striatum, or "striped body" consists of the
basal ganglia (basal nucleus) and the internal capsule. The basal ganglia is
made up of neurons, so it is gray matter. The internal
capsule is a group of tracts surrounded by myelinated axons, so
it is white. Because the internal capsule runs between the
caudate and lenticular nucleus of the basal ganglia, the
group of structures looks striped. The area is called the corpus striatum (striped body). The blood supply is from the striata artery. This thinly lined artery is calledy the "artery of stroke" because it ruptures easily if blood pressure is too high.
The basal ganglia, which is the
largest subcortical structure in the brain, is located near the thalamus. There are important extra pyramidal tract connections between the basal ganglia and the ventral lateral motor nucleus of the thalamus. The basal ganglia consists of the caudate nucleus and the lenticular nucleus, the latter consisting of the
putamen and the globus pallidus.
caudate nucleus is bounded on one side by
the lateral ventricle and is divided into a head, body and
tail. It contains endorphins, chemicals that, among
other things, produce a positive emotional state.
lenticular nucleus is also know as the
lentiform nucleus. Lentiform means lens-shaped in Latin.
It is located between the caudate nucleus and the island of
Reil with its anterior aspect being attached to the head of
the caudate nucleus. The putamen is the most lateral part of
the structure. When the globus pallidus, the more medial
part of the lenticular nucleus, is probed, sensations of
thirst are produced.
consider the claustrum to be part of the basal
amygdala, which is involved in
emotion, was once classified as part of the basal ganglia,
but is no longer categorized in this way. It is part of the limbic system. It is attached to the
tail of the caudate nucleus.
subthalamic nuclei and the substantia nigra
are both functionally related to the basal ganglia.
internal capsule lies between the
lenticular and caudate nuclei. It is a group of myelinated
fiber tracts including axons of
pyramidal and extrapyramidal upper motor neurons that connect the cortex to the cell bodies of lower motor neurons. Because so many
axons are clustered within the internal
capsule it is sometimes referred to as a bottleneck of fibers. This makes it a
very bad place to get a lesion.The internal capsule ends within
the cerebrum, just above the midbrain, but the axons that pass through it continue
down through brain stem and spinal cord. They descend through
the brainstem within two large bundles called the cerebral
peduncles or cruz cerebri.
striata, a branch of the middle
cerebral artery, takes blood to the internal capsule. As explained above the
striata is called the "artery of stroke" because it is very thin and prone
to hemorrhage. It supplies blood to many important nerve fibers as well as the nuclei of the basal ganglia.
Despite its close
proximity to the caudate nucleus and lenticular nucleus, the
internal capsule is not part of the basal ganglia. As stated
previously it forms part of the corpus
striatum along with the caudate and
term "rhinencephalon, which literally means "smell-brain,"
is used by many anatomists to refer to the limbic system.
Others make a distinction between these two terms
considering the olfactory tract and olfactory bulbs to be
part of the rhinencephalon but not of the limbic system.
Broca felt that the limbic lobe on the medial surface of the
hemispheres was the fifth lobe of the brain. The cortex
of the limbic system is barely convoluted.
It is phylogenetically older than the neo-cortex
which is heavily convoluted (gyri and sulci). The limbic lobe
consists of the hippocampal gyrus, cingulate gyrus,
subcollasal gyrus, and septal region..
The limbic system is sometimes called the
limbic lobe. This term is only descriptive; it
does not imply that this group of structures is comparable
to the lobes of the cerebral hemispheres which are
neo-cortex. The limbic structures are much older.
The limbic system
consists of both cortical and subcortical structures which
are located on the medial, inferior surfaces of the cerebral
hemispheres. Its components are phylogenetically related,
being some of the most ancient parts of the brain.
The cortical areas
classified as part of the limbic system include the
hippocampus, the cingulate gyrus, and the
hippocampus, is a gyrus found on the
medial edge of the temporal lobe. It is named for its shape,
as hippocampus means "sea horse." The hippocampus
is very close to the basal ganglia and to the lateral
ventricles. It is very important to memory especially in making new memories. It is an area where neurons die constantly and are replaced by new neurons. It is likely that this also occurs in other areas of the brain.
