Skeletal muscle contraction, initiation - type of stimulus and location / origin

Question

Skeletal muscle contraction, initiation - type of stimulus and location / origin - stimulus propagation from CNS, PNS (generation and movement of AP) - events at the target cell - cellular contraction mechanisms - end of contraction (relaxation). Skeletal muscle: make sure to list events at the NMJ, explain the cell structures associated with the sliding filament concept, and end with a removal of the stimulus / muscle relaxation. Include all critical structures, ions and their relevant functions...

Explanation / Answer

The skeletal muscle contraction: a)initiation : initiation of skeletal muscle contraction ny the nervous system and and is voluntary, the motor neurons from the spinal cord terminate at the neuromusclar junction then the nerve cells release the acetylcholine binding to its receptors by which efflux of potassium and influx of sodium through ion channels, then there is change in membrane potential,then the sarcoplasmic reticulum is stimulated then calcium is released which leads to myofibrils to interact. b)type of stimulus and location:the skeletal muscle cells must be stimulated by nerve impulses,one motor neuron may stimulate a few muscle cells. c)origin and stimulus propagation from CNS.PNS(generation and movement ofAP):the sequences of events leading to contraction is initiated in the CNS, either as voluntary activity from the brain or as reflex activity from the spinal cord, the motor neuron in the ventral horn of the spinal cord is activated and then action potential passes outward,pns then to motor end plate on each plate on each muscle fibre, at the motor end plate the AP causes realse of acetylcholinethen to the muscle fibre surface then to inside. d)cellular contractionmechanism-end of contraction(relaxation): when nerve impulse arrives at axon terminal of motor neurons and trigger release of acetylcholine then ach diffuses across synaptic cleft, binds to its receptors in the motor end plate and triggers AP, so another muscle AP doens not arise unless the ach is released from motor neuronsthen muscle ap travelling along transverse tubules opens calcium release channels in the sarcoplasmic reticulum membrane which allows calcium ions to flood in to the sarcoplasm then calcium binds to troponin on the thin filament exposing the binding sites for myosin then calcium is elevated then contraction (power strokes use ATP myosin heads bins to actin and release the thin filament are pulled toward center of sarcomere.ca+ release channels in SR close and ca+ active transport pumps use ATP to restore low level of ca+ in sarcoplasm then ca+ active transport pumps then troponin-tropomyosin complex slides back into position where it blocks the myosin binding sites on actin then muscle relaxes. e)list if events at the NMJ:the neuro muscular junction it is the site of the signal exchange, it transmit signal to the muscle fiber by releasing Ach causing muscle contraction,the ap reaches the axon terminal, then voltaged gated calcium gates open allowing ca+ to enter the axon terminal, then neurotransmitter vesicles fuse with the presynaptic membrane and ach is released in to the synaptic cleft via exocytosis then ach binds to post synatic receptors on the sarcolemma the binding causes ion channels tp open and allow sodium ions to flow across the membrane into the muscle cellthe flow os sodium ions across the membrane into the muscle cell gentrates AP which travels to the myofibril andresults in muscle contraction.(time is over to complete the answer)

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