brainstem and nuclei slides(1)
TRANSCRIPT
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Brainstem and NucleiBrainstem and Nuclei
Alex Forrest
Associate Professor of Forensic OdontologyForensic Science Research & Innovation Centre, Griffith University
Consultant Forensic Odontologist,
Queensland Health Forensic and Scientific Services,
39 Kessels Rd, Coopers Plains, Queensland, Australia 4108
Oral Biology
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COMMONWEALTH OF AUSTRALIA
Copyright Regulations 1968
WARNING
This material has been reproduced and communicated to you by, or onbehalf 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 may
be 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.
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Learning ObjectivesLearning Objectives
You should have a general picture of the important
relationships between the major brainstem nuclei associated
with the cranial nerves.
You should understand and be able to describe and discuss
how the relationships between these nuclei will be useful in
diagnosis of neurological lesions you may encounter duringpractice.
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Brainstem
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BrainstemBrainstem
The brainstem unites thebrain (cerebrum and
cerebellum) with the
spinal cord. It comprises
three parts:
midbrain
pons
medulla oblongata
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BrainstemBrainstem
The brainstem transmits allsensory and motor
pathways and information
between the brain and the
spinal cord.
In the brainstem, one finds
the central connections of
the cranial nerves and theirassociated nuclei.
http://www-
unix.oit.umass.edu/~psyc335c/lectures/hindbrain.gif
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Reticular FormationReticular Formation
Scattered deeply
throughout the brainstemare loosely organized
groups of material
collectively known as the
reticular formation, which
have important tasks in
relation of the level of
awareness orconsciousness, respiratory
and cardiac function, and
other things as well.
http://www.biology.eku.edu/RITCHISO/reticularformation.gif
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MidbrainMidbrain
The midbrain forms the
most superior part of thebrainstem.
It houses a canal which
connects a diamond-
shaped space in the
medulla oblongata called
the fourth ventricle, which
connects with the thirdventricle, lying between
the cerebral hemispheres
of the brain.
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MidbrainMidbrain
This canal joining them is called the cerebral aqueduct, and is
continuous with the central canal of the spinal cord.
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 102.
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MidbrainMidbrain
The part of themidbrain posterior to
the aqueduct is called
the roof of the
aqueduct, or thetectum, and on its
surface are four small
elevations called thecolliculi, arranged in
pairs.Netter, F. 1989, Atlas of Human Anatomy, Summit, New
Jersey, Ciba-Geigy Medical, Plate 109.
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MidbrainMidbrain
The colliculi are important in reflex activity. The upper pair is
associated with vision, the lower pair with hearing and balance.
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 109.
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MidbrainMidbrain
Therefore, the dorsal part of the midbrain is mainly given over
to the visual and auditory systems, and in the ventral part are
nuclei for the oculomotor (III) and trochlear (IV) nerves.
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 108.
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MidbrainMidbrain
The part anterior to the aqueduct is formed by the cerebral
peduncles which enter the cerebral hemispheres.
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 109.
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Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 108.
PonsPons
The pons is the part of the brainstem between the midbrain
and the medulla.
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Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 108.
PonsPons
It lies anterior to the connections of the cerebellum, and much
of its structure comprises fibres passing across the midline to
connect one cerebellar hemisphere with that on the other side.
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Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 108.
PonsPons
Posteriorly, the cerebellum attaches to the pons by means of
the cerebellar peduncles.
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PonsPons
In diagrams of the brainstem, the cerebellum is removed to give
visibility, and these cut peduncles appear as ovoid masses.
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-Geigy Medical, Plate 108.
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PonsPons
The dorsal portion of
the pons containssensory and motor
tracts, and the nuclei of
the abducens, facial
and trigeminal nerves.