The cingulate gyrus is immediately superior to
the corpus callosum. Although it is part of the limbic system it is cortical, albeit less convoluted than neocortex. Its role is a higher one than non-cortical limbic areas. A study by Dr. Mahzarin Banaji of Harvard University and and Dr. Liz Phelps of New York University using functional MRI demonstrated that when people see the face of a person of a different race the amygdala reacts with alarm and fear. The amygdala is much more primative than the cingulate gyrus. The functional imaging studies have shown the cingulate gyrus and part of the prefrontal cortex (high level cognition) quickly decide that there is no danger and give the all clear. According to Kluger, 2008 racism begins in the lower limbic system. You can take an on-line test to check your reaction to races and traits.
subcallosal gyrus is immediately inferior to
the corpus callosum.
components of the rhinencephalon include the
olfactory pathways, the amygdaloid bodies, the mamillary bodies, the dorsal-medial and ventral-anterior nuclear groups of the
thalamus, parts of the
reticular formation, and the
olfactory pathway originates in the nasal
area. As it passes posteriorly to enter the temporal lobe at
the hippocampal gyrus the olfactory tract is immediately
superior to the optic tract.
mamillary bodies are also known as the
mamillary nuclei. They are connected to the hippocampus,
the thalamus and the fornix.
region includes both the septum pellucidum,
which is a double walled structure located between the
corpus callosum and the fornix, and the septal nuclei.
fornix is a group of fibers that arises
from each hippocampus, and project to the contralateral
hippocampus. It links the rhinencephalon to both the
thalamus and the hypothalamus. It is connected to the septal
nuclei, the mamillary bodies, and anterior nucleus of the
The limbic system
is involved in recent memory, emotion, motivation and
reinforcement. According to Love and Webb (1992) responses
mediated by the limbic system include pleasure, satiety,
guilt, punishment, inhibition, wakefulness, alertness,
excitement, and autonomic activity.
Based on the
behavioral correlates of lesions to the limbic system, it
may also be involved in cortical speech and language
behavior. The characteristics of this involvement are not known at this time.
Lesions to the
limbic system can also cause a variety of behaviors,
including aggression, extreme fearfulness, altered sexual
behavior, and changes in motivation. Damage specifically to
the hippocampus can affect memory and emotion.
The cortex inhibits the activity of the limbic system. When this is compromised by alcohol or drugs limbic behavior occurs.
Lesions on the
olfactory pathways can cause anosmia, which is a loss of the
sense of smell.
uncinate fit is an epileptic seizure
that is preceded by an olfactory hallucination.
There are three
major types of axons, or nerve fibers, in the brain.
Efferent fibers take messages from the
brain to the peripheral nervous system. They are almost
always motor fibers. They consist of the pyramidal tract (volitional movement) and the extrapyramidal tract (automatic movement e.g dancing). The extrapyramidal tract includes the basal ganglia, the substantia nigra, the cerebellum,and the motor nuclei of the thalamus) McCaffrey, 2009)
fibers take messages from the periphery
back to the brain. They are almost always sensory fibers.
fibers connect structures within the brain.
There are two types of interconnecting fibers:
fibers, and association
fibers connect the hemispheres of the
brain. The corpus callosum, the anterior
commissure, and the posterior
commissure are all composed of commissural
The corpus callosum, which is Latin for "large
body" is the major group of commissural fibers. It is
located some distance down inside the longitudinal cerebral
fissure, the split that separates the
hemispheres. It contains at least 200 million axons. Most of
these fibers connect mirror image sites on the two
hemispheres; axons might connect Brodmann's area 3 in the
parietal lobe of the right hemisphere to area 3 in the
parietal lobe of the left hemisphere. Not all of the
connections follow this pattern, however. For example, area
17 in the occipital lobe is connected to areas 18 and 19 of
the other hemisphere rather than to area 17.
