The Central Nervous System

The Story of Phineas GageOn 13th. September 1848, an accidental explosion of a charge he had set blew

his tamping iron through his head.  The tamping iron was 3 feet 7 inches long and weighed 13 1/2 pounds.  It was 1 1/4 inches in diameter at one end (not circumference as in the newspaper report) and tapered over a distance of about 1-foot to a diameter of 1/4 inch at the other.  The

tamping iron went in point first under his left cheek bone and completely out through the top of his head, landing about 25 to 30 yards behind him.  Phineas was knocked over but may not have lost consciousness even though most of the front part of the

left side of his brain was destroyed.  Dr. John Martyn Harlow, the young physician of Cavendish, treated him with such success that he returned home to Lebanon, New

Hampshire 10 weeks later.

I. Formation of the Central Nervous System(CNS)

A. The CNS develops from the neural tube (extending down the dorsal median plane of an embryo).1. The neural tube eventually becomes the brain and spinal cord.

B. By the fourth week the tube begins to expand and form the brain.

C. The opening of the neural tube becomes the ventricles1. There are four ventricles which act as chambers in the brain.2. The ventricles are filled with cerebrospinal fluid.

Protection: the CSF protects the brain from damage by "buffering" the brain. into other words, 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. Hormones released into the CSF can be carried to remote sites of the brain where they may act.

II. Functional Anatomy of the BrainA. There are four main regions of the brain which include: Cerebral hemispheres (Cerebrum),

diencephalon, brain stem and the cerebellum

B. The Cerebral Hemispheres: The paired left and right superior parts of the brain and make up more than half the mass of the entire brain! This part of the brain involves conscious behaviors including; speech, memory, emotional responses, and voluntary movement, personality.

1. The surface is made of ridges (gyri) and grooves (sulci)

2. Fissures (deep grooves) divide the cerebrum into lobes3. The outermost area of the cerebrum

is made of gray matter (covering an underlying layer of white matter), and called the cerebral cortex. The remaining cerebral hemisphere tissue- the deeper white matter- is composed of bundles of nerve fibers carrying the impulses to or from the cortex.

a. One large fiber tract (bundle of nerves) called the corpus callosum, connects the right and left cerebral hemispheres

b. The basal nuclei is an internal island of gray matter deep within the cerebral cortex. It helps regulate the voluntary motor activities.

Lobes of the Cerebum

4. Surface lobes of the cerebrum include:a. Frontal lobe 1) Primary motor area- allows us to move our skeletal muscles under conscious control2) Broca’s area- motor speech area that directs muscles involved in speech, usually only present in left hemisphere. 3)High level intellectual reasoning are also believed to be in the anterior portion of the frontal lobe

b. Parietal lobe1. Somatic sensory areas- allows you to recognize pain, coldness and touch- The left side of the sensory cortex interprets impulses from the right side of the body and vice versa.

c. Occipital lobe1)Visual interpretation

d. Temporal lobe- 1) Auditory interpretation,

speech, memory, Wernicke’s area (language intrepretation)

Specialized areas of the Cerebrum:

Temporal lobe

Explain what type of impairment a person might experience if..

1. A sharp blow to the back of the head

2. Damage to the left frontal lobe just superior to the temporal lobe and anterior to the primary motor cortex

3. Stroke which damages the primary motor cortex closest to the temporal lobe

4. Prefrontal lobotomy

5. Damage to the hypothalamus

6. Damage to the brainstem directly at the pons

Question of the Week:What causes people to have a stuttering problem?

• Normal speech development. Young children may stutter when their speech and language abilities aren't developed enough to keep up with what they want to say. Most children outgrow developmental stuttering within four years.

• Inherited brain abnormalities. Stuttering tends to run in families. It appears that stuttering results from inherited (genetic) abnormalities in the language centers of the brain.

• Stroke or brain injury. Stuttering can sometimes result from a stroke, trauma or other brain injury.

• Mental health problems. In isolated cases, emotional trauma or problems with thoughts or reasoning lead to stuttering. This was once believed to be the main cause of stuttering, but it's now known that it's uncommon.

Factors that increase the risk of stuttering include:

• Having relatives who stutter. Stuttering tends to run in families.

• Delayed childhood development. Children who have developmental delays or other speech problems are more likely to stutter.

• Being male. Males are much more likely to stutter than are females.

• Stress. High parental expectations or other types of pressure

• http://serendip.brynmawr.edu/exchange/node/1683

Recent research on stuttering• PET imaging study was

performed comparing stutterers’ brains and non-stutterers’ brains. This study showed that stutterers may be using the right hemisphere of their brain when they are talking, which means that the left hemisphere (the one usually responsible for speech) is being interrupted

Research on stuttering• In the PET scans of the brain, the

stutterers’ brains showed decreased activity in the auditory cortex and hyperactivity in the speech center while reading, which means that stutterer is actually tuning himself out when he is talking, so that he cannot hear the stammering .

