1. How do Muscles Contract?
Action Potential – electrical signal, originates in the brain and travels along motor neurons (cells that make up a nerve)

2. Parts of a Motor Neuron
Neuromusc. Junction – area where the neuron meets the muscle.
synaptic cleft – small space b/w the two structures
terminal bouton- distal end of the neuron, which contains –
Synaptic vesicles – small “bubble-like” packets that contain ACh (Acetylcholine)
ACh – is a neurotransmitter (chemical that carries a signal from a neuron to a muscle cell or to another neuron)

7. S. vesicle fuses to distal membrane of neuron
ACh diffuses across cleft and binds to receptor sites on motor end plate –
generates another action potential – travels down T- tubule, which has cisternae on either side.
The cisternae, which are part of the sarcoplasmic retic., become permeable, and release Ca+2 ions to the outside – calcium diffuses to the myofibrils

8. Ca+ binds to troponin (ACTIN)
Changes the shape of troponin – revealing a binding site on actin
Cross-bridges of the MYOSIN bind to ACTIN (energized by ATP)
Cross-bridges pull ACTIN toward center of sarcomere then release, reattach closer, and pull
ATP needed for cross-bridges to attach and pull, also needed to detach. If ATP is not available, the muscle stays contracted.

9. ATP also needed to return Ca+2 to the S. Retic
ATP also needed to return Ca+2 to the S. Retic. – if not available, the muscle will keep contracting
Sarcolemma of the muscle releases an enzyme (Acetylcholinesterase – AChE) to degrade ACh when the muscle needs to stop contracting

10. Action Potenials of Muscle Youtube Videos