Cue Column | Notes Column

Parts of a neuron? | (1) Cell body/soma/cyton: nucleus + Nissl granules (rough ER), protein synthesis. (2) Dendrites: multiple, branched, receive signals. (3) Axon: single, long, transmits away from cell body. Axon hillock = trigger zone for AP.

Nissl granules significance? | Present in soma + dendrites; ABSENT in axon and axon hillock. Synthesize proteins (enzymes, NT precursors, structural proteins). Used for histological identification of neurons.

Myelin in PNS vs CNS? | PNS: Schwann cells (one cell myelinates ONE segment of ONE axon). CNS: Oligodendrocytes (one cell myelinates MULTIPLE axons simultaneously). Gaps = Nodes of Ranvier.

Functional classification? | Sensory/afferent: receptor → CNS. Motor/efferent: CNS → effector. Interneuron/association: within CNS only; connects S and M neurons. Most numerous in brain.

Structural classification? | Unipolar: 1 process $\frac{invertebrates}{embryonic}$. Pseudo-unipolar: T-shaped (DRG sensory neurons). Bipolar: 1 dendrite + 1 axon (retina, olfactory, inner ear). Multipolar: 1 axon + many dendrites (MOST CNS neurons).

Axon transport? | Anterograde (soma → terminal): carries vesicles, proteins. Retrograde (terminal → soma): carries signals, pathogens (e.g., herpes virus, tetanus toxin travel this way).

Summary

A neuron is the functional unit of the nervous system. Its soma contains Nissl granules (rough ER for protein synthesis). Dendrites receive; axon transmits. Myelin speed: PNS = Schwann cells, CNS = oligodendrocytes; gaps = nodes of Ranvier enabling saltatory conduction. Classification: sensory (afferent), motor (efferent), interneurons; also by morphology (uni-, bipolar, multipolar).