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.
Where is the spinal tract and nucleus of trigeminal nerve situated?
Its on the anteromedial aspect of the inferior cerebellar peduncle.
What information does the spinal tract and nucleus of trigeminal nerve rely?
Pain and temperature sensation from the face and scalp.
Where does axons from the spinal tract and nucleus of the trigeminal nerve project?
They cross to opposite sidem ascend as trigeminal lemniscus and end in Thalamus.
What afferent information is send through the vestibular nerve to the vestibular nuclei?
Unconscious depp sensation (equilibrium)
WHAT IS FOUND AT THE DORSAL (TEGMENTAL) PART OF MID-PONS AT THE LEVEL OF THE TRIGEMINAL NERVE?
- The trigeminal motor nucleus
- The trigeminal sensory nucleus
- The superior cerebellar peduncle
The medial longitudinal fasciculus, spinal lemniscus, medial lemniscus and trapezoid body.
Where is the trigeminal motor nuclei positioned?
Mid pons, in the tegmental area, each side of the 4th ventricle and medial to the main sensory trigeminal nucleus.
How is the efferent axons from trigeminal motor nucleus projecting?
It is passing along the mandibular nerve ( supplying muscles of mastication).
What afferent information is the trigeminal sensory nucleus recieving?
Touch sensation from face and scalp
Where and how does trigeminal sensory nucleus send efferent fibres?
Cross to opposite side and join axons from spinal nucleus of trigeminal. They form the TRIGEMINAL LEMNISCUS in rostral pons - midbrain - Thalamus.
Where is the Superior cerebellar peduncle situated?
It is posterolateral to the motornucleus of Trigeminal. (posteriolateral to the 4th ventricle)
WHAT IS SITUATED AT THE TEGMENTAL PART OF ROSTRAL PONS AT THE LEVEL OF 4 LEMNISCI?
*The superior cerebellar peduncle
* The lateral lemniscus
* The spinal lemniscus
*The Trigeminal lemniscus
* The medial lemniscus
(rostral part of 4th ventricle, reticular formation, medial longitudinal fasciculus, tectospinal tract, central tegmental tract)
