Structure and
Functions of the Brain
The brain is divided into three main parts:
the hindbrain, the midbrain, and the forebrain.
The Hindbrain
The hindbrain is composed of
the medulla, the pons, and the cerebellum. The medullalies next to
the spinal cord and controls functions outside conscious control, such as
breathing and blood flow. In other words, the medulla controls essential
functions. The pons affects activities such as sleeping,
waking, and dreaming. The cerebellumcontrols balance and
coordination of movement. Damage to the cerebellum impairs fine motor skills,
so a person with an injury in this area would have trouble playing the guitar
or typing a term paper.
The Midbrain
The midbrain is the part of
the brain that lies between the hindbrain and the forebrain. The midbrain helps
us to locate events in space. It also contains a system of neurons that
releases the neurotransmitter dopamine. The reticular formation runs
through the hindbrain and the midbrain and is involved in sleep and
wakefulness, pain perception, breathing, and muscle reflexes.
The Forebrain
The biggest and most complex part of the brain
is the forebrain, which includes the thalamus, the hypothalamus,
the limbic system, and the cerebrum.
Thalamus
The thalamus is a sensory way
station. All sensory information except smell-related data must go through the
thalamus on the way to the cerebrum.
Hypothalamus
The hypothalamus lies under
the thalamus and helps to control the pituitary gland and the autonomic nervous
system. The hypothalamus plays an important role in regulating body temperature
and biological drives such as hunger, thirst, sex, and aggression.
Limbic System
The limbic
system includes the hippocampus, the amygdala,
and the septum. Parts of the limbic system also lie in the thalamus and the
hypothalamus. The limbic system processes emotional experience. The amygdala
plays a role in aggression and fear, while the hippocampus plays a role in
memory.
Cerebrum
The cerebrum,
the biggest part of the brain, controls complex processes such as abstract
thought and learning. The wrinkled, highly folded outer layer of the cerebrum
is called the cerebral cortex. The corpus callosum is a band
of fibers that runs along the cerebrum from the front of the skull to the back.
It divides the cerebrum into two halves, or hemispheres. Each hemisphere is
divided into four lobes or segments: the occipital lobe, the parietal lobe, the
temporal lobe, and the frontal lobe:
·
The occipital lobe contains the primary visual cortex, which
handles visual information.
·
The parietal lobe contains the primary somatosensory cortex,
which handles information related to the sense of touch. The parietal lobe also
plays a part in sensing body position and integrating visual information.
·
The temporal lobe contains the primary auditory cortex, which is
involved in processing auditory information. The left temporal lobe also
contains Wernicke’s area, a part of the brain involved in language
comprehension.
·
The frontal lobe contains the primary motor cortex, which
controls muscle movement. The left frontal lobe contains Broca’s area,
which influences speech production. The frontal lobe also processes memory,
planning, goal-setting, creativity, rational decision making, and social
judgment.
Brain Hemispheres
Lateralization refers to the
fact that the right and left hemispheres of the brain regulate different
functions. The left hemisphere specializes in verbal processing tasks such as
writing, reading, and talking. The right hemisphere specializes in nonverbal
processing tasks such as playing music, drawing, and recognizing childhood
friends.
Roger Sperry, Michael Gazzaniga,
and their colleagues conducted some of the early research in lateralization.
They examined people who had gone through split-brain surgery, an
operation done to cut the corpus callosum and separate the two brain
hemispheres. Doctors sometimes use split-brain surgery as a treatment for
epileptic seizures.
Control of the Body
Because of the
organization of the nervous system, the left hemisphere of the brain controls
the functioning of the right side of the body. Likewise, the right hemisphere
controls the functioning of the left side of the body.
Vision and hearing
operate a bit differently. What the left eye and right eye see goes to the
entire brain. However, images in the left visual field stimulate receptors on
the right side of each eye, and in-formation goes from those points to the
right hemisphere. Information perceived by the right visual field ends up in
the left hemisphere.
In the case
of auditory information, both hemispheres receive input about what each ear
hears. However, information first goes to the opposite hemisphere. If the left
ear hears a sound, the right hemisphere registers the sound first.
The fact
that the brain’s hemispheres communicate with opposite sides of the body does
not affect most people’s day-to-day functioning because the two hemispheres
constantly share information via the corpus callosum. However, severing the
corpus callosum and separating the hemispheres causes impaired perception.
Split-Brain Studies
If a
researcher presented a picture of a Frisbee to a split-brain patient’s right
visual field, information about the Frisbee would go to his left hemisphere.
Because language functions reside in the left hemisphere, he’d be able to say
that he saw a Frisbee and describe it. However, if the researcher presented the
Frisbee to the patient’s left visual field, information about it would go to
his right hemisphere. Because his right hemisphere can’t communicate with his
left hemisphere when the corpus callosum is cut, the patient would not be able
to name or describe the Frisbee.
The same
phenomenon occurs if the Frisbee is hidden from sight and placed in the
patient’s left hand, which communicates with the right hemisphere. When the
Frisbee is in the patient’s left visual field or in his left hand, the patient
may not be able to say what it is, although he would be able to point to a
picture of what he saw. Picture recognition requires no verbal language and is
also a visual-spatial task, which the right hemisphere controls.
REFERENCE
SparkNotes Editors. “SparkNote on Neurons, Hormones, and the
Brain.” SparkNotes LLC. 2005. http://www.sparknotes.com/psychology/psych101/thebrain/
(accessed November 5, 2016).
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