PSY315-Study Guide 2-2

PSY315-Study Guide 2-2 - Chapter 6: Neurons Neurons:...

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Chapter 6: Neurons - Neurons : building block of the nervous system that specializes in communication o no mechanism for replacing once it is gone o all-or-nothing response: will fire fully or not at all (applies to axons of individual cells) o soma: cell body that contains the nucleus o dendrites: short extensions used to respond to excitations from other neurons and transmit them to the soma o axon: single long process that carries the nerve impulse o Collaterals: offshoots from the axon and contact other neurons o Myelin: fatty covering interrupted at regular intervals by nodes (of Ranvier) Greatly accelerates impulses o IN: at dendrites cell body (integrates and sends impulse) axon other neurons o Resting potential: condition of electrical tension in a resting neuron - Nerve Impulses: - All four substances (Sodium, chlorine, potassium, A-) have 2 o 1. Equalize across the membrane according to their own particular concentration gradients o 2. Equalize across the membrane according to their electrical gradients, balancing with all the other charged particles - Negative charged anions inside the cell (neural membrane)—large o Tendency to diffuse down their concentration gradient and line up alongside the inside of membrane negative charged inner lining - Sodium (Na+): abundance in extracellular fluid from dissolved salts o Electrically attracted by negative charges of A- o Trying to diffuse in to equalize its concentration across the membrane (until half and half on each side) - Chlorine (Cl-) and Potassium (K+): also abundant in extracellular fluid from dissolved salts
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o Passively distribute o Able to diffuse through chann els of the m e m br an e free m ove m e nt - Chlorine (Cl-): concentration gradient is imbalancing factor o Concentration gradient pushing it to equalize across the membrane and enter the cell o Extra Cl- move into the cell making it even more negative than the exterior - Potassium (K+): huge negative draw pulling it inside against concentration gradient o High concentration of K+ held electrically inside the cell with strong desire to flow out o Must balance itself according the three main forces: 1. Negative ions drawing into the cell 2. Concentration gradient urging it out 3. Accumulation of Na+ ions on the cell exterior fencing it in Three forces balanced = resting potential Interior charge has neutralized at a higher energy level than the outside. Remaining more negative on the whole (more negative on the inside with potential to flow out) - Firing of neuron: o Dendrites/soma must collect enough signals from neighboring cells to trip it o Inputs enter soma integrated o Net total reaches threshold firing begins o Axon hillock becomes permeable to Na+ o Na+ rushes into axon, moved by its concentration gradient and attracted by A- in the cell o Depolarization: Na+ rushed into axon and membrane collapses Electrical polarity of opposing charges across the membrane disappear o Axon is now replete with K+ and positive charges o K+ immediately rushes out to equalize the charge
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This note was uploaded on 10/27/2010 for the course NSD 225 taught by Professor Short during the Spring '08 term at Syracuse.

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PSY315-Study Guide 2-2 - Chapter 6: Neurons Neurons:...

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