13.1.1 Nerves - PrelimBio

Topic 13: Nerves
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT Point(s)
 identify that a nerve is a bundle of neuronal fibres
 perform a first-hand investigation using stained prepared slides
and/ or electron micrographs to gather information about the
structure of neurones and nerves
In this section we are going to study how signals from the eye and
ear are transmitted and processed by the brain. We’ll start by
looking at neurones.
The units which make up the nervous system
are the nerve cells or neurones (also called
neurons). There are three types:
1. Sensory neurones: transmit impulses
from sense organs to other neurones in
the central nervous system (CNS)
2. Motor neurones: transmit impulses
from the CNS to muscles and glands
3. Connector neurones: connect sensory
neurones with motor neurones, usually in
the brain and spinal cord.
No two neurones are exactly alike.
Each neurone is considered to have
three parts:
1. Cell body: this contains the
nucleus and forms the grey
matter of the CNS.
2. Dentrites: fine branching
extensions which conduct nerve
impulses towards the cell body.
3. Axon: a single, long extension
which conducts impulses away
from the cell body. This forms
the white matter of the CNS.
 Dendrites and axons
are collectively referred
to as neuronal fibres.
They consist of fluid-filled
tubes, the myelin sheath.
The myelin sheath is
gradually built up as
concentric layers which
are produced and
supported by special cells
(schwann cells) on the
The cell body of a neurone is usually in the brain or the spinal
cord, while the axon or the dendrites usually extend, as part of a
nerve, towards a sensory organ of an effector organ. Nerves can
often stretch over a long distance, for example from the spine to
the hand.
Nerve fibres are able to transmit messages rapidly along their
entire length and pass them to a successive neurone, over small
gaps called synapses.
The myelin sheath has small gaps called the nodes of Ranvier
between the Schwann cells. The ion channels that function in the
action potential are concentrated in the node regions of the
axons. Also, extracellular fluid is in contact with the neuronal
membrane only at these nodes.
The action potential actually ‘jumps’ from node to node, skipping
the insulated regions of the membrane between the nodes. The
greater the insulation through the myelin sheath, the faster
transmission of the nerve impulse.
Structure of Nerves
The cell bodies of neurones are usually situated in the grey
matter of the brain or the spinal cord. Some occur outside the
CNS in clusters called ganglia. Ganglia co-ordinate impulses.
Structure of Nerves
The nervous system is made up of millions of neurones. The
sensory motor fibres of the neurones are gathered into bundles
called nerves. The bundle is held together by a connective tissue
-Students to complete PRAC/DOT Point 7.3 Structures of
neurones and nerves

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