Chapter 14:
The Brain and Cranial
Nerves
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1
Development of the Brain
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Brain and spinal cord
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Ectoderm
neural tube
Three to four-week embryo:
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Prosencephalon
Mesencephalon
Rhombencephalon
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Development of the Brain
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Five-week embryo:
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telencephalon (cerebrum)
diencephalon (thalamus, hypothalamus and
epithalamus)
mesencephalon (midbrain)
metencephalon (pons and cerebellum)
myelencephalon (medulla oblongata).
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Development of the Brain
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Major Parts of the Brain
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Brain stem - continuation of the spinal cord;
consists of the medulla oblongata, pons and
midbrain.
Cerebellum - second largest part of the brain.
Diencephalon - gives rise to thalamus,
hypothalamus and epithalamus.
Cerebrum - largest part of the brain.
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The Brain
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Protective Coverings of the Brain
The cranium - skull
The cranial meninges (similar to spinal cord):
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dura mater ( 2 layers)
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Venous sinuses
No epidural space
Dense, irregular connective tissue
Subdural space contains interstitial fluid
arachnoid mater
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Avascular, web arrangement of delicate collagen and elastic fibers
Subarachnoid space contains CS
pia mater
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Thin transparent connective tissue adheres to brain and spinal cord
Interlacing bundles of collagen, elastic fibers, and network of blood vessels
providing oxygen and nutrition to brain
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14_02
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a.
b.
c.
Three extensions of the dura mater separate
parts of the brain:
Falx cerebri separate the two cerebral
hemispheres.
Falx cerebelli separate the two cerebellar
hemispheres.
Tentorium cerebelli separate the cerebrum
from the cerebellum.
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Extensions of the Dura Mater
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Brain Blood Flow and the Blood-Brain
Barrier
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Brain receives approximately 20% of the total
blood supply.
Internal carotid and vertebral arteries carry
blood to the brain.
Internal jugular veins return blood from the
brain.
Blood-brain barrier (BBB) protects brain from
harmful substances.
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Brain Blood Flow and the Blood-Brain
Barrier
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Carbohydrate storage limited in brain,
glucose supply must be continuous
Glucose deficiency may result in confusion,
dizziness, convulsion, and unconsciousness
Injury from trauma, inflammation or toxins
can cause breakdown of BBB
Passage of harmful substances may occur
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Cerebrospinal Fluid (CSF)
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Clear fluid
Circulates through cavities in the brain
(ventricles) and the spinal cord (central canal)
and also in the subarachnoid space
Absorbs shock and protects the brain and the
spinal cord
Helps transport nutrients and wastes from the
blood and the nervous tissue
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Cerebrospinal Fluid (CSF)
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Total volume 80 – 150 mL (3 – 5 oz)
Glucose, proteins, lactic acid, urea, cations
and anions
Rarely is ever any cells (maybe a couple of
WBC)
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Ventricles
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CSF – fills 4 cavities within the brain.
Lateral ventricles: cerebral hemispheres.
Third ventricle: diencephalon.
Cerebral aqueduct: midbrain.
Fourth ventricle: brain stem and the
cerebellum.
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Formation and Circulation of CSF in the
Ventricles
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CSF formed by filtration from network of
capillaries called choroid plexus located in
walls of ventricles
CSF circulates through subarachnoid space,
ventricles, and central canal
Ventricles are lined by ependymal cells.
Plasma is drawn from the choroid plexuses
through ependymal cells into the ventricles to
produce CSF.
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Formation and Circulation of CSF in
the Ventricles
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Circulation of CSF
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Wiley & Sons, Inc.
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Medulla Oblongata
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Continuous with upper spinal cord
Both motor and sensory tracts
Nuclei of cranial nerves VIII – XII
Pyramids – anterior aspect of the medulla
formed by the large corticospinal tracts
Inferior olivary nucleus – relay impulses from
proprioceptors to cerebellum
site for decussation of ascending and
descending tracts
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Centers of the Medulla Oblongata
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Vital centers contain nuclei that are reflex
centers for regulation of:
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Heart rate
Respiratory rate
Vasoconstriction
Nonvital centers
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vomiting, swallowing, sneezing, coughing and
hiccupping
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Pons
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superior to medulla
Connects spinal cord to brain
Links parts of brain
Relay related to voluntary skeletal movements
from cortex to cerebellum
Pneumotaxic and apneustic areas – help
control respiratory center
cranial nerve nuclei: V - VII
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Midbrain or Mesencephalon
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Extends from the pons to the diencephalon
Surrounds cerebral aqueduct
Conveys motor impulses from cerebrum to
cerebellum and spinal cord
 Cerebral peduncles
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axons of the corticospinal, corticopontine and
corticobulbar tracts.
