-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
1/20
The Nervous SystemThe Nervous System
Alex ForrestAssoci ate Profess or of For ensic Od ontol ogyForensic Science Research & Innovation Centre, Griffith UniversityConsultant Forensic Odontologist,Queensland Health Forensic and Scientific Services,
39 Kessels Rd, Coopers Plains, Queensland, Australia 4108
Oral Biology
COMMONWEALTH OF AUSTRALIA
Copyright Regulations 1968
WARNING
This material has been reproduced and communicated to you by, or on
behalf of, Griffith University, pursuant to Part VB of The Copyright Act 1968(The Act; a copy of the Act is available at SCALEPlus, the legal
information retrieval system owned by the Australian Attorney Generals
Department, at http://scaleplus.law.gov.au).
The material in this communication may be subject to copyright under the
Act. Any further reproduction or communication of this material by you maybe the subject of Copyright Protection under the Act.
Information or excerpts from this material may be used for the purposes of
private study, research, criticism or review as permitted under the Act, and
may only be reproduced as permitted under the Act.
Do not remove this notice.
Learning ObjectivesLearning Objectives
1. You should be able to construct a concept map of the
nervous system.
2. You should understand and be able to explain thebasic structural organization of the human nervous
system.
3. You should be able to explain the major structural and
functional characteristics of the somatic components of
the nervous system.
Intercellular CommunicationIntercellular Communication
The body depends not only on proper structure of its billions of
cells to function, but also on communication between thosecells.
Sometimes this is automatic, and sometimes it is under
conscious control.
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
2/20
There are two major communication systems in the body.
These are the nervous system and the endocrine system.
While both systems are designed to transmit information from
one area of the body to others, they do it in quite different ways.
Intersystem CommunicationIntersystem Communication
The nervous system is specialized to transmit selected
information very rapidly from one part of the body to another.
This information is often quite specific, and it can be very
accurately targeted.
Intersystem CommunicationIntersystem Communication
The endocrine system, by contrast, works far more slowly.
It operates by secreting hormones from ductless glands into the
blood-vascular system, and these are then circulated to other
organs and parts of the body.
Intersystem CommunicationIntersystem Communication
These two systems operate to control and integrate the body's
functions, enabling the body to look after itself and take care of
its needs.
Intersystem CommunicationIntersystem Communication
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
3/20
Nervous SystemNervous System
Today we examine aspects of the anatomy of the human
nervous system.
We will begin by discussing the basic layout of the nervous
system and its various divisions.
Then, we shall discuss the voluntary or somatic nervousstructures, and examine the mechanisms by which they
communicate with the brain through the spinal cord.
The organs of the nervous system include the brain and the
spinal cord as well as the various nerves of the body.
Also included are the specialised sense organs such as the
ears and eyes, and the tiny sense organs found in the skin and
in other organs of the body.
Nervous SystemNervous System
We can divide the
nervous system into
two major parts:
Central Nervous System
Peripheral Nervous System
Copyright Alex Forrest 2013
The central nervous
system comprises
the brain and spinal
cord.
It is called the CNS
because it occupies
a central midline
position in the body.
Copyright Alex Forrest 2013
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
4/20
The peripheral
nervous system (PNS)
comprises the afferent
(sensory) fibres, which
connect the sensory
end organs to the
central nervous
system, and the
efferent (motor) fibres,
which connect thecentral nervous
system to the effector
organs.
Copyright Alex Forrest 2013
It can be divided into a
somatic or voluntary
component, and a
visceral, or autonomic
or involuntary part.
The visceral system is
further subdivided into
a sympathetic and aparasympathetic part.
Copyright Alex Forrest 2013
Nervous SystemNervous System
The peripheral nervous system includes the 31 pairs of spinalnerves and the 12 cranial nerves.
The sympathetic trunks with their ganglia and branches also
belong to this system.
Individual spinal nerves can contain fibres of both somatic and
visceral nerves, and there is a very clear pattern of distributionof such fibres throughout the peripheral nervous system, as we
shall see.
They contain both afferent (incoming sensory) and efferent
(outgoing motor) fibres.
Nervous SystemNervous System
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
5/20
Sensory fibres connect with general sensory endings, which
are scattered profusely throughout the body.
These are biological transducers in which physical stimuli
create action potentials in nerve endings.
On reaching the central nervous system, the resulting nerveimpulse gives rise to reflex response, awareness of the
stimulus, or both.
Nervous SystemNervous System Sensory Nerve EndingsSensory Nerve Endings
General sensory nerve endings may be divided into:
Exteroceptors
Proprioceptors
Interoceptors
Cutaneous endings are called exteroceptors and are sensitive
to stimuli for pain, temperature, touch and pressure.
Proprioceptors in muscles, tendons and joints provide data forreflex adjustments of muscle action, and for awareness of
position and movement.
