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Chapter 9

Chapter 9. The Central Nervous System. About this Chapter. Emergent properties of the nervous system Anatomy and functions of the CNS Divisions of the brain and what each controls Integration of complex pathways for behavior Language, memory and others. Evolution of the Nervous System.

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Chapter 9

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  1. Chapter 9 The Central Nervous System

  2. About this Chapter • Emergent properties of the nervous system • Anatomy and functions of the CNS • Divisions of the brain and what each controls • Integration of complex pathways for behavior • Language, memory and others

  3. Evolution of the Nervous System • Nerve net – jellyfish • Simple brain & nerve cord – flatworm • Brain & nerve cord with ganglia – earthworm • Increasing forebrain – fish, bird & human • Olfactory – fish • Complex behavior – birds • Reasoning & cognition – humans

  4. Evolution of the Nervous System Figure 9-1: Evolution of the nervous system

  5. Embryonic Development of Nervous System • Neural plate to neural tube • Neural crest–PNS • Anterior forms brain • Forebrain • Midbrain • Hindbrain • Hollow ventricles • Spinal cord Figure 9-2: The embryonic nervous system develops into a hollow tube

  6. Embryonic Development of Nervous System Figure 9-3 a-c: The neural tube specializes into the six major regions of the nervous system.

  7. Central Nervous System: Overview • Brain • Spinal cord Figure 9-4a: ANATOMY SUMMARY: The Central Nervous System

  8. Protecting the Brain • Hair, skin, cranium • Venous sinus blood • Meninges • Dura mater • Arachnoid membrane • Pia mater • Cerebrospinal fluid Figure 9-4b, c: ANATOMY SUMMARY: The Central Nervous System

  9. Cerebrospinal Fluid • Produced by choroid plexus • Fills ventricles & subarachnoid space • A fluid pillow that floats the brain • Exchange transport • From blood • To brain tissue

  10. CSF Functions: The CSF has several functions: • it provides physical support for the brain; • it protects against acute changes in arterial and venous blood pressure; • it is a route of waste excretion, replacing in many ways the function of lymphatics [the brain has no lymphatics); • it is involved in intra-cerebral transport, ex. hypothalamic releasing factors; 5) it helps maintain the ionic homeostasis of the CNS.

  11. CSF Composition • A comparison of the composition of CSF and plasma reveals that: • 1. CSF proteins are 1 % that of plasma; • 2. CSF calcium levels are 50% that of plasma; • 3. CSF glucose levels are 60% that of plasma; • 4. CSF chloride and magnesium levels are higher than plasma; • 5. CO2 diffuses rapidly, and HCO3 slowly, from the plasma into the CSF.

  12. Spinal Tap: Clinically Relevant CSF Information Important information on CSF can be derived from the following parameters: • 1. opening pressure; • 2. gross appearance; • 3. total and differential cell count; • 4. bacterial culture and sensitivity; • 5. protein and glucose; • 6. analysis of immunoglobulins [detect chronic CNS inflammatory conditions); • 7. cytology [detect malignant cells).

  13. CSF Appearance • clear and colourless (normal); • bright red - This indicates the presence of blood. The appearance of fresh blood in all three tubes supports the diagnosis of a subarachnoid hemorrhage. A traumatic tap [blood vessel damaged as the needle enters the spinal canal) will be indicated by the presence of blood in the first sample, with the disappearance of blood in subsequent samples • xanthochromic (yellow) - If there is no liver failure (jaundice can cause CSF to be yellow), xanthochromic CSF suggests that a subarachnoid hemorrhage has recently occurred [within days). The yellow color is due to bilirubin generated in the CNS by the breakdown of hemoglobin released from ABC's. • turbid - This indicates the presence of white cells and is suggestive of a CNS infection.

