the central nervous system brain and spinal cord brought to you by the sodium ion, helping your...

The Central Nervous System

Brain and

Spinal CordBrought to you by the sodium ion, helping your nerves to do their best!

Anatomy• The Central Nervous

System is divided into two parts the brain and the spinal cord

• Brain - (1.2 -1.4 kg) about 3 lbs.

• 100 billion nerve cells

• Spinal Cord is about 45 cm long

Spinal Cord

• The spinal cord originates at the lower end of the medulla oblongata, at the bottom of the brainstem.

• It leaves the skull via a large opening called the foramen magnum, and extends about two-thirds of the way down the spine, as far as the first lumbar vertebra.

• The spinal cord is unique to the nervous system of vertebrates.

• In an adult it is roughly as thick as a finger.

• Spinal nerves from the spinal cord branch off to various parts of the body

Spinal Cord Structure

• The spinal cord is a double-layered cylindrical tube.

• There are two enlargements, cervical and lumbar.

• The outer layer of the spinal cord consists of white matter, myelin-sheathed nerve fibers.

• These are bundled into specialized tracts that conduct impulses triggered by sensory stimuli or they conduct motor impulses activating muscles and glands.

• The gray matter has a butterfly-shaped cross-section and is mainly composed of nerve cell bodies.

Reflex Arc• Connecting with the

cord are 31 pairs of spinal nerves.

• These feed sensory impulses into the spinal cord, which in turn relays them to the brain.

• Motor impulses generated in the brain are relayed by the spinal cord to the spinal nerves, which pass the impulses to muscles and glands.

• As shown in the diagram the spinal cord alone controls the reflex responses to some sensory impulses.

The Meninges• Composed of 3 layers of connective tissue

• Dura mater - thick and tough.

• Arachnoid - thin, delicate membrane.

• Pia mater - very thin, vascular membrane, adheres to brain and spinal cord.

Meninges of the Brain

Cerebrospinal fluid

• About 140 mL of this clear, liquid, fills the ventricles of the brain and the subarachnoid spaces around the brain and spinal cord.

• 99% water, also glucose, salts, protein and urea

CSF circulation

• Produced by the choroid plexus in the ventricles of the brain.

• Circulates through subarachnoid spaces of the brain and spinal cord

• Cushions the brain and spinal cord.

• Absorbed by the arachnoid granulations in blood sinuses in the brain.

Blood Brain Barrier• Capillaries near

the brain have very tight junctions.

• This restricts the materials that can pass through.

• Glucose, amino acids, O2, Ca+2

and erythromycin

pass easily into the brain.

• Urea, insulin and penicillin, pass very slowly

• Many drugs used in treating the brain cannot pass through this barrier.

Brain

• Composed of three main parts: Cerebrum, Cerebellum and the brain stem.

• For the Brain the gray matter (nerve cell bodies) is the outer part and the white matter (nerve fibers) is the inner part.

• This is the reverse of the situation found in the spinal cord!

Brain Stem

• Functions to connect the spinal cord to the brain.

• Coordinator of breathing, heart rate, sleep, wakefulness,

• Three regions: midbrain, pons and medulla oblongata

Pons

• The Pons (#3) is a bulge on the ventral surface of the brainstem.

• Functions as a link connecting various parts of the brain.

• Helps to regulate respiration.

• Also serves as a center for reflexes of the face.

• Helps control chewing and eye movements, facial expression, taste and equilibrium.

Medulla Oblongata

• Most inferior part of the brainstem.

• Consists of white matter (nerve fibers) and gray matter (nerve cell bodies)

• Controls heart rate, blood pressure and breathing. Also vomiting, sneezing, coughing and swallowing.

Midbrain

• Extends from the Pons about 2 cm.

• In many vertebrates this is the largest brain region.

• In humans most of its functions have been assumed by the cerebrum.

• Functions include: Pupil response to light, turning head to hear sound, righting reflexes

Pineal Body

• Also known as the epiphysis.

• Functions as an endocrine gland

• Secretes melatonin, which initiates the start of puberty in humans.

