Pons Flashcards
What are the 3 transverse sections of Pons?
- lower level (level of facial colliculus)
- middle level (level of trigeminal nerve)
- Upper level (level of 4 lemnisci)
What two main divisions are pons divided in by the transversely running fibres of the trapezoid body?
- Basilar part (Basis pontis) - the ventral part of pons.
- Tegmentum - the dorsal part of pons. Superiorly tegmentum of pons is continous w tegmentum of midbrain
Does the content of tegmentum vary in the 3 levels of pons?
yes.
How is all of the basilar pons structured?
numerous transverse pontocerebellar fibres arrising from pontine nulei.
How are pontocerebellar fibres projecting?
They are transverse in basilar pons and then cross the midline to contralateral cerebellum.
What are the transverse pontocerebellar fibres forming?
The middle cerebellar peduncle (brachium pontis)
What nerve is piercing the middle cerebellar peduncle?
The trigeminal nerve.
What more is seen in all levels of the ventral (basilar) pons?
The pyramidal tract - appear as small separate bundles running longitudinally between fascicles of the transverse pontine fibres.
What is the pyramidal tract including?
- corticospinal tract
- corticobulbar tract
What is seen at the dorsal/tegmental part of caudal pons at the level of facial colliculus?
- The trapezoid body
- Abducent nerve nucleus
- Facial motor nucleus
- Medial longitudinal fasciculus/bundle
- Vestibular nuclei
- Spinal tract and nucleus of the trigeminal nerve
What does the trapezoid body consist of?
acoustic fibres from the cochlear nuclei.
What forms the decussation of the trapezoid body?
Acoustic fibres crossing to opposite side of pons then ascending as the lateral lemniscus
Where does the lateral lemniscus ascend and terminate?
It ascend into rostral pons and midbrain and terminate in INFERIOR colliculus.
Where in tegmentum does the lateral lemniscus lie?
ANTERIOR (lateral) part of tegmentum.
What type of information does the lateral lemniscus carry and from where?
HEARING
From dorsal and ventral COCHLEAR nuclei (dorsal and ventral to the inferior cerebellar peduncle). Crossing
, forming the decussation of the trapezoid body, ascending as lateral lemniscus in the anterior tegmentum through pons and midbrain to the INFERIOR COLLICULUS.
Where is the abducent nerve nucleus situated?
In the posterior aspect of caudal pons near the floor of the 4th ventricle
- CALLED THE FACIAL COLLICULUS-
How is the abducent nerve efferents trajecting from the facial colliculus?
DOWNwards. Traverse medial lemniscus and pyramidal tract bundles. Emerge anteriorly at the junction between pons and pyramid of medulla supplying lateral rectus muscle.
Where is the facial motor nucleus located?
In the posterior part of caudal pons.
How is the facial efferent fibres trajeting from the facial motornucleus?
They encircle the abducent nucleus, then pass ANTEROlaterally to emerge at the junction between pons and OLIVE of medulla, supplying muscles of facial expression.
What is the medial longitudinal fasciculus/bundle?
It is an association tract, that link vestibular nuclei with motor occular nuclei in the brain stem to serve coordination of head and eye movement. It supplies extraoccular muscles.
Where is the medial longitudinal fasciculus/bundle situated?
it lies close to the midline and is found throughout the brain stem and descend into spinal cord
What muscles do the medial longitudinal fasciculus supply?
The extraoccular muscles through the occulomotor, trochlear and abducent nuclei.
How is the vestibular nuclei arranged and where is it situated?
Its four nuclei lying near to vestibular area of the floor of the 4th ventricle in the tegmental part of caudal pons (at the level of facial colliculus).
From where does the vestibular nuclei recieve afferent fibres and through what to where do they send efferents?
From the vestibular nerve.
Through vestibulo-occular fibres in the medial longitudinal fasciculus
To the Occulomotor, Trochlear and Abducent nuclei.