Ventrally, it contains
bundles of fibres
connecting the twocerebellar hemispheres.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
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PonsPons
Cranial nerves V VIIIexit the brainstem from
the pons, and many of
the cranial nuclei
associated with thetrigeminal nerve are
found here.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
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PonsPons
In the pons, it
becomes clear that
motor nuclei tend to
be situated more
medially than sensory
nuclei.
We also find thatnuclei with related
functions tend to be
grouped fairly close to
each other.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey, Ciba-
Geigy Medical, Plate 110.
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Medulla OblongataMedulla Oblongata
The medulla oblongata is
the most inferior part of
the brainstem, and is a
direct continuation of thespinal cord as it passes
through foramen magnum
into the cranium.
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It begins at the foramen magnum by convention.
This is an arbitrarily chosen border and does not reflect ananatomical change.
It ends at the inferior border of the pons.
Medulla OblongataMedulla Oblongata
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On the lateral surfacethere is a swelling on
each side known as the
olive, and anteriorly, a
second swelling close
to the midline called
the pyramid.
The pyramids are
separated by the
anteromedian fissure.
Medulla OblongataMedulla Oblongata
Grays Anatomy, Longmans, London, 38th
Ed 1989 p. 965
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The grey matter and
white matter of the
spinal cord get
rearranged in thisarea. The ventral grey
horns (motor) of the
spinal cord continueinto the regions of the
pyramids, where there
is extensive crossing-
over of fibres from oneside to the other
(pyramidal
decussation).
Medulla OblongataMedulla Oblongata
Netter, F. 1989, Atlas of Human Anatomy, Summit, New Jersey, Ciba-
Geigy Medical, Plate 108.
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Fibre tracts from the spinal cord continue into the medulla.
Above this, the architecture of the medulla bears littleresemblance to that of the spinal cord, and you might expect
this, since there are nuclei scattered throughout the region,
and these will give rise to new tracts as they approach the
brain.
Medulla OblongataMedulla Oblongata
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Clusters of nerve cell
bodies, called nuclei,are also found here.
Nuclei of cranial nerves
9 12 are found in the
medulla, and the
nucleus of VIII is partly
in the medulla and
partly in the pons.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
Medulla OblongataMedulla Oblongata
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Close to the olive, we observe the exit of cranial nerves IX XII.
Medulla OblongataMedulla Oblongata
Grays Anatomy, Longmans, London, 38th Ed 1989 p. 949.
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Grays Anatomy, Longmans, London, 38th Ed 1989 p. 952.
Medulla OblongataMedulla Oblongata
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Trigeminal Nerve (V)
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Trigeminal NerveTrigeminal Nerve
The cell bodies ofmost of the somatic
sensory neurons are
located in the
trigeminal ganglion, a
ganglion that in many
ways resembles the
dorsal root ganglionfound in spinal
nerves.
Modified from Grays Anatomy, Longmans, London, 38th Ed 1989 p. 1107
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Trigeminal NerveTrigeminal Nerve
The central
processes of these
cells form the bulkof the sensory root
of the trigeminal
nerve, and it enters
the side of thepons.
Grays Anatomy, Longmans, London, 38th Ed 1989 p. 951.
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Trigeminal NerveTrigeminal Nerve
Here, we need to recall what happens in a spinal nerve.
Recall that a sensory fibre terminates there in the dorsal horn.
In particular, fibres for pain and temperature terminate in the
substantia gelatinosa.
Also recall that fibres need not terminate in the spinal segment
in which they originated, but rather may ascend or descend a
variable number of segments in the dorsolateral fasciculusbefore reaching the dorsal horn.
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It turns out that there are similar structures in the brainstem
associated with the trigeminal nerve.
We find that there are three sensory nuclei which simulate
aspects of the dorsal gray horn, and a tract that simulates thedorsolateral fasciculus.
In particular, the nucleus of the spinal tract simulates (and is
continuous with) the substantia gelatinosa of the spinal cord.Histologically, we do not see any difference between the two.
