1. Brainstem &Diencephalon

2. LectureObjectives • Identify the gross features of the brainstem. • Briefly describe the internal structure of the brainstem (ascending and descending pathways, sensory and motor cranial nuclei, substantia nigra, red nucleus, olivary nucleus and reticular formation). • Describe the main connections of the sensory cranialnuclei. • Describe the main connections of the motor cranialnuclei. • Review the blood supply of thebrainstem. • Describe lesions in the brainstem such as medial medullary syndrome and lateral medullary syndrome. • Describe the main connections of the substantia nigra and the red nucleus. • Describe the main connections of Reticular Formation and correlate these connections with its mainfunctions. • Describe the anatomical features of the diencephalon; components, location andrelations.

3. Principal Parts of theBrain • Cerebrum • Diencephalon • Thalamus, hypothalamus& epithalamus • Cerebellum • Brainstem • medulla, pons& midbrain

4. BrainstemFunctions • Ascending and descendingtracts • Reflexcenters • Cardiovascular and respiratorycenters • Coughing, sneezing,swallowing • Nuclei of the cranialnerves • Motor and sensory • Consciousness andarousal

5. External Anatomy ofBrainstem: Ventrally • Midbrain • Cerebral peduncles (basis pedunculi) • Interpeduncularfossa • Pons • Basilarpons • Basilarsulcus • Bulbopontinesulcus • Medullaoblongata

6. External Anatomy ofBrainstem: Ventrally • Bulbopontinesulcus • Medullaoblongata • Ventral median fissure • Pyramids • Decussation ofpyramids • Olives • Pre‐olivary &post‐ olivary sulci • Inferiorcerebellar peduncles

7. External Anatomy ofBrainstem: Dorsally • Corpora quadrigemini (midbrain) • Superior & inferiorcolliculi • Cerebellarpeduncles • Lateral walls of 4thventricle • Gracile & cuneate tubercles (closed surface of medulla) • Inferior to 4thventricle • Rhomboid fossa • Pontine part • Medullary part(open medulla)

8. RhomboidFossa • Posterior mediansulcus • Medial eminence(pons) • Facialcolliculus • Caudal part of theeminence • Sulcus limitans • Striaemedullares • Trigons • Vagal trigon (morelateral‐inferior) • Hypoglossal trigon (moremedial‐ superior) • Vestibularareas • Lateral points of thefossa • Isthmus – superiorconstriction • Obex – inferiornarrowing

9. Midbrain Medulla Pons BrainstemStructure

10. Functional Distribution of BrainstemNuclei • Midline • GSE – III, IV, VI, XII • SVE – V, VII, IX, X,XI • GVE – III, VII, IX,X • Sulcuslimitans • GVA – n. of tractus solitarius • SVA – n. of tractussolitarius • GSA – V sensorynuclei • SSA – vestibular &cochlear

11. BrainstemNuclei

12. BrainstemNuclei

13. Internal Structures ofMedulla • Level of pyramidal decussation (closed part) • Cranial nervenuclei • Spinal tract & nucleusof trigeminal nerve • Motorpathways • Pyramids • – Decussation ofpyramids • Somatosensorypathways • Nucleus gracilis &cuneatus • Fasciculus gracilis& cuneatus

14. Internal Structures ofMedulla • Level of internal arcuate fibers (closedpart) • Cranial nervenuclei • Spinal tract & nucleusof trigeminal nerve • Motorpathways • Pyramids • Somatosensorypathways • Fasciculus gracilis& cuneatus • Nucleus gracilis &cuneatus • Internal arcuatefibers • –Decussation

15. Internal Structures ofMedulla • Level of olivary nucleus (openpart) • Cranial nervenuclei • Hypoglossalnucleus • Dorsal vagalnucleus • Vestibular nuclei • Nucleus of tractussolitarius • Spinal tract & nucleus of trigeminal nerve • Motor pathways • Pyramid • Olivarynucleus • Inferior cerebellarpeduncle • Somatosensorypathways • Mediallemniscus

16. Internal Structures of thePons • Caudalpart • Cranial nervenuclei • Nucleus ofabducent nerve • Motor nucleus of facial nerve • Motorpathways • Somatosensory pathways • Mediallemniscus

17. Internal Structures of thePons • Cranialpart • Cranial nervenuclei • Motor nucleusof trigeminalnerve • Main sensory nucleusof trigeminal • Motorpathways • Middle & superior cerebellarpeduncles • Pontinenuclei • Corticospinalfibers • Somatosensorypathways • Mediallemniscus

18. Internal Structures of theMidbrain • Level of inferior colliculi • Cranial nervenuclei • Nucleus of trochlearnerve • Mesencephalic nucleusof trigeminal nerve • Motorpathways • Inferiorcolliculi • Decussation ofsuperior cerebellarpeduncles • Substantianigra • Cruscerebri • Somatosensorypathways • Medial lemniscus

19. Internal Structures of theMidbrain • Level of the superior colliculi • Cranial nervenuclei • Nucleus ofoculomotor nerve • Motorpathways • Superiorcolliculi • Rednucleus • Substantianigra • Cruscerebri • Somatosensorypathways • Mediallemniscus

