Midbrain and Pons

To MBBS 2nd year

26-02-2017

By Dr. Laxman Khanal

Assistant professor, Department of anatomy

Identify the cranial nerves.

Identify this swelling in pons.

Q. Trigeminal nerve has its nuclei in which part of brain stem?a.Midbrainb.Ponsc. Medulla oblongatad.All of the above

Objectives

• To review the anatomy of the upper brainstem

• To develop a three-dimensional picture of the interior of the midbrainand pons.

• To know the positions of cranial nerve nuclei and the paths of variousascending and descending nerve tracts.

• To assess the signs and symptoms presented by a patient and identifythe exact location of a structural lesion.

External feature of midbrain and pons- anterior view

External feature- posterior view

Visible part: Tectum1. Corpora quadrigemina2. 4th CN

Visible part: Tegmental part1. Forms upper part of floor of 4th

ventricle2. Median sulcus3. Medial eminence (facial colliculus)4. Sulcus limitans

Pons:

• Pontine branches• AICA• Sup cerebellar artery

Midbrain:

• Posterior cerebral artery• Superior cerebellar artery

Which sections are important?

Facial colliculus

How to study the cross section

• Different level of cross sections should be differentiated by-

1. What is the CSF filled cavity ?

2. What are the cranial nerve nuclei?

3. What are the ascending tracts ?

4. What are the descending tracts?

Descending tract in brainstemCorticospinal fibersCorticonuclear fibersCorticopontocerebellar fibers

Ascending tract- #MSTLDC/Medial lemniscusSpinal lemniscusTrigeminal lemniscusLateral lemniscus

Spinal lemniscus1. Anterior spinothalamic tract2. Lateral spinothalamic tract3. Spinotectal tract

Medial longitudinal fasciculus

@ Trigeminal nerve@ Facial colliculus

66

7

Trapezoid body

MLF

Tegmentum

Basal part

Pontine nuclei

Transverse pontine fibers(pontocerebellar fibers)

Corticospinal and corticonuclear fibers

Superior and inferior cerebellar peduncle

MSTLMedial LSpinal LTrigeminal LLateral L

7

FC

TS – lower pons

TS – upper pons

Cranial nerve nucleiMain sensory nucleus of Vth nerveMotor nucleus of Vth nerveNo inferior cerebellar peduncle

Millard-Gubler syndrome: #P67Ventral pontine syndrome

• Ipsilateral medial squint• Ipsilateral facial palsy• Contralateral hemiplegia

Most common tumor of brainstemAstrocytoma of pons

Midbrian cross section

S1. Tectum 2. Cerebral peduncleTegmentumCrus cerebri

Interpeduncular fossa

Parkinson’s disease

Substantia nigra

Crus cerebri (motor zone)• Contains descending fibers1. Up to pons- FP+TP2. Up to motor nuclei of CNs- CN3. Up to spinal cord- CS

FP

TPCSCN

Pontine nucleus

Crossing of rubrospinal tract

Mesencephalic nucleus

MLF

MSTL MST

Crossing of sup cerebellar peduncle

To cerebellum

S

Blockage of cerebral aqueduct

Weber syndrome1. Crus cerebri2. Oculomotor nerve# COW

Benedict syndrome1. Red nucleus2. ML3. Oculomotor nerve