Research on stuttering• One group of researchers found a

connection between the functioning of the lateral and medial areas of the brain and stuttering. The lateral area of the brain controls the formation of words (Broca’s area), muscle movements (motor areas) and the understanding of language (Wernicke’s area) in what is known as closed-loop motor control.

Cerebral Lobe Review

http://www.youtube.com/watch?v=snO68aJTOpM

C. The Diencephalon or Interbrain1. Sits on top of the brain stem and is enclosed by the cerebral hemispheres.2. Composed of three main parts: Thalamus, epithalamus, and hypothalamus

a. Thalamus- A relay station for sensory impulses, allows us to recognize a sensation as pleasant or unpleasant, the impulse is eventually sent to the sensory cortex for localization and interpretation of the sensation

b. Hypothalamus- An important part of the autonomic system. Its job is regulating body temperature, water balance, appetite, and metabolism. Also includes the Limbic system- our emotional brain. The Limbic system is involved in our appetite, thirst, pain, sex, and pleasure centers. The pituitary gland is attached to the hypothalamus.

• c. Epithalamus- Forms the roof of the third ventricle. Important parts include the pineal body(produces melatonin into regulate sleep/wake cycles) and choroid plexus (forms cerebrospinal fluid).

D. The Brain Stem1. Attaches to the spinal cord.2. There are three parts of the brain

stem: midbrain, pons and medulla oblongata.

a. Midbrain- is mostly composed of nerve fiber tracts. It also contains the cerebral aqueduct which is a tiny canal that connects the third and fourth ventricle.

The corpora quadrigemina is dorsally located with rounded protrusions that are reflex centers for vision and hearing.

b. Pons- The bulging part of the brain stem that is composed mostly of nerve fiber tracts. It houses important nuclei that control our breathing.

***also important because it contains nerve fibers connecting the cerebellum to the rest of the brain, and allows facial

expressions

c. Medulla Oblongata- The lowest part of the brain stem that merges into the spinal cord. It controls important centers that help control blood pressure, heart rate, breathing, swallowing, and vomiting.

E. Reticular Formation1. Gray matter that runs along the brain stem.2. Involved in motor control of visceral organs. It also contains a special group of neurons called the reticular activating system that plays a role in consciousness and awake/sleep cycles.(RAS alerts a person when a friend speaks and enables that person to ignore other sounds and focus on the one sound.

F. The cerebellum1. Projects dorsally from under the occipital lobe of the cerebrum. It also contains two hemispheres with convoluted surfaces.2. Its job is providing involuntary control of body movements (balance), and posture.

II. Protection of the Central Nervous SystemA. The scalp and skin provide the first layer of protections.B. The skull and vertebral column provide the second layer.

C. A layer of connective tissue called the meninges provides the final protection for the CNS. There are three meningeal layers.1. Dura mater- the outermost layer that is tough and hard. 2. Arachnoid mater- the middle web-like layer3. Pia Mater- internal layer that clings to the surface of the brain

The picture below shows a brain with the dura removed from the cortex exposing the arachnoid membrane. The tiny protruding white parts seen near the center of the photo are the visible arachnoid granulations. The transparent

membrane over the entire brain surface is the arachnoid membrane.

• Four Regions of the brain

• Use your notes to write down the four main brain regions

Are you feeling brainy today?

D. Cerebrospinal fluid- the fluid that forms a watery cushion to protect the brain. 1. Its composition is similar to blood plasma2. Formed by the choroids plexus3. Circulated in arachnoid space, ventricles, and central canal of the spinal cord

You tube: Cerbrospinal fluid circulation

MRI showing pulsation Of CSF:

Hydrocephalus

• Imbalance in CSF produced and amount absorbed

• Obstruction

• Poor absorption

• Overproduction

E. Blood Brain Barrier- The barrier that keeps neurons separated from blood borne substances. The brain is dependent upon the constant internal environment more than any other organ in your body.

1. The barrier is created by the least permeable capillaries in the body.2. The astrocytes contribute to creating this barrier.3. Exclusion of many substances helps maintain the delicate balance required by the brain. However, the barrier fails to prevent the following substances from entering:Fats and fat soluble molecules, Respiratory gases, Alcohol, Nicotine, Anesthesia

Blood Brain Barrier MeningitisMeningitis is an inflammation of the membranes that surround the brain and spinal cord (these membranes are known as meninges). Meningitis is most commonly caused by infections with various pathogens, examples of which are Streptococcus pneumoniae and Haemophilus influenzae.

