PONS & MID-BRAIN

STRUCTURE/BLOOD SUPPLY/CRANIAL NERVES ATTACHMENTS

Lecture….by Prof. AnsariFriday, April 21, 2023

(for MBBS SEMESTER IV students only)

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The learning outcomes

• Draw the internal structure of pons and midbrain.

• Identify the cranial nerves attachments to pons and midbrain.

• Mention other nuclei present at these levels.

• Describe the blood supply of pons, midbrain & correlate the clinical situation with the Cerebrovascular accident.

• Identify the cross sections of pons and midbrain the - grey matter and white matter.

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A case of pontine hemorrhage • A 50 year-old male was admitted to the emergency room because of sudden

weakness on his right leg and arm. • An elevated arterial blood pressure (200/130 mmHg) was disclosed but his

general physical exam was otherwise unremarkable. • Neurological examination revealed a complete right-sided hemiparesis.

Consciousness was not impaired and there were no cerebellar signs or cranial nerves dysfunction.

• There were no signs of ipsi-lateral or contralateral VII nerve palsy but a supra-nuclear facial palsy was present.

• A mild dysarthria was recorded and the patient referred no dizziness, tinnitus or dysphagia. Previous medical history indicated untreated elevated blood pressure for the last 5 years.

• A computed tomographic (CT) scan showed a hematoma located in the left pontine tegmentum.

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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

7CROSS SECTION OF PONS

A cross section of mid-pons

• A. Superior vestibular nucleus• B. Main Sensory nucleus of Trigeminal• C. Motor nucleus of Trigeminal • D. Lateral vestibular nucleus• E. Pontine Nuclei• F. Dorsal Longitudinal Faciculus• G. Superior Medullary Velum• H. Fourth Ventricle• I. Medial Longitudinal Faciculus• J. Middle Cerebellar Peduncle (MCP)• K. Pontocerebellar fiber of MCP• L. Dorsal Nucleus of Vagus (motor)• M. Trigeminal Nerve Fibers (root)• N. Pontocerebellar fibers • O. Medial Lemniscus (Located medially to• the Anterolateral system and Lateral

Lemniscus.)• P. Pyramidal Tract and Corticopontine Tract• Q. Fibers of the Trigeminal Nerve• R. Olivary cerebellar fibers• S. Trapezoid Body (Auditory Decussation)

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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 body

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15OVERVIEW 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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A 69-year-old Moroccan man, with a medical history of untreated hypertension, developed suddenly diplopia, a droop of both upper eyelids with the inability to open his eyes. The symptoms were constant and did not fluctuate during the day

• He denied any weakness, numbness or change in mental status. Initial physical examination found bilateral ptosis with a limitation in adduction, elevation and depression of both eyes which was more marked on the right side. Both pupils were in miosis. The remaining neurological examination was strictly unremarkable. His blood pressure was 220/120mmHg on admission. Initial blood tests showed a normal full blood count, normal urea, electrolytes and C-reactive protein. Computed tomography (CT) of the brain revealed a spontaneously high-density lesion of the midbrain consistent with a midbrain hematoma.

• The oculomotor function gradually and completely improved over eight months of follow-up.

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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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A cross section of midbrain at inferior colliculus

• A. Midline of Tectum• B. Cerebral Aqueduct• C. Inferior Colliculus• D. Inferior Brachium and Lateral

Lemniscus• E. Anterolateral system • F. Medial Lemniscus• G. Substantia Nigra• H. Cerebral Peduncle• I. Corticobulbar Tract• J. Frontopontine Fibers• K. Corticospinal Tract• L. Pontine Nuclei• M. Interpeduncle Fossa• N. Decussation of Superior Cerebellar

Peduncle• O. Trochlear Nucleus• P. Periaqueductal Gray Matter• Q. Medial Longitudinal Faciculus• R. Reticular Formation• S. Parieto-occopitotemporal Pontine

Fibers

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Cross section of midbrain

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Inferior colliculus

SuperiorCerebellarPeduncle decussation

Substantia nigra

Cerebral peduncle

PAG

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Superior colliculus

Oculomotor fibers

Cross section of midbrain at the level of superior colliculus

• A. Cerebral Aqueduct• B. Red Nucleus• C. Interpeduncle Fossa• D. Oculomotor Nucleus• E. Superior Colliculus• F. Tectum• G. Lateral Lemniscus• H. Thalamus (Medial Genculata Nucleus)• I. Substantia Nigra • (pars compacta)• J. Substantia Nigra • (pars reticularis)• K. Oculomotor Fibers• L. Periaqueductal Gray Matter• M. Anterolateral System• N. Medial Lemniscus • O. Parieto-occopitotemporal Pontine

Fibers• P. Corticospinal Tract• Q. Corticobulbar Tract• R. Frontopontine Fibers

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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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26CIRCLE 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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