Sensory impulses from spinal cord to
thalamus
Cranial nerve nuclei III and IV
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Midbrain or Mesencephalon
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Tectum – situated posteriorly and contains
four rounded elevations
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two superior ones called superior colliculi
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Reflex centers for certain visual activities
two inferior ones called inferior colliculi
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Part of auditory pathway relaying impulses from
receptors for hearing in the ear to the thalamus
Startle reflex
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Midbrain or Mesencephalon
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Midbrain
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Substantia nigra:
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large area with dark pigments – dopamine
help control subconscious muscle activities
loss of neurons here is associated with Parkinson
disease.
Red nucleus:
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Axons from cerebellum and cortex form synapses
here
Help control voluntary movements of the limbs.
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Midbrain
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Reticular formation
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Extends from the upper part of the spinal
cord throughout the brain stem and into the
lower part of the diencephalon
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Part of the reticular formation called the
reticular activating system (RAS) consists
of sensory axons that project to the cerebral
cortex
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The RAS helps maintain consciousness
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The Cerebellum
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Second largest part of the brain
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The central constricted area is the vermis
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The anterior and posterior lobes control
subconscious aspects of skeletal movement
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The flocculonodular lobe on the inferior side
contributes to the equilibrium and balance
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The Cerebellum
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The Cerebellum
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Cerebellar cortex – gray matter in the form of
parallel folds called folia
Arbor vitae – tracts of white matter
Cerebellar peduncles –
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three pairs: superior, middle and inferior
Attach cerebellum to the brain stem
Functions – coordinate movements, regulate
posture and balance.
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Diencephalon
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Surrounds 3rd ventricle
Thalamus
Hypothalamus
Epithalamus
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Thalamus
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Superior to midbrain –
intermediate mass
Contains nuclei that
are relay stations for
sensory impulses to
cortex
Crude appreciation of
pain, temperature,
and pressure
Helps mediate motor
activities
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Hypothalamus
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Functions of the Hypothalamus
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Control of the ANS
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Connects nervous and endocrine systems
Rage and aggression
Body temperature
Regulates food and fluid intake
Circadian rhythms
Production of hormones that control pituitary
Production of antidiuretic and oxytocin
hormones
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Epithalamus
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Small region superior to the thalamus
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Consists of pineal gland which secretes a
hormone called melatonin
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Melatonin thought to promote sleep and set
body’s biological clock and circadian rhythms
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May be responsible for jet-lag and SAD
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Circumventricular organs
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monitor chemical changes in blood since
lacks BBB
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Hypothalamus, pineal gland, pituitary gland
Site of entry of HIV
Coordinate homeostatic activities of endocrine
and nervous systems
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14_table_02
The Cerebrum
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“seat of intelligence”
Cerebral cortex – gray matter (2-4 mm)
Gyri
Sulci
Fissures
Longitudinal fissure – right and left lobes
called Cerebral hemispheres
Corpus callosum
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The Cerebrum
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The Cerebrum
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White matter deep to cortex
Primarily myelinated axons extending to other
regions as fibers for –
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Basal ganglia – several groups of nuclei
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Association
Commissural
Projection
Help initiate and terminate movements
Suppress unwanted movements
Regulate muscle tone
Limbic system encircles upper part of brain stem
and corpus callosum
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Cerebrum
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Association fibers connect and transmit
nerve impulses between gyri in the same
hemisphere.
Commissural fibers connect gyri in one
cerebral hemisphere to the corresponding
gyri in the opposite hemisphere.
Projection fibers form ascending and
descending tracts that transmit impulses
from the cerebrum to other parts of the brain
and spinal cord
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Cerebral white matter
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Lobes of the Cerebrum
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Four lobes: frontal lobe, parietal lobe,
temporal lobe and occipital lobe
Central sulcus – separates the frontal and
parietal lobes
Precentral gyrus – primary motor area
Postcentral gyrus – primary somatosensory
area
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Basal Ganglia
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Three nuclei deep within each cerebral
hemisphere make up basal ganglia.
They are globus pallidus, putamen, and
caudate nucleus.
Help initiate and terminate movements,
suppress unwanted movements and regulate
muscle tone.
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Basal Ganglia
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The Limbic System
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A ring of structures on the inner border of the
cerebrum and floor of the diencephalon.
Includes cingulate gyrus, hippocampus,
dentate gyrus, amygdala, mammillary bodies,
thalamus, and the olfactory bulb.
“emotional brain” as it governs emotional
aspects of behavior.
Also involved in olfaction and memory.
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The Limbic System
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Functional Organization of the Cerebral
Cortex: Sensory Areas
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Primary somatosensory area – postcentral
gyrus.
