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Home : Other Subjects : Psychology Study Guides : 101 : Neurons, Hormones, and the Brain : Structure and Functions of the Brain
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Structure and Functions of the Brain
The Hindbrain
The hindbrain is composed of the medulla, the pons, and the
cerebellum. The medulla lies 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 cerebellum controls 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.
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