Visceral Nervous System Condensed Grayscale Slides(1)

Visceral Nervous SystemVisceral Nervous System

Alex ForrestSenior Lecturer in Forensic OdontologyForensic Science Research & Innovation Centre, Griffith UniversityConsultant Forensic Odontologist, Queensland Health Pathology and Scientific Services, 39 Kessels Rd, Coopers Plains, Queensland, Australia 4108

Oral Biology

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Learning Objectives Learning 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 the visceral component of the nervous system relates to the nervous system as a whole.

4. You should be able to explain the major structural and functional characteristics of the somatic and visceral components of the nervous system.

The visceral or autonomic 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.

Visceral Nervous System Visceral Nervous System

The visceral system responds to changes in somatic activity of the

body. Therefore the term “autonomic” is not

appropriate.

We use the term visceralwhich describes what the

system supplies.

Visceral Nervous System Visceral Nervous System

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

Afferent (Sensory) Pathways

Afferent Pathways Afferent Pathways

Afferent = “sensory”

The visceral sensory pathways resemble those of somatic nerves.

The cell bodies of the afferent neurons are located either in the dorsal 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.

Efferent (Motor) Pathways

Efferent Pathways Efferent 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.

The nerve cell bodies of the

primary (preganglionic)

neurons lie in the visceral motor parts

of various cranial nerve nuclei, or in

the lateral grey columns of the

spinal cord.

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


Their axons, which are usually myelinated, travel in cranial or spinal nerves

to enter the visceral ganglia.

Here they synapse with the secondary neurons.



The axons of these secondary neurons

are usually unmyelinated, and are distributed to

the effector organ.




Therefore, we talk of a preganglionic neuron and a postganglionic neuron in the motor or efferent pathway.

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


Note that the sympathetic preganglionic cell is short – it only has to reach to the ganglia of the sympathetic chain.



In contrast, the preganglionic parasympathetic cell is very long. Parasympathetic ganglia are often located on or close to the

organ that is being supplied.



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.

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 structural

differences between the two.

There are functional differences as well.


The sympathetic system is generally concerned with the expenditure of energy

and defence in emergencies.

These are widespread activities which require a

diffuse distribution.

Its functions, if discharged en masse, would be useful

to an individual in an attitude of “fight or flight”.

Sympathetic Division Sympathetic Division

Its functions include the elevation of the heart

rate, elevation of blood pressure, stimulation of

breakdown of liver glycogen, and dilatation

of the bronchioles.

Sympathetic Division Sympathetic Division


Parasympathetic Division Parasympathetic Division

The parasympathetic system is primarily

concerned with conservative and

restorative processes such as slowing the heart rate, contracting the pupils to

protect 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

In general, organs innervated by motor fibres

from both divisions respond to them in

opposite ways.

Through such balanced opposition, the two divisions coordinate responses to widely varying internal and external conditions. http://www.biology.eku.edu/RITCHISO/301notes2b.html

Parasympathetic Division Parasympathetic Division

Accordingly, the visceral nervous system is essential for the preservation of internal constancy, or homeostasis.

Sympathetic System

The cell bodies of sympathetic primary efferent neurons are

located in the grey matter of the spinal cord in the

thoracolumbar region, and some anatomists give the

system an alternative name for that reason:

“thoracolumbar system”.

Sympathetic SystemSympathetic System

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

Chusid, JG, Correlative Neuroanatomy &

Functional Neurology, Lange Medical

Publications, NY, 17th Ed, 1979, p. 140.



Sympathetic fibres are found leaving

the spinal cord only in spinal nerves T1-L2 and not in any other cranial or spinal nerves

anywhere in the body.


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

However, they require to be

distributed widely in the body, and so they tend to travel to other

more superior and inferior spinal nerves

by spreading themselves out along

the length of the sympathetic chain.

The sympathetic chain is a chain of connected ganglia running along the side of

the vertebral column.

They contain ganglia and synapses 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.



