Visceral Nervous System Slides(2)

7/27/2019 Visceral Nervous System Slides(2)

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Visceral Nervous SystemVisceral Nervous System

Alex Forrest

Senior Lecturer in Forensic OdontologyForensic Science Research & Innovation Centre, Griffith University

Consultant Forensic Odontologist,

Queensland Health Pathology and Scientific Services,

39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

Oral Biology


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COMMONWEALTH OF AUSTRALIA

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Do not remove this notice.


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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 the basic

structural organization of the human nervous system.

3. You should understand and be able to explain how thevisceral component of the nervous system relates to the

nervous system as a whole.

4. You should be able to explain the major structural andfunctional characteristics of the somatic and visceral

components of the nervous system.


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The visceral orautonomic nervous system includes part of both

the central and peripheral nervous systems.

Its peripheral part is concerned with the sensory and motor

innervation of viscera, glands, smooth muscle and blood

vessels.



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The visceral systemresponds to changes in

somatic activity of the

body. Therefore the term

autonomic is notappropriate.

We use the term visceral

which describes what thesystem supplies.


http://www.biology.eku.edu/RITCHISO/301notes2b.html


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Afferent (Sensory) Pathways


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Afferent PathwaysAfferent Pathways

Afferent = sensory

The visceral sensory pathways resemble those of somatic

nerves.

The cell bodies of the afferent neurons are located either in thedorsal root ganglia of spinal nerves or the cranial nerve ganglia.

Like the sensory somatic neurons, they do not synapse during

their passage from sensory end-organs to the CNS.

Their axons accompany those of somatic sensory neurons to

the central nervous system.


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Efferent (Motor) Pathways


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Efferent PathwaysEfferent Pathways

Unlike somatic motor pathways, two visceral neurons are

required in the visceral motor pathway, and that means that

there is a synapse in the pathway.

Therefore a ganglion will be found along any nerve carrying

visceral motor fibres to accommodate the nerve cell bodies of

the second neuron in the pathway.


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The nerve cellbodies of the

primary

(preganglionic)

neurons lie in thevisceral motor parts

of various cranial

nerve nuclei, or in

the lateral greycolumns of the

spinal cord.

From Grays Anatomy, Longman, London, 38th Edition, 1989. p 924.



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Their axons, which are

usually myelinated, travel

in cranial or spinal nerves

to enter the visceralganglia.

Here they synapse with

the secondary neurons.




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The axons of these

secondary neurons

are usually

unmyelinated, and

are distributed to

the effector organ.




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Therefore, we talk of a preganglionic neuron and a

postganglionic neuron in the motor or efferent pathway.

http://www.ualr.edu/klwennstrom/autonomic.gif


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Note that the sympathetic preganglionic cell is short it only

has to reach to the ganglia of the sympathetic chain.



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In contrast, the preganglionic parasympathetic cell is very long.

Parasympathetic ganglia are often located on or close to the

organ that is being supplied.



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You should note that there tend to be far more postganglionic

cells than there are preganglionic cells.

Therefore, each preganglionic neuron synapses with many (as

many as 20) postganglionic neurons.

This fact accounts for the wide diffusion of many autonomic

phenomena.


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Copyright Alex Forrest 2013

Now we have looked

at the two divisions of

the visceral system,the sympathetic and

the parasympathetic

divisions, and we have

seen the structuraldifferences between

the two.

There are functionaldifferences as well.


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The sympathetic system is

generally concerned with

the expenditure of energyand defence in

emergencies.

These are widespreadactivities which require a

diffuse distribution.

Its functions, if dischargeden masse, would be useful

to an individual in an

attitude of fight or flight.

Sympathetic DivisionSympathetic Division


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Its functions include the

elevation of the heart

rate, elevation of blood

pressure, stimulation ofbreakdown of liver

glycogen, and dilatation

of the bronchioles.

Sympathetic DivisionSympathetic Division



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Parasympathetic DivisionParasympathetic Division

The parasympathetic

system is primarily

concerned withconservative and

restorative processes such

as slowing the heart rate,

contracting the pupils toprotect the eyes from light,

and inhibiting the utilisation

of liver glycogen.

It has a restricted

distribution with more-or-

less local functions.http://www.biology.eku.edu/RITCHISO/301notes2b.html


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In general, organs

innervated by motor fibresfrom both divisions

respond to them in

opposite ways.

Through such balanced

opposition, the two

divisions coordinate

responses to widelyvarying internal and

external conditions. http://www.biology.eku.edu/RITCHISO/301notes2b.html

Parasympathetic DivisionParasympathetic Division


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Accordingly, the visceral nervous system is essential for the

preservation of internal constancy, or homeostasis.


