Brain Cranial Nerves (PowerPoint)

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					Dr. Michael P. Gillespie
Major Parts of the Brain
 Brain stem
 Cerebellum
 Diencephalon
 Cerebrum
Brain Stem
 Continuous with the spinal cord.
 Subdivisions
    Medulla Oblongata
    Pons
    Midbrain
 Posterior to the brain stem.
 Cerebellum = little brain.
 Superior to the brain stem.
 Subdivisions
    Thalamus
    Hypothalamus
    Epithalamus
 Di = through; encephalon = brain
 Supported on the diencephalon and brain stem.
 Largest part of the brain.
 Cerebrum = brain.
Brain Blood Supply
 Arteries
    Internal carotid arteries
    Vertebral arteries
 Veins
    Internal jugular veins
Brain Blood Flow
 The brain consumes about 20% of the oxygen and
  glucose used at rest.
 A brief slowing of blood flow may cause
 When activity of neurons and neuroglia in a certain
  portion of the brain increases, blood flow to that
  region increases.
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.
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.
Permeability of the BBB
 Water-soluble substances.
    Glucose crosses the BBB by active transport.
    Creatinine, urea, and most ions cross the BBB very
    Proteins and most antibiotic drugs do not cross the BBB.
 Lipid-soluble substances.
    Oxygen, carbon dioxide, alcohol, most anesthetic agents
     cross easily.
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”.
Protective Coverings
 Cranium
 Meninges.
   Dura mater (Outer layer).
       Two dural layers around the brain and one around the spinal
   Arachnoid mater (Middle layer).
   Pia mater (Inner layer).
 No epidural space around the brain.
Protective Coverings
 Extensions of dura mater separate parts of the brain.
 Falx cerebri – separates the two hemispheres of the
 Falx cerebelli – separates the two hemispheres of the
 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
 Circulates in the subarachnoid space (between the
  arachnoid mater and pia mater).
Formation of CSF in the
 CSF is formed in the ventricles.
    Formed by ependymal cells that cover the choroid
     plexuses of the ventricles.
Formation of CSF in the
 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
 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.
 Tumors, inflammation, developmental
  malformations can all cause hydrocephalus.
 Pressure buildup can damage the delicate nervous
 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.
Brain Stem
 Between the brain and spinal cord.
 3 regions.
    Medulla oblongata.
    Pons.
    Midbrain.
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.
Medulla Oblongata
 Cardiovascular center regulates the heartbeat and the
 diameter of the blood vessels.
Medulla Oblongata
 The medullary rhythmicity area adjusts the rhythm of
 the breathing and controls reflexes for vomiting,
 coughing, and sneezing.
Medulla Oblongata
 The nuclei for the following cranial nerves reside in
 the medulla:
   VIII (vestibulocochlear).
   IX (glossopharyngeal).
   X (vagus).
   XI (accessory).
   XII (hypoglossal).
 Pneumotaxic area and apneustic area regulate
 Nuclei for cranial nerves V (trigeminal), VI
  (abducens), VII (facial), and VIII (vestibulocochlear).
 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.
 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.
 Epithalamus.
    Contains the pineal gland which secretes melatonin.
 Thalamus.
    Relays sensory information to the cortex.
    Provides crude perception of touch, pressure, pain, and
 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.
 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.
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.
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.
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.
Cerebral Cortex Areas and
 Sensory areas – receive and interpret sensory
Cerebral Cortex Areas and
 Motor areas – initiate movements.
 Association areas – deal with integrative functions:
   Memory.
   Emotions.
   Reasoning.
   Will.
   Judgement.
   Personality.
   Intelligence.
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.
Motor Areas
 Primary motor area – located in the precentral gyrus of
  the frontal lobe.
 Broca’s speech area – coordinates the contractions of
  speech and breathing muscles.
Association Areas
 Somatosensory association area – integrates and
  interprets sensations.
 Visual association area – evaluates what is seen.
 Auditory association area – evaluates sounds.
Association Areas
 Wernicke’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.
 An inability to use or comprehend words.
 Damage 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
 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.
Cranial Nerve I - Olfactory
 Type: sensory.
 Function: smell.
 Anosmia – loss of sense of smell.
Cranial Nerve II – Optic Nerve
 Type: sensory.
 Function: vision.
 Anopia – blindness in one or both eyes.
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 don’t focus on the same object.
 Ptosis – drooping of the upper eyelid.
 Diploia – double vision.
Cranial Nerve IV – Trochlear
 Type: mixed (mainly motor).
 Function: movement of the eyeball.
 Diplopia and strabismus occur with trochlear nerve
Cranial Nerve V – Trigeminal
 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.
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
Cranial Nerve VII – Facial Nerve
 Type: mixed.
 Function: Propriception and taste. Facial expression.
  Secretion of saliva and tears.
 Injury produces bell’s palsy (paralysis of facial
Cranial Nerve VIII –
Vestibulocochlear Nerve
 Type: mixed (mainly sensory).
 Function: conveys impulses for equilibrium and
 Injury can cause vertigo, ataxia (muscular
  incoordination), nystagmus (rapid movement of the
  eyeball), and tinnitus.
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.
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.
Cranial Nerve XI – Accessory
 Type: 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
 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
Cranial Nerves
 I – Olfactory       VII – Facial
 II – Optic          VIII – Auditory
 III – Oculomotor     (Vestibulocochlear)
 IV – Trochlear      IX – Glossopharyngeal
 V – Trigeminal      X – Vagus
 VI – Abducens       XI – Spinal accessory
                      XII - Hypoglossal
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.
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

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