Interoceptors arise within the viscera. Central conduction is
through sensory visceral neurons, and will be discussed in the
next session.
Sensory Nerve EndingsSensory Nerve Endings GangliaGanglia
Nerve ganglia (singular = ganglion) are aggregations of nerve
cell bodies found on some peripheral nerves.They contain nerve cell bodies and their nerve fibres (axons),
as well as fibres derived from cells elsewhere which pass right
through or terminate within the ganglion.
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
6/20
They are present in the dorsal roots of the spinal nerves and
the sensory roots of V, VII, VIII, IX, X.
They also occur in association with visceral (or autonomic)
nerves.
GangliaGanglia Cells of the Nervous SystemCells o f the Nervous System
The two types of cell found in the nervous system are called
neurons (or nerve cells), and glia (specialised connective tissue
supporting cells).
Each neuron comprises
three parts:
NeuronsNeurons
https://reader008.{domain}/reader008/html5/0417/5ad5846760590/5ad5846cbbe58.jpg
A cel l bo dy
One or more branchingprojections called dendrites
An ax on
Sensory neurons (afferent neurons) transmit information to the
brain and spinal cord from the various parts of the body.
Motor neurons (efferent neurons) transmit information away
from the brain and out to various glands and muscles.
Interneurons connect sensory and motor neurons and transmit
information between the two.
NeuronsNeurons
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
7/20
Some neurons are myelinated. This means the axon is
surrounded by a whitish material called myelin.
NeuronsNeurons
http://ccins.camosun.bc.ca/~tonks/courses/psyc110/neuron.jpg
Myelin is
secreted by a
special cell
called a
Schwann cell,
which wraps
around theaxons of some
cells in the PNS.
NeuronsNeurons
https://reader008.{domain}/reader008/html5/0417/5ad5846760590/5ad5846ee50f3.jpg
Nodes occur in between
myelinated segments of axon,
and these are termed the
Nodes of Ranvier.
The presence of myelin tends
to speed up conduction in an
axon.
NeuronsNeurons
http://www.bmb.psu.edu/courses/bisci004a/nerve/ner
veb4.htm
GliaGlia
Glial cells, also known as neuroglia, are cells in the nervous
system that are not specialised for transmitting electrical
signals.
http://www.bmb.psu.edu/courses/bisci004a/nerve/nerveb4.htm
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
8/20
GliaGlia
Glial cells are actually aspecialised type of
connective tissue cell,
and they hold the
functioning neurons
together and protect
them.
They include Astrocytes,
Oligodendrocytes (which
produce the CNS myelin http://www.bmb.psu.edu/courses/bisci004a/nerve/nerveb4.htm
sheath), Microglia (CNS macrophages) and Ependymal cells in
the CNS, and the Schwann cells in the PNS.
They are implicated in some of the most serious central
nervous system neoplasia (cancers).
Central Nervous SystemCentral Nervous System
BrainBrain
CNS - BrainCNS - Brain
The cerebrum is the largest and most superior part of the brain
in man.
It features numerous gyri and sulci (or folds and valleys).
http://projects.edtech.sandi.net/brooklyn/humanbody/images/brain.gif
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
9/20
CNS - BrainCNS - Brain
It is divided by a large longitudinal fissure into right and left
cerebral hemispheres.
http://www.neuroscience.pomona.edu/Menu/Brain.JPG
CNS - BrainCNS - Brain
These hemispheres are connected by the corpus callosum which
comprises vast bundles of connections (myelinated axons).
https://reader008.{domain}/reader008/html5/0417/5ad5846760590/5ad58471c2193.jpg
http://www.ai.mit.ed
u/people/ekm/homer
-brain.jpg
The surface of the cerebrum is made
of gray matter. It is called the cerebral
cortex.
Gray matter comprises nerve cellbodies and dendrites with some glial
cells.
Inside the cerebrum lies white matter,
which is made up of bundles of
myelinated nerve axons or tracts.
CNS - BrainCNS - Brain
http://www.csit.fsu.edu/~beason/ph
oto2002/hw06/brain.jpg
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
10/20
CNS - BrainCNS - Brain
http://faculty.washington.edu/chudler/functional.html
Specific areas of the cerebral cortex have quite specific
functions.
For instance, the areas for vision lie in the occipital lobe.
Damage to this area can impair or destroy the ability to see.
The areas for auditory function lie in the temporal lobes.
General sensory and motor areas are mapped out on the post-
central and pre-central gyri respectively.
CNS - BrainCNS - Brain
http://www.ling.upenn.edu/undergrad/brain_regions.gif
CNS - BrainCNS - Brain
http://sds1.files.wordpress.com/2007/10/male_brain.gif
Gary Larsen,
from:
http://www.th.physik.un
i-
frankfurt.de/~jr/gif/carto
on/brain.jpg
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
11/20
CNS - BrainCNS - Brain
http://www.astro.univie.ac.at/~dsn/gerald/brain.jpg
Spinal CordSpinal Cord
CNS Spinal CordCNS Spinal Cord
The adult spinal cord is about half
a metre long, quite short when
you think of the overall length of
the body trunk.
