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The
Nervous System (part II)
Adrian
Whyte and Joanna Johnson, Contributor
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| KFC/ISSA
High School basketball match between
Calabar and Wolmer's played at
the National Stadium courts on
Monday, March 27. - Winston Sill
Photo |
THE
PERIPHERAL nervous system (PNS) consists
of the neurons not included in the brain
and spinal cord. Some peripheral neurons
collect information from the body and
transmit it toward the central nervous
system (CNS). These are called sensory
neurons. Other peripheral neurons transmit
information away from the CNS. These
are called motor neurons.
The
five sense organs or receptors are
also a very important part of this
system, namely eyes, ears, skin, tongue
and nose.
NEURONS
The single unit of the nervous system
is the neuron. These are cells that
carry messages through out the nervous
system.
The neuron is the basic functional
unit of the nervous system.
Whatever their specific function,
all neurons have the same physical
parts:the cell body, dendrites and
one axon.
Messages take the form of electrical
signals and are known as impulses.
A neuron carries impulses in only
one direction.
Neurons can be classified into three
types:
SENSORY
(RECEPTOR) NEURONS
These
carry impulses from the sense organs
to the brain and spinal cord. Receptors
detect external or internal changes
and send the information to the central
nervous system in the form of impulses
by way of the afferent neurons.
MOTOR
NEURONS
They
carry impulses from the brain and
spinal cord to muscles or glands.
In response to impulses, muscles contract
and glands secrete.
INTERMEDIATE
NEURONS
These
neurons connect sensory and motor
neurons and carry impulses between
them. They are found entirely within
the CNS.
A
neuron consists of three main parts:
CELL
BODY
This
is the largest part and it contains
the nucleus and much of the cytoplasm.
Most of the metabolic activity of
the cell is carried out here, including
the making of ATP.
DENDRITES
Short
branch extensions spreading out from
the cell body. They receive stimulus
and carry impulses from the environment
or from other neurons and carry them
toward the cell body.
AXON
An
axon is a long fibre that carries
impulses away from the cell body.
Each neuron has only one axon. This
ends in a series of small swellings
called axon terminals.
Neurons
may have dozens or even hundreds of
dendrites but usually one axon. The
Axons of most neurons are covered
with a lipid layer known as the myelin
sheath.
MEYLIN
SHEATH
This
both insulates and speeds up transmission
of action potentials through the axon.
Gaps or nodes in the myelin sheath
along the length of the axon are known
as the nodes of ranvier.
*
Adrian Whyte and Joanna Johnson
teach Biology at Ardenne High School
masterbio@gmail.com.
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