PONS & MID-BRAIN

STRUCTURE/BLOOD SUPPLY/CRANIAL NERVES ATTACHMENTS

Lecture….by Prof. AnsariSunday, April 9, 2023

(for BDS SEMESTER II students only)

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OBJECTIVES

• Structure of pons and midbrain.• Cranial nerves attachment.• Other nuclei present at these levels.• Blood supply• Cross section- grey matter and white matter.

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PONS• It is a part of brain stem.• It lies between midbrain and medulla oblongata.• It has a basilar part/ ventral part, and a dorsal part which

forms the floor of IV ventricle.• Three cranial nerves are related to pons, trigeminal nerve

is attached to the pons on ventral part.• Abducent nerve is related at the lower border of pons and

pyramid.• Occulomotor nerve arises at the upper border of pons, in

the interpeduncular fossa.

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CRANIALNERVESATTACHED AT THE BASEOF BRAIN

CRANIALNERVESATTACHED AT THE BASEOF BRAIN

6CROSS SECTION OF PONS

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BASILAR PART

TEGMENTUM PART

IVVENTRICLE

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Nuclei of cranial nerves in pons

• Facial nerve nuclei, motor / sensory/autonomic.

• Trigeminal nuclei, motor/ main sensory/spinal/ mesencephalic.

• Abducent nucleus / purely motor.• Nuclei pontis.

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Floor of IV ventricle

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White fibers at pons

• Corticopontine fibers

• Corticospinal fibers

• Corticopontocerebellar fibers

• Corticonuclear fibers

• Trapezoid body12

13OVERVIEW OF PONS

Mesencephalon

• It is at the cranial end of pons.

• It has a dorsal portion called as tectum.

• The ventral portion is called as cerebral peduncle.

• The space between the two cerebral peduncle is the interpeduncular fossa.

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Structures in the interpeduncular fossa

• 1.Optic nerve• 2.Optic chiasma• 3.Optic tract• 4.Tuber cinereum• 5.Mammillary bodies• 6.Ant.perforated

substance.• 7.Olfactory tract• 8.Pons• 9=Uncus

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Cross section of midbrain

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Inferior colliculus

SuperiorCerebellarPeduncle decussation

Substantia nigraSubstantia nigra

Cerebral peduncleCerebral peduncle

PAG

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Superior colliculus

Oculomotor fibers

Various nucleiat midbrain

• Oculomotor nucleus• Trochlear nucleus• Mesencephalic nucleus• Red nucleus• Substantia nigra• Edinger-Westphal nucleus

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White matter at mesencephalon

• Superior cerebellar peduncles decussations• Medial lemniscus/lateral lemniscus/trigeminal

lemniscus/spinal lemniscus• Crus cerebri

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Blood supply of pons &midbrain

• Cortical branches and central branches arise from basilar artery and circle of Willis.

• Pontine hemorrhage leads to bursting head ache, pinpoint pupil, and hyperthermia.

• Injury to the Corticospinal fibers leads to hemiplegia.

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21CIRCLE OF WILLIS

Red nucleus and substantia nigra• They are concerned with the extrapyramidal tract.

• Injury to these nuclei will result in tremors, Parkinsonism, and nystagmus.

• These symptoms can be corrected by supplementing the neurotransmitter dopamine.

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Periaqueductal gray

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Electrical stimulation of the PAG results in immediate and profound analgesia

• Stimulation of the dorsal and lateral aspects of the PAG (in the rat) can provoke defensive responses characterized by freezing immobility, running, jumping, tachycardia, and increase in blood pressure.

• Stimulation of the caudal ventrolateral PAG can result in an immobile, relaxed posture known as quiescence.

• It also plays a role in female copulatory behavior.

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Periaqueductal gray

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RED NUCLEUSCEREBRAL AQUEDUCT

References

• http://legacy.owensboro.kctcs.edu/gcaplan/anat/notes/api%20notes%20l%20central%20nervous%20system-brain.htm

• http://www.dartmouth.edu/~rswenson/NeuroSci/figures/Figure_15.htm

• http://instruct.uwo.ca/anatomy/530/530notes.htm#TOPICS

• http://www.mcqsonline.net/2009/05/brainstem-anatomy-mnemonics.html

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A 62-year old male has sustained several injuries from a car accident. Upon administering a neurological examination, you suspect that the

patient has damage to the right caudal medulla. Why do you think this?

A. The patient's right eye exhibits hypertropia and he complains of diplopia,B. The patient's tongue deviates towards to right when you asked him to stick it out

and his uvula deviates towards the left when you ask him to say, "aahhh". C. The patient has a loss of taste on the right anterior 2/3rds of his tongue D. The patient exhibits anosmia (inability to smell) E. The patient complains of excruciating pain on the right side of his face

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