Trigeminal NerveTrigeminal Nerve
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The three general sensory nuclei, from superior to
inferior, are:
mesencephalic nucleus
chief sensory nucleus
nucleus of the spinal tract
The tract associated with these is called the spinal tract,
or the tract of the spinal nucleus.
Trigeminal NerveTrigeminal Nerve
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Trigeminal NerveTrigeminal Nerve
These three nuclei run
from the medulla
oblongata up to the mid-region of the midbrain.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
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Trigeminal NerveTrigeminal Nerve
The chief sensory nucleus
and the nucleus of thespinal tract are nuclei of
common sensation.
In other words, it is herethat the cell bodies of
general sensory cells that
relay to higher centres are
located.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
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Trigeminal NerveTrigeminal Nerve
The mesencephalic
nucleus is a very specific
nucleus.
It deals with
proprioception, and isintimately involved with
reflex control of
mastication.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
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Trigeminal NerveTrigeminal Nerve
The need for speed inthis control is great, and
so this is the only
nucleus in the central
nervous system wherethe peripheral sensory
cell bodies lie within the
CNS.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
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Trigeminal NerveTrigeminal Nerve
Fibres from proprioceptiveorgans in TMJ, periodontal
ligaments, muscle spindles
in the muscles of
mastication, and
proprioceptive organs in
the sutures of the maxilla
terminate here.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
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Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
Trigeminal NerveTrigeminal Nerve
Central processes of
many of these
neurons pass directly
to the trigeminal motor
nucleus without
synapsing with an
interneuron.This establishes rapid
reflex control over the
biting forces exerted
during mastication.
T i i l NT i i l N
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Fibres from the TMJ
also relay to the chief
sensory nucleus to
provide conscious
information about the
joint position.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
Trigeminal NerveTrigeminal Nerve
T i i l NT i i l N
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Trigeminal NerveTrigeminal Nerve
The chief sensory
nucleus principally
subserves the function
of discriminative touch.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
T i i l NT i i l N
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Trigeminal NerveTrigeminal Nerve
The nucleus of the spinal
tract (also known as the
Spinal Nucleus) is, as we
have already said, partlyresponsible for the
perception ofsimple touch
and pressure.
Crucially, it also relays the
modalities ofpain and
temperature, but only
towards its more caudalend.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
Trigeminal NerveTrigeminal Nerve
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Trigeminal NerveTrigeminal Nerve
The spinal tract (often but
wrongly called the trigeminal
spinal tract) is in many ways
equivalent to the dorsolateral
fasciculus in the spinal cord.
It is continuous with it, andwithin it there is blending of
fibres from both spinal cord
and brainstem.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
Trigeminal NerveTrigeminal Nerve
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Trigeminal NerveTrigeminal Nerve
Sensory axons, entering the
pons through the trigeminal
sensory root, combine withother general sensory fibres
from other cranial nerves
with a sensory function (VII,
IX and X), and those from
the upper cervical spinal
segments that pass cranially
into the medulla, to form thespinal tract.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
Trigeminal NerveTrigeminal Nerve
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Some of the sensory fibres from cranial nerves also pass
through the foramen magnum and descend in what becomesthe dorsolateral fasciculus as far caudally as the third cervical
segment.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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There is also a physical arrangement of sensory fibres from
the different branches of the trigeminal nerve in the spinaltract. The fibres of V3 lie dorsally, those of V1 lie ventrally, and
those of V2 lie in between.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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The spinal tract, and therefore the spinal nucleus, serve as the
common centre for processing general sensory input from four
cranial nerves (V, VII, IX and X).
It is therefore inappropriate to refer to it simply as a trigeminal
nucleus, although many textbooks make this mistake.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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Because pain and temperature fibres from all of these nerves
terminate in the same portion of the spinal nucleus, there is a
possibility of referral of pain to areas subserved by other
nerves.
