The Brain (& CNS)

1. The Brain (& CNS) Lecture 12a BIOL241

2. Final Exam (Exam 4) • Chapters 11 – 15* • 100 points • Multiple choice, T/F, matching, fill in • Short answer, essays (2)* • Labeling (brain [including functions], cranial nerves, spinal cord)

3. Outline • Overview of the human brain • Tour through the brain – structures and functions • Cerebral hemispheres and higher mental functions • Meninges • Ventricles and CSF • Brain disorders

4. The Human Brain • Composed of wrinkled, pinkish gray tissue • Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem • Ranges from 750 cc to 2100 cc • Contains almost 98% of the body’s neural tissue • Average weight, adult: 1300 – 1400 gm (~3 lb) • 1010 to 1011 neurons • Trillions of connections • men = larger • Women = better connected

5. Major Regions and Landmarks Figure 14–1

6. Embryology of the Brain Table 14-1

7. Regions of the Adult Brain • Telencephalon (cerebrum) – cortex, white matter, and basal nuclei • Diencephalon – thalamus, hypothalamus, and epithalamus • Mesencephalon –midbrain (brain stem) • Metencephalon – pons (brain stem), cerebellum • Myelencephalon – medulla oblongata (brain stem)

8. Spinal Cord Central cavity surrounded by a gray matter core External to which is white matter composed of myelinated fiber tracts Brain Similar to spinal cord but with additional areas of gray matter Cerebellum has gray matter in nuclei Cerebrum has nuclei and additional gray matter in the cortex Basic Pattern of the Central Nervous System Figure 12.4

9. Some terms • nucleus: collection of neuron cell bodies in the CNS • tract: collection of axons in the CNS • ganglia: collection of neuron cell bodies in the PNS • nerve: collection of axons in the PNS • Cranial nerves • Spinal nerves

10. Tour of the brain • From caudal/inferior to rostral/superior

11. TheBrain Stem • Processes information between spinal cord and cerebrum or cerebellum • Controls automatic behaviors necessary for survival • Associated with 10 of the 12 pairs of cranial nerves (covered later) • Includes: • mesencephalon (midbrain) • pons • medulla oblongata • Note: some consider the diencephalon part of the brain stem as well

12. Brain Stem Figure 12.15a

13. Anatomy:Brain stem Most cranial nerves are located in the brain stem

14. Brain Stem Figure 12.15b

15. Posterior view

16. Medulla Oblongata • Most inferior part of brain, connects brain to spinal cord • Relays information • Pyramids – two longitudinal ridges formed by corticospinal tracts • Regulates autonomic functions: • regulates arousal, heart rate, blood pressure, pace for respiration and digestion • Cranial nerves IX, X, XI, XII come off or enter

17. Medulla Oblongata Figure 12.16c

18. Medulla Oblongata

19. Medulla Nuclei • Cardiovascular control center – adjusts force and rate of heart contraction • Respiratory centers – control rate and depth of breathing • Additional centers – regulate vomiting, hiccupping, swallowing, coughing, and sneezing

20. Pons

21. Pons • Involved in somatic and visceral motor control • Contain the nuclei for cranial nerves V, VI, VII, VIII • Contains nuclei of the reticular formation • Control of respiration that modifies the info from the medulla • Nuclei and tracts passing through to the cerebellum (motor and somatosensory info) • Nuclei and tracts to other portions of the CNS (just passing through)

22. Cerebellum

23. Cerebellum • “little brain” • Second largest part of brain (~10% mass) • Provides precise timing and appropriate patterns of skeletal muscle contraction to coordinate repetitive body movements and help learning complex motor behaviors • Adjusts the postural muscles of the body, controls balance and equilibrium • Has 2 hemispheres, covered with cerebellar cortex • Recognizes and predicts sequences of events • Cerebellar activity occurs subconsciously (as does all processing that occurs outside the cerebral cortex)

24. Cerebellum – side view

25. Cerebellum • Cerebellum receives impulses of the intent to initiate voluntary muscle contraction • Monitors all proprioceptive info and visual info about body position • Cerebellar cortex calculates the best way to perform a movement • Programs and fine tunes movements by detecting mismatches in intended and actual movements -- when learning to ride a bike, throw a curve ball or tie your shoe, cerebellum activity is high. When they become automatic, cerebellum is no longer involved

