The Central Nervous System

1. The Central Nervous System

2. Chapter 12 - The Central Nervous System • I. Brain and Embryonic Development • 1. Central Nervous System (CNS) begins 18th day • 2. Ectoderm of embryo thickens, folds, forms a neural tube • 3. Becomes brain and spinal cord • 4. Ends in a 3 pound structure

3. Where do these cells come from? • Founder cells line the inside of the neural tube • Divide, produce neurons (and glial cells), and migrate away from the center • Glial cells provide the pathway

4. II. Brain Development • Produce more cells than needed • 200 billion neurons in fetal brain • 100 billion neurons in newborn. • Cells that do not find a synaptic connection die

5. II. Brain Development • Spurt of production of grey matter during first 18 months of life

6. II. Brain Development • A second production wave before puberty: • First areas to mature are the areas involved in movement - then spatial orientation and language • Last areas to mature involve the higher order functions - reasoning

7. Mapping of 15 years of cortical development during childhood to early adulthood Red indicates more gray matter; blue indicates less gray matter as connections are pruned Nitin Gogtay MD, Jay N. Giedd MD, Leslie Lusk BA, Kiralee M. Hayashi BS, Deanna Greenstein PhD, A. Catherine Vaituzis, David H. Herman BS, Tom F. Nugent III AB, Liv Clasen PhD, Arthur W. Toga PhD, Judith L. Rapoport MD, and Paul M. Thompson PhD

9. http://www.youtube.com/watch?v=5SHc67Hep48

10. III. Cerebral Hemispheres • 1. Surface Anatomy a.Cortex (bark): 3 mm of grey matter b. Gyri: ridges on surface separated by grooves called sulci c. Fissures: deeper grooves separating brain regions • 1) Longitudinal fissure: between hemispheres • 2) Transverse fissure: between cerebrum & cerebellum

11. d. Lobes & divisions: • Two symmetrical cerebral hemispheres: • Frontal lobe • Parietal lobe • Occipital lobe • Temporal lobe

12. Pierre Broca (1861) Patients with slow, nonfluent speech -aphasia Neurosyphilitic lesion on one side of the brain Area which controlled speech

13. Dr. Penfield (1940) performed operations to alleviate patients' epileptic symptoms Stimulated cortex; asked patients to describe sensations

14. IV. Cerebral Cortex • 100 billion neurons covering the surface of the brain • Regional differences: • motor • sensory • association areas • prefrontal cortex • vision • taste • hearing • speech

16. V. Brain Development a. Development and Experience: • Development: Kittens whose eyes were sewn shut at 30-80 days after birth showed no development of the visual cortex (Schwartz,2002). • Experience: If neurons carry more traffic, they take over more space in the visual cortex.

17. Hebb (1949) - “neurons that fire together wire together” • Co-activated neurons become a cell assembly

18. Cerebral Cortex b. By middle of 20th century, evidence that cortex remodels continually with experience. Growth and remodel of a hippocampal neuron Maria Fischer, Stefanie Kaech, Darko Knutti & Andrew Matus, 1998, "Rapid Actin-Based Plasticity in Dendritic Spines". Neuron 20, p. 847-854. Actin-Based Plasticity in Dendritic Spines". Neuron 20, p. 847-854.

19. If memories are formed from experiences, these experiences must produce changes in the brain

20. New synaptic connections Sciencemag.org, 2008

21. Pruning connections Littleton lab at MIT, 2006

22. Brain Facts • 100 billion neurons in the human brain • Average brain neuron forms about 1,000 synaptic connections • Cells that fire together wire together • Brain remodels

23. T F The best time to teach a language or new activities is during the teen years.

24. T F The adult brain cannot produce new neurons.

25. Motor Areas • 1) Primary Motor Cortex • a) In frontal lobe of both sides • b) Contralateral (i.e. right controls left side of body) • 2) Premotor Cortex • a) Controls learned repetitive motor skills (i.e.dribbling, batting, piano) • b) Coordinates movements

26. Dyslexia means “faulty reading” Angular gyrus (AG) is located toward the back of the brain; AG translates the mass of words and letters we encounter daily into language. Dyslexia and language areas

28. 3) Broca's Area – speech production • a) Present in only one hemisphere (left) in 90%. Left hemisphere is dominant for speech in most people. • b) Word formation; memories of sequences of muscular movements needed to articulate words. • c) Works with Wernicke’s for word recognition .

29. c. Sensory Areas • 1) Primary Somatosensory Cortex a) Parietal lobe b) Receivse information from somatic sensory receptors c) Contralateral d) More sensitive areas have a larger amount of sensory cortex devoted • 2) Somatosensory association areas: integrates and analyzes somatic sensory inputs (temp., pressure, size, etc.)

