Brainstem 2 PONS. External features of Pons Pons Literally means bridge Wedged between the midbrain ...
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Transcript of Brainstem 2 PONS. External features of Pons Pons Literally means bridge Wedged between the midbrain ...
Brainstem 2
PONS
External features of Pons
Pons• Literally means
“bridge”• Wedged between the
midbrain & medulla.• Pons shows a convex
anterior surface with prominent transversely running fibres:Transverse pontine (pontocerebellar) fibers
PONS – VENTRAL SURFACE Basilar sulcus:• Divides the pons into 2
halves, occupied by basilar artery.
Transverse pontine (pontocerebellar) fibers:
• Originate from pontine nuclei, cross the midline & pass through the contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere.
Nerves emerging from Pons (4 nerves):
• Trigeminal (5th): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root.
• Abducent (6th): from sulcus between pons & pyramid.
• Facial (7th) & vestibulocochlear (8th): at the cerebellopontine angle (junction between medulla, pons & cerebellum).
• Both nerves emerge as 2 roots:
• from medial to lateral: motor root of 7th, sensory root of 7th vestibular part of 8th & cochlear part of 8th
The dorsal part of the pons may be regarded as continuation of the part of the medulla behind the pyramids.
Superiorly continuous with the tegmentum of the midbrain.
Occupied predominately by the reticular formation
Posterior surface help to form floor of fourth ventricle
The dorsal part is bounded laterally by inferior cerebellar peduncle in the lower part of the pons and superior cerebellar peduncle in upper part.
DORSAL PART
Midpons
Upper pons
PONS – DORSAL SURFACE
The posterior surface shows:• Upper half of the floor of 4th
ventricle• Superior cerebellar peduncle• Median sulcus• Sulcus limitans• Medial eminence• Vestibular area• Facial colliculus
PONS – DORSAL SURFACE
PONS – DORSAL SURFACE Separated from the medulla
by an imaginary line passing between the caudal margins of middle cerebellar peduncle.
• On either side, the median sulcus divides the area into 2 parts (from medial to lateral):
Medial eminence & facial colliculus: overlies abducent nucleus.
Vestibular area: overlies vestibular nuclei.
Internal structures
CAUDAL PART OF THE PONS• Divided into an anterior part
(Basis Pontis) & a posterior part (Tegmentum) by the Trapezoid Body (consists of acoustic fibres from cochlear nuclei to ascend into midbrain as lateral lemniscus and terminate in inferior colliculus).
Lateral lemniscus• Auditory pathway that conducts most
contralateral cochlear inputTrapezoid body• – Formed by decussating fibers of the ventral
cochlear nuclei
• The ventral portion is marked by numerous transversely oriented fascicles of pontocerebellar fibres that originate from scattered cell groups, the pontine nuclei, and that pass to the contralateral side of the cerebellum through the massive middle cerebellar peduncle.
The ascending fibres of the medial lemniscus become separated from the pyramid and displaced dorsally.
The Medial Lemniscus rotates 90 degrees and lies almost horizontally.
It contains spinal nucleus & tract of Trigeminal.
Deep origin of cranial nerve nuclei:Abducent nucleusFacial motor nucleus
CAUDAL PART OF THE PONS
AT THE LEVEL OF THE TRIGEMINAL NERVE Motor nucleus of the
trigeminal nerve: Lies in the lateral part of the floor of the 4th ventricle. Main sensory nucleus of
the trigeminal nerve:Reaches its maximum extent in the pons and it lies lateral to the motor nucleus. Superior cerebellar
peduncles form the lateral boundary of the 4th ventricle
ROSTRAL PONS• Superior Medullary
Velum: – Passes between the
two peduncles & forms the roof of the 4th ventricle.
• Medial longitudinal fasciculus: – Lie close to the
midline beneath the floor of the 4th ventricle.
• Contains:– Sensory and motor nuclei
for 4 cranial nerves • Trigeminal (5), Abducent
(6), Facial (7), and Auditory/Vestibular (8)
– Respiratory nuclei:Apneustic & pneumotaxic centers work w/ the medulla to maintain respiratory rhythm– Nuclei & tracts that process
and relay info to/from the cerebellum
– Ascending, descending, and transverse tracts that interconnect other portions of the CNS
The End