Anatomy and Physiology I
Chapter 14
The Brain and Cranial Nerves
The Brain
• Cerebrum
• Cerebellum
• Brainstem
The Cerebrum
• 83% of volume
• Cerebral hemispheres- 2
halves
• Longitudinal fissure- deep
groove that separates R and
L hemispheres
• Central sulcus- vertical
groove that divides frontal
and parietal lobes
The Cerebrum
• Corpus callosum- thick bundle of nerve fibers
connects R and L hemispheres
• Gyri- thick folds
• Sulci- shallow grooves
The Cerebrum
• Sensory perception, memory,
thought, judgment, voluntary
motor actions
• 4 lobes
– Frontal lobe
• Voluntary motor functions, motivation, foresight, planning,
memory, mood, emotion, social judgment, aggression
– Parietal lobe
• receive and interpret signals of general senses
• Taste, touch, some visual
– Occipital lobe
• Principal visual center
– Temporal lobe
• hearing, smell, learning, memory, some vision and emotion
Sulci
• Central sulcus
• Parieto-occipital sulcus
• Lateral sulcus
Lateral sulcus
The Cerebellum
• Posterior aspect, inferior to cerebrum
– 2nd largest region
– 10% of volume
The Cerebellum
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Outer surface- gray matter
Deeper layer- white matter
Arbor vitae- branching, fernlike pattern
Functions
– Monitor muscle contraction
– Learned movements
– Motor coordination
– Balance and
– equilibrium
The Brainstem
• Brainstem- diencephalon, midbrain, pons, and
medulla oblongata
– Ends at foramen magnum
Meninges
• 3 connective tissue membranes
• Between brain and skull
– Dura mater- very close to skull
– Arachnoid mater- transparent
– Pia mater- thin, delicate
• Closely follows contours of brain
• Protect the brain and provide structural
framework for arteries and veins
Ventricles
• 4 internal chambers
• Lateral ventricles- largest, cerebral hemispheres
• 3rd ventricle- connected to lateral ventricles
– Inferior to corpus callosum
• 4th ventricle- connects to
3rd ventricle
– b/t pons and cerebellum
• Produces CSF
CSF
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Clear, colorless liquid
Fills ventricles
Produced and reabsorbed at same rate
Continually flows through and around CNS
3 purposes
– Buoyancy- attain size, w/o being impaired by weight
– Protection- protects from striking cranium when head
is jolted
– Chemical stability- rinses wastes from nervous tissue
Brain Barrier System
• Brain: 2% of body wt, 15% of blood consumption,
20% of O2 and glucose consumption
• Brain barrier system- strictly regulates what
substances can get from bloodstream into brain
tissue
• Blood-brain-barrier (BBB)- tight junctions b/t
brain and capillaries
– Astrocytes completely seal off gaps
– Exclude harmful substances
– Allow necessary ones to pass
Blood Brain Barrier
• Highly permeable to H2O, glucose, and lipid
substances
– O2, CO2, alcohol, caffeine, nicotine, anesthetics
• BBB is an important protective device
– Obstacle to deliver meds
• Antibiotics
• Cancer drugs
– Complicates treatment of brain diseases
The Medulla Oblongata
• Begins at foramen magnum
• Autonomic functions
– Cardiac center
• Heart beat
– Vasomotor center
• Blood pressure
– Respiratory center
• breathing
The Pons
• Broad, anterior bulge, superior to medulla
oblongata
• Involved in
– Sleeping patterns
– Facial expressions/ sensations
– Eye movements
– Equilibrium/ posture
The Midbrain
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Short segment of brainstem
Anchors cerebrum to brainstem
Collaborates in fine motor control
Relays inhibitory signals to the thalamus
– Preventing unwanted movements
The Reticular Formation
• Runs vertically through brainstem
• Functions
– Somatic motor control
• maintain tone, balance, posture
• Relays signals from eyes and ears to cerebellum to integrate stimuli into
coordinated motor movements
– Cardiovascular control
• cardiac and vasomotor centers of medulla oblongata
– Pain modulation
• Pain signals from lower body get to cerebral cortex
– Sleep and consciousness
• alertness and sleep
– Habituation
• ignore repetitive, inconsequential stimuli while remaining sensitive to
others
The Thalamus
• Superior end of the brainstem
• “Gateway to cerebral cortex”
