Chapter 7 – Part 4The Nervous System

Protection of the Central Nervous Protection of the Central Nervous SystemSystem

1. Scalp and skin2. Skull and vertebral column3. Meninges4. Cerebro-

spinal fluid5. Blood brain

barrier

MeningesMeninges

The three connective tissue membranes covering and protecting the CNS structures are meninges.

Three layers:

1. Dura mater

2. Arachnoid mater

3. Pia mater

MeningesMeninges

1. Dura mater – outer most layer Feels tough & leathery

Folds inward in several

areas Double-layered external covering

1. Periosteum – attached to the inner surface of the skull

2. Meningeal layer – outer covering of the brain

MeningesMeninges

2. Arachnoid layer – middle meningeal layer

Web-like

3. Pia mater – innermost membrane of the meninges

Clings tightly to the surface of the brain and spinal cord, following every fold

Delicate layer

Cerebrospinal FluidCerebrospinal 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

Ventricles and Location of the Ventricles and Location of the Cerebrospinal FluidCerebrospinal Fluid

MeningitisMeningitis 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

Blood Brain BarrierBlood 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.

Blood Brain BarrierBlood 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.

Blood Brain BarrierBlood 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

Traumatic Brain InjuriesTraumatic 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

regenerateShows an area of subarachnoid hemorrhage with bleeding and an area of brain contusion where the white ischemic brain has died

Traumatic Brain InjuriesTraumatic 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.

Cerebrovascular Accident (CVA)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

Cerebrovascular Accident (CVA)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.

Alzheimer’s DiseaseAlzheimer’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.

Parkinson’s Disease 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

Huntington’s DiseaseHuntington’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

Treatment of Parkinson’s and Treatment of Parkinson’s and Huntington’s DiseaseHuntington’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