One treatment for
severe epileptic seizures is commissurectomy, an operation that severs
the corpus callosum. Both Gazzaniga and Sperry conducted
experiments on split-brain patients and noted
differences between the functions of the left and right
cerebral hemispheres. The right hemisphere appears to be
involved in the intuitive, holistic processing of
information and in spatial reasoning. The left hemisphere,
on the other hand, seems to be more adapted for logic and
analytical reasoning. Most importantly for speech
pathologists, it was found that the left hemisphere plays a
dominant role in the speech and language abilities of most
Of course, both
hemispheres are apparently involved to some extent in any
The other two
groups of commissural fibers are called the
commissure and the posterior
commissure. Both are connected to the corpus
Many of the
commissural fibers that connect the two temporal lobes pass
through the anterior
commissure. The anterior commissure also
connects the temporal lobe to the amygdala and to the
occipital lobe in the other hemisphere. The anterior
commissure is used by neurosurgeons to locate the circle of
Almost all parts
of the cortex receive commissural fibers. The "hand area" of
the primary sensory strip is one of the few areas that does
fibers connect areas within the same
hemisphere. The cell bodies of association fibers are the
most prevalent type of neuron found in the brain.
association fibers connect areas that are located in
different lobes of the brain. For example, the arcuate
fascicules, which connects Broca's area in the
frontal lobe with Wernicke's area in the temporal lobe, is
composed of long association fibers. The term arcuate
fascicules means "arching bundle" in Latin. Lesions to this
particular bundle of long association fibers will cause
association fibers connect areas that are located in
the same lobe. For example, the fibers which connect
Heschl's gyrus with the auditory association areas are short
Location and Description
diencephalon consists of the
thalamus,epithalamus (includes pineal
gland), subthalamus and hypothalamus. Some sources classify the
diencephalon as part of the brain stem. This is not the view
of the majority and, for the purposes of this class, the
diencephalon should be considered part of the cerebrum.
the thalamus and hypothalamus are located in the center of
the brain at the level of the temporal lobe. They are very
well protected in this area.
The thalamus is
located below the caudate nucleus and the fornix and is
medial to the lenticular nucleus. It is composed of two
bodies which are separated from one another by the third
ventricle, with one lying in each hemisphere. The two
thalamic bodies are connected to one another by another part
of the thalamus, the massa intermedia or thalamic adhesion,
which makes up part of the ventricle.
includes the pineal gland and is involved autonomic
The subthalamus is
located ventral to the thalamus and is important for motor
movement. It has connections to the basal ganglia, thalamus
is a solid structure that is located immediately inferior to
the thalamus. Part of it is also anterior to the thalamus.
It forms the floor and part of the lateral walls of the
thalamus has been described as the switchboard for the
cortex. It receives information from the cerebellum, the
basal ganglia and from all sensory pathways with the
exception of the olfactory tract; it integrates the messages
and sends them on to the cortex for further processing.
bodies are composed of several different nuclei which are
divided from one another by lamina or thin walls of tissue. The
thalamic nuclei can be divided into four groups based on
their functions; the specific relay
nuclei, the association
nuclei, the non-specific
nuclei, and a subcortical
Five areas of the
thalamus are classified as the ventral nucleus complex.
These include the lateral geniculate
medial geniculate body, the ventral posterolateral
nucleus, the ventral posteromedial
nucleus, and the ventral lateral/ventral
anterior nuclei. All of the above receive sensory
information and are considered specific relay nuclei. The
ventral lateral and ventral anterior are motor relay
is part of the visual information pathway. It receives
information from the superior colliculus of the midbrain and
then relays it to the visual areas of the cortex in the
The medial geniculate
processes auditory information. It receives messages from
the inferior colliculus of the midbrain and transfers them
to the auditory areas of the cortex in the temporal lobe.
nucleus or VPL is involved in the processing of
somatosensory information. Messages come in from the
spinothalamic tract and the medial lemniscus and are passed
on to the somato-sensory cortex found in the parietal lobe.
This nucleus mediates sensations of pain and temperature as
well as proprioception.
nucleus or VPM also handles sensory information. It
receives input from the trigeminothalamic tract which it
passes on to the somato-sensory cortex of the parietal lobe.
