Chapter 14

The Brain and Cranial Nerves

•Largest
organ in the body at almost 3 lb.

•Brain
functions in sensations, memory, emotions, decision making, behavior

Principal Parts of the Brain

•Cerebrum

•Diencephalon

–thalamus & hypothalamus

•Cerebellum

•Brainstem

–medulla, pons & midbrain

Protective Coverings of the Brain

•Bone,
meninges & fluid

•Meninges
same as around the spinal cord

–dura mater

–arachnoid mater

–pia mater

•Dura
mater extensions

–falx cerebri

–tentorium cerebelli

–falx cerebelli

Blood Supply to Brain

•Arterial
blood supply is branches from circle of Willis on base of brain (page 699)

•Vessels
on surface of brain----penetrate tissue

•Uses
20% of our bodies oxygen & glucose needs

–blood flow to an area increases
with activity in that area

–deprivation of O2 for 4 min
does permanent injury

•at
that time, lysosome release enzymes

•Blood-brain
barrier (BBB)

–protects cells from some toxins
and pathogens

•proteins
& antibiotics can not pass but alcohol & anesthetics do

–tight junctions seal together
epithelial cells, continuous basement membrane, astrocyte processes covering
capillaries

Cerebrospinal Fluid (CSF)

•80-150
ml (3-5oz)

•Clear
liquid containing glucose, proteins, & ions

•Functions

–mechanical
protection

•floats brain & softens
impact with bony walls

–chemical
protection

•optimal ionic concentrations
for action potentials

–circulation

•nutrients and waste products to
and from bloodstream

Drainage of CSF from Ventricles

•One
median aperture & two lateral apertures allow CSF to exit from the interior
of the brain

Reabsorption of CSF

•Reabsorbed
through arachnoid villi

–grapelike clusters of arachnoid
penetrate dural venous sinus

•20
ml/hour reabsorption rate = same as production rate

Hydrocephalus

•Blockage
of drainage of CSF (tumor, inflammation, developmental malformation,
meningitis, hemorrhage or injury

•Continued
production cause an increase in pressure --- hydrocephalus

•In
newborn or fetus, the fontanels allow this internal pressure to cause expansion
of the skull and damage to the brain tissue

•Neurosurgeon
implants a drain shunting the CSF to the veins of the neck or the abdomen

Medulla Oblongata

•Continuation
of spinal cord

•Ascending
sensory tracts

•Descending
motor tracts

•Nuclei
of 5 cranial nerves

•Cardiovascular
center

–force & rate of heart beat

–diameter of blood vessels

•Respiratory
center

–medullary rhythmicity area sets
basic rhythm of breathing

•Information
in & out of cerebellum

•Reflex
centers for coughing, sneezing, swallowing etc

XII = Hypoglossal Nerve

•Controls
muscles of tongue during speech and swallowing

•Injury
deviates tongue to injured side when protruded

•Mixed,
primarily motor

X = Vagus Nerve

•Receives
sensations from viscera

•Controls
cardiac muscle and smooth muscle of the viscera

•Controls
secretion of digestive fluids

VIII = Vestibulocochlear Nerve

•Cochlear
branch begins in medulla

–receptors in cochlea

–hearing

–if damaged deafness or tinnitus
(ringing) is produced

•Vestibular
branch begins in pons

–receptors in vestibular
apparatus

–sense of balance

–vertigo (feeling of rotation)

–ataxia (lack of coordination)

Injury to the Medulla

•Hard
blow to the back of the head may be fatal

•Cranial
nerve malfunctions on same side as injury;

loss of sensation or paralysis of throat or tongue;

irregularities in breathing and heart rhythm

Pons

•One
inch long

•White
fiber tracts ascend and descend

•Pneumotaxic
& apneustic areas help control breathing

•Middle
cerebellar peduncles carry sensory info to the cerebellum

•Cranial
nerves 5 thru 7

VII = Facial Nerve

•Motor
portion

–facial muscles

–salivary & nasal and oral
mucous glands & tears

•Sensory
portion

–taste buds on anterior
2/3’s of tongue

V = Trigeminal Nerve

•Motor
portion

–muscles of mastication

•Sensory
portion

–touch, pain, & temperature
receptors of the face

•ophthalmic
branch

•maxillary
branch

•mandibular
branch

Midbrain

•One
inch in length

•Extends
from pons to diencephalon

•Cerebral
aqueduct connects 3rd ventricle above to 4th ventricle below

Cerebellum

•2
cerebellar hemispheres and vermis (central area)

•Function

–correct voluntary muscle
contraction and posture based on sensory data from body about actual movements

–sense of equilibrium

Cerebellum

•Transverse
fissure between cerebellum & cerebrum

•Cerebellar
cortex (folia) & central nuclei are grey matter

•Arbor
vitae = tree of life = white matter

Thalamus

•1
inch long mass of gray mater in each half of brain (connected across the 3rd
ventricle by intermediate mass)

•Relay
station for sensory information on way to cortex

•Crude
perception of some sensations

Hypothalamus

•Dozen
or so nuclei in 4 major regions

–mammillary bodies are relay
station for olfactory reflexes;

infundibulum suspends the pituitary gland

•Major
regulator of homeostasis

–receives somatic and visceral
input, taste, smell & hearing information; monitors osmotic pressure,
temperature of blood

Functions of Hypothalamus

•Controls
and integrates activities of the ANS which regulates smooth, cardiac muscle and
glands

•Synthesizes
regulatory hormones that control the anterior pituitary

•Contains
cell bodies of axons that end in posterior pituitary where they secrete
hormones

