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Nervous System 7-21
| Two Main Types of Nervous System Cells | Neurons and Neuroglia |
| Neurons function is... | specialized to conduct nerve impulses |
| Neuroglia function is to... | protect the neurons |
| Dendrites | recieve messages |
| Axon | sends message to terminals |
| Axon terminals | pass message to next neuron with neurotransmitters |
| 3 Types of Neurons | Sensory neurons, Interneurons, Motor neurons |
| Sensory neurons | carry messages to the spinal cord and brain |
| Motor neurons | carry messages from the brain and spinal cord |
| 5 Types of Neuroglia | Astrocytes, Ependymal cells, Microglia, Oligodendrocytes, Schwann Cells |
| Astrocytes | Blood/Brain Barrier |
| Ependymal cells | make cerebrospinal fluid |
| Microglia | act as microbe-eating scavengers (they can move in/out BVs) |
| Oligodendrocytes | produce the myelin sheath around axons in the CNS (white matter) |
| Schwann Cells | produce the myelin sheath around axons in the PNS |
| What does myelin do? | speeds up nerve impulses |
| Myelination begins in the ... | fetus and continues into the teen years |
| fewer myelinated neurons means... | movements are slower and less coordinated |
| What makes a nerve cell work? | 1) Stimulus - A nerve impulse or action potential (AP) is created by a stimulus or a change in a neuron’s environment. - examples: Pressure, temperature, and chemical changes |
| more on AP | A stimulus that is strong enough to depolarize the membrane of the neuron is the only way to start the AP. It is an “all or none” principle. There is no such thing as a weak or strong AP. |
| 2) Depolarization | 2) At rest, a neuron (positive charge) on the outside of the membrane due to sodium ions, which carry a positive charge - stimulus causes sodium channels to open - allows sodium to move inside |
| What happens once the sodium is inside? | 3) the charge on the outside of the membrane changes from positive to negative, which is called depolarization-----So, the AP begins |
| Depolarization | 3) The nerve impulse continues (the disturbance in that section will cause the sodium channels in the next section to open) thus depolarizing that section, etc. “Like a wave occurs at a ball game” |
| Repolarization | 4) The section of membrane that depolarized quickly starts back towards its original state because potassium ions flow out. |
| 2 Ways Impulses Travel | Continuous conduction - unmyelinated axon Saltatory conduction - nerve impulse travels faster when the neuron is myelinated. When the impulse reaches the myelin, it “jumps” over around the myelin. |
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