The cerebrum is divided into two halves—the left and right cerebral hemispheres.
The hemispheres are connected by nerve fibers that form a bridge (called the
corpus callosum) through the middle of the brain. Each hemisphere is further
divided into lobes:
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Frontal lobe |
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Parietal lobe |
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Occipital lobe |
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Temporal lobe |
Each lobe has specific functions, but for most activities, several areas of
different lobes in both hemispheres must work together.
The frontal lobes are the largest of the four lobes
and are responsible for many different functions. The frontal lobes are considered
our emotional control center and home to our personality. It's involved in motor
function, problem solving, spontaneity, memory, language, initiation, judgment,
impulse control, and social and sexual behavior. The frontal lobes are extremely
vulnerable to injury due to their location at the front of the cranium,
proximity to the sphenoid wing, and their large size.
The frontal lobes are located at the front of each cerebral hemisphere and positioned
in front of or anterior to the parietal lobes and above and anterior to the temporal
lobes. It's separated from the parietal lobe by the primary motor cortex, which
controls voluntary movements of specific body parts associated with the precentral
gyrus. The prefrontal cortex plays an important part in memory, intelligence,
concentration, temper and personality.
The premotor cortex is a region found beside the primary motor cortex. It's
involved in planning actions, along with the basal ganglia, and refining
movements based upon sensory input. It guides eye and head movements and a
person’s sense of orientation.
There are important asymmetrical differences in the frontal lobes. The left
frontal lobe is involved in controlling language related movement, whereas the
right frontal lobe plays a role in non-verbal abilities. The frontal lobes are
also thought to play a part in spatial orientation.
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One of the most common effects of frontal damage can be a dramatic change in
social behavior. A persons personality can undergo significant changes after an
injury to the frontal lobes, especially when both lobes are involved. There are
some differences in the left versus right frontal lobes in this area. Left
frontal damage usually manifests as pseudodepression and right frontal damage as
pseudopsychopathic.
It also controls motor skills such as voluntary and coordinated movement and
speech. Broca's area, important in language production, is found in the frontal
lobe, usually on the left side. Broca's area is next to the region that controls
the movement of facial muscles, tongue, jaw and throat. If this area is damaged,
a person will have difficulty producing the sounds of speech, because of the
inability to move the tongue or facial muscles to form words. A person with
Broca's aphasia can still read and understand spoken language, but has
difficulty speaking and writing.
The parietal lobes interpret and integrate sensory
information simultaneously from different modalities. It controls tactile sensation,
response to internal stimuli, sensory comprehension, some language, reading, and
some visual functions. This allows a person’s memory and the new sensory information
received and gives meaning to objects, particularly determining spatial sense
and navigation.
The occipital lobes are located at the back of the brain and
enable humans to receive and process visual information. They influence how humans
process colors and shapes. The occipital lobe on the right interprets visual signals
from the left visual space, while the left occipital lobe performs the same function
for the right visual space.
The temporal lobes are involved in auditory
processing and are home to the primary auditory cortex. It's also involved in the
processing of semantics in both speech and vision, plus some behavior. It also
contains the hippocampus and plays a key role in the formation of long-term memory.
These lobes are located on each side of the brain at about ear level, and can be
divided into two parts. One part is on the bottom ventral of each hemisphere,
and the other part is on the side or lateral of each hemisphere. An area on the
right side is involved in visual memory and helps humans recognize objects and
peoples' faces. An area on the left side is involved in verbal memory and helps
humans remember and understand language. The rear of the temporal lobe enables
humans to interpret other people's emotions and reactions.
There's a region in the left temporal lobe called Wernicke's area. Damage to
this area causes Wernicke's aphasia. An individual can make speech sounds, but
they are receptive aphasia or meaningless because they don't make any sense.
