The Diencephalon
The diencephalon is located near the midline of
the brain, above the midbrain. Like the cerebral
cortex, the diencephalon develops from the
forebrain vesicle (the prosencephalon) - yet it is
more primitive than the cerebral cortex, and lies
underneath it.
The diencephalon surrounds
the 3rd ventricle and
contains the thalamic
structures.
The Diencephalon
 The thalamus functions as a relay station for all sensory
impulses to the cerebral cortex (except smell, which
belong to the hypothalamus). Pain, temp, touch, and
pressure are all relayed to the thalamus en route to the
higher centers of the cerebral cortex.
 While not precisely localized here (that occurs in the
cerebral cortex), all of these peripheral sensations are
processed in the thalamus in conjunction with their
attendant memories and the emotions they evoke.
The
Diencephalon
The epithalamus is superior and posterior to the
thalamus.
 It consists of the pineal gland (secretes melatonin)
and habenular nuclei (emotional responses to
odors).
epithalamus
thalamus
 More melatonin is
secreted in darkness
than light, and it is
thought to promote
sleepiness and help
regulate our
biological clocks.
•
The
Diencephalon
The hypothalamus controls many homeostatic
functions:
– It controls the Autonomic Nervous System (ANS).
– It coordinates between NS and endocrine systems.
– It controls body temperature (measured by blood
thalamus
flowing through it).
– It regulates hunger/thirst
and feelings of satiety.
– It assists with the internal
circadian clock by
regulating biological activity.
hypothalamus
The Cerebrum
The cerebral cortex is the “seat of our intelligence”–
it’s because of neurons in the cortex that we are
able to read, write, speak, remember, and plan our
life.
The cerebrum consists of an outer cerebral cortex,
an internal region of cerebral
white matter, and gray
matter nuclei deep within
the white matter.
The Cerebrum
During embryonic development, the grey matter of
the brain develops faster than the white matter the cortical region rolls and folds on itself.
Convolutions and grooves are created in the cortex
during this growth process.
 The folds are called gyri, the deepest of which are known
as fissures; the
shallower grooves between
folds are termed sulci.
The
Cerebrum
The prominent longitudinal fissure separates
the cerebrum into right and left cerebral
hemispheres. The central sulcus further divides
the
anterior frontal
lobe from the
more posteriorly
situated parietal lobe.
Note the precentral gyrus
and postcentral gyrus of
those two lobes.
The Cerebrum
 The precentral gyrus - located immediately anterior to
the central sulcus in the anterior lobe - contains the
primary motor area of the cerebral cortex. Another
major gyrus, the postcentral gyrus, which is located
immediately posterior to the central sulcus in the
parietal lobe, contains the primary somatosensory area
of the cerebral cortex.
 The parieto-occipital sulcus separates the parietal lobe
from the posterior-most occipital lobe.
The Cerebrum
The lateral cerebral sulcus (fissure) separates
the frontal lobe from two laterally placed
temporal lobes, hanging like ear muffs off the
sides. A fifth part of the cerebrum, the insula,
cannot be seen at the surface of the brain
because it lies within the lateral
cerebral sulcus, deep to
the parietal, frontal,
and temporal
lobes.
The Cerebrum
The lobes of the cerebrum correspond to the
bones of the braincase which bear the same
names.
parietal
parietal
frontal
temporal
occipital
temporal
occipital
parietal
occipital
temporal
frontal
frontal
The Cerebrum
Brodmann’s areas are numbered regions of cortex
that have been “mapped” to specific cognitive
functions.
 Sensory areas of cerebral cortex are involved in
perception of sensory information.
 Motor areas control execution of voluntary
movements.
 Association areas deal with more complex integrative
functions such as memory, personality traits, and
intelligence.
The Cerebrum
Brodmann’s areas: Numbered Regions of Cortical
tissue.
The
Cerebrum
The primary somatosensory area (areas 1, 2, and 3
– located in the postcentral gyrus of each parietal
lobe) receives nerve impulses for, and consciously
perceives the somatic sensations of touch,
pressure, vibration, itch, tickle, temperature
(coldness and warmth), pain, and proprioception
(joint and muscle position).
