Download Neuro Anatomy Lec.6 د.عبد الجبار الحبي طي The Pons Is the middle

Neuro Anatomy
‫عبد اجلبار احلبيـطي‬.‫د‬
Lec.6
The Pons
Is the middle part of the brain stem (also a part of the hind
brain) its pos. surface forms the upper 1/2 of the floor for
the 4th ventricle, the pons lies in contact with the clivus
(basilar part of the occipital bone, body of sphenoid &
dorsum sellae) its ventral (basilar) surface bulges
anteriorly and is continuous laterally with the middle
cerebellar peduncle on each side.
The basilar part: Is grooved by a longitudinal median sulcus (basilar sulcus)
which lodges the basilar artery, it is continuous on each
side (just outside the attachment of trigeminal nerve) as
middle cerebellar peduncle.
The pons is continuous above with the 2 crura of the mid
brain & below with the 2 pyramids of the medulla
oblongata.
The bulge of the basilar part is due to (produced by):
i.
ii.
iii.
Large no. of pontine nuclei.
Descending
corticopontine,
corticospinal
&
corticonuclear fibers.
Pontocerebellar fibers which goes to cerebellum via the
middle cerebellar peduncle.
The trigeminal nerve is the only cranial nerve attached to
the surface; it is seen at the junction between the basilar
part & the middle cerebellar peduncle.
The dorsal (tegmental) part: -
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Forms the upper 1/2 of the floor of the 4th ventricle, is
continuous above with the tegmentum of the mid brain &
below with the pos. surface of the upper 1/2 of the medulla
oblongata.
It contains the nuclei of the middle 4 cranial nerves (5th 8th) and also contains 4 sensory lemnisci (medial, lateral,
spinal & trigeminal).
The posterior surface of the Pons shows the following features:Pos. median sulcus.
On each side of which there is a vertical band of
swelling called medial eminence.
At the lower part of the medial eminence we can see
the facial colliculus contains the nucleus of the
abducent nerve.
Each medial eminence is limited laterally by sulcus
known as sulcus limitance.
At the upper part of sulcus limitance there is a
pigmented area known as substantia ferrigenea.
Lateral to the sulcus limitance there is vestibular area
contains some vestibular nuclei.
I.
II.
III.
IV.
V.
VI.
Nuclei in the Pons:
a-
Nuclei of trigeminal nerve ( 4 nuclei ) : 1. Motor nucleus: - gives motor fibers that join the
2.
mandibular nerve to supply the muscles of
mastication, mylohyoid & ant. Belly of digastric. in
addition to the nerves to the tensor palati &
tensor tympani muscles
Main sensory nucleus : it receive touch sensation form
the trigeminal area (side of the face and scalp)
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II
b-
3.
Mesencephalic
4.
sensation from the muscles of mastication, face &
eye ball.
Spinal nucleus: receive fibers of the spinal tract of
nucleus:
-
receives
proprioceptive
trigeminal nerve (pain & temperature from the
same side of the face and scalp).
Nucleus of the abducent nerve: - at the bottom of the facial
colliculus and it is surrounded by fibers of facial nerve
as they arise from the facial nerve nucleus , they loop
around the abducent nerve creating a swelling called
the facial colliculus
c-
Nuclei of facial nerve (3 in number): - One motor, one
parasympathetic (superior salivary) both of these nuclei lie in
the Pons, while the 3rd nucleus (I.e. sensory for
taste, the solitarius) lies in the medulla oblongata.
Superior salivary nucleus gives fibers distributed via chorda
d-
tympanic (sublingual & submandibular) & greater
superficial petrosal (to lacrimal & nasal glands).
Nuclei of vestibulo-cochlear nerve: - Vestibular & cochlear
nuclei.
The midbrain
Notice the last page of lec.-3- in 14/12/2008 about the
midbrain and now we will detail in some additions: The cerebral peduncle is divided into crus cerebri and
tegmentum by the substantia nigra.
