Central Nervous System

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Functional Anatomy of the Brain

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*weighs a little over 3 lbs.
*largest, most complex mass of nervous tissue in the body.

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4 major regions

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*cerebral hemispheres
*diencephalon
*brain system
*cerebellum

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Cerebral Hemispheres

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*paired
*enclose most of the brain system

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Gyri

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elevated ridges of tissue

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Sulci

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shallow grooves

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Furrows & Fissures

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deeper grooves which separate large regions of hte brain

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Longitudinal fissure

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separates the cerebral hemispheres

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Parietal lobe

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*somatic sensory area
*allows recognition of pain, temperature, light touch

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Occipital lobe

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*visual area

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Temporal lobe

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Olfactory area (smell)

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Frontal lobe

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*primary motor area
*conscious movement of skeletal muscle
*especially hands, face, mouth

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Broca's area

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*ability to speak
*located at the base of the precentral gyrus
**areas involved in higher learning are in the anterior part of the frontal lobes

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Speech area

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*junction of the temporal, parietal, and occipital lobes
*allows one to sound out words

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Gray matter (cerebral cortex)

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*cell bodies of neurons involved in above functions
*this cortical region is ridged to provide more surface area for thousands of neurons

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Cerebral white matter

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*under gray matter
*made of fiber tracts(bundles of nerve fibers) carrying impulses to or from the cortex

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Corpus callosum

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*connects cerebral hemispheres

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Basal nuclei

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*islands of gray matter in white matter
*helps regulate voluntary motor activities by modifying instructions sent to the skeletal muscle by the primary motor cortex
**individuals that have problems with basal nuclei are usually unable to walk normally or carry out other voluntary movements

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Huntington's chorea disease

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genetic disease in which the individual has abrupt, jerky and almost continuous movements

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Parkinson's disease

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*trouble getting muscle going
*persistent hand tremor in which the thumb and index finger make continuous circles with one another
*due to a deficit of the neurotransmitter dopamine

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Diencephalon (interbrain)

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* on top of the brain system
*enclosed by the cerebral hemispheres
*divided into hypothalamus, thalamus, and epithalamus

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Thalamus

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*relay station for sensory impulses passing upward to the sensory cortex where it is determined pleasant or unpleasant

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Hypothalamu

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*autonomic nervous system center by playing a role in the regulation of body temperature, water balance, and metabolism
*center for emotions
*part of the limbic system "emotional - visceral brain" where thirst, appetite, sex, pain, and pleasure are monitored
*requlates the pituitary gland
*prdouces 2 hormones

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Pituitary gland

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*hormones involved in development (puberty)

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Mammalian bodies

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*reflex centers involved in olfaction

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Epithalamus

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*includes the pineal body and the choroid plexus

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Choroid plexus

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*knots of capillaries that form the cerebrospinal fluid

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Brain Stem

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*size of the thumb in diameter and 3 inches long
*divided into midbrain, Pons, and medulla oblongata
*provides a pathway for ascending and descending tracts
*controls vitals such as breathing and blood pressure

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Reticular formation

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*mass of gray matter extending the entire length of the brain stem
*involved in motor control of the visceral organs

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Reticular activating system (RAS)

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*plays a role in consciousness and wake/sleep cycles
*damage may result in a coma

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Mid Brain

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*small part of stem
*extends form the mammilary bodies to the pons

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Cerebral Aqueduct

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*tiny canal that travels through the midbrain and connects the 3rd ventricle to the 4th ventricle
*composed primarily of 2 bulging fiber tracts (cerebral peduncle)

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Cerebral peduncle

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*convey ascending and descending impulses

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Corpora quadrigemina

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*bulging nuclei that are reflex centers
*involved with vision and hearing

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Pons

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*rounded structure, protrudes below the midbrain
*mostly fiber tracts
*involved in breathing

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Medulla Oblongata

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*inferior brain stem
*merges into the SC
*fiber tract area
*requlation of vital visceral activities
*controls heart rate, blood pressure, breathing, swallowing, and vomiting

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Cerebellum

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*large, cauliflower-like
*projects dorsally from under the occipital lobe
*2 hemispheres
*outer cortex gray matter
*inner region of white matter
*provides precise timing for skeletal muscle activity and controls balance and equilbrium
*fibers from the inner ear, eye and proprioceptors of skeletal muscles, tendons and other areas

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Proctection of the CNS

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*brain and spinal cord are protected by bone (skull and vertebral column)
*meninges (membrane)
*cerebrospinal fluid, CSF (watery cushion)

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Meninges

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*3 protective tissue membranes around the CNS structures

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Dura Mater

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*outermost layer
*double layered membrane around the brain
*1 layer attached to the skull (periosteal layer)
*1 layer is the outermost covering of the brain (meningeal layer)
*the 2 layers are fused together everywhere except where the inner membrane extends inward to form the fold that attaches the breain to the cranial cavity (falx cerebri)

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Arachnoid Mater

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*middle meningeal layer, looks like a cobweb
*thread-like extension spanning the subarachnoid space to attach it to the inner most membrane pia mater

