Term
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Function(s)
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Structure(s)
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Axon
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A nerve fibre: a single process extending from the
cell body of a neurone and carrying nerve impulses away
from it.
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Dendrite
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Carries nerve impulses from adjacent neurons into the
cell body.
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One of the shorter branching processes of the cell
body of a neurone. All dendrites have synaptic knobs
at the ends, which are the "connections" to
adjoining nerves.
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| Mixed Nerves |
Contain both motor and sensory nerve fibres running
to/from a particular region of the body.
(Examples include most large nerves such as the brachial
nerves, and all the spinal nerves.)
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Motor Neurone =
"Efferent Neurone"
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Transmitting impulses (electrical signals for communication
within the body) from the Central Nervous System (which
is sometimes referred to by the abreviation: CNS, and)
which consists of the brain and spinal cord, to muscles
& glands elsewhere in the body.
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See Figure (1) in the diagram above.
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Myelin Sheath
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Three key functions of Myelin Sheath are:
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Protection of the nerve fibre.
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Insulation of the nerve fibre.
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Increases the rate of transmission of nerve impulses.
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A complex material formed of protein and phospholipid
(fat) that is laid down as a sheath around the axons
of certain neurons.
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Nerve
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A nerve is a bundle containing 100s to 1000s of axons
(thread-like conductors) plus the associated connective
tissue and blood vessels.
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See the diagrams above.
Figures (1), (2) and (3).
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Neurilemma
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The sheath of the axon of a nerve fibre. The neurilemma
of a medullated fibre contains myelin laid down by Schwann
cells.
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Neurone
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A cell specialized to transmit electrical nerve impulses
and so carry information from one part of the body to
another.
"Neurone" = "Nerve Cell"
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Each neurone has an enlarged portion the
cell body (perikaryon), containing the
nucleus; from the body extend several processes (dendrites)
through which impulses enter from their branches. A
longer process, the nerve fibre (axon), extends
outwards and carries impulses away from the cell body.
This is normally unbranched except at the nerve ending.
The point of contact of one neurone with another is
known as a synapse.
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Nodes of Ranvier
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Key functions of Nodes of Ranvier include:
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Allowing nutrients and waste products to enter/leave
the neurone.
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Allowing nerve impulses to move along the neurone
through a process of
de-polarisation and re-polarisation of the nerve
membrane.
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Gaps that occur at regular intervals in the myelin
sheath of medullated nerve fibres, between adjacent
Schwann cells.
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Relay Neurone
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Located within the Central Nervous System (CNS), relay
neurons transmit the electrical impulses generated by
the stimuli to other nerves.
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See Figure (3) in the diagram above.
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Schwann Cells
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Schwann cells are the cells that lay down the protective
myelin sheath around the axon of medullated nerve fibers.
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Each Schwann cell protects one length of axon, around
which it twists as it grows - enveloping the axon.
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Sensory Neurone
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Transmit impulses inwards from sense organs to the
Central Nervous System (CNS).
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See Figure (2) in the diagram above.
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Synapse
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Reaching a synapse, an impulse causes the release of
a neurotransmitter, which diffuses across the gap and
triggers an electrical impulse in the next neurone.
(Some brain cells have more than 15,000 synapses.)
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The minute gap across which nerve impulses pass from
one neurone to the next, at the end of a nerve fibre.
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