The
nervous system is your body's decision and communication center. The central nervous system (CNS) is
made of the brain and the spinal cord and the peripheral nervous system (PNS)
is made of nerves. Together they control every part of your daily life, from
breathing and blinking to helping you memorize facts for a test. Nerves reach
from your brain to your face, ears, eyes, nose, and spinal cord... and from the
spinal cord to the rest of your body. Sensory nerves gather information from
the environment; send that info to the spinal cord, which then speed the
message to the brain. The brain then makes sense of that message and fires off
a response. Motor neurons deliver the instructions from the brain to the rest
of your body. The spinal cord, made of a bundle of nerves running up and down
the spine, is similar to a superhighway, speeding messages to and from the
brain at every second.
The brain is made of
three main parts: the forebrain, midbrain, and hindbrain. The forebrain
consists of the cerebrum, thalamus, and hypothalamus (part of the limbic
system). The midbrain consists of the tectum and tegmentum. The hindbrain is
made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla
are referred to together as the brainstem.
The cerebrum or cortex is the largest part of the human brain, associated
with higher brain function such as thought and action. The cerebral cortex is
divided into four sections, called "lobes": the frontal lobe,
parietal lobe, occipital lobe, and temporal lobe. Here is a visual representation
of the cortex
What do each of these lobes do?
- Frontal
Lobe- associated with reasoning, planning, parts of speech, movement,
emotions, and problem solving
- Parietal
Lobe- associated with movement, orientation, recognition, perception of
stimuli
- Occipital
Lobe- associated with visual processing
- Temporal
Lobe- associated with perception and recognition of auditory stimuli,
memory, and speech
Note that the cerebral cortex is
highly wrinkled. Essentially this makes the brain more efficient, because it
can increase the surface area of the brain and the amount of neurons within it.
We will discuss the relevance of the degree of cortical folding (or
gyrencephalization) later
A deep furrow divides the cerebrum into two
halves, known as the left and right hemispheres. The two hemispheres look
mostly symmetrical yet it has been shown that each side functions slightly
different than the other. Sometimes the right hemisphere is associated with
creativity and the left hemispheres is associated with logic abilities Nerve
cells make up the gray surface of the cerebrum which is a little thicker than
your thumb. White nerve fibers underneath carry signals between the nerve cells
and other parts of the brain and body.
The neocortex occupies
the bulk of the cerebrum. This is a six-layered structure of the cerebral
cortex which is only found in mammals. It is thought that the neocortex is a
recently evolved structure, and is associated with "higher"
information processing by more fully evolved animals (such as humans, primates,
dolphins, etc). For more information about the neocortex,
The
cerebellum, or "little brain", is similar to the cerebrum in that it
has two hemispheres and has a highly folded surface or cortex. This structure
is associated with regulation and coordination of movement, posture, and
balance.
The cerebellum is assumed to be much older than
the cerebrum, evolutionarily. What do I mean by this? In other words, animals
which scientists assume to have evolved prior to humans, for example reptiles,
do have developed cerebellums. However, reptiles do not have neocortex.
The
limbic system, often referred to as the "emotional brain", is found
buried within the cerebrum. Like the cerebellum, evolutionarily the structure
is rather old.
This system contains
the thalamus, hypothalamus, amygdala, and hippocampus. Here is a visual
representation of this system, from a midsagittal view of the human brain:
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