Term |
Function(s) |
Structure(s) |
Axon |
|
A nerve fibre: a single
process extending from the cell body of
a neurone and carrying nerve impulses away
from it. |
Dendrite |
Carries nerve impulses from
adjacent neurons into the cell body. |
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. |
| 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.) |
|
Motor
Neurone =
"Efferent Neurone" |
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. |
See Figure (1) in the diagram
above. |
|
|
Myelin
Sheath |
Three key functions
of Myelin Sheath are: |
A complex material formed
of protein and phospholipid (fat) that is
laid down as a sheath around the axons of
certain neurons. |
- Protection of the
nerve fibre.
- Insulation of the
nerve fibre.
- Increases the rate
of transmission of nerve impulses.
|
Nerve |
A nerve is a bundle containing
100s to 1000s of axons (thread-like conductors)
plus the associated connective tissue and
blood vessels. |
See the diagrams above.
Figures (1), (2) and (3). |
Neurilemma |
|
The sheath of the axon of
a nerve fibre. The neurilemma of a medullated
fibre contains myelin laid down by Schwann
cells. |
Neurone |
A cell specialized to transmit
electrical nerve impulses and so carry information
from one part of the body to another.
"Neurone" = "Nerve Cell" |
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. |
Nodes
of Ranvier |
Key functions of Nodes
of Ranvier include: |
Gaps that occur at regular
intervals in the myelin sheath of medullated
nerve fibres, between adjacent Schwann cells. |
- Allowing nutrients
and waste products to enter/leave
the neurone.
- Allowing nerve impulses
to move along the neurone through
a process of
de-polarisation and re-polarisation
of the nerve membrane.
|
|
|
Relay
Neurone |
Located within the Central
Nervous System (CNS), relay neurons transmit
the electrical impulses generated by the
stimuli to other nerves. |
See Figure (3) in the diagram
above. |
Schwann
Cells |
Schwann cells are the cells
that lay down the protective myelin sheath
around the axon of medullated nerve fibers. |
Each Schwann cell protects
one length of axon, around which it twists
as it grows - enveloping the axon. |
Sensory
Neurone |
Transmit impulses inwards
from sense organs to the Central Nervous
System (CNS). |
See Figure (2) in the diagram
above. |
Synapse |
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.) |
The minute gap across which
nerve impulses pass from one neurone to
the next, at the end of a nerve fibre. |