III. Traumatic Brain InjuriesA. Concussion- a slight brain injury, victim may be dizzy, or lose consciousness briefly but there is no permanent brain damage.B. Contusion- nervous tissue destruction occurs and the tissue does not regenerate. A severe brain stem contusion would cause someone to go into a coma.

How are they different?Contusions are localized, while concussions are widespread.* Contusions are macroscopic, while concussions are microscopic.BOTH are due to head traumaBOTH are serious, BOTH are common

C. Cerebral Edema (swelling) or hemorrhage (bleeding) - Swelling or bleeding of the brain due to an inflammatory response. This places pressure on brain tissue- this is a serious situation.

D. Cerebrovascular Accident (CVA) - commonly called a stroke. It is the result of a ruptured blood vessel supplying a region of the brain. The brain tissue that is supplied with oxygen from the vessel will die. The loss of function depends on the area of the brain affected and the severity of the stroke.

E. Alzheimer’s disease- A progressive degenerative disease affecting the brain. Victims experience memory loss, and confusion. (caused by plaques –protein deposits- in between the neurons)

F. Parkinson’s disease- A basal nuclei problem resulting from the degeneration of dopamine releasing neurons. Patients experience tremors, a shuffling gait, trouble getting their muscle going, and head nodding.

Meningial LayersProtection for the CNS

IV. Spinal NervesA. There is a pair of spinal nerves at the level of each vertebra for a total of 31 pairsB. Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cordC. Spinal nerves are named for the region from which they arise A dermatome is an area of skin that is

mainly supplied by a single spinal nerve.

Nerve PlexusesD. Complex networks of

nerves called plexuses serve the motor and sensory needs of the limbs. 1. Cervical plexus- origin of nerves- C1- C5, control mainly the muscles of the shoulder and neck.

2. Brachial plexus- C5 – C8 and T1, control mainly the arm

The pain in his shoulder and neck is intense, and the arm feels numb. Feeling returns within a few minutes. (it is more serious if it lasts more than 5 minutes.

A “stinger” or a “burner”

• 3. Lumbar plexus- L1 – L4, controls the lower abdomen, buttocks, leg and thigh

Innervates muscles in the calves, knees, groin, thighs, abdomen, and lower back.

• 4. Sacral plexus- L4 –L5 and S1 – S4, posterior surface of thigh, and leg, lower leg, foot, and gluteus medius. This plexus includes the sciatic nerve- largest in the body.

V. Cranial NervesA. Twelve pairs of cranial nerves extend from the brain to serve the head and neck region. The exception is the vagus nerve which extends into the thorax and abdomen. B. Most cranial nerves are mixed nerves; however three pairs are purely sensory. The optic (vision), olfactory (smell), and vestibulocochlear (balance and hearing). There is a chart on pg. 231- 232 that identify each cranial nerve by number, origin, function and how to test the nerve.

• Corpus callosum• Pineal gland/epithalamus• Cerebellum• Pons • Medulla oblongata• Cerebral cortex• Broca’s area• Thalamus• Hypothalamus• Frontal lobe• Choroid plexus

Identify the following brain structures

9

8 7

3

2

6

5

4

1

Question of the week: Why Do I Sometimes See Stars?

Answer: "Seeing stars" is a common visual complaint, but it is usually a normal and harmless occurrence. If you close your eyes and rub them, you will probably see spots and flashes of light. These images you see are called "phosphenes," an entoptic phenomenon characterized by the experience of seeing light without light actually entering the eye. Phosphenes are produced by pressure on the eyes. The pressure is translated into various patterns by the optic nerve.These stars, or spots of light, that you see can occur after a sneeze, a deep cough, a blow to the head or low blood pressure (such as standing up too quickly).

Some people see flashes or lines of light that often last up to 10 to 20 minutes. These flashes of light are generally caused by a spasm of blood vessels in the brain, called a "migraine." If a headache follows the flashes, it is called a "migraine headache." If these flashes or lines of light occur without a headache, it is called an "ophthalmic migraine," or migraine without a headache.

While usually harmless, frequent flashes of light can be a warning sign of something more serious. A comprehensive eye examination will be needed to determine the cause.

Brain Dissection Structures

External Anatomy Internal Anatomy

__ Spinal Cord __ corpus callosum

__ Cerebellum __ pons

__ Cerebrum __ pituitary gland

__ Gyri __ lateral ventricle

__ Sulci __ pineal gland

__ Olfactory bulb __ midbrain

__ occipital lobe __ hypothalamus

__ Optic chiasm __ thalamus

__ frontal lobe __ medulla oblongata

__ parietal lobe

__ temporal lobe

Sheep Brain

Cross-section Anatomy

Group Assignment

• Use the half sheet for a list of LABELS (flags) you will need to identify in the sheep brain

• INIVIDUAL assignment: – On a separate sheet of paper, list these

structures as you tag them and write down their functions

Study for your test!