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A/P - Ch. 9
Nervous System
| Question | Answer |
|---|---|
| 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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