neuromuscular junctions

motor neuron

nerves in the brainstem and spinal cord that stim. skeletal muscle.

neuromuscular junction

connection between a motor neuron and a muscle fiber.

synaptic cleft

space between motor neuron and muscle fiber.

ACh

AKA acetylcholine.

• example of a neurotransmitter which is a chem. messenger that sends intro throughout the body.

Ca⁺²

• alkaline earth metal group 2

• easily gives v.e.

• easily dissolves in a water and blood

• when charged and in the body, it is an ion w a +2 charge.

AChE

AKA acetylcholinesterase

• enzyme commonly associated with neuromuscular junctions.

• breaks down ACh when nerve impulses stop.

troponin and tropomyosin

• regulatory proteins embedded in actin filaments.

• controls when sarcomeres bind w myosin to form cross bridges.

• controls when sarcomeres contract.

neuromuscular junction steps

1. nerve impulse reaches end of motor neuron. vesicles carrying ACh fuse w cell membrane of fiber and it is released into synaptic cleft.

2. ACh diffuses across cleft, which stim. receptors.

3. receptors send electrical impulses down the T tubule, causing sarcoplasmic reticulum to release Ca⁺²

4. Ca⁺² binds w troponin on actin filaments so myosin can attach and grab them to allow muscle contraction.

STOPS WHEN: ACh stops being released, AChE breaks down remaining ACh, Ca⁺² back to SR, troponin and tropomyosin cannot bind w myosin, thus myosin can’t bind with actin and the sarcomere and muscle fiber relaxes.