BIOL 2P05 Lecture Notes - Depolarization, Mitochondrion, Exocytosis

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Nerve impulses can only travel in one direction: action potential can only depolarise the membrane in front, membrane behind is recovering from refractory period (previous action potential) Limits frequency with which neurones can transmit impulses. Factors affecting the speed of conductance: myelin, axon. Impulses travel faster in myelinated neurones saltatory conduction: schwann cells prevent diffusion of ions, flow of current between adjacent nodes of ranvier, thus, depolarisation only at nodes of ranvier, action potential jumps from node to node. Temp affects speed of conduction of impulses: higher temp increases rate of diffusion of ions. Impulses faster in an axon with larger diameter: small cells / large surface area:volume ratio / ion leakage weakens membrane, myelin stops ion leakage \ diameter only important for unmyelinated neurones. Synaptic cleft (gap) of 20 m separates two neurones at a synapse (junction of 2 neurones: presynaptic membrane is at the end of a neurone, postsynaptic membrane is at the next neurone in the chain.

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