Transcript Brain & Cranial Nerves

Brain & Cranial Nerves
Dr. Michael P. Gillespie
Major Parts of the Brain
 Brain stem – continuous with the spinal cord.
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Medulla oblongata.
Pons.
Midbrain.
 Cerebellum – posterior to the brain stem.
Major Parts of the Brain
 Diencephalon – superior to the brain stem.
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Thalamus.
Hypothalamus.
 Cerebrum – supported on the diencephalon
and brain stem.
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Largest part of the brain.
Brain Blood Supply
 Arteries
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Internal carotid arteries
Vertebral arteries
 Veins
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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
unconsciousness.
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.
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.
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The high osmotic pressure causes cells lining the
barrier to shrink and makes the membrane
“leaky”.
Protective Coverings
 Cranial Meninges.
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Dura mater.
Arachnoid mater.
Pia mater.
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).
Protective Coverings
 Extensions of the dura mater separate the
parts of the brain.
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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.
Formation of CSF in the
Ventricles
 CSF is formed in the ventricles.
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Formed by ependymal cells that cover the
choroid plexuses of the ventricles.
Formation of CSF in the
Ventricles
 There are 4 ventricles.
 Functions of CSF.
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Mechanical protection.
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Shock absorption.
Buoys the brain.
Chemical protection – optimal chemical environment.
Circulation – medium of exchange for wastes and
nutrients.
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.
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.
Brain Stem
 Between the brain and spinal cord.
 3 regions.
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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:
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VIII (vestibulocochlear).
IX (glossopharyngeal).
X (vagus).
XI (accessory).
XII (hypoglossal).
Pons
 Pneumotaxic area and apneustic area regulate
breathing.
 Nuclei for cranial nerves V (trigeminal), VI
(abducens), VII (facial), and VIII
(vestibulocochlear).
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.
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.
Diencephelon
 Epithalamus.
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Contains the pineal gland which secretes
melatonin.
 Thalamus.
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Relays sensory information to the cortex.
Provides crude perception of touch, pressure,
pain, and temperature.
Diencephelon
 Subthalamus.
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Controls body movements.
 Hypothalamus.
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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.
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.
Brain Injuries
 Concussion – an abrupt, temporary loss of
consciousness following a blow to the head.
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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.
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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.
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Rupture of large blood vessels.
Consequences – cerebral hematoma (localized
pool of blood, usually clotted), edema, and
increased intracranial pressure.
Cerebral Cortex Areas and
Functions
 Sensory areas – receive and interpret sensory
information.
Cerebral Cortex Areas and
Functions
 Motor areas – initiate movements.
 Association areas – deal with integrative functions:
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Memory.
Emotions.
Reasoning.
Will.
Judgement.
Personality.
Intelligence.
Sensory Areas
 Primary somatosensory area – receives sensations
for touch, proprioception, pain, itching, tickle, and
thermal sensations.
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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.
Aphasia
 An inability to use or comprehend words.
Aphasia
 Damage to Broca’s area results in nonfluent
aphasia.
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Inability to properly articulate to form words.
These people know what they wish to say, but
cannot speak.
Aphasia
 Damage to the auditory association area
results in fluent aphasia.
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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.
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
Nerve
 Type: mixed (mainly motor).
 Function: movement of the eyeball.
 Diplopia and strabismus occur with trochlear
nerve damage.
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.
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.
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 muscles).
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.
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
Nerve
 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 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.
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.