  14. CSF Cell Counts • CSF normally contains a small number of cells (usually lymphocytes and monocytes) and the total cell count is less than 5 cells/ cu mm. An increase in cell counts suggests either an infection of the CNS, or a number of CNS pathological conditions. The differential cell count provides further information regarding the possible cause of the CNS disease: • increased neutrophils - This indicates a bacterial meningitis. Other causes of an increased neutrophil count include a cerebral abscess, following seizures and following CNS hemorrhage; • increased lymphocytes - This indicates a viral meningitis. Lymphocyte counts are also elevated in meningitis, due to TB, syphilis, fungal and parasitic infections. Degenerative diseases of the CNS, such as multiple sclerosis, will also generate elevated lymphocyte counts. • “mixed reaction” - Here, there is an increase in neutrophils, lymphocytes and plasma cells. This is characteristic of TB meningitis, fungal meningitis and chronic bacterial meningitis; • increased plasma cells - This is a feature of TB meningitis and chronic inflammatory disorders, ex. multiple sclerosis; • leukemic cells - The presence of leukemic cells in the CSF indicates meningeal infiltration by leukemic cells. Leukemic cells typically appear in the CSF after several remissions have been achieved by chemotherapy. The blood-brain barrier prevents chemotherapeutic drugs from reaching the CNS and allows leukemic cells to escape treatment.

  15. Cerebrospinal Fluid Figure 9-5: ANATOMY SUMMARY: Cerebrospinal Fluid

  16. CSF Circulation

  17. Blood Brain Barrier • Extensive capillaries & sinuses • Tight junctions: limit permeability • Astrocyte foot processes: secrete paracrines • Protects brain: hormones & circulating chemicals • Many glucose transporters Figure 9-6: The blood-brain barrier

  18. Spinal Cord Regions • Cervical • Thoracic • Lumbar • Sacral Figure 9-4a: ANATOMY SUMMARY: The Central Nervous System

  19. The Skeleton

  20. Spinal Column

  21. Anatomy of Various Vertebrae

  22. Anatomy of a Vertebrae

  23. Spinal Cord Organization • Gray matter: mostly cell bodies • Dendrites & terminals • Spinal reflex integrating center • White matter • Bundles of myelinated axons • Ascending tracts – sensory • Descending tracts – motor • Dorsal roots • Ventral roots

  24. Spinal Cord Organization Figure 9-7: Specialization in the spinal cord

  25. Brain Overview • Trillion interneurons fill the brain • Up to 200,000 synapses each • Brain divisions • Cerebrum • Diencephalons • Midbrain • Cerebellum • Pons • Medulla oblongata

  26. Brain Overview Figure 9-9b, c: ANATOMY SUMMARY: The Brain

  27. Brain Stem Overview: Midbrain, Pons & Medulla • Many cranial nerves enter • Pyramids – nerve tracts crossover • Midbrain – eye movement control • Pons – breathing, signal relay • Medulla – involuntary functions • Examples: Blood pressure, vomiting • Reticular formation: • Network in brain stem • Arousal, sleep, pain, & muscle tone

  28. Brain Stem Overview: Midbrain, Pons & Medulla Figure 9-9d: ANATOMY SUMMARY: The Brain

  29. Cranial Nerves Table 9-1: The Cranial Nerves

  30. Diencephalon • Homeostatic control centers • Thalamus – relay & sensory integration • Hypothalamus: Homeostatic Functions • Hunger, stress • Thirst: body osmolarity • Flight/fight pathways • Anger & fear • Circadian rhythms • Coordinates with endocrine system

  31. Additonal Functions of Hypothalamus • heart rate • urinary bladder contraction • blood pressure • oxytocin release • vasopressin release • corticotropin-releasing hormone release[8] • thermoregulation • panting • sweating • thyrotropin inhibition • GI stimulation • satiety • neuroendocrine control • Gonadotropin-releasing hormone (GNRH), also known as Luteinizing-hormone-releasing hormone(LHRH) • pupillary dilation • shivering

  32. Diencephalon Figure 9-10: The diencephalon

  33. Pituitary and Pineal glands • Pituitary trophic & other hormones • Pineal • Melatonin • Sleep coordination Figure 9-10: The diencephalon

  34. Cerebrum • Gray and white matter areas • Higher brain functions • Hemispheres • Corpus callosum- interconnection • Cerebral laterialization • Left brain – language • Right brain – special skills

  35. Cerebrum Figure 9-11: The basal nuclei Figure 9-16: Cerebral lateralization

  36. More Cerebrum: • Basal nuclei –control of movement • Limbic System • Cingulate gyrus –role in emotion • Hippocampus –learning & memory • Amygdala –emotion & memory Figure 9-13: The limbic system

  37. Cerebral Cortex: Outer layer of neurons (1mm thick) • Perception: hearing, vision, olfaction, muscles & viscera • Reasoning, information integration • Directing voluntary behavior

  38. Cerebral Cortex: Outer layer of neurons (1mm thick) Figure 9-15: Functional areas of the cerebral cortex

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