PSYCH 100 Wiley Notes Chapter 3

PSYCH 100 Wiley Notes Chapter 3 - Neurons: Basic Units of...

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Neurons: Basic Units of the Nervous System Neurons A neuron is a cell that specializes in the transfer of information within the nervous system. Three classes of neurons: Sensory: Transmit information from sensory receptors to the brain (also termed afferent). Motor: Transmit commands from the brain to the muscles and glands of the body (also termed efferent). Interneurons: Interconnect sensory and motor neurons. Components of the Neuron o Dendrites receive information from adjacent cells. o Cell body of the neuron contains nucleus and cytoplasm. o Axon is an extension of the cell body. -Myelin insulates the nerve cell, speeds up conduction of nerve messages. -Terminal buttons of the axon release transmitter into the synapse. o Neuron Resting Potentials The membrane of the neuron separates charged ions, producing a voltage potential. The ions NA + and Cl - are found outside the membrane, whereas the ion K + is found inside the membrane. The membrane is slightly permeable to K + , so that at rest, the inside of the membrane is about -70 millivolts (mV) relative to the outside. At rest, very little NA + crosses the membrane (entry requires opening of channels through the membrane). Graded Potentials o Stimulation of the nerve membrane can open ion channels in the membrane, ions will move into or out of the membrane (depending on which channels open). o NA + ions flowing in will depolarize the membrane (membrane potential moves from -70 mV to say -60 mV. o K + ions flowing out of membrane will hyperpolarize the membrane (-70 mV to say -90 mV). o These graded potentials are a function of the magnitude of the stimulation of the nerve cell (are graded in size). o Graded potentials sweep along the nerve cell and degrade with time and distance. The Action Potential o If the graded potential passes threshold (often at about -60 mV), then NA + ions will flow into the cell, thus raising the membrane potential to +40 mV. o The entry of NA into the cell produces an upward spike of the membrane potential. o The restoration of the membrane potential back to -70 mV is produced by an opening of channels to K + ions (that then flow out of the membrane, restoring the membrane potential). o
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PSYCH 100 Wiley Notes Chapter 3 - Neurons: Basic Units of...

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