Brain Basics

The brain is an amazingly compact, yet complex organ that conducts all the processes of human life, from the most basic reflex actions to the highest intellectual and analytical thoughts. This three-pound wonder contains as many nerve cells as there are stars in the sky, and by continued exploration of our “inner universe” scientists have begun to unravel some of its secrets. In particular, there is progress in understanding the mysteries of learning and memory: where information is stored, how we access it, and why we forget.

What is the brain?

The brain is fundamentally a mass of highly organized neural tissue containing internal chambers and passageways. Unlike other cells in the body, neurons (nerve cells) communicate with each other. They do so by generating electrical signals that are passed along precise routes, guided by chemical messengers. Anatomically, the brain is divided into four major sectors: the cerebrum (ser-EE-brum), the cerebellum (ser-e-BEL-um), the diencephalon (dy-en-SEF-a-lon), and brain stem.

1. The cerebrum is the familiar “helmet” part of the brain that is responsible for all higher mental functions such as consciousness, intellect, memory, sensations and direction of movements. The cerebrum is covered by a layer called the cerebral cortex (cortex means “bark”), commonly referred to as “gray matter.” This layer bears the characteristic folds and convolutions of the brain, and it is here where conscious thought takes place and memories are stored. Beneath the gray matter is “white matter,” a labyrinth of nerve fibers that act like electrical circuits, relaying information to and from the gray matter. 

The cerebrum is divided into halves or hemispheres by a deep central groove, and beneath that, a membrane. The two hemispheres have different functions: the left side controls speech, writing, and the interpretation of language and mathematical calculation, while the right side controls spatial visualization and analysis by touch. Interestingly, each half of the brain controls the other side of the body’s muscles, hearing and vision. [diagram] 

Somewhat lesser fissures separate the cerebral cortex into lobes: 

• Frontal lobe – primary conscious control of skeletal muscles
• Prefrontal lobe – abstract intellectual functions, such as predicting the consequences of an event or action
• Temporal lobes (on the sides) – conscious perception of sounds and smells
• Hippocampus (within the temporal lobes) – important for memorization and comprehension of language
• Entorhinal (en-toh-RY-nal) cortex – controls majority of input to and output from the hippocampus
• Occipital lobe (rear) – vision
• Parietal lobe (upper rear) – conscious perception of touch, pressure, pain, vibration, taste and temperature

In all lobes there are centers for interpreting sensory stimuli and initiating motor activities. [diagram]

2. The cerebellum is located at the rear of the skull, just under the back part of the cerebrum and nestled against the brain stem. It coordinates complicated movements and automatically adjusts the postural muscles of the body to maintain balance and equilibrium. The cerebellum also controls, programs and refines movements that are consciously learned and creates movement patterns that can become automatic. Like the cerebrum, it is covered by a layer of cortex. [diagram] 

3. Deep inside the cerebrum is the diencephalon, which translated literally means “through the head.” It is comprised of the thalamus (THAL-a-mus) and hypothalamus. 

• The thalamus is a relay station that filters sensory information incoming from the rest of the body and forwards it to the appropriate area of the cerebral cortex. Different parts of the thalamus provide awareness of emotional states, information about position, touch, pressure, pain and temperature; visual information; and auditory information. 

• The hypothalamus contains centers that control and/or coordinate behavioral drives such as hunger and thirst; the muscle movements that arise from rage, pleasure, pain and sexual arousal; autonomic functions such as breathing, digestion and blood pressure; hormone production; the “flight or fight” response to stress; the regulation of body temperature; and the circadian rhythms that govern our sleep cycles. 

4. The brain stem is the deepest and lowest part of the brain that connects to the spinal

cord. It is comprised of three areas that function on an unconscious level to relay information and are involved in the control of reflex responses, heart rate, blood pressure and digestion. In general, each higher level of the brain controls more sophisticated functions, the highest being the cerebral cortex.