Nervous System
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| What are neurons? | Nerve cells specialized to transmit messages
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| Cell Body of a Neuron | Nucleus and metabolic center of the cell
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| Processes | Fibers that extend from the cell body
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| Dendrites (neurons may have hundreds of these) | Conduct impulses toward the cell body
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| Axons | Conduct impulses away from the cell body
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| 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
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| Synaptic Cleft | Gap between adjacent neurons
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| Synapse | Junction between nerves
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| Myelin Sheath | Whitish, fatty material covering axons to insulate them
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| Schwann Cells | Produce myelin sheaths in jelly roll-like fashion around axons (PNS)
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| Nodes of Ranvier | Gaps in myelin sheath along the axon
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| Oligodendrocytes | Produce myelin sheaths around axons of CNS
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| KNOW ABOUT MYELIN SHEATHS | Myelin sheaths speed the nerve impulse transmission
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| Neuroglia | Support cells in the CNS
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| Neuroglia Functions | Support, insulate, and protect neurons
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| 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
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| Describe Microglia | 1. White blood cells
2. Smallest and rarest
3. Spider-like phagocytes
4. Dispose of debris and pathogens
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| Describe Oligodendrocytes | 1. "A cell with a few branches"
2. Wrap around nerve fibers in the central nervous system
3. Produce myelin sheaths
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| 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
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| Describe Schwann Cells | 1. Part of PNS neurological cells
2. Form myelin sheaths in the PNS
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| 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
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| Action potential Initiation and Generation: Step 1 | A stimulus depolarizes the neuron's membrane
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| Action potential Initiation and Generation: Step 2 | The membrane is now permeable to sodium as sodium channels open
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| Action potential Initiation and Generation: Step 3 | A depolarized membrane allows Na+ to flow outside the mebrane
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| Action potential Initiation and Generation: Step 4 | A stimulus leads to the movement of ions, which initiates an action potential in the neuron
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| 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
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| 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)
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| Propagation of the Action Potential | If enough Na+ enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon
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| All-or-none Response | The nerve impulse either is propagated or is not
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| KNOW ABOUT MYELIN SHEATHS | Fibers with myelin sheaths conduct nerve impulses more quickly
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| 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
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| 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)
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