Terms Nucleus A collections of neuron cell bodies in the CNS Ganglion A

Terms nucleus a collections of neuron cell bodies in

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Terms Nucleus: A collections of neuron cell bodies in the CNS. Ganglion: A collection of neuron cell bodies in the PNS. Tract: A bundle of axons in the CNS.
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Nerve: A bundle of axons in the PNS. Resting membrane potential (RMP) •Creating a RMP: Neurons can rapidly change their membrane potential. It can be electrically stimulated and can respond to things electrical due to the separation of the plasma membrane of oppositely charged ions. All cells are polarized, the value is negative. •Voltage: Electrical potential energy due to separation of the plasma membrane of oppositely- charged ions (-70 mV). Roles of the Na+ and K+ ATPase in the RMP •The concentration of Na+ and K+ on each side of the membrane are different. Na+ is higher outside the cell and K+ is higher inside the cell. (1) K+ flows down its concentration gradient. (2) as positive K+ leaks out, a negative voltage develops on the membrane interior, it pulls K+ back in. (3) At -90mV, the concentration and electrical gradients for K+ are balanced. (4) Na+ entry through a few leakage channels reduces the negative membrane potential slightly (to -70mV). (5) Na+ -K+ pumps maintain the concentration gradients, resulting in the resting membrane potential. A cell at rest leaks out K+ and leaks in Na+ through open channels. Measurement of RPM •The potential difference between an electrode inside a neuron and the ground electrode in the extracellular fluid is approximately -70mV. Passive (leakage) and active (gated) channels •Channels in plasma membrane 1. Passive or leakage channels: Always open. 2. Active or gated channels: Signal required to open or close. *Chemically gated: Open when the appropriate chemical binds (neurotransmitter). *Voltage-gated: Open and close in response to changes in the membrane potential.
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Graded potentials : They are short-lived, localized changes usually in dendrites or cell body. They can be depolarizations or hyperpolarizations. Their magnitude varies directly with stimulus strength. The stronger the stimulus the more the voltage changes and the farther the current flows. Action potential : Neuron send signals over long distances is by generating and propagating (transmitting) action potential. Only cells with excitable membranes (neuron and muscle cells) can generate action potential. A total amplitude of 100mV (from -70mV to +30mV). Depolarization (caused by Na+ flowing into the cell) is followed by repolarization (is caused by K+ flowing out of the cell) and often a short period of hyperpolarization (Is caused by K+ continuing to leave the cell). It does not decay with distance. Resting state (No ions move through voltage gated channels). Generator or receptor potential (1) (2) (3)
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Postsynaptic potential (1) Threshold •Not all depolarization events produce action potential. Depolarization must reach threshold values if an axon is to fire.
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  • Fall '08
  • axon terminal

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