• All info passes through thalamus to cerebrum
– Taste, smell, hearing, equilibrium, vision, touch,
pain, pressure, heat, cold
• Memory and emotional functions
– Limbic system
The Hypothalamus
• Control center of autonomic nervous system and
endocrine system
• Homeostatic regulation
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Hormone secretions
Autonomic effects
Thermoregulation
Food and H2O intake
Sleep and circadian rhythms
• Memory
• Emotional behavior
The Limbic System
• Center of emotion and learning
• Memory
– Gratification center
• Sense of pleasure and reward when stimulated
– Aversion center
• Unpleasant sensations when stimulated
The Cranial Nerves
• 12 pair (I-XII)
• Communicates with body
– Arise from base of brain
– Lead to muscles and sense organs mainly in head
and neck
• Sensory- I, II, VIII
• Motor- III, IV, VI, XI, XII
• Both- V, VII, IX, X
I. Olfactory Nerve
• Function: Sense of smell
• Composition: Sensory
• Clinical Test: Determine
whether subject can
smell aromatic
substances
– Coffee, vanilla, clove, oil,
soap
• Effect of Damage:
impaired sense of smell
II. Optic Nerve
• Function: Vision
• Composition: Sensory
• Clinical Test: Test peripheral
vision and visual acuity
• Effect of Damage:
Blindness in part or all of
visual field
III. Oculomotor Nerve
• Functions: Controls muscles that
turn eyeballs up, down, medially
– Controls iris, lens, and upper lid
• Composition: Motor
• Clinical Test: Look for pupil
shape differences
– Test pupillary response to light
– Test ability to track moving
objects
• Effect of Damage: Drooping
eyelid, dilated pupil, inability to
move eye in some directions,
double vision, difficulty focusing
IV. Trochlear Nerve
• Function: Controls a muscle that rotates eyeball
medially
• Composition: Motor
• Clinical Test: Test ability of eye to rotate
inferolaterally
• Effect of Damage:
double vision,
inability to rotate eye
inferolaterally
V. Trigeminal Nerve
• Function: Important in facial
sensations
• Composition: Both
• Clinical Test: Test facial
sensation of forehead, cheeks,
and chin.
– Test subjects ability to open
mouth against resistance
• Effect of Damage: Loss of
sensation from face and
impaired chewing
VI. Abducens Nerve
• Function: Controls a
muscle that turns
eyeball laterally
• Composition: Motor
• Clinical Test: Test
lateral eye movement
• Effect of Damage:
Inability to turn eye
laterally, at rest eye
will turn medially
VII. Facial Nerve
• Function: Important
nerve of facial muscles
and taste
• Composition: Both
• Clinical Test: Test tongue
for taste response, test
ability to make facial
expressions
• Effect of Damage:
inability to control facial
muscles, sagging due to
loss of muscle tone,
distorted sense of taste
VIII. Vestibocochlear Nerve
• Function: Hearing and
equilibrium
• Composition: Sensory
• Clinical Test: Look for
nystagmus, test
hearing, balance,
ability to walk in a
straight line
• Effect of Damage:
deafness, dizziness,
nausea, loss of
balance, nystagmus
IX. Glossopharyngeal Nerve
• Function: Food ingestion,
salivation
– Sensations from the
tongue, throat, and outer
ear
• Composition: Both
• Clinical Test: Test gag
reflex, swallowing, and
coughing
• Effect of Damage:
impaired swallowing
X. Vagus Nerve
• Function: Control of cardiac,
pulmonary, digestive, and
urinary functions
• Composition: Both
• Clinical Test: Speech
abnormalities, swallowing
abnormalities, absence of gag
reflex, weak or hoarse voice,
inability to cough
• Effect of Damage: Hoarseness
or loss of voice, impaired
swallowing
XI. Accessory Nerve
• Function: Controls swallowing
and neck and shoulder
muscles
• Composition: Motor
• Clinical Test: Test ability to
rotate head and shrug
shoulders against resistance
• Effect of Damage: impaired
movement of head, neck, and
shoulders, difficulty shrugging
shoulder on damaged side
XII. Hypoglossal Nerve
• Function: Controls tongue
movements
• Composition: Motor
• Clinical Test: Note deviations
of the tongue as subject
protrudes and retracts it
• Effect of Damage: impaired
speech and swallowing,
inability to protrude tongue if
both sides damaged, deviation
of tongue toward injured side