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BRAIN STEM EXTERNAL FEATURES

BRAIN STEM EXTERNAL FEATURES. Dr. Ahmed Fathalla Ibrahim. BRAIN. PROSENCEPHALON (FOREBRAIN): TELENCEPHALON: Cerebral hemispheres (cavities: 2 lateral ventricles) DIENCEPHALON: thalamus, hypothalamus, epithalamus & subthalamus (cavity: 3 rd ventricle) MESENCEPHALON (MIDBRAIN)

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BRAIN STEM EXTERNAL FEATURES

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  1. BRAIN STEM EXTERNAL FEATURES Dr. Ahmed Fathalla Ibrahim

  2. BRAIN PROSENCEPHALON (FOREBRAIN): • TELENCEPHALON: Cerebral hemispheres(cavities: 2 lateral ventricles) • DIENCEPHALON: thalamus, hypothalamus, epithalamus & subthalamus(cavity: 3rd ventricle) MESENCEPHALON (MIDBRAIN) • Cavity: cerebral aqueduct RHOMBENCEPHALON (HINDBRAIN) • METENCEPHALON: Pons & cerebellum • MYELENCEPHALON: Medulla • Cavity: 4th ventricle

  3. BRAIN STEM 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)

  4. BRAIN STEM 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

  5. BRAIN STEM CONNECTION TO CEREBELLUM: • Midbrain:by superior cerebellar peduncle • Pons:by middle cerebellar peduncle • Medulla oblongata:by inferior cerebellar peduncle

  6. BRAIN STEM 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

  7. BRAIN STEMVENTRAL SURFACE

  8. BRAIN STEMVENTRAL SURFACE

  9. BRAIN STEMVENTRAL 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

  10. BRAIN STEMVENTRAL SURFACE 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)

  11. BRAIN STEMVENTRAL SURFACE

  12. BRAIN STEMVENTRAL SURFACE 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. BRAIN STEMVENTRAL SURFACE 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. BRAIN STEMVENTRAL SURFACE

  15. BRAIN STEMVENTRAL SURFACE 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

  16. BRAIN STEMDORSAL SURFACE

  17. BRAIN STEMDORSAL SURFACE MEDULLA • Divided into 2 portions: • Caudal 2/3: Closed Medulla: • Rostral 1/3: Open Medulla

  18. BRAIN STEMDORSAL SURFACE CLOSED MEDULLA • Contains the rostral continuation of central canal • Composed of: • Dorsal median sulcus: divdes 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

  19. BRAIN STEMDORSAL SURFACE 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

  20. BRAIN STEMDORSAL SURFACE

  21. BRAIN STEMDORSAL SURFACE 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

  22. BRAIN STEMDORSAL SURFACE

  23. BRAIN STEMDORSAL SURFACE 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)

  24. FOURTH VENTRICLE

  25. FOURTH VENTRICLE

  26. FOURTH VENTRICLE

  27. FOURTH VENTRICLE

  28. 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

  29. 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

  30. 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

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