It lies inside the vertebral columnin the spinal canal.
The core of the cord consists of
gray matter, and the outside is
white matter, the opposite of what
we find in the cerebrum.
http://www.back.com/anatomy-lumbar.html
The white matter comprises bundles of myelinated nerve fibres
- spinal tracts - which provide conduction paths to and from the
brain.
Ascending tracts send information to the brain (sensory), and
descending tracts carry information from the brain (motor).
The spinal cord provides the link between the CNS and the rest
of the body through the PNS. It also provides reflex arcs for
rapid control.
CNS Spinal CordCNS Spinal Cord
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
12/20
The spinal cord and
the dorsal root ganglia
are directly
responsible for
innervation of the
body, except for most
of the head andviscera, which are
innervated by Cranial
Nerves.
CNS Spinal CordCNS Spinal Cord
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Afferent (sensory)
fibres enter the cord
through the dorsal
roots of the spinal
nerves, while efferent
(motor) fibres leave by
way of the ventralroots.
This is known as the
Bell-Magendie Law.
CNS Spinal CordCNS Spinal Cord
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Grays Anatomy, London, Longman, 37 th Ed, 1989, p. 1088
CNS Spinal CordCNS Spinal Cord
The spinal cord is a
cylindrical structure, slightly
flattened dorso-ventrally. It
occupies the spinal canal in
the vertebral column.
Protection is provided by the
vertebrae and their ligaments,
and by the meninges and a
cushion of cerebrospinal fluid.
The segmented nature of the
spinal cord is demonstrated
by the presence of 31 pairs ofspinal nerves.
There is, however, little
evidence of segmentation in
its internal structure.
CNS Spinal CordCNS Spinal Cord
http://www.bmb.psu.edu/courses/bis
ci004a/nerve/fig17-1.jpg
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
13/20
In the spinal cord,
the white matter of
the cord lies on the
outside, and
comprises bundles
of axons ascending
to the brain and
brainstem, ordescending from the
brain and
brainstem.
CNS Spinal CordCNS Spinal Cord
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
A tract occurs in the central nervous system, and may be
thought of as a group of axons that serve a similar function, that
are grouped together.
It is almost the CNS equivalent of a PNS nerve.
CNS Spinal CordCNS Spinal Cord
Spinal Cord Grey MatterSpinal Cord Grey Matter
As seen in transverse
section, the grey matter
has a roughly butterfly-
shaped outline. It containsa small central canal.
Dorsal and ventral grey
commissures surround the
central canal.
Modified from: Grays Anatomy, London, Longman, 37 th Ed,
1989, p.928
CNS Spinal CordCNS Spinal Cord
The cells of the dorsal horn and the intermediate zone consist
mainly of tract cells, and internuncial neurons which receive
incoming sensory connections (afferents) from the dorsal rootfibres, and connect either on motor cells (for reflex loops), or
on tract cells for communication with higher centres. Note
particularly, however, the substantia gelatinosa (see next
slide).
The ventral horn consists mostly of motor cell bodies.
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
14/20
CNS Spinal CordCNS Spinal Cord
Modified from: Grays Anatomy, London, Longman, 37 th Ed, 1989, p.928
Dorsal HornDorsal Horn
The dorsal horn is where many of the peripheral sensory fibres
terminate to connect with other neurons that either ascend to
the brain/brainstem or form reflex loops for rapid reactions.
As we said previously, the substantia gelatinosa is found here,
and it plays a major role in the perception of pain.
Ventral HornVentral Horn
The efferent, or motor, part of the grey matter is found in the
ventral horn.
White MatterWhite Matter
The white matter consists of nerve fibres, neuroglia and blood
vessels.
Its whiteness is due to the large proportion of myelinated
nerve fibres present.
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
15/20
White MatterWhite Matter
Within each
funiculus are tracts
of fibres, some of
which may be
ascending, that is
taking data to
supraspinal levels,
descending, or
carrying efferent
data from higher
levels, or Modified from: Grays Anatomy, London, Longman, 37th Ed, 1989, p.930
intersegmental, which is to say that they consist of tracts of
fibres connecting a number of segments.
White MatterWhite Matter
A fibre tract is defined as a bundle of fibres having the same
origin, termination and function.
The origin is the locus of the cell bodies, and the termination is
the point at which the fibres synapse with the cell bodies of the
next neurons in the chain.
Afferent fibres
from the dorsal
root enter the
spinal cord in
an area knownas the
dorsolateral
tract because
of its
relationship to
the dorsolateral
sulcus.
