Lectures3+4-Chapter_2-BiologicalFoundations

Result of this sequence is an action potentialthe

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Unformatted text preview: “repolarize” the membrane potential. Result of this sequence is an action potential—the principal signaling event in the nervous system. Action Potential is the Main Means for Neuronal Communication Brief in duration (last about 1 ms) Singular event that cannot be modified: All-or-none in nature – no such thing as “bigger” or “smaller” action potentials Is “self-regenerating” as it proceeds down an axon: Because of voltage-gated channels that are present in the membrane of the axon along its entire length, action potentials propagate down axons by voltage changes at the “front” of the wave of electrical propagation without decay to the axon terminal. 49 How Sensory Information Gets Into the Brain Sensory receptor neurons are stimulated, and action potentials are produced in neighboring sensory neurons Neurotransmitter is released by these sensory neurons onto the dendrites of an interneuron, causing a Na+ influx that makes its membrane potential reach threshold, triggering an action potential in the interneuron “receptor potentials” Sensory Transduction: the energy in a physical stimulus is transformed in to neural signals 50 SYNAPSES Very small physical gaps at the junction where two neurons meet Signal transmission between neurons Synapse: A very small physical gap at the junction where two neurons meet Presynaptic neuron = the neuron that carries action potentials toward a synapse Postsynaptic neuron = the neuron that receives the signal from a synapse Signals are transmitted across the synapse with neurotransmitters: Specialized chemicals are involved in neural transmission. There are also a special subclass of synapses that have gap junctions going from one neuron to the next – these are specialized sets of molecules that electrically couple the inside of one nerve cell to the inside of the other, carrying the depolarization electrically The amount of depolarization delivered to a postsynaptic neuron determines whether the threshold for an action potentail will be reached, and the...
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