Brain

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Brain Cranial Nerves

• Dr. Michael P. Gillespie

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Major Parts of the Brain

• Brain stem
• Cerebellum
• Diencephalon
• Cerebrum

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Brain Stem

• Continuous with the spinal cord.
• Subdivisions
• Medulla Oblongata
• Pons
• Midbrain

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Cerebellum

• Posterior to the brain stem.
• Cerebellum little brain.

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Diencephalon

• Superior to the brain stem.
• Subdivisions
• Thalamus
• Hypothalamus
• Epithalamus
• Di through encephalon brain

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Cerebrum

• Supported on the diencephalon and brain stem.
• Largest part of the brain.
• Cerebrum brain.

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Brain Blood Supply

• Arteries
• Internal carotid arteries
• Vertebral arteries
• Veins
• Internal jugular veins

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Brain Blood Flow

• The 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.

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Brain Blood Flow

• An 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.

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Blood Brain Barrier

• The 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.

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Permeability of the BBB

• Water-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.

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Breaching the BBB

• The 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.

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Protective Coverings

• Cranium
• Meninges.
• 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.

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Protective Coverings

• Extensions 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.

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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).

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Formation of CSF in the Ventricles

• CSF is formed in the ventricles.
• Formed by ependymal cells that cover the choroid
  plexuses of the ventricles.

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Formation of CSF in the Ventricles

• There 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.

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Hydrocephalus

• Abnormalities 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.

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Hydrocephalus

• Tumors, 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.

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Hydrocephalus
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Brain Stem

• Between the brain and spinal cord.
• 3 regions.
• Medulla oblongata.
• Pons.
• Midbrain.

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Medulla Oblongata

• A 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.

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Medulla Oblongata

• Cardiovascular center regulates the heartbeat and
  the diameter of the blood vessels.

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Medulla Oblongata

• The medullary rhythmicity area adjusts the rhythm
  of the breathing and controls reflexes for
  vomiting, coughing, and sneezing.

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Medulla Oblongata

• The nuclei for the following cranial nerves
  reside in the medulla
• VIII (vestibulocochlear).
• IX (glossopharyngeal).
• X (vagus).
• XI (accessory).
• XII (hypoglossal).

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Pons

• Pneumotaxic area and apneustic area regulate
  breathing.
• Nuclei for cranial nerves V (trigeminal), VI
  (abducens), VII (facial), and VIII
  (vestibulocochlear).

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Midbrain

• The 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.

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Cerebellum

• The 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.

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Diencephelon

• Epithalamus.
• Contains the pineal gland which secretes
  melatonin.
• Thalamus.
• Relays sensory information to the cortex.
• Provides crude perception of touch, pressure,
  pain, and temperature.

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Diencephelon

• Subthalamus.
• 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.

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Cerebrum

• Sensory 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.

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Brain Injuries

• Concussion an abrupt, temporary loss of
  consciousness following a blow to the head.
• Most common brain injury.
• Signs headache, drowsiness, lack of
  concentration, confusion, amnesia.

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Brain Injuries

• Contusion bruising of the brain due to trauma
  and includes leakage of blood.
• Signs - immediate loss of consciousness,
  transient cessation of respiration, decreased
  blood pressure.

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Brain Injuries

• Laceration 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.

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Cerebral Cortex Areas and Functions

• Sensory areas receive and interpret sensory
  information.

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Cerebral Cortex Areas and Functions

• Motor areas initiate movements.
• Association areas deal with integrative
  functions
• Memory.
• Emotions.
• Reasoning.
• Will.
• Judgement.
• Personality.
• Intelligence.

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Sensory Areas

• Primary 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.

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Motor Areas

• Primary motor area located in the precentral
  gyrus of the frontal lobe.
• Brocas speech area coordinates the
  contractions of speech and breathing muscles.

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Association Areas

• Somatosensory association area integrates and
  interprets sensations.
• Visual association area evaluates what is seen.
• Auditory association area evaluates sounds.

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Association Areas

• Wernickes (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.

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Aphasia

• An inability to use or comprehend words.

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Aphasia

• Damage to Brocas area results in nonfluent
  aphasia.
• Inability to properly articulate to form words.
• These people know what they wish to say, but
  cannot speak.

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Aphasia

• Damage 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.

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Cranial Nerve I - Olfactory

• Type sensory.
• Function smell.
• Anosmia loss of sense of smell.

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Cranial Nerve II Optic Nerve

• Type sensory.
• Function vision.
• Anopia blindness in one or both eyes.

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Cranial Nerve III - Oculomotor

• Type 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 dont focus on the same object.
• Ptosis drooping of the upper eyelid.
• Diploia double vision.

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Cranial Nerve IV Trochlear Nerve

• Type mixed (mainly motor).
• Function movement of the eyeball.
• Diplopia and strabismus occur with trochlear
  nerve damage.

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Cranial Nerve V Trigeminal Nerve

• Type 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.

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Cranial Nerve VI - Abducens

• Type 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.

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Cranial Nerve VII Facial Nerve

• Type mixed.
• Function Propriception and taste. Facial
  expression. Secretion of saliva and tears.
• Injury produces bells palsy (paralysis of facial
  muscles).

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Cranial Nerve VIII Vestibulocochlear Nerve

• Type 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.

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Cranial Nerve IX Glossopharyngeal Nerve

• Type 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.

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Cranial Nerve X Vagus Nerve

• Type 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.

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Cranial Nerve XI Accessory Nerve

• Type mixed (mainly motor).
• Function Proprioception. Swallowing, movement
  of head and shoulders.
• If the nerves are damaged the SCM and Trapezius
  become paralyzed.

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Cranial Nerve XII Hypoglossal Nerve

• Type 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.

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Cranial Nerves

• I Olfactory
• II Optic
• III Oculomotor
• IV Trochlear
• V Trigeminal
• VI Abducens

• VII Facial
• VIII Auditory (Vestibulocochlear)
• IX Glossopharyngeal
• X Vagus
• XI Spinal accessory
• XII - Hypoglossal

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Cranial Nerves

• On 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.

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Cranial Nerves

• Some 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 sensory
• M Motor
• B Both