Brainstem

1. Brainstem • COMPONENTS: • Midbrain: most rostal part • Pons • Medulla oblongata: most caudal part • EMBRYOLOGICAL ORIGIN: • Midbrain: arises from mesencephalon • Pons & medulla: arise from rhombencephalon or hindbrain (together with cerebellum)

2. Brainstem • COMPONENTS: • Midbrain: most rostal part • Pons • Medulla oblongata: most caudal part • EMBRYOLOGICAL ORIGIN: • Midbrain: arises from mesencephalon • Pons & medulla: arise from rhombencephalon or hindbrain (together with cerebellum)

3. Brainstem • COMPONENTS: • Midbrain: most rostal part • Pons • Medulla oblongata: most caudal part • EMBRYOLOGICAL ORIGIN: • Midbrain: arises from mesencephalon • Pons & medulla: arise from rhombencephalon or hindbrain (together with cerebellum) Anterior view

4. Brainstem • COMPONENTS: • Midbrain: most rostal part • Pons • Medulla oblongata: most caudal part • EMBRYOLOGICAL ORIGIN: • Midbrain: arises from mesencephalon • Pons & medulla: arise from rhombencephalon or hindbrain (together with cerebellum) Posterior view

5. Brainstem

6. Brainstem • SITE: • It lies on the basilar part of occipital bone (clivus). • The midbrain is continuous rostrally with diencephalon of forebrain. • The pons is continous rostrally with midbrain & caudally with medulla. • The medulla is continuous caudally with spinal cord at the margin of foramen magnum.

7. Brainstem • CONNECTION TO CEREBELLUM: • Midbrain: by superior cerebellar peduncle • Pons: by middle cerebellar peduncle • Medulla oblongata: by inferior cerebellar peduncle

8. Brainstem • IMPORTANCE: • Pathway of tracts between cerebral cortex & spinal cord • Site oforigin of nucleiof cranial nerves (from 3rd to 12th) • Site of emergence of cranial nerves (from 3rd to 12th) • Contains groups of nuclei & related fibers known as reticular formation responsible for: control of level of consciousness, perception of pain, regulation of cardiovascular & respiratory systems

10. Brainstem • Ventral surface • MEDULLA: • Ventral median fissure: • It divides the medulla into 2 halves. • Its lower part is masked by decussation of pyramidal (corticospinal) fibers. • Pyramid: • It lies on either side of ventral median fissure. • It is an elevation produced by corticospinal tract. Anterior view

11. Brainstem- Ventral Surface of Medulla • MEDULLA: • Olive: • It lies lateral to the pyramid & separated from it by the ventrolateral sulcus. • It is an elevation produced by inferior olivary nucleus. • Nerves emerging from Medulla (4 nerves): • Hypoglossal (12th): between pyramid & olive • Glossopharyngeal (9th), vagus (10th) & cranial part of accessory (11th): dorsolateral to olive (from above downwards)

12. Brainstem - Ventral Surface of Pons PONS: • Basilar sulcus • It divides the pons into 2 halves. • It is occupied by basilar artery. • Transverse pontine (pontocerebellar) fibers: • Originate from pontine nuclei. • Cross midline & pass through contralateral middle cerebellar peduncle to enter the opposite cerebellar hemisphere.

13. Brainstem - Ventral Surface of Pons PONS: • Nerves emerging from Pons (4 nerves): • Trigeminal (5th): from the middle of ventrolateral aspect of pons, as 2 roots: a small medial motor root & a large lateral sensory root • Abducent (6th): at junction between pons & pyramid • Facial (7th) & vestibulocochlear (8th):at cerebellopontine angle (junction between medulla, pons & cerebellum). Both nerves emerge as 2 roots: from medial to lateral:motor root of 7th , sensory root of 7th , vestibular part of 8th & cochlear part of 8th