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Sympathetic System


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The cell bodies of

sympathetic primaryefferent neurons are

located in the grey matter

of the spinal cord in the

thoracolumbar region, andsome anatomists give the

system an alternative

name for that reason:

thoracolumbar system.

Sympathetic SystemSympathetic System

http://soma.npa.uiuc.edu/courses/bio303/Image56.jpg


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Chusid, JG, Correlative

Neuroanatomy &

Functional Neurology,

Lange Medical

Publications, NY, 17th Ed,

1979, p. 140.


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Sympathetic fibresare found leaving

the spinal cord only

in spinal nerves T1-

L2 and not in any

other cranial or

spinal nerves

anywhere in thebody.


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http://inside.salve.edu/walsh/autonomic_system.jpg

However, they

require to bedistributed widely in

the body, and so they

tend to travel to other

more superior andinferior spinal nerves

by spreading

themselves out along

the length of thesympathetic chain.


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The sympathetic chain is a

chain of connected gangliarunning along the side of

the vertebral column.

They contain ganglia andsynapses to connect

preganglionic and

postganglionic sympathetic

motor cells.

McMinn RMH & Hutchings RT, A Colour Atlas of

Human Anatomy, Wolfe Medical Publications,

2nd Edition, p. 196.



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Preganglionic fibres

leave the spinal cord

in the ventral root of

the spinal nerve, andpass into the

common spinal part,

and then into the

ventral ramus.

Grays Anatomy, Longman, London, 38th Edition, 1989. p 924.


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From the ventral ramus, a branch carrying myelinated

preganglionic fibres, called the white ramus communicans,

branches out to connect with the sympathetic chain.

http://publish.uwo.ca/~jkiernan/segm.gif



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When it gets to the

sympathetic chain, thepreganglionic fibres in it

can either synapse in the

sympathetic ganglion, or

they may ascend ordescend before doing

so.

This is how they pass tolevels other than T1-L2.

Grays Anatomy, Longman, London, 38th

Edition,1989. p. 1125.



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Therefore, while only

spinal nerves T1-L2have these white

communicating rami,

they are able to spreadpreganglionic fibres to

every level along the

sympathetic chain

before they synapsewith secondary

neurons.


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Ganglia in the sympathetic chain now need a method of getting

their postganglionic fibres back out of the chain and into spinal

nerves or other pathways for wide distribution in the body.



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They do this by sending a second communicating ramus, this

time containing unmyelinated postganglionic fibres, out to each

spinal nerve.



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This is called the grey ramus communicans, and every spinal

nerve possesses one.



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Grays Anatomy, Longman, London, 38th Edition,

1989. p. 1125.

So that sympathetic

fibres can be distributed

to all parts of the body,

the grey communicating

ramus enters the spinalnerve in the short

common spinal nerve,

and then is distributed

along both dorsal andventral rami.



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Recall that not all postganglionic fibres pass out in the grey

ramus communicans at the spinal level at which they synapsed.

Sometimes they ascend or descend several levels beforeexiting the sympathetic chain.

And sometimes, they simply pass directly to blood vessels in

the vicinity of the ganglion, rather than travelling in a grey

ramus communicans at all.



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Why do you think sympathetic fibres often travel with arteries?

Could there be a reason for this apparently eccentricbehaviour? After all, it is not the pattern followed by other

nerves


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Sympathetic System: Cranial PartSympathetic System: Cranial Part

The cranial part of the sympathetic is the bit with which we asdental and dentally-related practitioners need to be familiar.


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In the neck, the ganglia of the eight spinal nerves have been

consolidated into only three ganglia:


Represents the fused ganglia of C1C4

Represents the fused ganglia of C5 and C6

Formed by the fusion of C7 and T1.

Superior Cervical Ganglion

Middle Cervical Gangl ion

Stellate Ganglion


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Origin Unknown


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As we said before, some sympathetic fibres run in the walls of

arteries.

Sympathetic fibres run from the superior end of thesympathetic chain to form a plexus in the wall of the internal

carotid artery, called the internal carotid plexus. The

connection between this and the superior cervical ganglion is

called the internal carotid nerve.



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The internal carotid nerve begins at the cranial pole of the

superior cervical ganglion. It is therefore an ascending

continuation of the sympathetic trunk. It accompanies the

internal carotid artery through its canal into the cranial cavity

where it forms the internal carotid plexus in the wall of the artery.


