Chapter 14:
The Brain and Cranial
Nerves
Copyright 2009, John Wiley & Sons, Inc.
Development of the Brain
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Three to four-week embryo: prosencephalon,
mesencephalon and rhombencephalon.
Five-week embryo: telencephalon
(cerebrum), diencephalon (thalamus,
hypothalamus and epithalamus),
mesencephalon (midbrain), metencephalon
(pons and cerebellum) and 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
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The cranium
The cranial
meninges: dura
mater, arachnoid
mater and pia
mater.
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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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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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Ventricles
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CSF-filled 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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Choroid plexuses- networks of capillaries in
the walls of the ventricles.
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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CSF from the lateral
ventricles →
interventricular
foramina → third
ventricle → cerebral
aqueduct → fourth
ventricle →
subarachnoid space
or central canal.
CSF is reabsorbed
into the blood by
arachnoid villi.
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Medulla Oblongata
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PyramidsBulges on the anterior
aspect of the medulla.
Formed by the large
corticospinal tracts that
pass from the cerebrum
to the spinal cord.
A common site for
decussation of
ascending and
descending tracts.
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Centers of the Medulla Oblongata
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Vital centers:
Cardiovascular centerRespiratory centerAlso includes centers for vomiting,
swallowing, sneezing, coughing and
hiccupping.
Houses five pairs of cranial nerves, VIII-XII.
Portion of the ventricle found here is the
fourth ventricle.
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Midbrain or Mesencephalon
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Extends from the pons to the diencephalon.
Part of the ventricle found here- cerebral
aqueduct.
Cerebral peduncles: axons of the corticospinal,
corticopontine and corticobulbar tracts.
Tectum- situated posteriorly and contains four
rounded elevations: two superior ones called
superior colliculi and two inferior ones called
inferior colliculi.
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Midbrain or Mesencephalon
Midbrain
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Substantia nigra: large area with dark
pigments. Help control subconscious muscle
activities. Loss of neurons here is associated
with Parkinson disease.
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Red nucleus: Help control voluntary
movements of the limbs.
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Contains cranial nerves III-IV.
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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- three pairs: superior,
middle and inferior. Attach cerebellum to the
brain stem.
Functions- coordinate movements, regulate
posture and balance.
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Thalamus
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Intermediate mass
Several nuclei:
Major relay station for
most sensory
impulses.
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Hypothalamus
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Inferior to the
thalamus.
Consists of
mammillary body,
median eminence,
infundibulum, and a
number of nuclei.
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Functions of the Hypothalamus
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Control of the ANS.
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Production of hormones
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Regulation of emotional and behavioral
patterns, eating and drinking, body
temperature, and circadian rhythms.
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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 induces sleep.
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The Cerebrum
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“seat of intelligence”
Cerebral cortex- gray matter.
GyriSulciLongitudinal fissureCerebral hemispheres-
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The Cerebrum
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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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Cerebral white matter
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Commissural tractsCorpus callosum:
Association tractsProjection tracts-
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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
Copyright 2009, John Wiley & Sons, Inc.
Functional Organization of the
Cerebral Cortex: Motor Areas
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Primary motor areaprecentral gyrus.
Broca’s speech arealeft cerebral
hemisphere.
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Functional Organization of the Cerebral
Cortex: Association Areas
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Somatosensory association area- posterior to
primary somatosensory area.
Visual association area- occipital lobe.
Auditory association area- temporal lobe.
Wernicke’s area- left temporal and parietal
lobes.
Prefrontal cortex- anterior portion of the
frontal lobe.
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Hemispheric Lateralization
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Brain Waves
Electroencephalogram:
Recording of the
electrical activity within
the brain.
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Alpha waves
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Beta waves
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Theta waves
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Delta waves
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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 nerves.
Origin: midbrain.
Controls movement of
the eyeball.
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Trigeminal (V) nerve
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Largest cranial nerve.
Mixed nerve.
Three branches:
opthalmic, maxillary
and 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
Vagus (X) Nerve
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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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End of Chapter 14
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