Anatomy of the

Neuroanatomy block-Anatomy-Lecture 5

Editing file Objectives

At the end of the lecture, students should be able to:

01 List the components of brain stem. 02 Describe the site of brain stem 03 Describe the relations between components of brain stem & their relations to . 04 Describe the external features of both ventral & dorsal surfaces of brain stem Color guide 05 List emerging from brain stem 06 Describe the site of emergence of each cranial nerve ● Only in boys slides in Green ● Only in girls slides in Purple ● important in Red ● Notes in Grey Development of Brain Brain stem

● The brain develops from the cranial part of neural tube. ● The brainstem is the region of the brain that connects the ● The cranial part is divided into 3 parts: with the spinal cord. ● Site: It lies on the basilar part of occipital bone (clivus). - Subdivided into: ● Parts from above downwards : 1. Telencephalon: (cavities: 2 ) 1. Midbrain Two cerebral hemispheres. Forebrain 2. 2. Diencephalon: (cavity: 3rd ventricle) 3. Medulla oblongata thalamus, hypothalamus, epithalamus & subthalamus ● Connection with cerebellum: Each part of the brain stem is connected to the Midbrain - (cavity: ) cerebellum by cerebellar peduncles (superior, middle & inferior). - (cavity: 4th ventricle) - Subdivided into: 1. Pons 2. Cerebellum 3. Medulla oblongata

3 Sagittal section of Brain

4 Functions of the Brain Stem

Pathway of tracts between cerebral cortex & spinal cord (ascending and descending tracts). 1 Site of origin of nuclei of cranial nerves (from 3rd to 12th). 2 Site of emergence of cranial nerves (from 3rd to 12th). 3 Contains groups of nuclei & related fibers known as responsible for: - Control of level of consciousness 4 - Perception of pain - Regulation of cardiovascular & respiratory systems - A vehicle for sensory information

5 Medulla oblongata

Ventral surface Dorsal surface Ventral surface ● Continuation of ventral median Cudal part (Closed medulla) Ventral fissure of spinal cord. Divides the medulla into 2 halves. median ● Its lower part is marked by ● Cavity: Central canal. fissure decussation of most of pyramidal ● Composed of: (corticospinal) fibers (75 % -90%). 1. Dorsal median sulcus: divides the closed medulla into 2 halves. 2. Fasciculus gracilis: on either side of dorsal median ● An elevation, lies on either side of sulcus. ventral median fissure. 3. Gracile tubercle: an elevation produced at the upper Pyramid Ventral median ● Produced by corticospinal tract fissure part of fasciculus gracilis, marks the site of gracile (descending motor tract). Dorsal surface nucleus. 4. Fasciculus cuneatus: on either side of fasciculus gracilis. ● An elevation, lies lateral to the 5. Cuneate tubercle: an elevation produced at the pyramid. upper part of fasciculus cuneatus, marks the site of Olive ● Produced by inferior olivary nucleus cuneate nucleus (important in control of movement). Fasciculus cuneatus Fasciculus Cranial part (open medulla) gracilis 1. Hypoglossal (12th): Nerves - From sulcus between pyramid & olive. ● Cavity: 4th ventricle. 2. Glossopharyngeal ( 9th), vagus (10th) emerging ● On either side, an inverted V-shaped sulcus divides & cranial part of accessory (11th): the area into 3 parts (from medial to lateral): (4) - From sulcus dorsolateral to olive 1. Hypoglossal triangle: overlies hypoglossal nucleus. (from above downwards). 2. Vagal triangle: overlies dorsal vagal nucleus. 3. Vestibular area: overlies .

6 Pons

Transverse pontine Basilar sulcus (pontocerebellar) Nerves emerging (4) fibers Ventral surface

1. Trigeminal (5th): - From the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root. Ventral Originate from pontine 2. Abducens (6th): nuclei, cross the midline & surface Divides the pons - At the junction between the pons & pyramid. pass through the into 2 halves, 3. Facial (7th) & Vestibulocochlear (8th): contralateral middle occupied by - At (junction between to basilar artery. medulla, pons & cerebellum). Both nerves enter the opposite emerge as 2 roots (from medial to lateral): . motor root of 7th, sensory root of 7 th , vestibular part of 8th & cochlear part of 8th. Dorsal surface

Schwannomas can compress this angle (CN VIII in particular)

● Separated from open medulla by an imaginary line passing between the margins of middle cerebellar peduncle. Dorsal ● On either side of median sulcus, it divides into 2 parts (from medial to lateral) : 1. Medial eminence & : overlies . surface 2. Vestibular area: overlies vestibular nuclei. ● The dorsal surfaces of open medulla and pons lie in the caudal 1/3rd and the rostral 2/3rd of the floor of the 4th ventricle respectively.

7 Midbrain

Ventral surface

● Large column of descending fibers (crus cerebri or basis Crus pedunculi), on either side, separated by a depression called cerebri the interpeduncular fossa. Ventral surface ● Nerve emerging from Midbrain (one): 1. Oculomotor (3rd): - From medial aspect of crus cerebri.

Dorsal surface ● Marked by 4 elevations: 1. Two superior colliculi: concerned with visual reflexes. 2. Two inferior colliculi: forms part of auditory pathway.

Dorsal surface ● Nerve emerging from Midbrain (one): 1. Trochlear (4th): - Cudal to the inferior colliculus (The only cranial nerve emerging from the dorsal surface of brainstem).

8 Practice Q5: The cavity of the closed medulla is? Q1: Basilar sulcus of the pons is occupied by? A. 4th ventricle A. basilar nerve B. Median sulcus B. basilar artery C. Central canal C. basilar vein D. Dorsal median sulcus D. basilar nucleus Q6: The only cranial nerve emerging from the dorsal surface of brainstem is? Q2: the basilar sulcus is a part of which of the following? A. Trochlear (4th) A. dorsal surface of medulla B. Oculomotor (3rd) B. ventral surface of medulla C. Vagus (10th) C. dorsal surface of pons D. Facial (7 th) D. ventral surface of pons Q7: The two superior colliculi are concerned with? Q3: The cranial nerve that emerges from ventral surface of midbrain is? A. Auditory pathway A. Trochlear (4th) B. Facial reflexes B. Oculomotor (3rd) C. Sensory pathway C. Vagus (10th) D. Visual reflexes D. Facial (7th) Q8: Regarding the medulla oblongata, which one of the following is correct? Q4: Which one of the following is the site of the inferior colliculus? A. The pyramid is lateral to olive. A. In the ventral surface of medulla, lateral to the olive. B. The cuneate tubercle is lateral to gracile tubercle. B. In the dorsal surface of medulla, medial to the vagal triangle. C. The hypoglossal nerve is the most lateral nerve emerging from it. C. In the ventral surface of midbrain, lateral to the medial eminence. D. The cerebellum is connected to it by middle cerebellar peduncle. D. In the dorsal surface of midbrain, above the trochlear nerve.

Answers: Q1(B) Q2(D) Q3(B) Q4(D) Q5(C) Q6(A) Q7(D) Q8(B) 9 Members board

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