PONS & MID-BRAIN STRUCTURE/BLOOD SUPPLY/CRANIAL NERVES ATTACHMENTS Lecture….by Prof. Ansari Wednesday, April 26, 2017 (for MBBS SEMESTER II students only)

OBJECTIVES STRUCTURE OF PONS AND MIDBRAIN. CRANIAL NERVES ATTACHMENT. OTHER NUCLEI PRESENT AT THESE LEVELS. BLOOD SUPPLY CROSS SECTION- GREY MATTER AND WHITE MATTER.

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.

CRANIAL NERVES ATTACHED AT THE BASE OF BRAIN

CROSS SECTION OF PONS

IV VENTRICLE TEGMENTUM PART BASILAR PART

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.

Floor of IV ventricle

WHITE FIBERS AT PONS CORTICOPONTINE FIBERS CORTICOSPINAL FIBERS CORTICOPONTOCEREBELLAR FIBERS CORTICONUCLEAR FIBERS TRAPEZOID BODY

OVERVIEW 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.

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

Cross section of midbrain Inferior colliculus Substantia nigra Superior Cerebellar Peduncle decussation PAG Cerebral peduncle

Superior colliculus Oculomotor fibers

VARIOUS NUCLEI AT MIDBRAIN Oculomotor nucleus Trochlear nucleus Mesencephalic nucleus Red nucleus Substantia nigra Edinger-Westphal nucleus

White matter at mesencephalon Superior cerebellar peduncles decussations Medial lemniscus/lateral lemniscus/trigeminal lemniscus/spinal lemniscus Crus cerebri

BLOOD SUPPLY OF PONS &MIDBRAIN CORTICAL BRANCHES AND CENTRAL BRANCHES ARISE FROM BASILAR ARTERY AND CIRCLE OF WILLIS. PONTINE HAEMORRAGE LEADS TO BURSTING HEAD ACHE, PINPOINT PUPIL, AND HYPERTHERMIA. INJURY TO THE CORTICOSPINAL FIBERS LEADS TO HEMIPLEGIA.

CIRCLE 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 SUPPLIMENTING THE NEUROTRANSMITTER DOPAMINE.

Periaqueductal gray

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 characterised 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.

CEREBRAL AQUEDUCT PAG RED NUCLEUS

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

A 62-year old male has sustained several injuries from a car accident 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". (Your Answer) 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