Thalamus

• Consists of two oval masses of gray matter covered by a thin layer of white matter

• Functions as a major relay center for all sensory information, except smell, to the cerebrum.

Hypothalamus

• Forms the walls of the third ventricle.

• Important relay station between the cerebral cortex and the lower autonomic centers.

• Link between brain and pituitary gland.

• Maintains fluid balance, is the thirst center.

• Regulates body temperature, hunger and sexual behavior

Amygdala

• Is it a snake, or a stick? • First, a mysterious object is

seen and projected onto the retina of the eye.

• A message is sent through the optic nerve to the hypothalamus.

• The hypothalamus then sends a message to both the cortex and the amygdala.

• The amygdala sends a fear message to the hypothalamus.

• The cortex sends reason messages back to the hypothalamus.

Cerebellum

• Also called arbor vitae.

• Coordinates muscle activities enabling smooth muscle movements.

• Helps to maintain muscle tone and posture.

• Helps to maintain balance.

Cerebrum

• This is the largest region of the brain. (85%)

• Surface is called the cerebral cortex (gray matter-cell bodies)

• The many folds allow for a large area.

• Sensory and Association areas are located in the cerebral cortex

Cerebral Cortex• Areas of the cerebral cortex seem to have specific jobs.

• Sensory areas receive information from receptors.

• Motor areas control voluntary muscle movements.

• Association areas coordinate speech, memory,

learning.

Memory• Was originally thought to be in a specific site. (engram)

• Memories seem to be located throughout the cerebral cortex.

• They involve associations between thoughts, feelings, sights, textures etc.

• The basis for learning appears to be a change in the ability of a synapse to transmit an impusle

• Increasing strength of impulses between various neurons seems to be at the heart of memory.

Speech• Broca’s area and Wernicke’s area involved in speech.

• Both are in the left hemisphere.

• Broca’s seems to function in producing speech.

• Wernicke’s in understanding speech.

• Other areas for language seem to involve reading, processing grammar, foreign language etc.

Peripheral Nervous System

• Sensory and Motor neurons are part of the Peripheral nervous system.

• Peripheral is divided into Voluntary (Somatic) and Autonomic Nervous Systems

Autonomic Nervous System

• Composed of the parasympathetic and sympathetic systems.

• Sympathetic - reactions to fear and stress - dilates pupil, accelerates heart

• Parasympathetic - help body to store energy - undoes what sympathetic does.

• The Vagus nerve is a major nerve in the the Parasympathetic system.

How we see!• Light rays enter the eyes

by passing through the cornea, and striking the light sensitive nerve cells (rods and cones) in the retina.

• Visual processing begins in the retina.

• Light energy produces chemical changes in the retina's light sensitive cells.

• These cells produce electrical activity.

• Nerve fibers from these cells join at the back of the eye to form the optic nerve.

• Cone cells for color vision

• Rod cells for black and white.

How we see! – cont.

• The optic nerve of each eye meets the other at the optic chiasm.

• Medial nerves of each optic nerve cross, but lateral nerves stay on the same side. The overlap of nerve fibers allows for depth perception.

• Electrical impulses are communicated to the visual cortex of the brain by way of the optic nerve.

• The visual cortex makes sense of the electrical impulses, and either files the information for future reference or sends a message to a motor area for action.

Eye Structure• Aqueous humor - a

clear watery fluid between the cornea and the lens. It is responsible for nourishing the cornea, iris, lens, and maintaining the intraocular pressure.

• Canal of Schlemm - moves the aqueous from the front chamber in the eye through aqueous veins into the bloodstream.

• Ciliary Body - is made up of the ciliary muscle which helps the lens to focus and controls the intraocular pressure of the eye. It is also where the aqueous humor is made.

Eye Structure• Conjunctiva - a

transparent mucous membrane that covers the outer surface of the eyeball except for the cornea. It also lines the inner surface of the eyelid.

• Cornea - the clear cone over the front part of the eye. It is responsible for most of the optical power of the eye.

• Choroid - a layer of the eye found between the retina and the sclera. It contains major blood vessels and provides nourishment to the outer layers of the retina.

