Dr. Michael P. Gillespie

Major Parts of the BrainBrain stemCerebellumDiencephalonCerebrum

Brain StemContinuous with the spinal cord.Subdivisions

Medulla OblongataPonsMidbrain

CerebellumPosterior to the brain stem.Cerebellum = little brain.

DiencephalonSuperior to the brain stem.Subdivisions

ThalamusHypothalamusEpithalamus

Di = through; encephalon = brain

CerebrumSupported on the diencephalon and brain

stem.Largest part of the brain.Cerebrum = brain.

Brain Blood SupplyArteries

Internal carotid arteriesVertebral arteries

VeinsInternal jugular veins

Brain Blood FlowThe brain consumes about 20% of the oxygen

and glucose used at rest.A brief slowing of blood flow may cause

unconsciousness.When activity of neurons and neuroglia in a

certain portion of the brain increases, blood flow to that region increases.

Brain Blood FlowAn interruption of blood flow for 1 to 2

minutes impairs neural function.Total deprivation of oxygen for 4 minutes

causes permanent injury.If the blood entering the brain has a low level

of glucose, mental confusion, dizziness, convulsions, and loss of consciousness may occur.

Blood Brain BarrierThe blood-brain barrier (BBB) protects the

brain from harmful substances and pathogens.

It prevents the passage of many substances from the blood to the brain tissue.

Tight junctions seal together endothelial cells of brain capillaries.

Astrocytes selectively allow some substances through and not others.

Permeability of the BBBWater-soluble substances.

Glucose crosses the BBB by active transport.Creatinine, urea, and most ions cross the BBB

very slowly.Proteins and most antibiotic drugs do not cross

the BBB.Lipid-soluble substances.

Oxygen, carbon dioxide, alcohol, most anesthetic agents cross easily.

Breaching the BBBThe BBB prevents the passage of harmful

substances into the brain, but it also prevents the passage of useful drugs.

Drugs are injected in a concentrated sugar solution to facilitate passage.The high osmotic pressure causes cells lining

the barrier to shrink and makes the membrane “leaky”.

Protective CoveringsCraniumMeninges.

Dura mater (Outer layer). Two dural layers around the brain and one around

the spinal cord.Arachnoid mater (Middle layer).Pia mater (Inner layer).

No epidural space around the brain.

Protective CoveringsExtensions of dura mater separate parts of

the brain.Falx cerebri – separates the two

hemispheres of the cerebrum.Falx cerebelli – separates the two

hemispheres of the cerebellum.Tentorium cerebelli – separates the

cerebrum from the cerebellum.

Cerebrospinal Fluid (CSF)Clear colorless liquid.Protects the brain and spinal cord from

chemical and physical injuries.Carries oxygen, glucose, and other

needed chemicals from the blood to the neurons and neuroglia.

Circulates in the subarachnoid space (between the arachnoid mater and pia mater).

Formation of CSF in the VentriclesCSF is formed in the ventricles.

Formed by ependymal cells that cover the choroid plexuses of the ventricles.

Formation of CSF in the VentriclesThere are 4 ventricles.Functions of CSF.

Mechanical protection. Shock absorption. Buoys the brain.

Chemical protection – optimal chemical environment.

Circulation – medium of exchange for wastes and nutrients.

HydrocephalusAbnormalities of the brain can interfere with

drainage of CSF from the ventricles and subarachnoid space.

CSF pressure increases causing hydrocephalus.

In infants this causes the fontanels to budge.

HydrocephalusTumors, inflammation, developmental

malformations can all cause hydrocephalus.Pressure buildup can damage the delicate

nervous tissue.A surgeon can implant a drain line called a

shunt to divert CSF.In adults, hydrocephalus may occur after

head injury, meningitis, or subarachnoid hemorrhage.

Hydrocephalus

Brain StemBetween the brain and spinal cord.3 regions.

Medulla oblongata.Pons.Midbrain.

Medulla OblongataA continuation of the spinal cord.Sensory (ascending) tracts and motor

(descending) tracts travel through the white matter of the medulla.

Many nerves decussate (cross over) in the medulla.

Medulla OblongataCardiovascular center regulates the

heartbeat and the diameter of the blood vessels.

Medulla OblongataThe medullary rhythmicity area adjusts the

rhythm of the breathing and controls reflexes for vomiting, coughing, and sneezing.

Medulla OblongataThe nuclei for the following cranial nerves

reside in the medulla:VIII (vestibulocochlear).IX (glossopharyngeal).X (vagus).XI (accessory).XII (hypoglossal).

PonsPneumotaxic area and apneustic area

regulate breathing.Nuclei for cranial nerves V (trigeminal), VI

(abducens), VII (facial), and VIII (vestibulocochlear).

MidbrainThe midbrain or mesencephalon contains

the superior colliculi (visual actvities) and inferior colliculi (auditory pathways).

The midbrain contains the substantia nigra which release dopamine to help control subconscious muscle activities. Loss of these neurons results in Parkinson disease.

Cranial nerves III (oculomotor) and IV (trochlear) originate here.

CerebellumThe second largest part of the brain.A main function of the cerebellum is to

evaluate how well movements are being carried out and correct for discrepancies. This helps to “smooth out” movements.

DiencephelonEpithalamus.

Contains the pineal gland which secretes melatonin.

Thalamus.Relays sensory information to the cortex.Provides crude perception of touch, pressure,

pain, and temperature.

DiencephelonSubthalamus.

Controls body movements.

Hypothalamus.Controls and integrates activities of the ANS.Regulates emotional and behavioral patterns.Regulates cicadian rhythms.Regulates eating and drinking behavior.Produces hormones oxytocin and ADH.

