Brain Structures and Their Functions

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: 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. (Go here for more information about cortical folding)

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. 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 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, click here.

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. Go here for more discussion of the neocortex or go to the following web site for a more detailed look at evolution of brain structures and intelligence: "Ask the Experts": Evolution and Intelligence

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. Here is a visual representation of this system, from a midsagittal view of the human brain:

Click on the words to learn what these structures do:

• Thalamus
• Hypothalamus
• Amygdala
• Hippocampus

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. Look at a good example of this here.

The brain stem is made of the midbrain, pons, and medulla. Click on the words to learn what these structures do:

• Midbrain
• Pons
• Medulla

Brain Structure

This image shows the major lobes of the brain. You need to know where the major lobes are located and what each lobe does in terms of function (see below for functional descriptions)



Here we see the interior of the brain. Again you need to know the locations and functions of these labeled parts of the brain.

Outside the brain

This is an outside view of the brain. The brain is split into the left and right hemispheres by the longitudinal fissure. The different brain areas are segmented by deep grooves, called sucli , and by functional aspects. The largest part of the human brain is the cerebral cortex(cortex means bark in latan). This is an appropriate name, because the brain does its computation only on the six surface layers.
The very back part of the brain contains the cerebellum (little brain), which is attached to the Hindbrain. The Cerebellum is not very well understood, but it has been implicated in the coordination of movement. It is very old on an evolutionary scale, and you probably can't live without one.
Above the cerebellum lies the occipital lobe , which processes visual information.
Moving counter-clockwise, the next area is the parietal lobe , which processes many different sensory areas, and so might be an association area.
In front of the parietal lobe lies the Primary Sensory area. This area receives somatosensory input (touch sensations) from the entire body in a topographical mapping.
Right next to the Primary Sensory area is the Motor Area . If you were designing a brain you would want the Sensory areas right next to the Motor areas so that an organism could react very quickly to an incoming stimulus (like a baseball flying towards your head).
The Frontal Lobe handles the most complex thoughts. Damage to this area causes personality changes as well as other afflictions.

Other Areas That You Need to Know:

Inside the brain

This inside view of the brain shows the Limbic Lobe , which is not visible from outside the brain. The limic lobe has been implicated in sexual and emotional behavior as well as the encoding of some memories.
The Basal Ganglia is a collection of nerve bundles that is primarily responsible for motor programming.
The Thalamus is a collection of pathways that connects peripheral sensory organs to the various sensory corticies. Behind the Thalamus is the Pineal Gland , which controls body rhythms and sexual activity.
The Hypothalamus controls the visceral nervous system, guiding actions such as thirst, temperature regulation, and glanduar secretions in the organs.

Brainstem

This is a dissection of the very oldest portion of the brain, the part of the brain that sits on top of the spinal cord.
The Midbrain controls reflex patterns associated with vision and hearing.
The Pons serves as a relay station between the cerebral cortex and the cerebellum.
The Medulla controls vital functions such as respiration and heartbeat.
The Cerebellum controls sychronized movements.

Directions in the Brain

As we begin to talk about brain scans and locations of lesions, we need a common way of describing directions in the brain. The scanners that we use typically take slices, or planes, through the brain, and the major slices are given names.
The Median Plane cuts lengthwise through the middle of the brain.
The Saggital Plane is parallel to the Median Plane, but off the main axis.
The Coronal Plane is perpendicular to the Median Plane, running right between your ears.
The Horizontal Plane runs parallel to the ground as you stand upright.