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The limbic system is a set of evolutionarily basic or primitive brain structures
located on top of the brainstem and buried under the cortex. The limbic system is
another subcortical structure that consists of structures and nerve fibers located
deep within the cerebrum. This system connects the hypothalamus with other areas of
the frontal and temporal lobes, including the amygdala and hippocampus.
Limbic system structures are involved in many of our emotions and motivations,
particularly those that are related to survival. The limbic system controls the
experience and expression of emotions, as well as some automatic functions of the
body.
By producing emotions (such as fear, anger, pleasure, and sadness), the
limbic system enables people to behave in ways that help them communicate and
survive physical and psychologic upsets. The limbic system is also involved in
feelings of pleasure that are related to our survival, such as those experienced
from eating and sex.
The two large limbic system structures, the amygdala
and hippocampus have important roles in memory.
The amygdala is responsible for determining what
memories are stored and at what location in the brain. It's thought that this
determination is based on how huge an emotional response an event invokes.
The hippocampus sends memories out to the appropriate
part of the cerebral hemisphere for long-term storage and retrieves them when
necessary. The hippocampus is also involved in the formation and retrieval of
memories, and its connections through the limbic system help connect those memories
to the emotions experienced when the memories form.
Damage to the amygdala or hippocampus may result in an inability to form new memories.
Part of the forebrain known as the diencephalon is also
included in the limbic system. The diencephalon is located beneath the cerebral hemispheres
and contains the thalamus and
hypothalamus.
The thalamus is involved in sensory perception and
regulation of motor functions. It connects areas of the cerebral cortex that are
involved in sensory perception and movement with other parts of the brain and spinal
cord that also have a role in sensation and movement. The hypothalamus is a very
small but important component of the diencephalon. It plays a major role in regulating
hormones, the pituitary gland, body temperature, the adrenal glands, and many other
vital activities.
The thalamus is a relay and preprocessing station for the many nerve impulses that
pass through it. Impulses carrying similar messages are grouped in the thalamus,
then relayed to the appropriate brain areas.
The hypothalamus is the main neural control center
in the brain that controls endocrine glands. The pituitary gland lies just below
the hypothalamus and is a small endocrine gland that secretes a variety of hormones
which are organic chemicals that regulate the body's physiological processes. When
the hypothalamus detects certain body changes, it releases regulating factors or
chemicals that stimulate or inhibit the pituitary gland. The pituitary gland then
releases or blocks various hormones. Because of this close association between the
nervous and endocrine systems, together they are called the neuroendocrine system.
The hypothalamus also regulates visceral or organ-related activities, food and
fluid intake, sleep and wake patterns, sex drive, emotional states, and
production of antidiuretic hormone (ADH) and oxytocin. The pituitary gland
produces both these hormones.
The epithalamus is the most posterior or back portion of the diencephalon. It
contains a vascular network involved in cerebrospinal fluid production.
Extending from the epithalamus posteriorly is the pineal body, or pineal gland.
Its function is thought to control body rhythms.
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| Limbic System Structures: |
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Amygdala
An almond shaped mass of nuclei involved in emotional responses,
hormonal secretions, and memory. |
Cingulate Gyrus
A fold in the brain involved with sensory input concerning emotions and
the regulation of aggressive behavior. |
Fornix
An arching, fibrous band of nerve fibers that connect the hippocampus to
the hypothalamus. |
Hippocampus
A small nub that acts as a memory indexer sending memories out to the
appropriate part of the cerebral hemisphere for long-term storage and
retrieving them when necessary. |
Hypothalamus
About the size of a pearl, this structure directs a multitude of
important functions. It wakes you up in the morning, and gets the
adrenaline flowing. The hypothalamus is also an important emotional
center, controlling the molecules that make you feel exhilarated, angry,
or unhappy. |
Olfactory Cortex
It receives sensory information from the olfactory bulb and is involved
in the identification of odors. |
Thalamus
A large, dual lobed mass of gray matter cells that relay sensory signals
to and from the spinal cord and the cerebrum. |
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