Ch. 7 (p. 248 – 255) P ROTECTION OF THE CNS

O BJECTIVE C HECKLIST Name the three meningeal layers, and state their functions. Discuss the formation and function of the cerebrospinal fluid and the blood-brain barrier. Compare characteristics of concussions and contusions. Describe CVAs(strokes) and their impact on brain function.

P ROTECTION OF THE CNS  Nervous tissue is very delicate and is easily damaged  Your body protects the brain and spinal cord by enclosing them within …  The skull and vertebral column  Membranes (meninges)  Cerebrospinal fluid  Protection from harmful substances in the blood is provided by the blood brain barrier.

T HE M ENINGES  There are three connective tissue membranes covering the CNS.  They serve several functions:  Cover and protect the CNS  Protect blood vessels  Contain cerebrospinal fluid  Form partitions in the skull

D URA M ATER  Dura mater is the outermost and strongest membrane covering the CNS.  It is a double-layered external covering  Fused together and folds inward, partitioning the brain

D URA M ATER

We do not see this on the sheep brain, but this is what it WOULD look like… It can divide up sections of the brain

A RACHNOID M ATER  Arachnoid mater is the middle meningeal membrane covering the CNS  Beneath is the subarachnoid space  Thread-like extensions span this space and secure the arachnoid mater to the pia mater.  This space is filled with cerebrospinal fluid and blood vessels serving the brain.

A RACHNOID M ATER This is the only mater visible on the sheep brain

A RACHNOID M ATER

P IA M ATER  Pia Mater is the innermost meningeal membrane covering the CNS  Clings to the surface of the brain, following every fold  Very delicate and rich with blood vessels supplying the brain

M ENINGITIS  Meningitis is the inflammation of the meninges.  It is caused by either bacteria or viruses that may spread into the nervous tissue.  The condition is usually diagnosed by taking a sample of CSF from the subarachnoid space in the lumbar region of the spine. Video: Meningitis Video: Meningitis

C EREBROSPINAL F LUID (CSF)  Similar to blood plasma composition  Formed by the choroid plexus (of the epithalmus)  Forms a watery cushion to protect the brain  Circulated in arachnoid space, ventricles, and central canal of the spinal cord  Also helps supply brain with nutrients

V ENTRICLES AND L OCATION OF CSF

C EREBROSPINAL F LUID (CSF)  CSF is absorbed into the venous blood in the dural sinuses through the arachnoid villi.

C EREBROSPINAL F LUID (CSF) MRA is often used to evaluate the blood vessels of the neck and brain

H YDROCEPHALUS  Hydrocephalus occurs when CSF accumulates in and around the brain, exerting pressure.  In newborns, the entire cranium enlarges.  In adults, hydrocephalus can result in brain damage.  Treatment involves inserting a shunt into the ventricles that drains the fluid into a vein in the neck.

B LOOD -B RAIN B ARRIER (BBB)  Includes the least permeable capillaries of the body (due to tight junctions)  Glucose, water, essential amino acids pass easily through the walls of the capillaries  Excludes many potentially harmful substances such as metabolic waste (urea, toxins, many proteins, and drugs)

B LOOD B RAIN B ARRIER (BBB)  Useless against some substances  Fats and fat soluble molecules  Respiratory gases  Alcohol  Nicotine  Anesthesia

T RAUMATIC B RAIN I NJURIES  Traumatic Brain Injuries are a leading cause of accidental death in the U.S.  A concussion occurs when the brain injury is slight but there is no permanent damage.  A contusion occurs when brain tissue is destroyed  A contusion of the brain stem results in coma. Why?  After head blows, death can result from bleeding or edema, why? Video: Concussions Video: Concussions

C EREBROVASCULAR A CCIDENTS (CVA S )  Cerebrovascular Accidents (CVAs), AKA: Strokes are the 3 rd leading cause of death in the U.S.  CVAs occur when blood circulation to the brain area is blocked  Caused by either a blood clot or a ruptured blood vessel  When this occurs, brain tissue dies.  Temporary restriction of blood flow is known as Transient Ischemic Attach (TIA) and can last 5-50 minutes.  Defects are not permanent but serve as a warning for CVAs. Video: Strokes Video: Strokes

O BJECTIVE C HECKLIST Name the three meningeal layers, and state their functions. Discuss the formation and function of the cerebrospinal fluid and the blood-brain barrier. Compare characteristics of concussions and contusions. Describe CVAs(strokes) and their impact on brain function.

Q UESTIONS, C OMMENTS ?