Anatomy and Physiology I

Chapter 14The 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• 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

• 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

• 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– 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