Abstract square

1. INTERNAL STUCTURE
OF PONS

2. PONS
The pons is also called metencephalon, 2.5 cm long and extends from cranial end of medulla
oblongata to the cerebral peduncles of midbrain.
Anterioly, it is related to clivus separated by basilar artery, laterally middle cerebellar peduncle
and posteriorly to the fourth ventricle.

3. In transverse sections, the pons is seen to be divisible into ventral and dorsal parts.
The ventral or basilar part is continuous inferiorly with the pyramids of the medulla, and on
each side with the cerebellum through the middle cerebellar peduncle.
The dorsal or tegmental part is a direct upward continuation of the medulla.
INTERNAL STRUCTURE OF PONS

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Basilar Part/Ventral Part
Grey Matter
It is represented by the nuclei pontis which are scattered among longitudinal and transverse
fibres.
The pontine nuclei form an important part of the cortico-ponto-cerebellar pathway.
White Matter
It consists of longitudinal and transverse fibres.
1.The longitudinal fibres include:
-The corticospinal and corticonuclear (pyramidal) tracts.
-The corticopontine fibres ending in the pontine nuclei.
2.The transverse fibres are pontocerebellar fibres beginning from the pontine nuclei and going
to the opposite half of the cerebellum, through the middle cerebellar peduncle.

5. Tegmental Part/Dorsal Part
However, the structure of the tegmental part differs in the upper and lower parts of the pons.
Tegmentum in the Lower Part of Pons
Grey Matter
1.The sixth nerve nucleus lies beneath the facial colliculus.
2.The seventh nerve nucleus lies in the reticular formation of the pons.
3.The vestibular and cochlear nuclei lie in relation to the inferior cerebellar peduncle.
4.The spinal nucleus of the trigeminal nerve lies in the lateral part.
5.Other nuclei present include the superior salivatory and lacrimatory nuclei.
White Matter
1.The trapezoid body or corpus trapezoideum is a transverse band of fibres lying just behind
the ventral part of the pons.
2.The medial lemniscus forms a transverse band on either side of the midline, just behind the
trapezoid body.

6. 3.The lateral spinothalamic tract (spinal lemniscus) lies lateral to the medial lemniscus.
4.The inferior cerebellar peduncle lies lateral to the floor of the fourth ventricle.

7. Tegmentum in the Upper Part of Pons
Grey Matter
The special features are the motor, and superior sensory nuclei of the trigeminal nerve.
The motor nucleus is medial to the superior sensory nucleus.
White Matter
1.Immediately behind the ventral part of the pons, we see bands of fibres made up (from medial
to lateral side) of the medial lemniscus, the trigeminal lemniscus, the spinal lemniscus.
2.The superior cerebellar peduncles lie dorsolateral to the fourth ventricle (replacing the inferior
peduncle seen in the lower part of the pons).
3.The medial longitudinal bundle is made up of fibres that interconnect the nuclei of the cranial
nerves III, IV, VI, VIII and the spinal root of the XI.

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