30. 3) Visual Areas a) Primary visual cortex: largest cortical sensory area b) Visual association area: interprets & evaluates visual stimuli in light of past visual experiences so we recognize people, places & things 4) Auditory Areas a) Primary auditory cortex: pitch, rhythm & loudness from cochlea b) Auditory association area: perception of sound stimulus as speech, music, thunder, noise, etc. 5) Olfactory cortex: odors 6) Gustatory cortex: taste

31. Visual areas- is the brain complex? • Extrastriate cortex - streams of information of what and where. • Dorsal pathway -what; color and form • Ventral pathway- where; movement

32. e. Lateralization of Cortical Functioning 1) Cerebral dominance: left hemisphere dominant for language; 90% left; other hemisphere involved in visual-spatial skills, intuition, emotion, art appreciation. 2) Most left-dominant people are right-handed. 3) 10% of population is right hemisphere dominant; many left-handed, more males. 4) Lack of dominance (mutuality) may result in dexterity, ambidexterity, or dyslexia due to cerebral confusion.

33. Connections: a. Corpus callosum provides connections between the cortical areas of 2 hemispheres. b. Association fibers: connections within same hemisphere c. Projection fibers: fibers connect cortex to rest of nervous system

34. Attention and cognition Movement Basal Nuclei

35. a. Afferent impulses enter from all senses and body parts and synapse at least once in the thalamus b. Sensory relay Thalamus

36. Emotional response Body temperature Food intake Water balance Sleep-wake cycles Endocrine system control center Hyothalamus

37. Brain Stem Pons a. Conduction tracts (pons = bridge) b. Several cranial nerve pairs originate here (V, VI, and VII) c. Pneumotaxic center: maintains normal rhythm of breathing (with medullary centers)

38. Medulla Oblongata a. Cranial nerves XII, IX, X, XI, VIII associated with medulla b. Functions 1) Cardiovascular center a) Cardiac center: force and rate of contraction b) Vasomotor center: blood pressure via smooth muscles in vessels 2) Respiratory centers: rate and depth of breathing with pons

40. G. Cerebellum 1. Anatomy • a. Hemispheres connected by vermis • b. Gyri; convoluted • c. Lobes • d. Arbor vitae: treelike appearance when cross-sectioned

41. 2. Cerebellar Processing: • a. Cerebral motor cortex informs cerebellum of voluntary muscle contraction • b. Equilibrium • c. Cerebellar cortex calculates best way to coordinate force, direction, and extent of muscle contraction to: • prevent overshoot, • maintain posture, • ensure coordinated movements

42. Emotional or affective brain (feelings) Functional Brain Systems:Limbic System

43. 1. Controls stereotypic functions (often called nuclei) respiration, cardiovascular function, digestion, levels of alertness, sleep 2. Disregards 99% of sensory stimuli as unimportant Reticular Formation

44. I. Protection of Brain • Meninges • a. Functions • 1) Cover & protect CNS • 2) Protect vessels & enclose venous sinuses • 3) Contain CSF • 4) Form skull partitions

45. Dura Mater (Pia, Arachnoid, Dura) • 1) Double-layered most external membrane • 2) Periosteal layer attached to inner skull surface • 3) Dural sinuses collect venous blood and return to internal jugular veins

46. c. Arachnoid Mater • Web-like space • Arachnoid villus: knoblike projection of arachnoid through dura • d. Pia Mater: thin layer clinging to brain’s surface & spinal cord

47. CSF • Reduces brain weight by 97% & protects brain & spinal cord from trauma, nourishes • Choroid plexuses: hang from roof of each ventricle & produces the CSF • In adults, CSF volume is about 150ml replaced/8 hours so 500ml is formed daily

48. 4. Blood-Brain Barrier • a. Maintains stable environment for brain • b. Blood-borne substances in brain capillaries separated from EC space & neurons by tight junctions • c. Selective barrier except: fat-soluble molecules, alcohol, nicotine

49. Homeostatic Imbalances • a. Concussion: slight injury but no permanent damage • b. Contusion: tissue destruction • c. Subdural or subarachnoid hemorrhage: blow results in bleeding • d. Cerebral edema: swelling of the brain following injury

50. 2. Cerebrovascular Accidents or CVAs • a. Also called strokes • b. Circulation to brain area is blocked and tissue dies • 1) Ischemia: deprivation of blood to any tissue • c. 80% of those with massive CVA die in first attack • d. Paralysis, language difficulties, etc. are result