9.4 Chapter Human Structure and Function

Somantic motor neurons

motor neurons in spinal cord that activate skeletal muscle fibers

Axons

In each motor neuron, extends to muscle fiber it serves, bundle together to create nerves

Neuromuscular junction/ Motor end plate

Junction where branches split and connect with muscle fiber

Axon terminal

End of axons, filled with synaptic vessels that contain ACh

Synaptic Cleft

Separates axons from muscle fibers

Axon potential

Large change in membrane potential that spreads within cell

Acetylocholine(ACH)

Neurotransmitter, chemical messenger, in contraction

Chemically gated ion channels

Opened or closed by chemical messengers, ACh, cause small change in membrane potential

Voltage gated ion channels

Open or close in response to membrane potential, depolarization by chemically gated ion channels opens voltage gated

Junctional folds

grooves that provide large surface area for for ACh receptors 

End plate potential (EPP)

Local depolarization caused by ACh binding

4 parts of contraction

Events at neuromuscular junction, Muscle fiber excitation, Excitation-contraction coupling, Cross-bridge cycle

Events at neuromuscular junction

Motor neuron sends action potential to axon, Motor neuron’s axon terminal releases ACh into synaptic cleft, ACh binds receptors on junctural folds of sarcolemma, ACh binding causes end plate potential 

Muscle fiber excitation

End plate potential causes action potential in sarcolemma

Excitation-contraction coupling

Action potential in sarcolemma travels in T tubules, Sarcoplasmic reticulum releases calcium, Calcium binds to troponin shifting tropomyosin to help myosin bind to actin

Cross bridge cycling

Contraction occurs via cross bridge cycling