14. Brainstem - Ventral Surface of Midbrain • MIDBRAIN: • It is formed of a large column of descending fibers (crus cerebri or basis pedunculi),on either side • The 2 crura cerebri are separated by a depression (interpeduncular fossa) • Nerve emerging from midbrain (one): • Occulomotor (3rd): From medial aspect of crus cerebri

15. Brainstem - Dorsal Surface of Medulla • Divided into 2 parts: • Caudal 2/3: Closed medulla • Rostral 1/3: Open medulla

16. Brainstem - Dorsal Surface of Medulla • CLOSED MEDULLA • Containsthe rostral continuation of central canal. • Composed of: • Dorsal median sulcus: divides the closed medulla into 2 halves. • Fasciculus gracilis: on either side of dorsal median sulcus. • Gracile tubercle: an elevation produced at the upper part of fasciculus gracilis, marks the site of gracile nucleus. • Fasciculus cuneatus: on either side of fasciculus gracilis. • Cuneate tubercle:an elevation produced at the upper part of fasciculus cuneatus, marks the site of cuneate nucleus.

17. Brainstem - Dorsal Surface of Medulla • OPEN MEDULLA • Forms the lower part of floor of 4th ventricle. • On either side, an inverted V-shaped sulcus divides the area into 3 parts (from medial to lateral): • Hypoglossal triangle: overlies hypoglossal nucleus • Vagal triangle: overlies dorsal vagal nucleus • Vestibular area: overlies vestibular nuclei

18. Brainstem - Dorsal Surface of Medulla • PONS • Forms the upper part of floor of 4th ventricle. • Separated from the medulla by an imaginary line passing between the caudal margins of middle cerebellar peduncle. • On either side, a sulcus divides the area into 2 parts (from medial to lateral): • Medial eminence:overlies abducent nucleus. • Vestibular area: overlies vestibular nuclei.

19. Brainstem - Dorsal Surface of Medulla • MIDBRAIN: • Marked by 4 elevations: • Two superior colliculi: concerned with visual reflexes. • Two inferior colliculi: forms part of auditory pathway. • Nerve emerging from midbrain (one): • Trochlear (4th): just caudal to inferior colliculus (the only cranial nerve emerging from dorsal surface of brain stem)

20. Fourth Ventricle

21. Fourth Ventricle • Cavity of hindbrain • Diamond (rhomboid) in shape • Triangular in cross section • Communications: • Rostrally: with cerebral acqueduct (cavity of midbrain) • Caudally with central canal (cavity of spinal cord) • Lateral walls (boundaries): superior & inferior cerebellar peduncles

22. Fourth Ventricle • Roof: • Upper part:superior cerebellar peduncle & superior medullary velum (a layer of pia & ependyma bridging the space between the 2 peduncles) • Middle part: cerebellum • Lower part: inferior medullary velum (a layer of pia & ependyma), has a central defect that forms the median aperture of 4th ventricle

23. Fourth Ventricle • Floor (rhomboid fossa): formed of: • Whole dorsal surface of pons • Open medulla (dorsal surface of rostral 1/3 medulla) • Apertures:provide communication between 4th ventricle & subarachnoid space for circulation of CSF • One median aperture (Foramen of Magendi): in the roof of 4th ventricle • Two lateral apertures (Foramena of Luschka): at cerebellopontine angle

24. Fourth Ventricle

25. Brainstem - Ventral Surface

26. Brainstem - Ventral Surface

27. Brainstem - Medulla Cross-section through the medulla at the level of the sensory decussation.

28. Brainstem - Medulla Cross-section through the medulla at the level of the caudal part of the 4thventricle.

29. Brainstem - Pons The pons: level of the right VI nerve nucleus and the intrapontine courseof the facial nerve and, on the left, of the nuclei of V.

30. Brainstem - Midbrain The midbrain: level of the inferior colliculus and decussation of thesuperior cerebellar peduncle.

31. Brainstem - Midbrain The midbrain: level of the superior colliculus and the red nucleus.

33. Brainstem - Dorsal Surface of Medulla Lamina tecti (quadrigemina)