For example, pain in a lower posterior tooth (classically a
lower 8) may be felt as an earache as well, and may even
involve temporary deafness in the ipsilateral ear until theinflammation is relieved.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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The peripheral sensory fibres all synapse within the chief
sensory nucleus and the spinal nucleus, and CNS neurons
take the information to other destinations.
These include the trigeminal motor nucleus, the motor nucleus
of VII (you screw your face up if someone touches it lightly
and unexpectedly, and you close your eyes if the cornea of the
eye is touched). Connections therefore occur between thesenuclei at this level.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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In fact, there is a tremendous amount of crosstalk between
nuclei of the brainstem, and this results in many of the effectswe see in living people.
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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Other destinations include the hypoglossal nucleus (tongue),
nucleus ambiguus (cough, gag and vomit reflexes), the
thalamus (emotional response and relays to the cortex), thereticular formation (awareness together with other centres,
including awareness of changes in external conditions such as
air movements, temperature etc.).
Trigeminal NerveTrigeminal Nerve
Trigeminal NerveTrigeminal Nerve
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Trigeminal NerveTrigeminal Nerve
The central motor fibres of
the trigeminal nerveoriginate in other brain
centres and descend to
terminate in the trigeminal
motor nucleus.
This nucleus lies medial to
the chief sensory nucleus.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
Trigeminal NerveTrigeminal Nerve
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gg
Here they synapse with
peripheral fibres, whose
cell bodies make up thisnucleus.
Their axons form the bulk
of the motor root of V,
which exits the cranium
through the foramen ovale
and connects with the
sensory trunk of V3 shortlyafterwards.
Modified from: Grays Anatomy,
Longmans, London, 38th Ed 1989 p. 953
Trigeminal NerveTrigeminal Nerve
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Most of these motor fibres originate from the opposite side of
the brain, but not all of them, which means there is a certain
amount of insurance if the tracts on one side are injured ordestroyed, for example, during a stroke.
gg
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Facial Nerve (VII)
Facial NerveFacial Nerve
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The nuclei of importance with respect to the facial nerve
include .
Facial NerveFacial Nerve
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the facial motor
nucleus for the somatic
motor function of the
nerve, the superior
salivatory nucleus for
supply of theparasympathetic
secretomotor fibres to
the salivary glands,
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
Facial NerveFacial Nerve
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the lacrimal nucleusfor parasympathetic
secretomotor fibres to
the lacrimal gland, and
the nucleus of thesolitary tract which
supplies taste fibres.
Netter, F. 1989, Atlas of Human
Anatomy, Summit, New Jersey,
Ciba-Geigy Medical, Plate 111.
Facial NerveFacial Nerve
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Recall that general sensory functions of VII are subserved by
the nucleus of the spinal tract in the brainstem.
Facial NerveFacial Nerve
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The motor nucleus of thefacial nerve lies in the
pons medially to the
nucleus of the spinal
tract, and slightly inferior
to the chief sensory
nucleus of the trigeminal
nerve.
Modified from: Grays Anatomy,
Longmans, London, 38th
Ed 1989 p. 953
Facial NerveFacial Nerve
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Motor fibres originatingin the facial motor
nucleus pass towards
the abducens nucleus,
which they wind aroundbefore exiting from the
brainstem en route for
the internal acoustic
meatus.
Modified from: Grays Anatomy, Longmans, London, 38th Ed
1989 p. 959.
Facial NerveFacial Nerve
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The sharp angle made bythe fibres as they wind
around the abducens
nucleus is called theinternal genu, as opposed
to the external genu of the
nerve in the facial canal of
the temporal bone.
Modified from: Grays Anatomy,
Longmans, London, 38th
Ed 1989 p. 953
Learning ObjectivesLearning Objectives
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You should have a general picture of the important
relationships between the major brainstem nuclei associated
with the cranial nerves.
You should understand and be able to describe and discuss
how the relationships between these nuclei will be useful in
diagnosis of neurological lesions you may encounter during
practice.
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The End