CerebrumSensory areas interpret sensory impulses.Motor areas control muscular movement.Association areas function in emotional

and intellectual processes.Basal areas regulate gross muscle

movements and regulate muscle tone.Limbic system functions in survival

behaviors.

Brain InjuriesConcussion – an abrupt, temporary loss of

consciousness following a blow to the head.Most common brain injury.Signs – headache, drowsiness, lack of

concentration, confusion, amnesia.

Brain InjuriesContusion – bruising of the brain due to

trauma and includes leakage of blood.Signs - immediate loss of consciousness,

transient cessation of respiration, decreased blood pressure.

Brain InjuriesLaceration – tear of the brain usually from a

skull fracture or gunshot wound.Rupture of large blood vessels.Consequences – cerebral hematoma (localized

pool of blood, usually clotted), edema, and increased intracranial pressure.

Cerebral Cortex Areas and FunctionsSensory areas – receive and interpret sensory

information.

Cerebral Cortex Areas and FunctionsMotor areas – initiate movements.Association areas – deal with integrative

functions:Memory.Emotions.Reasoning.Will.Judgement.Personality.Intelligence.

Sensory AreasPrimary somatosensory area – receives

sensations for touch, proprioception, pain, itching, tickle, and thermal sensations.Located in the postcentral gyrus of the parietal

lobes.

Primary visual area.Primary auditory area.Primary gustatory area – taste.Primary olfactory area.

Motor AreasPrimary motor area – located in the

precentral gyrus of the frontal lobe.Broca’s speech area – coordinates the

contractions of speech and breathing muscles.

Association AreasSomatosensory association area – integrates

and interprets sensations.Visual association area – evaluates what is

seen.Auditory association area – evaluates sounds.

Association AreasWernicke’s (posterior language) area –

interprets the meaning of speech.Common integrative area.Premotor area – controls learned skilled

movements.Frontal eye field area – controls voluntary

scanning movements of the eyes.

AphasiaAn inability to use or comprehend words.

AphasiaDamage to Broca’s area results in nonfluent

aphasia.Inability to properly articulate to form words.These people know what they wish to say, but

cannot speak.

AphasiaDamage to the auditory association area

results in fluent aphasia.Faulty understanding of spoken words.

Word deafness – inability to understand spoken words.

Word blindness – inability to understand written words.

Cranial Nerve I - OlfactoryType: sensory.Function: smell.Anosmia – loss of sense of smell.

Cranial Nerve II – Optic NerveType: sensory.Function: vision.Anopia – blindness in one or both eyes.

Cranial Nerve III - OculomotorType: mixed (mainly motor).Function: movement of the upper eyelid

and eyeball. Accomodation of the lens for nearn vision and constriction of the pupil.

Strabismus – deviation of the eye in which both eyes don’t focus on the same object.

Ptosis – drooping of the upper eyelid.Diplopia – double vision.

Cranial Nerve IV – Trochlear NerveType: mixed (mainly motor).Function: movement of the eyeball.Diplopia and strabismus occur with trochlear

nerve damage.

Cranial Nerve V – Trigeminal NerveType: mixed.Function: conveys impulses for touch, pain,

temperature and proprioception. Chewing.Trigeminal neuralgia (tic douloureux) – pain

to branches of the trigeminal nerve.Dentists apply anesthetic to branches of this

nerve.

Cranial Nerve VI - AbducensType: mixed (mainly motor).Function: movement of the eyeball.With damage to this nerve the eye cannot

move laterally beyond the midpoint and usually points medially.

Cranial Nerve VII – Facial NerveType: mixed.Function: Propriception and taste. Facial

expression. Secretion of saliva and tears.Injury produces bell’s palsy (paralysis of

facial muscles).

Cranial Nerve VIII – Vestibulocochlear NerveType: mixed (mainly sensory).Function: conveys impulses for equilibrium

and hearing.Injury can cause vertigo, ataxia (muscular

incoordination), nystagmus (rapid movement of the eyeball), and tinnitus.

Cranial Nerve IX – Glossopharyngeal NerveType: mixed.Function: taste and somatic sensations from

the posterior 1/3 of the tongue. Elevates the pharynx during swallowing and speech. Stimulates the secretion of saliva.

Injury causes decreased salivary secretion, loss of taste, and difficulty swallowing.

Cranial Nerve X – Vagus NerveType: mixed.Function: taste and somatic sensations.

Swallowing, coughing, and voice production. Regulates GI tract and heart rate.

Injury interferes with swallowing, paralyzes vocal cords, and causes the heart rate to increase.

Cranial Nerve XI – Accessory NerveType: mixed (mainly motor).Function: Proprioception. Swallowing,

movement of head and shoulders.If the nerves are damaged the SCM and

Trapezius become paralyzed.

Cranial Nerve XII – Hypoglossal NerveType: mixed (mainly motor).Function: Proprioception. Movement of the

tongue during speech and swallowing.Injury results in difficulty in chewing,

speaking, and swallowing. When protruded, the tongue curls towards the affected side and atrophies on the affected side.

Cranial NervesI – OlfactoryII – OpticIII – OculomotorIV – TrochlearV – TrigeminalVI – Abducens

VII – FacialVIII – Auditory

(Vestibulocochlear)IX –

GlossopharyngealX – VagusXI – Spinal

accessoryXII - Hypoglossal

Cranial NervesOn Old Olympus’ Towering Tops A Fin And

German Viewed Some Hops.This mnemonic device helps you memorize

the names of the cranial nerves.The first letter from each word corresponds

to the first letter of each cranial nerve.

Cranial NervesSome Say Marry Money, But My Brother

Says Big Brains Matter Most.This mnemonic device helps you memorize

the sensory / motor distribution of the cranial nerves.

S = sensoryM = MotorB = Both