CNS Chapter 13

1. CNSChapter 13

2. PROTECTION AND NOURISHMENT OF THE CNS A. CNS is well-protected from internal/external change 1. Blood brain barrier (BBB)--protection from toxins, etc. 2. Skull and vertebrae--protection from physical insults 3. Meninges--nourishment from blood and protection 4. Cerebrospinal Fluid (CSF)

3. Blood Brain Barrier • Specialized system of capillaries that protects the brain from harmful substances in the blood stream • the BBB strictly limits transport into the brain through both physical (tight junctions) and metabolic (enzymes) barriers. • Thus the BBB is often the rate-limiting factor in determining permeation of therapeutic drugs into the brain. • Additionally, BBB breakdown is theorized to be a key component in central nervous system (CNS) associated pathologies.

4. FUNCTIONAL ORGANIZATION OF THE BRAIN AND SPINAL CORD General brain organization • Major divisions are the forebrain, midbrain, and hindbrain • Relationship to the human brain • The Brain: Form and Function • Cerebrum (sulci and lobes) • Functional organization of the cortex (lobes) • Spatial relationships reflect functional interaction • Broca's area is projects to the premotor cortex • Wernicke's area receives sensory input from visual and auditory cortices as well as other brain areas • Example: Language involves many brain areas

5. FUNCTIONAL ORGANIZATION OF THE BRAIN AND SPINAL CORD • Functional organization is conserved in mammals • Topographical mapping in somatomotor cortex, etc. • Limbic system -- Emotions (e.g., aggression and fear), memory acquisition, pleasure, etc. • Human Brain: Pushing the limits (go to discovery education)

6. FUNCTIONAL ORGANIZATION OF THE BRAIN AND SPINAL CORD • Spinal Cord • General organization • An extension of the brain • Functions • Relays information to and from brain • Ascending and decending paths in the spinal cord • Spinal cord is also involved in various reflexes 1) • Example 1: Withdrawal reflex (see Text) 2) • Example 2: Crossed-extensor reflex 3) • Example 3: Micturition reflex involves control from higher centers ** **

7. Meninges (3 membranous layers) • Dura mater • Strong, white fibrous tissue; outer layer of meninges and inner periosteum of the cranial bones • Arachnoid membrane • Delicate • cobwebby layer • between the dura mater and pia mater

8. Meninges (3 membranous layers) • Pia matter • Innermost, transparent layer • Adheres to the outer surface of the brain and spinal cord • Contains blood vessels • Ends in a slender filament called filumterminale at the sacrum, blends with the dura mater to form a fibrous cord that disappears into the periosteum of the coccyx

10. Meningitis • an infection or inflammation of the meninges • caused mostly by bacteria such as: • Neisseria meningitides (meningococcal) • Streptococcus pneumoniae • Viral infections, mycoses (fungal infections), and tumors may also cause meningitis • May be self-limiting or fatal • Spinal meningitis involves only the meninges of the cord • Signs & Symptoms • Fever, Severe headache, Neck stiffness and pain STOP

11. Cerebrospinal Fluid • Functions • Protection: • The CSF acts to cushion a blow to the head and lessen the impact. • Buoyancy: • Because the brain is immersed in fluid, the net weight of the brain is reduced from about 1,400 gm to about 50 gm. Therefore, pressure at the base of the brain is reduced. • Excretion of waste products: • The one-way flow from the CSF to the blood takes potentially harmful metabolites, drugs and other substances away from the brain. • Endocrine medium for the brain: • The CSF serves to transport hormones to other areas of the brain.

12. Ventricles • Fluid filled spaces • 1st and 2nd (lateral)  one in each hemisphere • 3rd  thin, vertical pocket below and medial to 1st and 2nd • 4th tiny, found where cerebellum attaches to brainstem

13. CSF Formation • Formed by the choroid plexus (in all ventricles)

14. CSF Circulation • Flows from ventricles 1 and 2 to the 3rd via the interventricular foramen (Foramen of Monro) • Ventricles 3 and 4 are connected by the cerebral aqueduct (Aqueduct of Sylvius) • CSF then flows into the subarachnoid space • Absorption into the blood stream takes place in the superior sagittal sinus through arachnoid villi

15. CSF Circulation • When the CSF pressure is greater than the venous pressure, CSF will flow into the blood stream • However, the arachnoid villi act as "one way valves"...if the CSF pressure is less than the venous pressure, the arachnoid villi will NOT let blood pass into the ventricular system.

