Download Brain and Cranial Nerves

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
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Principal Parts of the Brain
• Cerebrum
• Diencephalon
– thalamus &
hypothalamus
• Cerebellum
• Brainstem
– medulla, pons &
midbrain
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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
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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
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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
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Origin of CSF
• Choroid plexus = capillaries covered by ependymal cells
– 2 lateral ventricles, one within each cerebral hemisphere
– roof of 3rd ventricle
– fourth ventricle
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Drainage of CSF from Ventricles
• One median aperture & two lateral apertures allow CSF to
exit from the interior of the brain
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Flow of Cerebrospinal Fluid
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Reabsorption of CSF
• Reabsorbed through arachnoid villi
– grapelike clusters of arachnoid penetrate dural venous sinus
• 20 ml/hour reabsorption rate = same as production rate
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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
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Medulla Oblongata
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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
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Ventral Surface of Medulla Oblongata
• Ventral surface bulge
– pyramids
– large motor tract
– decussation of most fibers
• left cortex controls right muscles
• Olive = olivary nucleus
– neurons send input to
cerebellum
– proprioceptive signals
– gives precision to movements
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Dorsal Surface of Medulla Oblongata
• Nucleus gracilis & nucleus cuneatus = sensory neurons
– relay information to thalamus on opposite side of brain
• 5 cranial nerves arise from medulla -- 8 thru 12
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XII = Hypoglossal Nerve
• Controls muscles of
tongue during speech
and swallowing
• Injury deviates tongue
to injured side when
protruded
• Mixed, primarily
motor
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XI = Spinal Accessory Nerve
• Cranial portion
– arises medulla
– skeletal mm of throat & soft
palate
• Spinal portion
– arises cervical spinal cord
– sternocleidomastoid and
trapezius mm.
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X = Vagus Nerve
• Receives sensations
from viscera
• Controls cardiac muscle
and smooth muscle of
the viscera
• Controls secretion of
digestive fluids
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IX = Glossopharyngeal Nerve
• Stylopharyngeus m.
(lifts throat during
swallowing)
• Secretions of parotid
gland
• Somatic sensations &
taste on posterior 1/3
of tongue
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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)
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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
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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
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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
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VI = Abducens Nerve
• Lateral rectus eye
muscle
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V = Trigeminal Nerve
• Motor portion
– muscles of mastication
• Sensory portion
– touch, pain, &
temperature receptors of
the face
• ophthalmic branch
• maxillary branch
• mandibular branch
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Midbrain
• One inch in length
• Extends from pons to
diencephalon
• Cerebral aqueduct
connects 3rd
ventricle above to
4th ventricle below
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Midbrain in Section
• Cerebral peduncles---clusters of motor & sensory fibers
• Substantia nigra---helps controls subconscious muscle activity
• Red nucleus-- rich blood supply & iron-containing pigment
– cortex & cerebellum coordinate muscular movements by sending
information here from the cortex and cerebellum
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Dorsal Surface of Midbrain
• Corpora quadrigemina = superior & inferior colliculi
– coordinate eye movements with visual stimuli
– coordinate head movements with auditory stimuli
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IV = Trochlear Nerve
• Superior oblique eye
muscle
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III = Oculomotor Nerve
• Levator palpebrae raises
eyelid (ptosis)
• 4 extrinsic eye muscles
• 2 intrinsic eye muscles
– accomodation for near
vision (changing shape
of lens during reading)
– constriction of pupil
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Reticular Formation
• Scattered nuclei in medulla, pons & midbrain
• Reticular activating system
– alerts cerebral cortex to sensory signals (sound of
alarm, flash light, smoke or intruder) to awaken
from sleep
– maintains consciousness & helps keep you awake
with stimuli from ears, eyes, skin and muscles
• Motor function is involvement with
maintaining muscle tone
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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
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Cerebellum
• Transverse fissure between cerebellum & cerebrum
• Cerebellar cortex (folia) & central nuclei are grey matter
• Arbor vitae = tree of life = white matter
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Cerebellar Peduncles
• Superior, middle & inferior peduncles attach to brainstem
– inferior carries sensory information from spinal cord
– middle carries sensory fibers from cerebral cortex & basal ganglia
– superior carries motor fibers that extend to motor control areas
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Diencephalon Surrounds 3rd Ventricle
• Surrounds 3rd ventricle
• Superior part of walls is thalamus
• Inferior part of walls & floor is hypothalamus
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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
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Thalamic Nuclei
• Nuclei have different roles
– relays auditory and visual impulses, taste and somatic sensations
– receives impulses from cerebellum or basal ganglia
– anterior nucleus concerned with emotions, memory and acquisition
of knowledge (cognition)
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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
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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
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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
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Subthalamus & CVO
• Subthalamus
– small area just inferior to thalamus
– work with basal ganglia, cerebrum & cerebellum to
control body movements
• Circumventricular organs
– in walls of 3rd & 4th ventricles
– monitor changes in blood chemistry because lack
blood brain barrier (parts of hypothalamus, pineal &
pituitary gland)
– sites of entry of HIV virus into brain (dementia)
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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
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Lobes and Fissures
• Longitudinal fissure (green)
• Frontal lobe
• Central sulcus (yellow)
– precentral & postcentral gyrus
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Parietal lobe
Parieto-occipital sulcus
Occipital lobe
Lateral sulcus (blue)
Temporal lobe
Insula
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Insula within Lateral Fissure
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Cerebral White Matter
• Association fibers between gyri in same hemisphere
• Commissural fibers from one hemisphere to other
• Projection fibers form descending & ascending tracts
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Basal Ganglia
• Connections to red nucleus, substantia nigra & subthalamus
• Input & output with cerebral cortex, thalamus &
hypothalamus
• Control large automatic movements of skeletal muscles
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Limbic System
• Parahippocampal & cingulate gyri & hippocampus
• Emotional brain--intense pleasure & intense pain
• Strong emotions increase efficiency of memory
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Brain Injuries
• Causes of damage
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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
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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
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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
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Association Areas of Cerebral Cortex
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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)
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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
• damage to common integrative area or auditory association
area
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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
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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)
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Alpha -- awake & resting
Beta -- mental activity
Theta -- emotional stress
Delta -- deep sleep
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II -- Optic Nerve
• Connects to retina
supplying vision
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I -- Olfactory Nerve
• Extends from
olfactory mucosa of
nasal cavity to
olfactory bulb
• Sense of smell
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Developmental Anatomy of the NS
• Begins in 3rd week
– ectoderm forms thickening (neural plate)
– plate folds inward to form neural groove
– edges of folds join to form neural tube
• Neural crest tissue forms:
– spinal & cranial nerves
– dorsal root & cranial nerve ganglia
– adrenal gland medulla
• Layers of neural tube form:
– marginal layer which forms white matter
– mantle layer forms gray matter
– ependymal layer forms linings of cavities
within NS
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Dorsal View of Neural Groove
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Development of Principal Parts
• By end of 4th week, 3
anterior enlargements
occur
– prosencephalon
– mesencephalon
– rhombencephalon
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Development of Principal Parts
• By 5th week, 5 enlarged areas exist
• Prosencephalon
– telencephalon
– diencephalon
• Mesencephalon
• Rhombencephalon
– metencephalon
– myelencephalon
• Neural tube defects
– associated with low levels of folic acid (B vitamins)
– spina bifida is failure to close of vertebrae
– anencephaly is absence of skull & cerebral hemispheres
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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
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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
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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
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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
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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
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