 Each point within the area “maps” impulses from a
specific part of the body (depending on the number of
receptors present there rather than on the size of the
body part).
The Cerebrum
For example, a larger region of the
somatosensory area receives impulses from the
lips and fingertips than from the thorax or hip.
 This distorted somatic sensory
map of the body is known as the
sensory homunculus (little man).
 This allows us to pinpoint
(feel exactly) where somatic
sensations originate.
The Cerebrum
• The primary motor
area (area 4 – located in the
precentral gyrus of the frontal lobe) controls
voluntary contractions of specific
muscles or groups of muscles.
– The motor cortex also has a
homunculus map, with
more cortical area devoted
to muscles involved in
skilled, complex, or
delicate movement.
The Cerebrum
The 1 visual area is located at the posterior tip of
o
the occipital lobe mainly on the medial surface
The 1o gustatory area is located just inferior to the
1o somatosensory area
The 1o auditory area is
in the superior part of the
temporal lobe
The 1o olfactory area is in
the inferomedial temporal lobe
The Cerebrum
The cerebral white matter consists primarily of
myelinated axons in three types of tracts.
 Association tracts contain axons that conduct nerve
impulses between gyri in the same hemisphere.
 Commissural tracts conduct nerve impulses between
corresponding gyri from one hemisphere to another.
 Projection tracts convey impulses to lower parts of the
CNS (thalamus, brain stem, or spinal cord) or visa versa.
The
Cerebrum
The corpus callosum is one of the three important
groups of commissural tracts (the other two being
the anterior and posterior commissures) – it is a
thick band of axons that connects corresponding
areas of the two hemispheres.
 Through the corpus callosum, the left motor cortex
(which controls the right
body) is linked to
the right motor
cortex (which
controls the left body).
The Cerebrum
The outer surfaces of the gyri are not the only
areas of gray matter in the cerebrum. Recall
that the telencephalon consists of the cortex,
and also the basal nuclei.
 The basal nuclei are conspicuous centers of cell
bodies deep in the cortex. The 3 basal nuclei help
initiate and terminate movements, suppress
unwanted movements, and regulate muscle tone.
The
Cerebrum
 The basal nuclei also control subconscious contractions of
skeletal muscles. Examples include automatic arm swings
while walking and true laughter in response to a joke.
The Limbic System
Encircling the upper part of the brain stem and
the corpus callosum is a ring of structures on
the inner border of the cerebrum
and floor of the
diencephalon that
constitutes the
limbic system.
The
Limbic
System
 The limbic system does not represent any one part of the
brain – it is more a functional system composed of parts of
the cerebral cortex, diencephalon, and midbrain.
• The limbic system is sometimes called the
“emotional brain” because it plays a primary role in
promoting a range of emotions, including pleasure,
pain, docility, affection, fear, and anger.
– Together with parts of the cerebrum, the limbic system
also functions in memory.

Hemispheric Lateralization
Although the brain is almost symmetrical on its right and
left sides and shares performance of many functions, there
are subtle anatomical and physiological differences
between the two hemispheres.
 Each
hemisphere specializes in performing certain unique functions,
a feature known as hemispheric lateralization. Despite some
dramatic differences, there is considerable variation from one
person to another. Also, lateralization seems less pronounced in
females.

Hemispheric Lateralization
In most people, the left hemisphere is more important for
reasoning, numerical and scientific skills, spoken and
written language, and the ability to use and understand sign
language.

Conversely, the right hemisphere is more specialized for
musical and artistic awareness; spatial and pattern
perception; recognition of faces and emotional content of
language; discrimination of different smells; and generating
mental images of sight, sound, touch, and taste.
Brain Waves
The billions of communicating brain neurons
constantly generate detectable signals called brain
waves. Those we can more easily measure are
generated by neurons close to the brain surface,
mainly neurons in the cerebral cortex.
 Electrodes placed on the
forehead and scalp can be
used to make a record called
an electroencephalogram.