26. Mesencephalon

27. Mesencephalon • Also called midbrain • Processes sight, sound, and associated reflexes • Maintains consciousness • Cranial nerve nuclei III and IV • 2 basic divisions • tectum (roof) • tegmentum

28. Mesencephalon • Process of visual and auditory sensations • corpora quadrigemina(in tectum) = superior colliculi (visual reflex) and inferior colliculi (auditory reflex) • Substantianigra(in tegmentum) • Neurons inhibit activity of cerebral nuclei by releasing dopamine • If damaged, results in less dopamine released and muscle tone increases: muscle rigidity, difficulty initiating movement = Parkinson’s Disease • Reticular formation: maintain consciousness

29. Midbrain Nuclei Figure 12.16a

30. Mesencephalon

31. Diencephalon Figure 12.12

32. Diencephalon • Located under cerebrum and cerebellum • Links cerebrum with brain stem • Integrates sensory information and motor commands • Cranial nerve II

33. Diencephalon • Pineal Gland • Secretes hormone melatonin • Thalamus: • relays and processes sensory information • Hypothalamus: • hormone production • emotion • autonomic function

34. Diencephalon: Thalamus • Paired, egg-shaped masses connected at the midline by the intermediate mass • Nuclei project to and receive fibers from the cerebral cortex Figure 14–9

35. Thalamus • Sensory Relay station • All sensory that is projected to the cerebral cortex stops here first except smell • Filters ascending sensory information for primary sensory cortex • Relays information between basal nuclei and cerebral cortex • Mediates sensation, some motor activities, cortical arousal (thus learning, and memory)

36. Diencephalon: Hypothalamus • Lies below thalamus Figure 14–10a

37. Hypothalamus • Captain of the Autonomic nervous system, master overseer of homeostasis • Emotions and behavior: mediates perception of pleasure, fear, and rage • Regulation of body temperature, blood pressure, digestive tract motility, rate and depth of breathing, and many other visceral activities • Food intake (drives) • Water balance/thirst • Day/night rhythms • Endocrine functions- ADH and oxytocin

38. Structures of the Hypothalamus • Mamillarybodies: • Relay station for olfactory information • control reflex eating movements

39. Pituitary Gland • Major endocrine gland, controls all others • Connected to hypothalamus via infundibulum (stalk) • Interfaces nervous and endocrine systems because it is controlled by the hypothalamus

40. Telencephalon • Basal nuclei • Cerebrum

41. The Basal Nuclei (Ganglia) Figure 14–14b, c

42. Basal Nuclei • Also called basal ganglia • Masses of gray matter found deep within the cortical white matter • The corpus striatum is composed of three parts • Caudate nucleus • Lentiform nucleus = putamen and the globuspallidus • Fibers of internal capsule running between and through caudate and lentiform nuclei • Direct subconscious activities

43. Functions of Basal Nuclei • Are involved with: • Subconscious control of skeletal muscle tone • Regulate attention and cognition • Regulate intensity of slow or stereotyped movements (walking, lifting) • Inhibit antagonistic and unnecessary movement • Subconscious habit learning • May store simple movement patterns

44. Basal Nuclei Figure 12.11b

45. Cerebrum • Largest part of brain (make up 83% of its mass) • Controls higher mental functions including all conscious thoughts and experience including all intellectual functions (more about this later) • Processes somatic sensory and motor information • Divided into left and right cerebral hemispheres • Surface layer of gray matter (cerebral cortex)

46. (Cerebral) Cortex • Gray matter covering cerebral hemispheres • Accounts for 40% of the mass of the brain • Folded surface increases surface area • Elevated ridges = gyri (gyrus) • Shallow depressions = sulci (sulcus) • Deep grooves = fissures

47. Cerebral Gray and White Matter • Gray matter: • Cell bodies • Found in cerebral cortex and basal nuclei • White matter: • Fiber tracts (axons) • Deep to cerebral cortex • Surrounding basal nuclei

48. White Matter of the Cerebrum • Myelinated fibers (axons) • Association fibers: • arcuate: local • longitudinal: within one hemisphere • Commissural: between hemispheres • Projection: link cerebral cortex with rest of CNS Figure 14–13

49. Examples • Projection Fibers: Internal capsule • all ascending and descending projection fibers to and from cerebral cortex, passes though basal nuclei • Commissural fibers: corpus callosum • Connect the two cerebral hemispheres

50. Fiber Tracts in White Matter Figure 12.10b