two hemispheres of the brain are covered by a layer of cells
called the cortex. (Cortex means "bark" in Latin.) The
surface of the cortex is ridged, as it is made up of
gyri and sulci.
gyrus is a raised fold of tissue.
sulcus is a groove between two gyri.
A particularly deep sulcus is called a
fissure as in the fissure of Rolando or the central sulcus which separates the frontal and parietal lobes. So sometimes the labels can be interchangeable.
A convolution includes both a gyrus and
Because it is
convoluted, a large amount of cortical tissue fits into a
relatively small area.
basal ganglia or basal nuclei is made up of two structures, the
caudate nucleus and the
caudate nucleus is bounded on one side by
the lateral ventricle and is divided into a head, body and
nucleus is a lens-shaped structures that has
two components: the globus pallidus and the putamen. The
putamen is the more lateral of the two. The basal ganglia is a very important part of the extrapyramidal tract. It is the basal ganglia that is responsible for a natural and spontaneous smile, which is quite different from the phony smiles we see in photographs, which originate in the cortex and are transmitted on the pyramidal tract which is responsible for volitional movement.
internal capsule lies between the
lenticular and caudate nuclei. It is a group of myelinated
(therefore white) afferent and descending fiber tracts including the
pyramidal tract that connects the cortex to other parts of
the central nervous system. The pyramidal tract begins as a corona radiata
(radiating crown) from motor cells in the premotor, primary
motor (where most of the motor cells originate), and primary sensory areas of the cortex and converges
into the internal capsule.The capsule itself ends within
the cerebrum, but the axons that pass through it continue
down to the brain stem, and spinal cord.
Because so many
axons join together to pass through this area, the internal
capsule is sometimes referred to as a bottleneck of fibers.
Despite its close
proximity to the caudate nucleus and lenticular nucleus, the
internal capsule is not part of the basal ganglia.
capsule and the basal ganglia are collectively referred to
as the corpus striatum.
This is the most ancient and
primitive part of the brain. It is sometimes called the
rhinencephalon as the term "rhino" means
nose in Latin and some of this area is dedicated to the
processing of olfactory stimuli.
The limbic system
is involved, among other things, with emotion and
memory, particularly new memories.
This subcortical structure sits
within the brain at the level of the temporal lobe. It is
well protected in this location.
The thalamus is
made up of three parts, including two thalamic bodies and
the tissue that connects them which is called the
intermedia, or the interthalamic
adhesion. The thalamic bodies are separated
by the third ventricle, one of the spaces in the brain that
is filled with cerebral spinal fluid. The massa intermedia
lies within the third ventricle.
receives and organizes sensory information from the
periphery. Messages from all sensory modalities with the
exception of smell pass through the thalamus on their way to
cortical centers and other structures for further
processing. (Information about smell travels directly to the
information, including touch and kinesthesia passes from the
thalamus to the parietal lobe.
information comes into the thalamus from the
colliculi of the midbrain. It is processed by
the medial geniculate
bodies of the thalamus before being sent to
the temporal lobe. In the temporal lobe, it first arrives at
Heschl's gyrus, which is the primary auditory
From there it is sent to association areas for further
comes into the thalamus from the superior
colliculi of the midbrain. It is processed by
the lateral geniculate
bodies of the thalamus and sent to the
in the occipital lobe. The visual association areas, also in
the occipital lobe, further analyze the information. There are two very important motor relay nuclei in the thalamus: the ventral lateral and ventral anterior. These nuclei receive signals from the basal ganglia and in turn send signals to the motor cortex. They are part of the extrapyramidal tract..
Lesions in the
thalamus can cause a type of aphasia.
hypothalamus is located immediately below the thalamus. Part
of it is also slightly anterior to the thalamus. The
hypothalamus regulates the functioning of the pituitary
gland, so it controls basic biological functions like
appetite, body temperature, sex drive, etc. The hypothalamus
is the part of the brain that makes you shiver when you are
cold and sweat when you are hot. A part of the hypothalamus
monitors the level of glucose in the blood and, when it
notices a significant decrease, it sends messages to the
stomach producing sensations of hunger.
Insipidus, the most serious type of diabetes,
is caused by lesions in the hypothalamus, or between the
hypothalamus and the pituitary gland.
While the thalamus
is mainly an input structure, sending messages to higher brain
areas, the hypothalamus is an output structure, sending
messages to glands and other parts of the body.
Stem and Cerebellum
is the most superior part of the brain stem. The
quadrigemina, the red nucleus, the substantia
nigra, the cerebral
peduncles, and the cell bodies of two cranial
nerves are located in the midbrain.
quadrigemina consists of the tectum which is the roof of the
brain stem, and of four protrusions located on the tectum
which are called colliculi.
colliculi are involved in vision. They relay
information to the lateral geniculate bodies of the
colliculi are involved in hearing. They relay
information to the medial geniculate bodies of the
nucleus is part of the extrapyramidal tract
and connects the cerebellum to the thalamus and spinal cord.
substantia nigra is a group of dark colored
cell bodies which produce dopamine. It is also part of the
peduncles connect the pons to the cerebrum.
The nuclei of
cranial nerve III, the oculomotor cranial nerve, and of
cranial nerve IV, the trochlear cranial nerve which both
provide innervation for eye movement are also located in the
word "pons" is Latin for "bridge." Fibers found there
connect the brain stem to the cerebellum.
The cell bodies
for cranial nerves V and VI, the trigeminal and abducens, as
well as nuclei of cranial nerve VII, the facial nerve, are
structure, which is the most inferior part of the brain
stem, sits on top of the superior end of the spinal cord.
Because it has a rounded shape, it was once called "the
bulb." (The term "bulbar" refers to the brain stem.) It is
involved in circulation and respiration and has several important
pyramids, which mark the
decussation of the pyramidal tract, lie on either side of
the median fissure.
olivary nuclei are posterior to the
pyramids. They are involved in the processing and relay of
The cell bodies of
cranial nerves VIII-XII are located here. Some of the nuclei
of CN VII are also found in the medulla.
"cerebellum" means "little brain" in Latin. This structure
has two hemispheres, each of which is divided into lobes and
is covered by the cortex. It is one of the newer parts of
the brain and is very important for the production of
speech. It organizes muscle activity and plays a role in the
coordination of fine motor movements and also in balance.
receives both motor and sensory input, and so is the center
of a feedback loop. All motor messages that
leave the brain also go to the cerebellum, including
information about the strength of the impulses. The
cerebellum integrates motor output so that movements are
smooth and coordinated. Muscle spindles, joints and tendons
send information about movement back to this area. The
cerebellum then relays these messages to the cortex,
completing the feedback loop.
Lesions here will
cause cerebellar or ataxic
dysarthria which involves jerky, uncoordinated
movements of the speech musculature.
The cerebellum is
connected to the brain stem by three pairs of tracts called
The Spinal Cord
spinal cord contains the cell bodies of the spinal nerves as
well as their afferent and efferent fibers. It begins below
a large opening in the base of the skull called the
and extends downward, surrounded and protected by the
vertebral column. It does not continue through the whole
length of the column, terminating instead slightly above the
level of the waist. The part of the vertebral column that
lies below the spinal chord is called the cauda
which is Latin for horse's tail.