Protection of the Central Nervous System Enclosing it in bone Skull & vertebral column Enclosing it in membranes Meninges = connective tissue membranes that cover & protect CNS structures Watery cushion Cerebrospinal fluid (CSF)

Protection of the Central Nervous System (P. 249) Figure 7.17a

Meninges From most superficial to deepest: dura mater, arachnoid mater, pia mater Dura mater Double-layered external covering Periosteal layer—attached to inner surface of the skull Meningeal layer—outer covering of the brain Folds inward in several areas

Meninges Arachnoid mater Middle layer Web-like Pia mater Internal layer Clings to the surface of the brain

Meninges Figure 7.17b

The subarachnoid space is filled with CSF; And arachnoid villi= specialized projections

Meningitis Inflammation of meninges Threat to brain because bacteria/viruses may spread into CNS tissue Encephalitis = brain inflammation

Hydrocephalus “Water on the Brain” CSF accumulates & exerts pressure on brain because something obstructs its drainage In babies, brain size increases In adults, brain damage may occur because nervous tissue is crushed

Hydrocephalus in a Newborn Figure 7.19

Cerebrospinal Fluid (CSF) Similar to blood plasma composition (make-up) Different because contains less protein, more vitamin C, & ion composition differs Formed by the choroid plexus continually Forms a watery cushion to protect the brain Circulated in arachnoid space, ventricles, and central canal of the spinal cord Drains at a constant rate to maintain pressure & volume Lumbar spinal tap is used to get a sample of CSF

Some of this fluid continues down the spinal cord. Cerebral Spinal Fluid Circluates from the 2 lateral ventricles into the third ventricle, then through the cerebral aqueduct of the mid brain and into the fourth ventricle. Some of this fluid continues down the spinal cord. Ordinarily it forms and drains at a constant rate to maintain pressure and volume.

Ventricles and Location of the Cerebrospinal Fluid Figure 7.18a–b

Ventricles and Location of the Cerebrospinal Fluid (P. 250) Figure 7.18c

Blood-Brain Barrier Keeps neurons separated from bloodborne substances Includes the least permeable capillaries of the body Can pass through: Water Glucose Essential Amino Acids Fats Respiratory Gases Fat-Soluble Molecules (alcohol, nicotine, anesthesia)

Blood-Brain Barrier Continued . . . CanNOT pass through: Metabolic Wastes (urea, toxins, proteins, most drugs) Nonessential Amino Acids Potassium Ions

Traumatic Brain Injuries Concussion Slight brain injury but no permanent brain damage Contusion Nervous tissue destruction occurs & tissue does not regenerate Intracranial Hemorrhage Bleeding from ruptured vessels in the brain Cerebral Edema Swelling of brain due to inflammatory response May compress and kill brain tissue

Cerebrovascular Accident (CVA) Commonly called a stroke Blood circulation to brain area is blocked by blood clot or ruptured blood vessel Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result

Transient Ischemic Attack (TIA) Temporary (5 – 50 minutes) brain ischemia (restriction of blood flow) “incomplete stroke”

Alzheimer’s Disease Progressive degenerative brain disease that results in dementia Memory loss, short attention span, language loss Caused by shortage of ACh & structural changes in the brain Drugs ease symptoms by inhibiting ACh breakdown

Parkinson’s Disease Basal nuclei problem caused by degeneration of dopamine-releasing neurons As a result, basal nuclei become overactive, causing tremors Drug L-dopa helps alleviate symptoms Drug deprenyl slows deterioration

Huntington’s Disease Genetic Massive degeneration of basal nuclei & later the cerebral cortex Wild, jerky, flapping movements called chorea Treated with drugs that block dopamine’s effects