Eye Structure 2

• Fovea - is located in the center of the macula. It provides the sharpest vision.

• Iris - a colored circular muscle that gives us the color of our eyes. It controls the amount of light that gets into the eye.

• Lens - is responsible for bringing rays of light into focus on the retina

• Macula - a small central area of the retina responsible for fine vision.

• Optic Nerve - carries the light impulses for sight from the retina to the brain.

Eye Structure• Retina – the active area

of the eye where the rods and cones are found.

• Rods – Black and white light receptor cells mostly found in the peripheral part of the retina. They are responsible for night vision.

• Cone cells – cells that are sensitive to color. Located near the fovea. They need a high intensity of light. Not good at night.

• Sclera - the protective outer layer of the eye.

• Vitreous - a clear jello-like substance between the lens and the retina that provides the structural support to the eye.

Color Blindness

• 12 to 20% of white, male pop. is colorblind.

• Caused by a sex-linked recessive gene.

• The full Ishihara test consists of a set of 38 plates and tests in-depth for color blindness.

• The plates here are a small representative sample, but will help spot the most common forms of colorblindness.

• On this first plate everyone should see the number 25.

People with normal vision should see the number 29.Color blind people will see just spots.

People with normal vision will see the number 45

People with normal vision should see the number 6

People with normal vision should see the number 8The full test has 38 different plates like these.

The tapetum reflects light back to the retina.This allows the cat to gather more light and see in the dark.

This is also why cat’s, dogs and deer’s eyes shine in the dark.

Owl Eyes-Note the lack of a tapetum

The Owl sees well in the dark because its pupil is so large!

Chemical pathway of vision

• When light activates rhodopsin, it produces an electric current along the cell.

• This electric impulse reaches a ganglion cell, and then the optic nerve.

• The nerves reach the optic chasm, where the nerve fibers from the inside half of each retina cross to the other side of the brain, but the nerve fibers from the outside half of the retina stay on the same side of the brain.

Visual Cortex• The optic nerve fibers

eventually reach the back of the brain (occipital lobe).

• This is where vision is interpreted and is called the primary visual cortex.

• Some of the visual fibers go to other parts of the brain to help to control eye movements, response of the pupils and iris, and behavior

Optical Illusions• Touch requires solid

contact (usually); taste involves liquid contact; smell, gaseous contact; and hearing depends upon a relay of vibrations from an object through another medium (usually air), resulting in contact.

• we see things at a distance via light energy that has reflected off of the surface.

• Optical illusions occur through the following pathways:

• Limitations of the structure of the eye.

• How the information is processed in the brain.

Animation Optical illusions

These illusions give the impression of movement. There is no movement! The eye has limits as to how it can construct an image.

Explanation of previous illusion

• The world we live in is three dimensional.

• We try to convert a two dimensional object into a 3D one.

• In the previous optical illusion, our mind tries to make sense of these 2D objects.

• The shading used in this drawing is completely incongruous.

• We lo0k at a bit of the illustration that looks appropriately shaded but then find it conflicts with the shading in nearby areas.

• The eyes keep jumping around the drawing trying to map out a 3D solution that would make the shading illustration make sense, but it never seems to work.

The power of the mind to interpret

• Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

The objects are not actually moving! Your eyes are making them move!

No real movement here as well!

Focus on the dot in the center. Move your head back and forth. What appears to happen?

Animorphosis• A conical or cylindrical mirror is

placed on the drawing or a painting to transform a flat distorted image into a three dimensional picture that can be viewed from many angles.

• The deformed image is painted on a plane surface surrounding the mirror.

• By looking uniquely into the mirror, the image appears undeformed

Disappearing EffectThe brain can lose track of an image that is there!

Afterimages

• The retina can be overstimulated and continue to report an image when it is not there.

• Or it can cause the color to change

A skull or a woman looking into a vanity mirror?

Rabbit looking left or a duck looking right?

Two different stair cases could be seen here!

Man playing a horn or a woman’s face?

Build this box for extra credit!

Where does the middle column end?

How many legs does this elephant have?