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Pia Mater

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*clings tightly to the surface of the brain and spinal cord, following each fold

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Subarachnoid space

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*filled with CSF

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Arachnoid villi

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*specialized projections through the dura mater
*where CSF is absorbed into the venous blood in the dural sinuses

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Meningitis

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*an inflammation of the meninges
*It is caused by bacteria or virus and may spread into nervous tissue
*diagnosed by taking a sample of CSF form the subarachnoid space

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Cerebrospinal fluid (CSF)

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*similar to plasma
*continually formed by the choroid plexus

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Choroid Plexus

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*clusters of capillaries hanging from the roof in each of the brain's ventricles
*forms a watery cushion in and around the brain and SC, protecting it from blows and other trauma
*continuously flows inside the brain and circulates from the 2 lateral ventricles (cerebral hemispheres) into the 3rd ventricle (diencephalons) and then, into the 4th ventricle dorsal to the pons and medulla oblongata
*CSF flows into the central canal of the spinal cord
*CSF returns to the blood in the dural sinuses through the arachnoid vili
*forms and drains at a costant rate to maintain constant pressure and volume (150ml)
*composed of glucose, protein, and salt, any significant changes indicates meningitis, tumors, multiple sclerosis

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Lumbar (spinal) Tap

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*withdrawal of CSF for testing

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Hydrocephalus

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*occurs when CSF accumulates and exerts pressure on the brain due to a blockage
*may occur in a new born baby causing the head to enlarge and the brain to decrease in size
*may cause brain damage in adults, because the skull will not expand
*treated surgically by insterting a shunt to direct excess CSF to a vein in the neck

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Blood Brain Barrier

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*neurons are kept separate from blood born substances
*composed of the least permeable capillaries in the body
*only glucose, water amino acids, can pass
*metabolic waste: urea, drugs, are prevented from entering and are pumped from the brain into blood across capillary walls
*Useless against fats, respriratory gasses, and fat soluble molecules that diffuse easily through all membranes
*nicotine, alcohol, and anesthetics can cross

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Traumatic Brain Injuries

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*leading cause of accidental death

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Concussion

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*brain injury is slight
*may cause dizziness, or brief loss of consciousness
*no permanent damage

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Contusion

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*result of marked tissue destruction
*if only the cortex is damaged, the person will remain conscious
*if the brain stem is damaged, a coma results (RAS)

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Cerebral edema

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*intracranial hemorrhage (bleeding from ruptured vessels)
*individuals are usually alert after head injury, but deteriorate neurologically as compression of brain tissue occurs

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Alzheimer's Disease

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*progressive degenerative disease
*results in dementia
*50% of nursing home patients
*may begin in middle age
*symptoms: memory loss, moody, confusion, irritability, hallucinations
*structural changes occur in the cognitive and memory areas
*abnormal proteins and twisted fibers appear in the neurons
*localized brain atrophy
*unknown cause

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Stroke

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*cerebrovascular accident (CVAS)
*blood flow to the brain is blocked
*caused by a ruptured vessel or clot
*less than 1/3 of victims are alive 3 years later

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Spinal cord

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*glistening white continuation of the brain stem
*17 inches long
*2 way conduction pathway to and from the brain
*major reflex center
*enclosed in the vertebral column and extends from the foramen magnum to the 1st - 2nd lumbar vertebrae
*cushioned and protected by meninges which cover all the way into the vertebral canal
*spinal taps are done at L3 or below, no damage can be done to the spinal cord
*31 pairs of spinal nerves

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Cauda equine

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*collection of spinal nerves leaving the inferior end of the spinal ocrd through the vertebral canal
*looks like a horse tail

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Gray matter of the Spinal Cord & Spinal Roots

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*looks like a butterfly or an H in a cross section
*has two dorsal (posterior) horns, 2 anterior (ventral) horns, and 2 lateral horns
*surrounds central canal of the cord that constains CSF

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Dorsal Horns

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*house associated neurons whose fibers enter the cord by the dorsal root and cell bodies are located in the dorsal root ganglion
*if the dorsal root ganglion is damaged, sensation to that body area is lost

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Ventral Horns

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*contains cell bodies of motor neurons of the somatic nervous system whose axons are in the ventral root of the cord
**dorsal and ventral root fuse to form spinal nerves

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Flaccid paralysis

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*caused by damage to the ventral root
*nerve impulses do not reach the muscles
*no voluntary movement of muscles
*muscle atrophy

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White Matter of the Spinal Cord

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*mostly myelinated fiber tracts, some running to higher centes, some to the brain, and some conducting impulses to the other side of the spinal cord
*3 columns: tracts made up of axons with the same function: posterior, lateral, anterior
*if spinal cord is transected, spastic paralysis occurs, affected muscles stay healthy because they are stimulated by spinal reflex arcs and these muscles move.
*movements are involuntary and uncontrollable
*there is a loss of sensation in the body areas below the point of cord destruction

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Quadriplegic

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*when injury is high in the spinal cord and all 4 limbs are affected

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Paraplegic

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only the legs are paralyzed