Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)

7/27/2019 Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)

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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

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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.


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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.


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.


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.



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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.


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.



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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.


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.



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.



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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.


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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


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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


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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


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It is divided by a large longitudinal fissure into right and left

cerebral hemispheres.

http://www.neuroscience.pomona.edu/Menu/Brain.JPG


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.


http://www.csit.fsu.edu/~beason/ph

oto2002/hw06/brain.jpg


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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.


http://www.ling.upenn.edu/undergrad/brain_regions.gif


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


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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.



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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.


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.



Grays Anatomy, London, Longman, 37 th Ed, 1989, p. 1088


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.


http://www.bmb.psu.edu/courses/bis

ci004a/nerve/fig17-1.jpg


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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.



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.


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


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.


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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.


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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.


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.


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.



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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


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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).


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.




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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.


A spinal nerve

therefore appears to

arise from the spinal

cord by two roots.

The ventral root

contains efferent ormotor 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.


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.




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Each ramus will

therefore contain

both afferent and

efferent somatic

fibres.



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.



The ventral rami

form the major

nerve plexuses ofthe body, and

contribute to the

nerve trunks seen in

most of the body

during dissection.



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.



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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

Introduction to Nervous System and Spinal Nerves Condensed Grayscale Slides(1)

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