•Regulates
rage, aggression, pain, pleasure & arousal

•Feeding,
thirst & satiety centers

•Controls
body temperature

•Regulates
daily patterns of sleep

Epithalamus

•Pineal
gland

–endocrine gland the size of
small pea

–secretes melatonin during
darkness

–promotes sleepiness & sets
biological clock

•Habenular
nuclei

–emotional responses to odors

Subthalamus & CVO

–sites
of entry of HIV virus into brain (dementia)

Cerebrum

(Cerebral Hemispheres)

•Cerebral
cortex is gray matter

overlying white matter

–2-4 mm thick containing
billions

of cells

–grew so quickly formed folds

(gyri) and grooves (sulci or fissures)

•Longitudinal
fissure separates left

& right cerebral hemispheres

•Corpus
callosum is band of white matter connecting left and right cerebral hemispheres

•Each
hemisphere is subdivided into 4 lobes

Lobes and
Fissures

•Longitudinal fissure (green)

•Frontal lobe

•Central sulcus (yellow)

–precentral
& postcentral gyrus

•Parietal lobe

•Parieto-occipital sulcus

•Occipital lobe

•Lateral sulcus (blue)

•Temporal lobe

•Insula

Limbic System

•Emotional
brain--intense pleasure & intense pain

•Strong emotions increase
efficiency of memory

Brain Injuries

•Causes
of damage

–displacement
or distortion of tissue at impact

–increased
intracranial pressure

–infections

–free
radical damage after ischemia

•Concussion---temporary
loss of consciousness

–headache,
drowsiness, confusion, lack of concentration

•Contusion--bruising
of brain (less than 5 min unconsciousness but blood in CSF)

•Laceration--tearing
of brain (fracture or bullet)

–increased
intracranial pressure from hematoma

Sensory Areas of Cerebral Cortex

Receive sensory information from the thalamus

Primary
somatosensory area = postcentral gyrus = 1,2,3

Primary
visual area = 17

Primary
auditory area = 41 & 42

Primary
gustatory area = 43

Motor Areas of Cerebral Cortex

•Voluntary
motor initiation

–Primary motor area = 4 =
precentral gyrus

•controls
voluntary contractions of skeletal muscles on other side

–Motor speech area = 44 =
Broca’s area

•production
of speech -- control of tongue & airway

Association Areas of Cerebral Cortex

•Somatosensory area = 5 & 7
(integrate & interpret)

•Visual association area = 18
& 19 (recognize & evaluate)

•Auditory association
area(Wernicke’s) = 22(words become speech)

•Gnostic area = 5,7,39 & 40
(integrate all senses & respond)

•Premotor area = 6 (learned
skilled movements such as typing)

•Frontal eye field =8 (scanning
eye movements such as phone book)

Aphasia

•Language
areas are located in the left cerebral hemisphere of most people

•Inability
to use or comprehend words = aphasia

–nonfluent
aphasia = inability to properly form words

•know what want to say but can
not speak

•damage to Broca’s speech
area

–fluent
aphasia = faulty understanding of spoken or written words

•faulty understanding of spoken
or written words

–word
deafness = an inability to understand spoken words

–word
blindness = an inability to understand written words

Hemispheric Lateralization

•Functional specialization of
each hemisphere more pronounced in men

•Females have larger connections
between 2 sides

•Damage to left side produces
aphasia

•Damage to same area on right
side produces speech with little emotional inflection

Electroencephalogram (EEG)

•Brain
waves are millions of nerve action potentials in cerebral cortex

–diagnosis of brain disorders
(epilepsy)

–brain death (absence of
activity in 2 EEGs 24 hours apart)

•Alpha
-- awake & resting

•Beta
-- mental activity

•Theta
-- emotional stress

•Delta
-- deep sleep

II -- Optic Nerve

•Connects
to retina supplying vision

I -- Olfactory Nerve

•Extends
from olfactory mucosa of nasal cavity to olfactory bulb

•Sense
of smell

Aging & the Nervous System

•Years
1 to 2

–rapid
increase in size due to increase in size of neurons, growth of neuroglia,
myelination & development of dendritic branches

•Early
adulthood until death

–brain
weight declines until only 93% by age 80

–number
of synaptic contacts declines

–processing
of information diminishes

–conduction
velocity decreases

–voluntary
motor movements slow down

–reflexes
slow down

Cerebrovascular Accident (CVA)

•Third
leading cause of death after heart attacks and cancer

•2
types of strokes

–ischemic
due to decreased blood flow

–hemorrhagic
due to rupture of blood vessel

•Risk
factors

–high
blood pressure, high cholesterol, heart disease, diabetes, smoking, obesity,
alcohol

•Tissue
plasminogen activator (t-PA) used within 3 hours of onset will decrease
permanent disability

Transient Ischemic Attack (TIA)

•Episode
of temporary cerebral dysfunction

•Cause

–impaired
blood flow to the brain

•Symptoms

–dizziness,
slurred speech, numbness, paralysis on one side, double vision

–reach
maximum intensity almost immediately

–persists
for 5-10 minutes & leaves no deficits

•Treatment
is aspirin or anticoagulants; artery bypass grafting or carotid endarterectomy

Alzheimer Disease (AD)

•Dementia
= loss of reasoning, ability to read, write, talk, eat & walk

•Afflicts
11% of population over 65

•Loss
of neurons that release acetylcholine

•Plaques
of abnormal proteins outside neurons

•Tangled
protein filaments within neurons

•Risk
factors -- head injury, heredity

•Beneficial
effects of estrogen, vitamin E, ibuprofen & ginko biloba