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Conduction of action potential

Conduction of action potential. Conduction of action potential (AP). Initially AP only occurs on a particular area of the nerve cell In order for nerve impulse to travel along the neuron, the AP must be conducted along the neuron

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Conduction of action potential

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  1. Conduction of action potential

  2. Conduction of action potential (AP) • Initially AP only occurs on a particular area of the nerve cell • In order for nerve impulse to travel along the neuron, the AP must be conducted along the neuron • When Na+ flows into the neuron as a result of open sodium gates, the positive charge inside causes the next sodium gate to open, causing another AP • This occurs over ad over again, until the end of the neuron

  3. Once sodium gates have opened and closed, they cannot be activated for a short time (refractory period) thus impulse can only move forward, not backwards • The impulse moves even faster in myelinatedfibres because the impulse (AP) jumps from node to node (node=exposed axon)

  4. Brain break!!!

  5. The Schwann cells make up the myelin sheath • Most long fibers (both axons and dendrites) are covered by myelin sheath • Invertebrates do not have myelinated fibers, therefore move very slowly

  6. Threshold • Stimuli for initiation of AP can be anything, depending on the type of receptor • But, stimulus must have a certain intensity for nerve to fire – called the threshold • If stimulus is below the threshold nerve does not fire • (called “all-or-none” response) • Therefore speed and intensity of nerve impulse never vary

  7. …. However, the frequency of the impulse and the number of nerves firing will vary • These are both dependent on the intensity of the stimulus • Also, different nerves will have different thresholds • Since nerves are in bundles this means that a warm plate will fire some nerves in the bundle but not others, whereas a hot plate will fire far more nerves

  8. Transmission across a synapse • Nerve impulses (AP’s) must be transferred from one neuron to another • This occurs by way of the synapse

  9. When a nerve impulse travels to a synaptic ending Ca2+ flows to ending • Causes synaptic vesicles to fuse with a pre-synaptic membrane and secrete neurotransmitter substances into the synaptic cleft (by exocytosis) • Neurotransmitter diffuses across the synaptic cleft • Transmitters (ex. Acetyl-choline: parasympathetic and Noradrenalin: sympathetic) bind to receptor sites on post-synaptic membrane

  10. An enzyme (cholinesterase) is released after the neurotransmitter is released to destroy it • Otherwise, the Na+ gate wouldn’t close and the nerve could not fire • Insecticides block cholinesterase • The neurotransmitter substances can either excite or inhibit the next neuron • Whether or not the neuron “fires” depends on the amount of excitation compared to the amount of inhibition

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