Sensory information mediated by the trigeminal nerve is
processed in this area. For example, information about
toothaches is carried by this tract.
ventral lateral and ventral anterior
VL/VA are motor relay nuclei of the
thalamus. They process motor information. They get input
from the cerebellum and the basal ganglia and send output
to the motor and premotor cortex in the frontal lobe. As
lesions here will affect motor abilities, knowledge of these
nuclei is extremely important.
nuclei form connections between different
areas of the thalamus. They are involved in the integrating
and correlating processes that it performs. Three parts of
the thalamus are classified as association nuclei. These
include the pulvinar, the lateral posterior
nucleus, and the dorsal medial
pulvinar receives information from
other thalamic nuclei and from the superior colliculus. It
sends output to association areas in the parietal, occipital
and temporal lobes. The medial and lateral geniculate bodies
are located on top of the pulvinar but are not a part of it.
nucleus, or the LP, integrates input that it
receives from other thalamic nuclei.
medial nucleus receives input from the amygdaloid
bodies, the hypothalamus, and from other thalamic nuclei. It
sends information to the pre-frontal cortex. As this nucleus
connects parts of rhinencephalon with one of the motor areas
of the frontal lobe, it may be involved in the hypothesized
connection between the limbic system and communication.
Two parts of the
thalamus are categorized as non-specific nuclei. They are
intralaminar nucleus and part of the ventral anterior
nucleus, a motor relay.
to the intralaminar nucleus from the basal ganglia, the
reticular formation, and other thalamic nuclei. It sends
output to many different cortical areas.
ventral anterior and ventral lateral motor nuclei receive input from the basal ganglia and other
structures as well as from within the thalamus and send it
to the pre-motor ( planning/programming) and pre-frontal cortex of the frontal lobe.
The ventral lateral nucleus is part of the motor feedback
circuit between the cortex and the cerebellum.
One portion of the
thalamus, the reticular
nucleus, is classified as
subcortical. This name does not refer
to the location of the structure, as all parts of the
thalamus are subcortical according to this definition.
Instead, the reticular nucleus is labeled this way because
it does not project to the cortex. Its input is from
other thalamic nuclei and its output is also to thalamic nuclei.
hypothalamus is considered a nodal point in the pathways
mediating autonomic, emotional, endocrine, and somatic
functions. It is involved in the following specific
Release of some
hormones from the pituitary gland.
regulation of the body.
Intake of food and
nervous system pathways:
The hypothalamus is connected to reticular nuclei in the
brain stem that relay axons that control autonomic motor
functions. They are particularly involved with coughing and
vomiting reflexes as well as the reflexes involved in
expelling inspirated substances. The larynx spasms violently
in response to food (liquid or solid) getting into the
The hypothalamus is connected to the septum and the
amygdaloid bodies, which are part of the limbic system, via
a group of fibers called the stria terminalis. Reciprocal connections
exist between the hypothalamus and the thalamus, pituitary
gland, brain stem, and the temporal lobe.
is composed of several groups of nuclei and regions,
including the preoptic area, the supraoptic
nucleus, the dorsal-medial
nucleus, the ventral-medial
nucleus, the lateral region, and the
preoptic area is located in the anterior
portion of the hypothalamus. It is involved in temperature
regulation of the body, including the dilation of peripheral
blood vessels and sweating.
supraoptic area is inferior to the
preoptic area and just above the optic chiasm. It is
connected to the pituitary gland and regulates water intake
and output via control of the kidneys.
nucleus is also involved in water
regulation. Both the supraoptic area and the paraventricular
nucleus produce ADH or antidiuretic
dorsal-medial and the
involved in the control and expression of emotions like
rage, fear, and extreme anxiety.
lateral region contains the
apostat, which monitors the level
of glucose in the blood and sends messages to the stomach
provoking hunger when the blood sugar level drops to a
posterior region is involved in controlling
the body's temperature in cold environments. This area
produces shivering by causing the muscles of the body to
vibrate at a rate of between seven and thirteen Hertz. This
area also controls sexual behavior.
Lesions in the
hypothalamus may cause obesity, loss of the ability to
control body temperature, or loss of interest in sex. Damage
to the hypothalamus or to connections between the
hypothalamus and the pituitary gland may cause diabetes
insipidus which is far more serious than sugar diabetes, the
more common form of the disease.