NT binds to Na+ channel receptor, Na+ gates open, Na+ enters cell (depolarization)

• K+ leaves muscle cell (repolarization)

• after crossing synapse, excess NT is removed from the cleft

acetylcholinesterase

enzyme that degrades neurotransmitter

process of excitation-contraction coupling

• AP travels along the sarcolemma, down T-tubules to triads

• Ca is released from terminal cisternae of SR

• Ca binds to troponin and changes shape

• Troponin-tropomyosin complex changes position- exposes active sites on thin filaments; myosin head then forms a cross bridge with actin

• contraction cycle is initiated