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 memorise 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. Afferent neurones
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. Efferent neurones 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 oblongata. Often the pons, and medulla
oblongata are referred to together as the brainstem.
The Cerebrum: 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.
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 gyrencephalisation) 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 hemisphere is associated
with logic abilities. The corpus callosum is a bundle of axons which
connects these two hemispheres.
Nerve cells
make up the gray surface of the cerebrum which is a little thicker than your
thumb. White nerve fibres 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).
The Cerebellum: 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.
Limbic System: 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.
Thalamus- a
large mass of gray matter deeply situated in the forebrain at the topmost
portion of the diencephalon. The structure has sensory and motor functions.
Almost all sensory information enters this structure where neurons send that
information to the overlying cortex. Axons from every sensory system (except
olfaction) synapse here as the last relay site before the information reaches
the cerebral cortex.
Hypothalamus -
part of the diencephalon, ventral to the thalamus. The structure is involved in
functions including homeostasis, emotion, thirst, hunger, circadian rhythms,
and control of the autonomic nervous system. In addition, it controls the
pituitary.
Brain Stem: Underneath the limbic system is the brain
stem. This structure is responsible for basic vital life functions such as
breathing, heartbeat, and blood pressure. Scientists say that this is the
"simplest" part of human brains because animals' entire brains, such
as reptiles (who appear early on the evolutionary scale) resemble our brain
stem.
Midbrain/
Mesencephalon - the rostral part of the brain stem, which includes the tectum
and tegmentum. It is involved in functions such as vision, hearing, eye movement,
and body movement. The anterior part has the cerebral peduncle, which is a huge
bundle of axons travelling from the cerebral cortex through the brain stem and
these fibres (along with other structures) are important for voluntary motor
function.
Pons- part
of the metencephalon in the hindbrain. It is involved in motor control and
sensory analysis... for example, information from the ear first enters the
brain in the pons. It has parts that are important for the level of
consciousness and for sleep. Some structures within the pons are linked to the
cerebellum, thus are involved in movement and posture.
Medulla
Oblongata - this structure is the caudal-most part of the brain stem, between
the pons and spinal cord. It is responsible for maintaining vital body
functions, such as breathing and heart rate.
