Nervous system controls and coordinates all the essential functions of the human body! It receives and relays info about activities within the body and monitors and responds to internal and external changes.

Neurons: 'Wiring' of Nervous System (N.S.). A cell that carrys messages throughout N.S. .

Neuron Anatomy

1. Dendrites: Look like branches. Receives messages, carries them to the cell body.

2. Cell Body: Enlarged part of neuron. Contains nucleus, many mitochondrion, most other organelles.

3. Axon: Long thin fiber carrying impulses away from cell body.

4. Axon Terminals: Small, branched axon fibers at end of axon.

5. Myelin Sheath: Fatty insulation around axons to help keep electrical impulses from jumbing to neighboring neurons & "shorting" them out!

6. Synapse: Tiny gap ('break' in circuit) between axon terminals & dendrites of next neuron. Neurotransmitters (chemicals) transmit impulse across the gap.

Movement of Nerve Impulse:

Impulses (electrical activity) always move from

dendrite--->cell body--->axon--->axon terminal--->synapse--->dendrite of next neuron.

Neurotransmitter molecules move across synapse from axon of 1st neuron to dendrite of 2nd neuron.

[Notes onCentral & Peripheral Nervous Systems & Reflexes]

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Nerve Impulse

(Read pp. 602-604) & see handout!

Impulse: Electrical activity moving along neuron.

Threshold: All or none principal. If stimulus is too weak, no impulse is started. If stimulus is stronger than threshold, the impulse starts.

Resting potential: difference in electrical charge across a neuron cell membrane (positive outside & negative inside). Results from fact K+ leaks out faster than Na+ moves in, so + charge builds up outside (- charge inside).

Depolarization: Stimulus causes pumps to move Na+ inside, causing inside to become +. This is beginning of impulse. This causes next pump to move Na+ in,.. etc., so impulse moves.

Repolarization: After Na+ moves in, the pump moves K+ out, to reset neuron with + charge outside, - charge inside. Last action of repolarization moves K+ back in, and Na+ out. This takes a split second, so impulse is only able to move 1 direction.

Action Potential: Changes in the + or - balance (where the Na+ is) of the neuron membrane that results in an impulse.

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Slichter