Modified from:

Netter, F. 1989,

Atlas of HumanAnatomy,

Summit, New

Jersey, Ciba-

Geigy Medical,

Plate 125.


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Modified from: Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 125.

It contains many sympathetic vasoconstrictor fibres, and

communicates with the trigeminal and pterygopalatine ganglia,

with II, III, IV and VI, and with the ciliary ganglion.



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The branch to the

pterygopalatine

ganglion, called the

deep petrosal

nerve,joins thegreater petrosal

nerve to form the

nerve of the

pterygoid canal.


Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 127.


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Netter, F. 1989, Atlas

of Human Anatomy,

Summit, New Jersey,

Ciba-Geigy Medical,

Plate 127.


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Parasympathetic System

Parasympathetic SystemParasympathetic System


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In this system, the preganglionic fibres are usually long, with

the parasympathetic ganglion being located on, or even in, the

organ supplied. Postganglionic fibres are usually very short.



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Preganglionic fibres

are limited to the

cranial and sacral

regions, a fact that

leads to thealternative name: the

craniosacral system

for the

parasympatheticsystem.



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They occur in

cranial nerves

III, VII, IX and X,

and in spinal

nerves S2-S4.



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Chusid, JG, Correlative

Neuroanatomy &

Functional Neurology,

Lange Medical

Publications, NY, 17th Ed,1979, p. 141.



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In the cranial part of the parasympathetic system there are four

parasympathetic motor ganglia:

The Ciliary Ganglion

The Pterygopalatine Ganglion

The Otic Ganglion

The Submandibular Ganglion




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The ciliary ganglion lies in the orbit, the pterygopalatine

ganglion lies in the pterygopalatine fossa, the otic ganglion inthe infratemporal fossa, and the submandibular ganglion is

associated with the capsule of the submandibular salivary

gland.



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Facial Nerve (VII)

The Facial Nerve (VII)The Facial Nerve (VII)


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Parasympathetic

fibres originate in the

Superior Salivatory

Nucleus of the

midbrain.

They emerge fromthe midbrain in the

sensory root of VII,

the nervus

intermedius, and

travel in the facial

nerve.




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They continue until just before the nerve exits the stylomastoid

foramen and then leave the main nerve trunk to contribute to

the chorda tympani.

http://info.med.yale.edu/caim/cnerves/cn7/cn7_graphics/fig7_18a.gif



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This exits the skull via the anterior canaliculus for the chorda

tympani which is found at the medial end of the petrotympanic

fissure, and passes to join the lingual nerve.



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From the lingual nerve, they pass to the submandibular ganglion

where they synapse with the postganglionic fibres which are

known as the secretomotor fibres for the submandibular and

sublingual salivary glands.



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From Grays Anatomy, Longman, London, 38th

Edition, 1989. p 1105.

( )( )

Other fibres pass tothe pterygopalatine

ganglion via the

tympanic plexus,

the greatersuperficial petrosal

nerve and the

nerve of the

pterygoid canal.



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Here they synapse with the postganglionic fibres which are

relayed via the zygomatic branch of the maxillary division of Vto the lacrimal gland, and by branches from the ganglion to the

minor salivary glands of the nose and palate.

( )( )


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Glossopharyngeal Nerve (IX)

The Glossopharyngeal Nerve (IX)The Glossopharyngeal Nerve (IX)


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The efferent

fibres in this

nerve pass tothe parotid

salivary

gland.

y g ( )y g ( )



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They originate in the inferior salivatory nucleus and travel first

in IX, then in its tympanic branch which passes up through the

tympanic canaliculus in the roof of the jugular fossa.

These fibres traverse the tympanic plexus which also contains

sympathetic fibres from the caroticotympanic nerve from the

carotid plexus.



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They enter the

lessersuperficial

petrosal nerve

at this point, and

this nerve exitsthe temporal

bone and exits

the cranium via

foramen ovaleto reach the otic

ganglion.



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Grays Anatomy, Longmans, London, 38th Ed 1989 p. 1105

They synapse withthe postganglionic

secretomotor fibres

in the otic ganglion

which then run inthe auriculotemporal

nerve to reach the

parotid salivary

gland.


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Vagus Nerve (X)

The Vagus Nerve (X)The Vagus Nerve (X)


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Fibres arise in the dorsal

nucleus of vagus and travelin the nerve trunk and in its

pulmonary, cardiac,

oesophageal, gastric and

intestinal branches.

These fibres are relayed in

minute ganglia which lie in

the walls of the individualviscera.

Grays Anatomy,

Longmans,

London, 38th Ed

1989 p. 1117


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