Primary visual area – occipital lobe
Primary auditory area – temporal lobe
Primary gustatory area – base of the
postcentral gyrus
Primary olfactory area – temporal lobe
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Functional Organization of the Cerebral
Cortex: Sensory Areas
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Sensory areas allow perception of
information
Motor areas for execution of voluntary
movements
Association areas for complex integrative
functions of memory, personality, and
intelligence
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Functional Organization of the
Cerebral Cortex: Sensory Areas
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Primary Somatosensory Area
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Post-central gyrus
Primary somatosensory areas 1, 2, and 3
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Receives from somatic sensory receptors of
touch, pressure, vibration, itch, tickle,
temperature, pain, and proprioception
Perception of these sensations
Each point receives input from specific part of
face or body
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Other primary sensory areas
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Visual area 17
Auditory areas 41 and 42
Gustatory area 43
Olfactory area 28
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Functional Organization of the
Cerebral Cortex: Motor Areas
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Motor Areas
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Primary motor area 4
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Voluntary contractions of specific muscles or
groups
Broca’s speech areas 44 and 45
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Functional Organization of the
Cerebral Cortex: Association Areas
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Functional Organization of the Cerebral
Cortex: Association Areas
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Somatosensory association area – posterior
to primary somatosensory areas 5 & 7
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Determine shape and texture by touching
Sense relationship of one body part to another
Stores memories of past somatic experiences
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Functional Organization of the Cerebral
Cortex: Association Areas
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Visual association areas 18 & 19 – occipital
lobe
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Relates present to past visual experiences
Essential for recognizing and evaluating what has
been seen
Facial recognition areas 20, 21, and 37
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Store information
Allow recognition
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Functional Organization of the Cerebral
Cortex: Association Areas
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Auditory association area 22 – temporal lobe
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Recognize a particular sound as speech, music,
or noise
Orbitofrontal area 11
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Identify odors
Discriminate between odors
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Functional Organization of the Cerebral
Cortex: Association Areas
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Wernicke’s area 22 and possibly areas 39
and 40 – left temporal and parietal lobes
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Interprets meaning of speech by translating
words into thoughts
Common integrative areas 5, 7, 39, & 40
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Integrates sensory interpretation from association
areas and impulses from other areas allowing
thoughts based on sensory input
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Functional Organization of the Cerebral
Cortex: Association Areas
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Prefrontal cortex areas 9, 10, 11, & 12 –
anterior portion of the frontal lobe
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Personality
Intellect
Complex learning
Judgment, reasoning, conscience, intuition, and
abstracts
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Others
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Premotor area 6 –
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specific groups of muscle to contract in specific
sequences
Memory bank for complex movements
Frontal eyelid area 8 – voluntary scanning
movements of eyes
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Hemispheric Lateralization
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Cranial Nerves
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12 pairs
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Sensory, motor and mixed nerves
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Name as well as roman numeric numbers to
identify the nerves
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Olfactory (I) Nerve
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Sensory nerve
Sense of smell
Olfactory cells
converge to
become olfactory
nerve
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Optic (II) Nerve
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Sensory nerve
Ganglion cells in the
retina of each eye join
to form an optic nerve
Nerve of vision
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Oculomotor (III) Nerve
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Motor cranial nerve
Originates in the
midbrain
Supply extrinsic
eye muscles to
control movements
of the eyeball and
upper eyelid
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Trochlear (IV) Nerve
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Motor cranial
nerve
Smallest of the 12
cranial nerve
Controls
movement of the
eyeball
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Trigeminal (V) nerve
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Largest cranial nerve
Mixed nerve
Three branches:
1.
opthalmic
2.
maxillary
3.
mandibular
Deal with sensation
of touch, pain and
temperature
Motor axons supply
muscles of
mastication
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Abducens (VI) Nerve
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Motor cranial nerve
Originates from the
pons
Cause abduction of
the eyeball (lateral
rotation)
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Facial (VII) Nerve
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Mixed cranial nerve
Sensory portion
extends from the
taste buds of the
anterior two-thirds of
the tongue
Motor portion arises
from the pons and
deal with facial
expression
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Vestibulocochlear (VIII) Nerve
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Sensory cranial
nerve
Originates in the
inner ear
Vestibular branch
carries impulses
for equilibrium
Cochlear branch
carries impulses
for hearing
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Glossopharyngeal (IX) Nerve
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Mixed cranial nerve
Sensory axons carry
signals from the taste
buds of the posterior
one – third of the
tongue
Motor neurons arise
from the medulla and
deal with the release
of saliva
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Vagus (X) Nerve
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Vagus (X) Nerve (see table 14.4)
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Mixed cranial nerve
Distributed from the head and neck into the
thorax and abdomen
Sensory neurons deal with a variety of
sensations such as proprioception, and
stretching
Motor neurons arise from the medulla and
supply muscles of the pharynx, larynx, and
soft palate that are involved in swallowing
and vocalization
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Accessory (XI) Nerve
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Motor cranial nerve
Divided into cranial
accessory and spinal
accessory nerves
Supplies
sternocleidomastoid
and trapezius muscles
to coordinate head
movements
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Hypoglossal (XII) Nerve
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Motor cranial
nerve
Conduct nerve
impulses for
speech and
swallowing
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14_table_04a
14_table_04b
14_table_04c
14_table_04d
End of Chapter 14
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