Brain Waves
Summing waves of different frequency produces
some characteristic, and diagnostic patterns.
 Alpha (10–12 Hz (cycles/sec) waves are present when
awake but disappear during sleep.
 Beta (14–30 Hz) waves are present with sensory input
and mental activity when the nervous system is active.
 Theta (4–7 Hz) waves indicate emotional stress or a brain
disorder.
 Delta (1–5 Hz) waves appear only during sleep in adults
but indicate brain damage in an awake adult.
Brain Waves
• Electroencephalograms are useful both in studying
normal brain functions, such as changes that occur
during sleep, and in diagnosing a variety of brain
disorders, such as epilepsy, tumors, trauma,
hematomas, metabolic abnormalities, sites of trauma,
and degenerative diseases.
– The EEG is also utilized to determine if “life” is
present, that is, to establish or confirm that brain
death has occurred.
The Twelve
Cranial
Nerves
Cranial Nerves
Cranial Nerves
Designation
Spinal
Cranial
C1-8, T1-12, L1-5, S1-5,
Roman Numerals
Co1
I – XII
Number
31 pairs
12 pairs
Origin
Spinal cord
Brain
Number of roots
2 - a dorsal and a ventral
root
Contents
Mixed
Target
Limbs/Trunk
Single root
Most mixed; some
sensory only
All in the Head/Neck
(vagus n leaves)
Spinal and cranial nerves are compared in this table.

Cranial Nerves
The major functions of the 12 pairs of cranial nerves are
detailed in the
following
slides.
This is a picture of a masterful dissection, showing
the cranial nerves in-situ (as they are “in place”).
Cranial Nerves
CN I is the
olfactory nerve
(sense of smell).
Cranial Nerves
CN II is the optic
nerve (sense of
sight).
Cranial Nerves
CN III, IV, and VI innervate the extraocular
muscles that allow us to move our eyes.
 CN III also supplies motor
input to our eyelid
muscles and
facilitates
pupillary
constriction.
Cranial Nerves
CN V is the trigeminal nerve (the major
sensory nerve of the face).
 It has three large
branches, each of
which supplies an
area of the face:
•ophthalmic
•maxillary
•mandibular
Cranial Nerves
• CN VII is the facial nerve. It has 5 large somatic
branches which innervate the muscle of
facial expression. It also carries some
taste sensations
(anterior 2/3 of tongue).
– Paralysis of
CN VII is called
Bell’s Palsy and leads
to loss of ability to close
the eyes and impairment of
taste and salivation.
Cranial Nerves
CN VIII is the vestibulocochlear nerve. From
the inner ear, the vestibular component carries
information on balance, while the cochlear
component enables hearing.
 Damage of CN VIII causes vertigo, ringing in the
ears, and/or deafness.
Cranial
Nerves
CN IX is the glossopharyngeal nerve. This nerve
carries some taste sensations as well as ANS
impulses to salivary glands and the
mechanoreceptors of the carotid body and
carotid sinus (senses changes in BP).
Cranial Nerves
CN X is the
vagus nerve
(“the
wanderer”),
which carries
most of the
parasympathetic
motor efferents
to the organs of
the thorax and
abdomen.
Cranial
Nerves
CN XI is the spinal accessory nerve. This nerve
supplies somatic motor innervation to the
Trapezius and Sternocleidomastoid muscles.
Cranial
Nerves
CN XII is the glossopharyngeal nerve. This is a
very large nerve (a lot of resources) to be
devoted solely to the tongue – it takes a lot
more coordination than you might guess to
chew, talk, and swallow without injuring our
tongue.
End
of
Chapter
14
Copyright 2012 John Wiley & Sons, Inc. All rights reserved.
Reproduction or translation of this work beyond that permitted in
section 117 of the 1976 United States Copyright Act without
express permission of the copyright owner is unlawful. Request for
further information should be addressed to the Permission
Department, John Wiley & Sons, Inc. The purchaser may make
back-up copies for his/her own use only and not for distribution or
resale. The Publisher assumes no responsibility for errors,
omissions, or damages caused by the use of these programs or
from the use of the information herein.