Preganglionic fibres leave the spinal cord in the ventral root of the spinal nerve, and

pass into the common spinal part,

and then into the ventral ramus.

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


When it gets to the sympathetic chain, the

preganglionic fibres in it can either synapse in the sympathetic ganglion, or

they may ascend or descend before doing

so.

This is how they pass to levels other than T1-L2.

Grays Anatomy, Longman, London, 38th Edition, 1989. p. 1125.

Sympathetic SystemSympathetic System Sympathetic SystemSympathetic System


Therefore, while only spinal nerves T1-L2have these white

communicating rami, they are able to spread preganglionic fibres to every level along the

sympathetic chain before they synapse

with secondary neurons.


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.



They do this by sending a second communicating ramus, this time containing unmyelinated postganglionic fibres, out to each

spinal nerve.



This is called the grey ramus communicans, and every spinal nerve possesses one.


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 spinal

nerve in the short common spinal nerve, and then is distributed along both dorsal and

ventral rami.


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 before exiting 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.

Sympathetic SystemSympathetic System Sympathetic SystemSympathetic System

Why do you think sympathetic fibres often travel with arteries?

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

nerves …

Sympathetic System: Cranial PartSympathetic System: Cranial Part

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

In the neck, the ganglia of the eight spinal nerves have been consolidated into only three ganglia:


Represents the fused ganglia of C1 –C4

Represents the fused ganglia of C5 and C6

Formed by the fusion of C7 and T1.

Superior Cervical Ganglion

Middle Cervical Ganglion

Stellate Ganglion


Origin Unknown

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

Sympathetic fibres run from the superior end of the sympathetic 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.


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 Human

Anatomy, Summit, New Jersey, Ciba-

Geigy Medical, Plate 125.


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.

The branch to the pterygopalatine

ganglion, called the deep petrosal

nerve, joins the greater 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.

Netter, F. 1989, Atlas of Human Anatomy,

Summit, New Jersey, Ciba-Geigy Medical,

Plate 127.

Parasympathetic System


Parasympathetic SystemParasympathetic System

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.



Preganglionic fibres are limited to the cranial and sacral regions, a fact that

leads to the alternative name: the craniosacral system

for the parasympathetic

system.


They occur in cranial nerves

III, VII, IX and X, and in spinal nerves S2-S4.


Chusid, JG, Correlative Neuroanatomy &

Functional Neurology, Lange Medical

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

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


The ciliary ganglion lies in the orbit, the pterygopalatine ganglion lies in the pterygopalatine fossa, the otic ganglion in the infratemporal fossa, and the submandibular ganglion is associated with the capsule of the submandibular salivary

gland.


Facial Nerve (VII)


Parasympathetic fibres originate in the Superior Salivatory

Nucleus of the midbrain.

They emerge from the midbrain in the sensory root of VII,

the nervus intermedius, and travel in the facial

nerve.

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

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

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


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.



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.



Other fibres pass to the pterygopalatine

ganglion via the tympanic plexus,

the greater superficial petrosal

nerve and the nerve of the

pterygoid canal.

Here they synapse with the postganglionic fibres which are relayed via the zygomatic branch of the maxillary division of V to the lacrimal gland, and by branches from the ganglion to the

minor salivary glands of the nose and palate.


Glossopharyngeal Nerve (IX)


The efferent fibres in this

nerve pass to the parotid

salivary gland.

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

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.



They enter the lesser

superficial petrosal nerve

at this point, and this nerve exits the temporal

bone and exits the cranium via foramen ovale

to reach the otic ganglion.


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

They synapse with the postganglionic secretomotor fibres in the otic ganglion which then run in

the auriculotemporal nerve to reach the

parotid salivary gland.


Vagus Nerve (X)

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

Fibres arise in the dorsal nucleus of vagus and travel in 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 individual

viscera. Grays Anatomy, Longmans,

London, 38th Ed 1989 p. 1117

The End

Visceral Nervous System Condensed Grayscale Slides(1)

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