The Central Nervous System

1. The Central Nervous System

2. Protection of the CNS • The brain and spinal cord are protected by several layers: • Skeletal tissue (cranium and vertebral column) • Meninges (layers of tissue that cushion the brain) • Dura mater • Arachnoid tissue • Pia mater • Cerebrospinal fluid • Shock-absorbing medium • Provides a optimum and stable environment for generating nerve impulses • Provides a medium for the exchange of nutrients and wastes between blood and nervous tissue.

3. Blood-Brain Barrier • The meninges protect the CNS by preventing direct circulation of blood through the brain and spinal cord • Capillary endothelial cells have tight junctions • Special neurons called astrocytes stimulate tight junctions • substances that can pass through the lipid bilayerare unrestricted (O2, CO2, H2O, alcohol, caffeine, nicotine, steroids) • Substances that need to be transported across the lipid bilayer are restricted (glucose, amino acids, ions) • Some substances cannnot pass BBB (some harmful substances, toxins, posions, infectious agents, some hormones)

4. Spinal Cord • Functions as centre for reflex actions.

5. Spinal Cord • Communicates between brain and spinal nerves.

6. Spinal Cord • Gray matter shaped like butterfly or letter "H” • Coloured by unmyelinated cell bodies and short fibres; made of axons of sensory neurons, dendrites/cell bodies of motor axons, and interneurons.

7. Spinal Cord • White matter is coloured white due to myelinated long fibres of interneurons; this outermost region contains interneurons grouped into dorsal tracts that send information toward brain (ascending tracts) or into ventral tracts that carry information down from brain (descending tracts).

8. Spinal Cord • Tracts cross over so that left side of brain controls right side of body.

9. The Brain

10. Divisions of the Brain The brain is divided into: • medulla oblongata • cerebellum • pons • midbrain • hypothalamus • thalamus • cerebrum

11. Ventricles • The brain also has four interconnected cavities or ventricles, filled with cerebrospinal fluid

12. Brain Stem • medulla oblongata • pons • midbrain

13. Brain Stem Medulla oblongata: • lies between spinal cord and pons anterior to cerebellum • contains centres for heartbeat, respiration, vasoconstriction • contains reflex centres for vomiting, coughing, swallowing, etc.

14. Brain Stem Pons: • means "bridge” • contains tracts bridging the cerebellum with the rest of CNS • helps regulate breathing rate and some reflexes

15. Brain Stem The midbrain: • processes sensory information from eyes, ears and nose • has a role in eye movement and control of skeletal muscles • has reflex centres for head movements in response to visual, auditory, and tactile stimuli • also is a relay centre visual and auditory information between hindbrain and forebrain

16. Diencephalon Hypothalamus: • forms floor of third ventricle of brain • functions in homeostasis by regulating hunger, sleep, thirst, temperature, water balance, blood pressure • controls the pituitary gland (link between nervous and endocrine systems)

17. Diencephalon Thalamus: • is in roof of third ventricle • serves as central relay station for sensory impulses (except smell) traveling to appropriate regions of the cerebrum

18. Cerebellum • Below posterior portion of cerebrum, separated from brainstem by fourth ventricle - surface is gray matter, interior is mostly white matter • Functions in unconscious coordination of balance, posture, reflexes and body movements • Also coordinates fine voluntary movements using input from specialized sensory neurons in the skeletal muscles and joints called proprioreceptors

19. Cerebrum • responsible for consciousness and is largest portion of brain • outer layer is the unmyelinated cerebral cortex • cortex is divided into right and left cerebral hemispheres connected by corpus callosum • cortex is 2-4 mm thick, and is highly folded into grooves (or sulci)

20. Cerebrum • Various regions of the cerebrum specialize: • Frontal lobe - contains primary motor cortex for voluntary skeletal muscles, premotor area for planning movements, Broca’s area for speech and prefrontal area for decision making, creativity, personality traits • Parietal lobe– contains primary sensory cortex which handles information from skin, muscles, visceral organs, taste buds – also helps to process information about body position and orientation • Temporal lobe – auditory cortex – interprets characteristics of sound and hearing • Occipital lobe – contains primary visual cortex

21. Cerebrum

22. Limbic System • Composed of basal ganglia, contains neural pathways that join frontal lobes, temporal lobes, thalamus, and hypothalamus. • Causes person to experience pain, pleasure, rage, addiction, etc., to guide behaviour to increase survival. • Also critical in learning and long- and short-term memory.

23. The brain is a wonderful organ. It starts working the moment you get up and does not stop until you get into the office . ~ Robert Frost • My girlfriend and I went on a picnic. I don't know how she did it, but she got poison ivy on the brain. When it itched, the only way she could scratch it was to think about sandpaper. ~ Steven Wright