Synapse – The site of connection between a neuron and a cell. Neurotransmitter – A chemical released at the neuron’s synapse that communicates with the cell Motor Neuron – Neuron that controls effectors (such as skeletal muscle movement) Neuromuscular Junction – Synapse where a motor neuron and a muscle fiber meet Synaptic Cleft – Space that separates the neuron and the muscle fiber

An action potential is conducted down a motor neuron

The motor neuron terminal releases the neurotransmitter acetylcholine (ACh) into synaptic cleft

ACh binds to ACh receptors on the sarcolemma.

The sarcolemma is stimulated which sends an action potential throughout the sarcolemma and deep into the muscle fiber through T- Tubules

The action potential reaches the sarcoplasmic reticulum, which opens calcium channels

Calcium ions diffuse from the sarcoplasmic reticulum into the sarcoplasm where they bind with troponin molecules

Tropomyosin molecules move and expose specific binding sites for the myosin heads on actin

Actin and Myosin link, forming cross-bridges

POWER STROKE!!! In other words the myosin heads use ATP to pull the thin filaments towards the center of the sarcomere by cocking their heads

When sarcomeres shorten, the thick and thin filaments do not change length, rather the thin filament slides past the thick filament.

If contraction is to continue, ADP and P are released from myosin heads

New ATP binds to myosin head which releases the linkage between myosin and actin

Actin and Myosin form cross bridge once again Power Stroke Thin filament slides past thick filament ADP and P released

To relax, the neuron releases acetylcholinesterase, an enzyme that breaks down ACh

Action potential down the sarcolemma is eliminated

Calcium molecules are released from troponin and are transported back into the sarcoplasmic reticulum

Troponin and Tropomyosin molecules inhibit the myosin heads from attaching to actin

Muscle is relaxed, yet ready to be stimulated again