20. Spinal cord & Brainstem Labeled Sections: ExternalLink • http://www.bellarmine.edu/faculty/mwiegand/atlas/ cover.html

21. Blood Supply toBrainstem • Blood supply to BS is from posteriorcirculation • Vertebrala. • Anterior spinala. • PICA • Basillara. • AICA • Paramedianbranches • Circumferentialbranches • Short &long • SCA • PCA

22. Blood Supply toBrainstem

23. Blood Supply:Medulla • Anterior spinala. • Vertebrala. • PICA

24. MedullaryLesions Lateral medullary(Wallenberg) Medial medullarysyndrome syndrome

26. Blood Supply:Pons • Caudalpons • Basilara. • Paramedian • Circumferential • AICA • Rostralpons • Basilara. • Paramedian • Circumferential • SCA

27. Blood Supply:Midbrain • Paramedian branches (Basilara.) • PCA • –Quadrigeminal • SCA

28. Midbrain Lesions Weber’ssyndrome Benedikt’ssyndrome

32. ReticularFormation • Scattered nuclei in medulla, pons &midbrain • Lateral one third have small cells (parvocellular) • Receive sensory inputs and corticalinputs • Medial two thirds have large cells (magnocellular) • Output to spinal cord, brainstem nuclei, thalamus, hypothalamus & cerebral cortex

33. Reticular FormationFunctions • The reticular formation modulates (excite or inhibit) the activitiesof: • Sensory systems – e.g.pain • Motor systems – e.g. muscle tone, segmental reflexes, eyemovements • Autonomic systems – e.g. respiration, blood pressure, cardiacfunction • Consciousness – e.g. vital centers in the brainstem, awareness, attention &arousal

34. Organization of ReticularFormation • Reticular formation organized into three longitudinalcolumns • Midline raphe group • Parasagittal medial zone • Parasagittal lateralzone

35. Organization of ReticularFormation • Fourth set of nuclei that have common cerebellar projections (precerebellar reticular nuclei) • Coordination ofmuscle contraction • Paramidian reticular nucleus of themedulla • Lateral reticular nucleus of the medulla • Reticulotegmental nucleusof thepons

36. RapheNuclei • Serotonin projectingcells • Rostral group (upper pons & midbrain) • Project to cerebellum, cerebrum (cortex, basal ganglia, limbicsystem) • Involved in the regulation of forebrainactivity • Sleep, memory processing,mood • Caudal group (lower pons & medulla) • Receives nociceptive input from brainstem & spinalcord • Involved in the regulation ofpain

37. Medial Reticular Zone • The effector part of the reticularformation • Provides most of the ascending & descendingprojection • Most inputs come from the lateral reticular zone (sensory somatic & visceral) • Ascending projections form the Ascending Reticular Activating System(ARAS) • Alter the levels of consciousness & state ofattention • Conscious activities of the cerebral cortex require excitatory influences from the ARAS • Descending projections regulate muscle tone, spinal reflexes & motor activity through • Medial (pontine) reticulospinaltract • ↑ muscle tone spinalreflexes • Lateral (medullary) reticulospinaltract • ↓ muscle tone spinalreflexes

38. Medial Reticular Zone • Locus ceruleus inpons • contain norepinephrine & extensive projections throughoutCNS • Ascending projections are part of theARAS • Involved in the mood, memory and regulation of motoractivity

39. Lateral ReticularZone • Receives extensive afferents to mediate cranial nerve reflexes and visceralfunctions • Output is mainly to medialzone • Otherprojections • Pedunculopontine nucleus (acetylcholineneurons) • Projects to the substantia nigra, subthalamic nucleus, motor cortex, & medialzone • – All have important motor controlfunctions

40. Organization of Reticular Formation NeurotransmitterDistribution

41. Reticular Formation: Neurotransmitter Pathways &Functions

42. TheDiencephalon

43. Thalamus:Structure • From medial tolateral: • Medialn. • Dorsomedialn. • Anterior n. • Internal medullarylamina • Intralaminarn. • – Lateraln. • External medullarylamina • – Reticular n. • Internalcapsule

44. Thalamus: LateralNucleus • Subdividedinto: • Dorsal tier • Lateral dorsal(LD) • Lateral posterior(LP) • Pulvinar (Pu) • Ventraltier • Ventral anterior(VA) • Ventral lateral(VL) • Ventral posterior(VP) • Ventral posterolateral(VPL) • Ventral posteromedial(VPM) • Posterior nucleus (Po) • Medial & lateral geniculate nuclei

45. SpecificNuclei

46. Non‐specificNuclei

48. Hypothalamus • Location • Boundaries • Laminaterminalis • Hypothalamicsulcus • 3rdventricle

49. Hypothalamus:Nuclei • Divisions • In coronalsection • Periventricular • Medial • Fornix • Lateral

50. Hypothalamus:Nuclei • Divisions • In sagittalsection • Chiasmatic (anterior, supraoptic) • Tuberal(middle) • Mamillary(posterior)