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A/P - Ch. 9

Nervous System

What are neurons? Nerve cells specialized to transmit messages
Cell Body of a Neuron Nucleus and metabolic center of the cell
Processes Fibers that extend from the cell body
Dendrites (neurons may have hundreds of these) Conduct impulses toward the cell body
Axons Conduct impulses away from the cell body
KNOW ABOUT AXONS 1. Neurons only have one axon arising from the cell body at the axon hillock 2. End in axon terminals 3. Axon terminals are separated from the next neuron by a gap 4. Axon terminals contain vesicles with neurotransmitters
Synaptic Cleft Gap between adjacent neurons
Synapse Junction between nerves
Myelin Sheath Whitish, fatty material covering axons to insulate them
Schwann Cells Produce myelin sheaths in jelly roll-like fashion around axons (PNS)
Nodes of Ranvier Gaps in myelin sheath along the axon
Oligodendrocytes Produce myelin sheaths around axons of CNS
KNOW ABOUT MYELIN SHEATHS Myelin sheaths speed the nerve impulse transmission
Neuroglia Support cells in the CNS
Neuroglia Functions Support, insulate, and protect neurons
Describe astrocytes 1. Largest and most abundant, star-shaped cells 2. Brace and repair neurons 3. Form barrier between capillaries and neurons 4. Control the chemical environment of the brain
Describe Microglia 1. White blood cells 2. Smallest and rarest 3. Spider-like phagocytes 4. Dispose of debris and pathogens
Describe Oligodendrocytes 1. "A cell with a few branches" 2. Wrap around nerve fibers in the central nervous system 3. Produce myelin sheaths
Describe Ependymal Cells 1. Epithelial cells that line cavities of the brain and spinal cord 2. Make and secrete cerebral spinal fluid 3. Cilia assist with circulation of cerebrospinal fluid
Describe Schwann Cells 1. Part of PNS neurological cells 2. Form myelin sheaths in the PNS
Describe a Resting Neuron 1. Plasma membrane at rest is polarized 2. Inside is more - than the outside, the cell stays at rest 3. Fewer + ions are inside the cell than outside the cell 4. K+ is the major + ion inside the cell 5. Na+ is the major + ion outside the cell
Action potential Initiation and Generation: Step 1 A stimulus depolarizes the neuron's membrane
Action potential Initiation and Generation: Step 2 The membrane is now permeable to sodium as sodium channels open
Action potential Initiation and Generation: Step 3 A depolarized membrane allows Na+ to flow outside the mebrane
Action potential Initiation and Generation: Step 4 A stimulus leads to the movement of ions, which initiates an action potential in the neuron
Action potential Initiation and Generation: Step 5 A graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive
Action potential Initiation and Generation: Step 6 If the stimulus is strong enough and Na+ influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)
Propagation of the Action Potential If enough Na+ enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon
All-or-none Response The nerve impulse either is propagated or is not
KNOW ABOUT MYELIN SHEATHS Fibers with myelin sheaths conduct nerve impulses more quickly
Repolarization K+ ions rush out of the neuron after Na+ ions rush in, repolarizing the membrane; involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge
KNOW ABOUT REPOLARIZATION Until repolarization is complete, a neuron cannot conduct another nerve impulse; initial ionic conditions are restored using a sodium-potassium pump (uses ATP to restore - 3 Na+ ions ejected from cell wall while 2 K+ are returned to the cell)
Created by: savvysparks



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