1. Chapter 7 – Part 4 The Nervous System

2. Protection of the Central Nervous System
Scalp and skin
Skull and vertebral column
Meninges
Cerebro spinal fluid
Blood brain barrier

3. Meninges
The three connective tissue membranes covering and protecting the CNS structures are meninges.
Three layers:
Dura mater
Arachnoid mater
Pia mater

4. Meninges Dura mater – outer most layer Feels tough & leathery
Folds inward in several areas
Double-layered external covering
Periosteum – attached to the inner surface of the skull
Meningeal layer – outer covering of the brain

5. Meninges Arachnoid layer – middle meningeal layer
Web-like
Pia mater – innermost membrane of the meninges
Clings tightly to the surface of the brain and spinal cord, following every fold
Delicate layer

6. Cerebrospinal Fluid Similar to blood plasma composition
Formed by the choroid plexus
Forms a watery cushion to protect the brain
Continually circulated in arachnoid space, ventricles, and central canal of the spinal cord

7. Ventricles and Location of the Cerebrospinal Fluid

8. Meningitis Meningitis - inflammation of the meninges
Serious threat to the brain because bacterial or viral meningitis may spread into the nervous system of the CNS.
Usually diagnosed by taking a sample of cerebrospinal fluid
Procedure is called a lumbar (spinal) tap

9. Blood Brain Barrier
No other body organ is so absolutely dependent on a constant internal environment as is the brain.
Other body tissues can withstand the rather small fluctuations in the concentrations of hormones, ions, and nutrients that continually occur, particularly after eating or exercise.
If the brain were exposed to such chemical changes, uncontrolled neural activity might result!
Remember that certain ions are involved in initiating nerve impulses and some amino acids serve as neurotransmitters.

10. Blood Brain Barrier
Neurons are kept separated from bloodborne substances by a blood-brain barrier.
Composed of the least permeable capillaries of the body
Of water-soluble substances, only water, glucose and essential amino acids can easily pass through the walls of these capillaries.
Metabolic wastes (urea, toxins, proteins, and most drugs) are prevented from entering the brain.

11. Blood Brain Barrier
The astrocytes contribute to the barrier, but the relative impermeability of the capillaries is most responsible for providing this protection.
Useless against some substances
Fats and fat soluble molecules
Respiratory gases
Alcohol
Nicotine
Anesthesia

12. Traumatic Brain Injuries
Concussion
Slight brain injury
May be dizzy, “see stars”, or lose consciousness briefly
No permanent brain damage
Contusion
Nervous tissue destruction occurs
Nervous tissue does not regenerate
Shows an area of subarachnoid hemorrhage with bleeding and an area of brain contusion where the white ischemic brain has died

13. Traumatic Brain Injuries
Hemorrhaging and Edema
Cerebral edema - swelling of the brain due to inflammatory response to injury
After head blows, death may result from intracranial hemorrhage (bleeding from ruptured vessels) or from cerebral edema.
Both may compress and kill brain tissue
Individuals who are initially alert and lucid following head trauma and then begin to deteriorate neurologically later are most likely hemorrhaging or suffering the consequences of edema.

14. Cerebrovascular Accident (CVA)
Commonly called a stroke
Third leading cause of death in the US
Occur when blood circulation to a brain area is blocked (blood clot or a ruptured blood vessel)
Brain tissue supplied with oxygen from that blood source dies
Loss of some functions or death may result

15. Cerebrovascular Accident (CVA)
Fewer than 1/3 of those surviving a CVA are alive 3 years later.
Some patients recover at least partly, because undamaged neurons spread into areas where neurons have died and take over some lost functions.
Most of the recovery seen after brain injury is due to this phenomenon.

16. Alzheimer’s Disease
Progressive degenerative brain disease that ultimately results in dementia (mental deterioration)
Mostly seen in the elderly, but may begin in middle age
Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons
Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death
5-15% of people over 65 develop this condition.

17. Parkinson’s Disease
Results from a degeneration of the dopamine-releasing neurons, and as those neurons degenerate, the dopamine-deprived basal nuclei they target become overactive
Typically strikes people in their 50s and 60s (Michael J. Fox is an exception)
Cause of Parkinson’s is still unknown
Symptoms include:
Persistent tremor at rest exhibited by head nodding and “pill-rolling” movement of the fingers
Forward-bent walking posture and shuffling gait
Stiff facial expression
Trouble initiating movement or getting their muscles going

18. Huntington’s Disease
Genetic disease that leads to massive degeneration of the basal nuclei and later of the cerebral cortex
Strikes during the middle age
Symptoms:
Initial - wild, jerky, and almost continuous flapping movements
Later - marked mental deterioration
Progressive and usually fatal within 15 years of onset of symptoms

19. Treatment of Parkinson’s and Huntington’s Disease
Parkinson’s disease
Signs and symptoms – Inhibition of the motor drive
Treatment – usually treated with drugs that enhance dopamine’s effects
Huntington’s disease
Signs and symptoms - Overstimulation of the motor drive (opposite of Parkinson’s disease)
Treatment – usually treated with drugs that block dopamine’s effects