Are the lines parallel or do they slope?

Find the man’s face in the coffee beans. If you can find it in under 3 seconds it implies that the right half of your brain

is more developed than most.

Faces or Places?

How many human faces do you see!

How do the sizes of the middle circles compare?

The two vertical lines are the same length!

Which figure is taller?

Read the message in the triangle

ROCKS

IN THE

THE STREET

Teach reflects as learn!

Find Good and Evil!

What do you see?

Do you see a face or a word?

If you stare at the picture long enough you should see a giraffe!

The two diagonal lines are the same shade of pink!

• crazy nuts illusion

wavy illusion

• Dancing Dice

• Julian Beever

• animated optical illusions

StrokeTwo main kinds

Alzheimers Disease• The cause is not fully

understood. • It is believed there

may be genetic factors involved.

• There is a breakdown of proteins resulting in the formation of protein deposits (senile plaques) within the brain.

• The disease causes an increasing deficiency of acetylcholine in the brain.

• As levels of the chemical decrease, plaques form creating bundles of fibers (neurofibrillary tangles).

• Infection and environmental factors may also influence the progress of the disease.

Traumatic Brain injury• Traumatic brain injury

(TBI) is the fourth leading cause of death in the United States and is the leading cause of death in persons aged 1-44 years.

• 2 million traumatic brain injuries occur each year, and $25 billion is spent per year in in social and medical management of people with such injuries.

• 50% of all trauma deaths are secondary to traumatic brain injury (TBI), and gunshot wounds to the head caused 35% of these.

A young man arrived in the emergency department after experiencing a gunshot wound to the brain. The entrance was on the left occipital region. A CT scan shows the skull fracture and a large

underlying cerebral contusion. The patient was taken to the operating room for debridement of the wound and skull fracture, with repair of the dura mater. He was discharged in good neurological condition,

with a significant visual field defect.

Bullets and Physics• Bullets hitting the body transfer all of their energy to the tissues.

• The heavier the bullet and the faster it moves the more damage it can potentially cause.

• The laws of physics state that energy is directly related to the weight of the bullet, meaning that if the weight doubles, the energy doubles.

• But energy also increases by the square of the velocity. Doubling the speed increases the energy fourfold.

• The purpose of a gun is to make a bullet go faster

• The picture shows a Glock 19, the type of pistol used to shoot Gabrielle Giffords.

Two types of damage from bullets

• 1. The first type of injury is caused by the direct blow or crush of the bullet.

• 2. The second injury type is caused by the shock waves of the bullet.

• The tissue surrounding the wound is affected by a temporary vacuum that can be as much as 40 times as large as the bullet itself.

• This tissue cavity gets stretched and deformed and then reforms itself numerous times, like ripples in the water.

• The higher the velocity of the bullet, the larger the cavity of tissue that is at risk for damage

Gunshot wounds to the head

• Gunshot wounds to the head are difficult to predict.

• There isn't a lot of room for movement of the brain or swelling in the skull.

• If a bullet enters the head and bounces around, the permanent cavity (bullet track) may be large, but the damage from the temporary cavity that forms is even worse.

• There is no room for the brain to move and the shock waves often cause irreversible damage.

• For some lucky people, if the bullet velocity is high and there is no side to side movement (wobble) and it passes through non-critical parts of the brain, less damage occurs and survival is possible.

Treatment• An air tube is used to ensure adequate ventilation.

• Blood pressure is kept above 90 mm Hg.

• Cervical spine is stabilized.

• The patient may be given sedatives to induce a coma-like state.

• The GCS scale shown is used to assess mental functioning.

• A GCS score lower than 6 indicates a severe injury.

• Surgery will be performed to remove pieces of bone, dura mater, dead brain tissue.

• Unless easily reached the bullet, often is not removed.

• Pts. Eye Opening Best Verbal Best Motor

• 6 … … Follows commands

• 5 … Appropriate Localizes pain

• 4 Spontaneous Inappropriate Withdraws to pain

• 3 In response to voice Moaning Flexion

• 2 In response to pain Incomprehensible Extensio

• 1 None None None