The Human Brain : From Neurone to Nervous System

THE NERVE CELL : OVERVIEW


  1. A Nerve Cell (Neurone) has characteristic features including:
    • a cell body (perikaryon) containing the cell nucleus and synthetic machinery, and processes called dendrites, the site of synaptic inputs to the neurone.
    • a single nerve fibre (axon), a specialised process which can be very long (~1 metre in humans),
    • axon terminals that release a neurotransmitter to influence the activity of a post-synaptic cell

  2. Neurones are specialised cells that communicate rapidly with each other, often over long distances, by passing electrical impulses (action potentials, APs) along their axonal membranes.

  3. Axon terminals form synapses, close contacts with another cell, and release chemical neurotransmitters that can excite or inhibit that cell.

  4. The commonest transmitters in the CNS are glutamate (excitatory) and GABA (inhibitory).

  5. The axonal cytoplasm contains neurotubules that serve as a track along which packages of chemicals are transported throughout the neurone, a process called axoplasmic transport.

  6. When transected, peripheral nerve axons can regenerate, and reconnect with skeletal muscle cells.

  7. In neurodegenerative diseases, such as Alzheimer's disease, neurones can degenerate and die; these neurones often develop abnormal inclusions such as Lewy Bodies, and 'tangles'.

  8. Neurones are supported by Glial cells, including astrocytes, oligodendrocytes and Schwann cells. Myelin is produced by Schwann cells in peripheral nerves, and by oligodendrocytes in the CNS.

  9. In demyelinating diseases, such as Multiple Sclerosis, oligodendrocytes are damaged and die; the typical lesion of multiple sclerosis is the 'plaque'.
Key Words: Action Potential, cell membrane; synapses; neurotransmitters; axoplasmic transport, neurotubules; axonal regeneration; neurodegeneration, inclusion bodies.