Nervous System

Topics: Neuron, Nervous system, Action potential Pages: 4 (604 words) Published: January 17, 2015
Nervous System

Functions of the Nervous System
1. Detect changes and feel sensations
2. Initiate responses to changes
3. Organize and store information

Divisions
1. Central Nervous System – brain and spinal cord
2. Peripheral Nervous System – cranial nerves and spinal nerves (relays info to/from the CNS) - Autonomic Nervous System

Nerve Tissue – neurons (nerve fibers) and specialized cells (Schwann, neuroglia) 1. Neuron cell body contains the nucleus; cell bodies are in the CNS or trunk; protected by bone 2. Axon carries impulses away from the cell body; dendrites carry impulses toward it 3. Schwann cells in PNS:

- Layers of cell membrane form the myelin sheath to electrically insulate neurons - nodes of Ranvier: spaces between adjacent Schwann cells
- Nuclei & cytoplasm of Schwann cells form the neurolemma – essential for regeneration of damaged axons or dentrites

4. Oligodendrocytes: In CNS, form myelin sheaths
- microglia phagocytize pathogens and damaged cells
- astrocytes contribute to blood brain barrier and regulate localized blood flow

5. Synapse: space between axon of one neuron and dendrites or cell body of next neuron - Neurotransmitter carries the impulse across a synapse and is then destroyed by a chemical inactivator; synapses make impulses one way

Types of Neurons – nerve fibers

1. Sensory – carry impulses from receptors to the CNS
- Somatic – from skin, skeletal muscles, joints
- Visceral – from internal organs

2. Motor – carry impulses from CNS to effectors
- Somatic – to skeletal muscle
- Visceral – to smooth muscle, cardiac muscle, glands

Nerves and Nerve Tracts

1. Sensory – made only of sensory neurons

2. Motor – made only of motor neurons

3. Mixed – made of motor and sensory

4. Nerve tract – white matter; a nerve in the CNS

The Nerve Impulse

1. Polarization – neuron membrane has a + charge outside and – charge inside 2....
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