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Lecture

2. Action Potential Propogation.docx

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Department
Kinesiology
Course Code
Kinesiology 2230A/B
Professor
Glen Belfry

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Lecture 2 Recall • Scaffolding proteins help muscles keep their shape • Binding sights for proteins involved in signaling cascades Titin: attached to myosin Nebulin: attached to actin Give the muscle strength, allow it to shorten Muscular Dystrophy is a dissolving of the proteins involved in distrophin (which connects actin to the sarcolemma) and the muscle is unable to shorten. Over time the membranes disintegrate and it leads to loss of function. Z line: at the end of the sarcomere M line: down the middle Initiation of Muscle Contraction 1. Alpha-motor neuron is stimulated and propagates the action potential along the nerve  Depolarization (where there is a movement of charge across cell membrane) moves along nerve 2. Action potential crosses neuromuscular junction  You can have one nerve stimulating multiple muscle fibres 3. Action potential enters muscle and causes calcium release  Calcium is released, cross bridges interact  Muscle shortens Action Potential Action potential: rapid and sustained depolarization of the nerve membrane • Membrane must first reach threshold before action potential can occur. Resting Membrane Potential There has to be a change in polarity that reaches a certain threshold. -70mv inside cell originates because of permeability to potassium of the membrane  Membrane permeable to K+: any potassium outside the cell will leak inwards  As the quantity inside the cell increases so does the voltage  Membrane proteins are negative. Stays inside cell.  Chloride is repelled outside of the cell because of the negative charge Result is a small negative charge Depolarization: Positive spike of charge in cell membrane Repolarization: environment being manipulated to its original state 1. Na+ Voltage gated channels open and leads to an influx of sodium inside cell o For a brief moment the cell will be + charged The change in voltage along nerve propagates AP to next area because of voltage gated channels react to the change in polarity. It is the continual movement of sodium outside of the cell entering the cell that leads to action potential 2. K+ channels open and potassium rushes outside cell o restores the resting membrane potential. o Originally it was because of the sodium outside and potassium inside. o Fixed polarity but the elements are changed. The events up to now have just been reactions to change in polarity. 3. Na+/K+ pump that restores sodium outside and potassium inside o This is an energy requiring process o Sodium potassium ATPase Some ATP that is being regenerated through aerobic metabolism is going to be utilized within nervous tissue. • The SA node is surrounded by an artery that gives it its own blood flow. Always has oxygen available to do this aerobically Nerve Conduction Velocity Different types of axons: Non-myelinated: does not have insulation/covering • Some of the impulse is leaked into surrounding tissue Myelinated: series of myelinated areas. These propagate the AP faster • Myelin is composed of about 80% lipids and about 20% protein. • In myelinated axons, action potentials do not propagate as waves but recur at successive nodes – Nodes of Ranvier - and in effect “hop” along the axon • Skeletal muscle that has to generate force fast (fast twitch fibres) are myelinated Saltatory Conduction The gaps between myelin sheath cells are nodes of Ranvier. The electrical impulse jumps from one node to the next in 120 m/s. This is called saltatory conduct
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