Download Anat3_02_Brain_And_Cranial_Nerves

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
Cerebellum
 Posterior to the brain stem.
 Cerebellum = little brain.
Diencephalon
 Superior to the brain stem.
 Subdivisions
 Thalamus
 Hypothalamus
 Epithalamus
 Di = through; encephalon = brain
Cerebrum
 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
unconsciousness.
 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
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 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
cord.
 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
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
Ventricles
 CSF is formed in the ventricles.
 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.
 Mechanical protection.
 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.
Hydrocephalus
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).
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.
 Contains the pineal gland which secretes melatonin.
 Thalamus.
 Relays sensory information to the cortex.
 Provides crude perception of touch, pressure, pain, and
temperature.
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.
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.
 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
Functions
 Sensory areas – receive and interpret sensory
information.
Cerebral Cortex Areas and
Functions
 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.
Aphasia
 An inability to use or comprehend words.
Aphasia
 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
speak.
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.
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.
 Diplopia – 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
 I – Olfactory
 VII – Facial
 II – Optic
 VIII – Auditory
 III – Oculomotor
(Vestibulocochlear)
 IX – Glossopharyngeal
 X – Vagus
 XI – Spinal accessory
 XII - Hypoglossal
 IV – Trochlear
 V – Trigeminal
 VI – Abducens
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