Lecture, Feb. 18 (Chapter 11) Neurons Question 1 ? neuron structure & function The input (which occurs on the dendrites or soma) is a change in membrane potential The potential difference becomes greater (more negative), or smaller (less negative) The change is caused by input from a sensory cell or by another neuron A voltage change produced by sensory cell is called a ?receptor potential? Change caused by a neuron is called a ?synaptic potential? Both types of potential are called ?graded potentials?, meaning that the change in voltage can be positive or negative and assume any value (within reason) The output is the release of neurotransmitter at the synaptic cleft Causes a change in the postsynaptic membrane potential This is also a graded potential (a synaptic potential) The area of integration is the region on the soma (cell body) where a nerve spike is initiated, the spike initiation zone (SIZ) The SIZ is usually at the point where the axon leaves the soma (axon hillock) The SIZ integrates ALL the graded potentials that are occurring at a given moment Integration = sums graded potentials These graded potentials represent information, so the area of integration is integrating information If the change in membrane voltage at the SIZ is large enough (depolarization) then a spike (action potential) is sent down the axon This is the output of the neuron (actually, the release of neurotransmitter the action potential causes is the output, as stated earlier) Either a spike is produced or no spike is produced, so the output is NOT graded, it is all-or-none Either there is, or there is not, an action potential (Although I didn?t mention it in lecture, each action potential a given neuron produces follows the same pattern of voltage change ? i.e., for a given neuron all the APs look alike)
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