White MatterWhite Matter
Modified from: Grays Anatomy, London, Longman, 37 th Ed, 1989, p.930
These fibres give off short ascending and descending
branches, and the entire fibre terminates in the substantiagelatinosa of the segment of entry, or the next segment
caudally or rostrally.
The dorsolateral tract is sometimes known as the Zone of
Lissauer.
White MatterWhite Matter
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
16/20
MeningesMeninges
The central nervous system is delicate and vulnerable to
damage.
It is therefore surrounded and cushioned by a series of
membranes and fluid spaces which help absorb mechanical
stress.
These membranes are called the meninges, and they are, in
turn, surrounded by bone.
MeningesMeninges
The meningeal layers
are, from superficial
to deep:
Dura mater
Arac hnoid mate r
Pia Mater
Cerebro-spinal fluid
CSF circulates in the
subarachnoid space.Grays Anatomy, London, Longman, 37 th
Ed, 1989, p. 1088
CSF circulates in the subarachnoid space.
It also fills spaces in the brain that are termed ventricles. CSF is
filtered from the blood by the choroid plexus and passes intothe ventricles.
It then circulates around the spinal cord and brain before
returning to the blood system via the arachnoid granulations
into the cranial venous sinuses.
MeningesMeninges
Peripheral Nervous SystemPeripheral Nervous System
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
17/20
Copyright Alex Forrest 2013
Somatic or
"voluntary" nerve
fibres are found in all
cranial and spinal
nerves.
They are motor infunction.
Sensory Somatic FibresSensory Somatic Fibres
Nerve impulses from exteroceptors and proprioceptors are
conducted centrally by primary sensory neurons whose cell
bodies are located in the dorsal root ganglia (or a cranial nerve
ganglion).
Sensory Somatic FibresSensory Somatic Fibres
On entering the spinal cord, the dorsal root fibres divide into
ascending and descending branches.
These are distributed as necessary for reflex responses and fortransmission of sensory data to the brain.
They enter the dorsolateral tract of the segment of arrival, or
ascend or descend a number of segments before entering this
tract. They then synapse with either an internuncial neuron or
directly with a tract cell.
Note that the dorsal
root ganglia contain
no synapses.
They contain only the
bodies of the sensoryneurons, whose
axons pass from the
sensory endings.
These cells are
referred to as
primary sensory
neurons.
Sensory Somatic FibresSensory Somatic Fibres
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
18/20
Motor Somatic FibresMotor Somatic Fibres
The somatic efferent neurons for the innervation of skeletal
muscle are the axons of neurons in the anterior grey column of
the spinal cord.
Again, only one cell is required to reach the muscle and
terminate in a motor end-plate.
Motor Somatic FibresMotor Somatic Fibres
A spinal nerve
therefore appears to
arise from the spinal
cord by two roots.
The ventral root
contains efferent ormotor fibres.
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Motor Somatic FibresMotor Somatic Fibres
The dorsal root
contains afferent or
sensory fibres, and
is associated with adorsal root ganglion
which contains the
cell bodies of the
primary sensory
neurons.
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Shortly after leaving
the spinal cord, the
two roots unite to
form a commonspinal nerve which
emerges through
the intervertebral
foramen and
immediately divides
into a dorsal and a
ventral ramus.
Motor Somatic FibresMotor Somatic Fibres
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
19/20
Each ramus will
therefore contain
both afferent and
efferent somatic
fibres.
Motor Somatic FibresMotor Somatic Fibres
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
The dorsal rami are
usually smaller than
the ventral ones,
and turn posteriorly
to innervate
muscles and skin
over the posteriorregions of the neck
and trunk.
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Motor Somatic FibresMotor Somatic Fibres
The ventral rami
form the major
nerve plexuses ofthe body, and
contribute to the
nerve trunks seen in
most of the body
during dissection.
Grays Anatomy, London, Longman, 37 th Ed, 1989, p.924
Motor Somatic FibresMotor Somatic Fibres
There is no synapse along the length of a somatic efferent
peripheral nerve (which emerges in the ventral root), and
therefore no somatic ganglion exists on this root.
Motor Somatic FibresMotor Somatic Fibres
-
7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)
20/20
Copyright Alex Forrest 2013
We will discuss the
visceral division of
the Peripheral
Nervous System in a
later session.
Cranial NervesCranial Nerves
There are twelve cranial nerves.
They are traditionally numbered using Roman numerals, in the
order that they emerge from the brainstem.
Cranial NervesCranial Nerves
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
XII
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abd ucens
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Acc ess ory
Hypoglossal
Smells
Sees
Moves eye
Moves eye
Eats, feels face
Moves eye
Moves face, salivates
Hears and balances
Swallows, feels throat, salivates
Speaks, swallows, digests, controls heart
Shrugs shoulders, turns head
Moves tongue
The End