The crus contains the following descending tracks: a) Cortico-spinal fibers: - occupy the middle 3/5th of the
crus cerebri.
b) Cortico-nuclear fibers: - situated medially to the Corticospinal.
c) Cortico-pontine fibers: - occupy the medial 1/5th and the
lateral 1/5th of the crus according to the site of
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origin of these fibers, the fibers coming from the
frontal lobe occupy the medial 1/5th, while those
coming from the occipital and temporal lobes
occupy the lateral 1/5th of the crus (there will form
Cortico-ponto-cerebellar pathway from cerebral
cortex to cerebellar cortex).
Substantia nigra separates the crus cerebri from the
tegmentum & is an important extrapyramidal centre.
Each crus cerebri has the following relations:  Laterally : on each side
- Trochlear nerve , optic tract (cross the crus from behind forward )
- Some blood vessels (posterior cerebral , superior cerebellar arteries
and basal vein)
 Medially :
- Posterior perforated substance (pierced by striate or central
branches).
- Occulomotor nerve
The tegmentum: Is continuous below with the tegmental part of the Pons,
the part of the tegmentum at the level +of the superior
colliculus
contains
red
nucleus
(an
important
extrapyramidal centre), While at the level of inferior
colliculus the tegmentum receives the decussation of the
2 superior cerebellar peduncles.
The nuclei in the midbrain:
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i- The nucleus of the occulomotor nerve : at the level of
superior colliculus , it is a motor nucleus supplies 5
of the extra-ocular muscles , and also contains
edinger-westphal nucleus as a parasympathetic
part whose fibers goes to ciliary ganglion to supply
constrictor pupillae muscle and ciliary body .
ii- Nucleus of the trochlear nerve: - in the lower part of
midbrain at the level of inf. Colliculus.
iii- Red nucleus: - in the tegmentum at the level of sup.
Colliculus , it receives afferent from the frontal
cortex , corpus striatus and cerebellum , while it
sends efferent as: -
 Rubro-veticular
 Rubro-spinal
 Rubro-thalamic
Fibers or tracts
The cerebellum
It lies in the posterior cranial fossa, behind the Pons and
medulla oblongata and encloses with them the 4th
ventricle. It has two surfaces (sup. and inf.), two notches
(the ant. and pos. – the anterior one receives the back of
the brain stem, while the posterior receives the falx
cerebelli). It consist of two hemispheres connected by
narrow median vermis, the part of vermis seen from
above is the superior vermis, while that seen from inferior
surface is the inferior vermis.
The outer cortex grey mater is highly folded with
numerous transversely running fissures, the part of cortex
between the fissures are called the folia of cerebellum.
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The superior surface shows fissure prima that separates
anterior lobe from middle lobe. The inferior surface shows
a depressed area called vallecula, at the bottom of this
vallecula the inferior vermis lies (forms by nodule, uvula &
pyramid). The inferior surface also shows the tonsil of
cerebellum situated on each side of the inferior vermis.
Cerebellum has three fissures: a) Fissure prima: - intervenes between the anterior lobe
and the middle lobe.
b) Postero-lateral fissures:
- lies on the inferior surface
between the flocculo-nodular lobe and middle lobe.
c) Horizontal fissure: - extends along the lat. & pos. border
of the hemisphere between the superior and inferior
Borders of the hemisphere.
Lobes of the cerebellum: i-
Anterior lobe: - in front of the fissure prima and its
ii-
part that extending above the superior medullary
velum is called the lingula.
Middle lobe: - extends from fissure prima and
iii-
postero-lateral fissure, the tonsil is part of this
lobe.
Flocculo-nodular lobe : consist of the nodule of the
vermis and two floculli one on each side
Functional division of cerebellum: i-
Archi-cerebellum: - include flocculo-nodular lobe and
ii-
the lingula, related to vestibular apparatus.
Paleo-cerebellum : is the anterior lobe minus the
lingula and is connected to the spinal cord
iii- Neo-cerebellum: - consists of the middle lobe and is
connected with cerebral cortex via the pontocerebellar pathway.
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Blood supply of the cerebellum: a. Superior cerebellar artery
b. Anterior inferior cerebellar artery
c. Posterior inferior cerebellar artery
From basilar artery
From vertebral artery
The medulla of cerebellum contains four intracerebellar nuclei
arranged from lateral to medial as dentate, emboliform,
globose and fastegial nuclei embedded within the white
mater of cerebellum.
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