How do Muscles Contract Action Potential electrical signal

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

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)

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

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.

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 – ACh. E) to degrade ACh when the muscle needs to stop contracting

ACTION POTENIALS OF MUSCLE YOUTUBE VIDEOS http: //www. youtube. com/watch? v=Zsc. XOv. Dg. Cm. Q http: //www. youtube. com/watch? v=Cepe. YFvqmk 4