16. Hydrocephalus • Overproduction of CSF • An obstruction at some point within the ventricular system • Problems with CSF absorption • Can lead to • Compression of soft brain tissue • Coma and or death

17. The Brain • One of the largest organs in an adult (3lbs) • Brainstem (3 divisions) • Performs sensory, motor, and reflex functions • Vital = cardiac, vasomotor, respiratory • Not vital = vomiting, coughing, sneezing, and etc… • Brainstem (Midbrain, Pons, and Medulla oblongata) • Site of Reticular Formation (RF) • Affects state of arousal (sleep-wake cycle, hibernation cycle)

18. The Brainstem • Midbrain • Contains major motor supply to the muscles controlling eye movements and relays information for some visual and auditory reflexes • Cranial nerve reflexes • acts as a relay station, as a point of integration for sensory input and in perception of pain • Overlapping maps for visual, auditory, and somatosensory input • Multisensory neurons integrate more than one sensory input

19. The Brainstem • Pons • Face sensation and movement • Medulla oblongata • At base of brainstem • Controls heartbeat, blood pressure, and breathing • site of regulatory centers

20. STOP

21. The Cerebellum • 2nd largest part of the brain • 2 hemispheres separated by a central section called the vermis • Arbor vitae = internal white matter, leaf pattern

22. Function of the Cerebellum • Skeletal muscle control • Coordinating the activities of groups of muscles • Maintains balance • Controls posture • Subconsciously makes movements smooth, efficient, and coordinated • Compares impulses from the cerebrum and muscles

23. The Diencephalon • Located between the cerebrum and midbrain • Contains the thalamus, hypothalamus, and pineal body • Thalamus • Conscious recognition of crude, less critical sensations of pain, temperature, and touch • Relays sensory impulses except olfactory to the cerebrum • Emotionally associates sensory impulses with feeling of pleasant and unpleasant • Arousal

24. The Diencephalon • Hypothalamus • Lies beneath the thalamus • Links nervous system to the endocrine system • Regulates and coordinates autonomic activities • Crucial part of the route where emotions can express themselves in changed bodily functions • Synthesize hormones essential in maintaining water balance • Arousal • Regulates appetite • Maintains normal body temperature

25. The Diencephalon • Pineal body • Regulates biological clock • Produces some horomones • Melatonin = regulates sleep wake cycles

26. Spinal Cord • Lies within the spinal cavity of the vertebra • Surrounded by meninges, CSF, adipose tissue, and blood vessels • Extends from the Foramen magnum (big hole at the base of the skull) to lower border of 1st lumbar vertebra • Oval shaped • 2 bulges (cervical and lumbar) Significance? • 2 deep grooves (ant. median fissure = deep and wide, and post. median sulcus = groove)

27. Spinal Cord • Nerve Roots (side projections) • Dorsal nerve root • Carry sensory information into the spinal cord • Ascending tracts • Ventral nerve root • Carry motor information away from or out of the spinal cord • Descending tracts

28. STOP

29. The Cerebrum • Largest and uppermost region of the brain • Right and left hemispheres (divided into 5 lobes) • Frontal • Parietal • Temporal • Occipital • Insula (island of Reil) • Gyri • Hills (some are named) • Sulci • Shallow grooves

30. The Cerebrum • Sensory Functions (Cerebral Cortex) • Somatic senses • Touch • Pressure • Temperature • Proprioception • Motor Functions (Cerebral Cortex) • Pre-central Gyrus = controls individual muscles • Area anterior to the pre-central gyrus controls groups of muscles

32. The Cerebrum • Consciousness • Awareness of one’s self, environment and other beings • Depends on impulses from cortical neurons to the reticular activating system • Which functions as the arousal system • Crucial in maintaining consciousness • Drugs that affect this system include • Barbiturates = suppress • Amphetamines = stimulate

33. The Cerebrum • Language • Ability to speak and write words & understand spoken and written words • Speech centers (frontal, parietal, & temporal lobes) • Aphasias = lesions in the speech centers

34. The Cerebrum • Emotions • Subjective experiencing and objective expressing of emotions involve functioning of the limbic system • Anger, fear, pleasure, & sorrow • Limbic System = “emotional brain” • Lie on medial surface of the cerebrum • Primary connections with other parts of the brain (i.e. thalamus, hypothalamus)

35. The Cerebrum • Memory • One of our major mental activities • Short & long term • Involve the temporal, parietal, and occipital lobes • Engrams • Structural traces in the cerebral cortex that comprise long term memories • Linked to the limbic system (experiences in memory)

38. THE END