1.3 Overview of the Nervous System and the Neuron

Two main divisions of the nervous system

The central nervous system (CNS) includes the brain and spinal cord and processes information. The peripheral nervous system (PNS) connects the CNS to the rest of the body, with a somatic branch (voluntary muscle movement) and an autonomic branch (involuntary functions), split further into sympathetic (arousal, 'fight or flight') and parasympathetic (calming, 'rest and digest').

The neuron: structure

Neurons are cells specialized for communication. Dendrites receive signals, the cell body (soma) integrates them, the axon carries the impulse (often insulated by fatty myelin sheath for speed), and axon terminals release chemical messengers into the synapse, the gap between neurons.

How neurons fire

A neuron rests at negative charge until stimulation causes an action potential — a brief electrical impulse that fires once a threshold is reached (all-or-none principle). The impulse travels down the axon; at the terminal, neurotransmitters are released across the synapse and bind to receptors on the next neuron, which may excite or inhibit it.

Key terms

Central nervous system (CNS)

Brain and spinal cord; processes and coordinates information.

Peripheral nervous system (PNS)

Nerves connecting the CNS to the rest of the body; includes somatic and autonomic divisions.

Sympathetic vs. parasympathetic

Sympathetic arouses the body for action ('fight or flight'); parasympathetic calms it ('rest and digest').

Action potential

A brief electrical impulse that fires down a neuron's axon once a threshold is reached (all-or-none).

Synapse

The small gap between neurons where neurotransmitters are released to transmit signals.

Try an AP-style question

Which part of the neuron receives messages from other neurons?

1. Dendrites
2. Axon terminals
3. Myelin sheath
4. Axon