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Central Nervouse System

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* During equilibrium more potassium outside then inside - Conduction of the Action Potential ● As the action potential is conducted along the axon, the potential doesn’t change size or shape (because we get a lot of positive charge) ● This is b/c the potential is regenerated at each point along the axon ● No regeneration, potential decreases= graded conduction Regeneration of Action Potential 1. After reaching threshold, Na enter through the voltage-gated channel 2. ThE ENTRY OF NA causes the membrane potential to reach +30 MV 3. The positive charge opposes Na entry (equilibrium) 4. Positive charge spread along the membrane depolarizes adjacent parts and the process repeats ● Membrane depolarization opens voltage-gated NA channels and Na enter the neuron (2) ● tHE SPREAD OF charge (2) depolarized adjacent points along the membrane, open voltage gated channels, Na enters (3) etc (4,5) ● Backward spread (2,4) of charge doesn’t open -Refractory Period- 1. Absolute refractory period: a. Lasts about 1 msec (1/1000 sec) b. Sodium channel closed an inactivated, so the neuron will not generate another action potential c. Limits neuron to max of 2000 action potential per second 2. Relative refractory period: 3. Last 3 to 4 sec4. Hard to generate action potential, but possible➔ Conduction Velocity◆ Speed of conduction in uninsulated axon varies from .1 meter/sec to 35 meter/ sec- depends on axonal thickness◆ Thick axon= fast conduction, more charge carrier ◆ Slow conduction, fewer charge carrier ★ Saltatory Conduction in Myelinated Axon ○ Many axons are insulated by myelin, which is made by Schwann cells in the peripheral nervous system ■ Voltage gates are located at the end of myelin not inside (neuron) ○ Current flows to the next node ranvier so the action potential jumps from node to node (Saltatory conduction) ○ Action potential can fail at two nodes and still be regenerated ○ Speed of saltatory conduction in up to 120 meters ❖ Two Types of Synapses➢ Chemical Synapse ■ Terminal filled w/ vesicles that release NT ■ Synaptic delay ■ Can be modulated ● Electrical synapse ○ Tight junction ○ Fast/ no cleft ○ Electrical potential travels directly to next neuron Events in the Chemical Synapse1. Neurotransmitter manufactured in cell body by ribosomes along with rough endoplasmic reticulum (ER) 2. Moved by smooth ER to the Golgi apparatus and packaged into synaptic vesicles ● Microtubules transport synaptic vesicles ( and other material included enzymes that can synthesize NT down the axon to the synaptic terminal) - just transfer stuff ❏ Action potential invades synaptic terminal

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