Midbrain (“mesencephalon”)

1. Midbrain (“mesencephalon”) • One inch in length • Extends from pons to diencephalon • Cerebral aqueduct connects 3rd ventricle above to 4th ventricle below

2. Structures of the Mesencephalon • Tectum: • 2 pairs of sensory nuclei (corpora quadrigemina): • superior colliculus (visual) • inferior colliculus (auditory)

3. Relationship of mesencephalon to pons and cerebellum

4. Structures of the Mesencephalon • Tegmentum: • red nucleus (many blood vessels) • substantia nigra (pigmented gray matter)

5. Structures of the Mesencephalon • Cerebral peduncles: • nerve fiber bundles on ventrolateral surfaces • contain: • descending fibers to cerebellum • motor command (pyramidal) fibers

6. Mesencephalon in Section • Red nucleus-- rich blood supply & iron-containing pigment • Substantia nigra---helps controls subconscious muscle activity • cortex & cerebellum coordinate muscular movements by sending information here from the cortex and cerebellum • Cerebral peduncles---clusters of motor & sensory fibers

7. The Mesencephalon Figure 14–8a

8. Midbrain(“mesencephalon” of the brainstem)

9. Summary: The Mesencephalon Table 14-4

10. Reticular Formation(Don’t forget this diffuse structure!) Motor function: helps regulate muscle movements Sensory function: Reticular activating system (RAS) Stimulation  increased cortical activity Inactivation  sleep

11. Reticular Activating System • RAS filters out repetitive, weak, irrelevant stimuli. • LSD removes the filtering effect  sensory-overload. Head Trauma (eg., lightweight boxers)  concussion (mild, transient loss of consciousness)  coma (loss of consciousness, hours to lifetime).

12. The Cerebellum Figure 14–7a

13. Cerebellum Adjusts postural muscles Fine-tunes conscious and subconscious movements

14. Cerebellar Peduncles • Three paired fiber tracts • Superior peduncles connect the cerebellum to the midbrain • Middle peduncles connect the pons to the cerebellum • Inferior peduncles connect the medulla to the cerebellum and carry ascending and descending cerebellar tracts from the spinal cord. • All fibers in the cerebellum areipsilateral

15. Structures of the Cerebellum Figure 14–7b

16. Cerebellum Arbor Vitae

17. Arbor Vitae • Highly branched, internal white matter of cerebellum • Cerebellar nuclei: • embedded in arbor vitae • relay information to Purkinje cells

18. Purkinje Cells • Large, branched cells • Found in cerebellar cortex • Receive input from up to 200,000 synapses

19. Disorders of the Cerebellum • Ataxia: • damage from trauma or stroke • intoxication (temporary disturbance) • disturbs muscle coordination

20. Summary: The Cerebellum Table 14-3

21. What are the main components of the diencephalon and their functions?

22. Filters ascending sensory information for primary sensory cortex Relays information between basal nuclei and cerebral cortex Integrates sensory information and motor commands The Diencephalon Figure 14–5a

23. The Diencephalon • Thalamus, epithalamus, and hypothalamus Figure 14–9

24. The Third Ventricle • Separates left thalamus and right thalamus • Intermediate mass: • projection of gray matter • extends into ventricle from each side

25. Thalamic Nuclei • Lateral geniculate nucleus: relays visual information • Medial geniculate nucleus: relays auditory information • Lateral group: involved in emotional states and integration of sensory information

26. Summary: Thalamic Nuclei Table 14-5

27. Hypothalamus • Located below the thalamusit caps the brainstem and forms the inferolateral walls of the third ventricle • Mammillary bodies • Small, paired nuclei; Relay station for olfactory pathways • control reflex eating movements • Infundibulum – stalk of the hypothalamus; connects to the pituitary gland

28. Diencephalon The DiencephalonHypothalamus

29. The Hypothalamus • Lies below thalamus Figure 14–10a

30. 8 Functions of the Hypothalamus • Provides subconscious control of skeletal muscle • Controls autonomic function • Coordinates activities of nervous and endocrine systems

31. Functions of the Hypothalamus • Secretes hormones: • antidiuretic hormone(ADH) by supraoptic nucleus • oxytocin(OT) by paraventricular nucleus

32. Functions of the Hypothalamus • Produces emotions and behavioral drives: • the feeding center (hunger) • the thirst center (thirst)

33. Functions of the Hypothalamus • Coordinates voluntary and autonomic functions • Regulates body temperature: • preoptic area of hypothalamus

34. Functions of the Hypothalamus • Controls circadian rhythms (day–night cycles): • suprachiasmatic nucleus

35. Summary: The Hypothalamus Table 14-6

36. Epithalamus Pineal Gland • Above the thalamus • Pineal gland • secretes melatonin:a hormone involved with sleep regulation, sleep-wake cycles, and mood

37. Questions?

38. Cerebrospinal Fluid (CSF) • 80-150 ml (about ½ cup) • Clear liquid containing glucose, proteins, & ions • Functions • mechanical protection • floats brain & softens impact with bony walls • chemical protection • optimal ionic concentrations for action potentials • circulation • nutrients and waste products to and from blood

39. CSF Composition Differs from plasma: no (or very few) cells protein is lower ionic concentrations are different pH  affects brain blood flow & respiratory rate.

40. Blood Brain Barrier Ependymal cells around choroid plexus (which produce CSF) have tight junctions. Capillaries of brain tissue have tight junctions between endothelial cells. Astrocytes wrap the small vessels. Many antibiotics and chemotherapy agents can not pass from blood to brain.

41. Blood Brain Barrier – details to know Break-Down radiation, infection, neoplasm (cancer), manitol (intentional disruption) facilitated diffusion glucose, amino acids simple diffusion Small, neutrally charged molecules (i.e., lipid soluble molecules) pass easily. • Water, CO2, O2, • alcohol, caffeine, nicotine, heroin • “general” anesthetics

42. Brain Blood Flow Sources: 2 internal carotids (R and L) 2 vertebral arteries and “Circle of Willis” (Study in more detail in lab.) 14% of cardiac output, and uses 20% of oxygen used by body

43. Brain Blood Flow

44. Brain Blood Flow Flow depends on CO2 more than O2 concentration • High CO2  increased blood flow • Low CO2  decreased blood flow Hyperventilation  blow off CO2  low blood flow  dizzy spell Other Factors: extreme blood pressures intracranial pressure blood viscosity

45. Brain Blood Flow: Clinical Issues • Low blood sugar (eg., too much insulin) starves neurons • Mass (tumor, blood clot)  decreased flow • Heart attack  decreased flow and confusion • 10 seconds without blood  pass out • 4 minutes  permanent brain damage • lysosomes release enzymes

46. Medical Example: Subdural Hematoma An subdural hematoma is a blood collection Between the dura and arachnoid mater (external to the brain) Since the skull cannot expand, the brain shifts across the midline.

47. Clinical Cases:Bleeding in the Brain • Epidural Bleed • Subdural Hematoma • Intraparenchymal Bleed

48. Clinical Cases:Bleeding in the Brain • Epidural Bleed • Subdural Hematoma • Intraparenchymal Bleed

49. Clinical Cases:Bleeding in the Brain • Epidural Bleed • Subdural Hematoma • Intraparenchymal Bleed(s)

50. Medical Examples • Meningitis is inflammation of the meninges due to bacterial or viral infection. • Encephalitis is inflammation of the brain