The Organization of the Brain

If you open up the skull and look at the brain, one of the first things you’ll like notice is that anatomically, the “one” brain is really two halves called hemispheres. These two halves are connected by a large bundle of nerve fibers called the corpus collosum.

Structurally, there are three main divisions of the brain: forebrain, midbrain, and hindbrain. Each of these divisions consists of many substructures that are involved in various behaviors and activity.

The brain is a complex, integrated system. All of its components work together to produce the complexity of human behavior. The concept of localization refers to the idea that there are specific parts of the brain for specific components of behaviors. Various parts work together to produce vision, hearing, speech, and so forth. Neurological techniques such as post-mortem brain examination, CT (co-axial tomography) scans, MRI (magnetic resonance imaging) scans, and PET (positron-emission tomography) scans have been used to identify and explore these systems.

Forebrain

The human forebrain is involved in a wide range of mental processes, including the sensing, perceiving, and processing of information. It is also involved in thinking, problem solving, organizing, and language functions.

The human forebrain consists of four sections:

• Cerebral cortex: If you think of the brain as a mushroom, with a top and a stalk, then the cerebral cortex is the top of the mushroom. It’s divided into two halves, called cerebral hemispheres (the left and the right — pretty creative, I know). These halves are connected by a bundle of nerve fibers known as the corpus collosum. Without the corpus collosum, the halves wouldn’t be able to communicate with each other.

The figure shows the four major divisions of the cerebral cortex and their corresponding functions:

• • Frontal lobe: Planning, organizing, coordinating, and controlling movements (in an area known as the primary motor cortex), reasoning, and overall monitoring of the thinking process
  • Parietal lobe: Sensation, spatial and somatosensory (bodily) awareness
  • Temporal lobe: Hearing, language, and other verbal activity
  • Occipital lobe: Vision
• Limbic system: Located on the underside of the mushroom top (the cerebral cortex), the limbic system is involved in learning, memory, emotional behavior, and mating or reproduction.
• Basal ganglia: This part of the brain is involved in controlling movement.
• Thalamus: This “neural switchboard” is a relay station for the different parts of the brain. However, it is more than simply a connection. It analyzes inputs to construct organized outputs.
• Hypothalamus: The hypothalamus takes part in the control of the endocrine system and works with the limbic system to control behaviors such as aggression, eating, protection, and mating.

Midbrain

The midbrain is involved in the auditory and visual processes and in motor control. The midbrain consists of the following divisions and their respective areas of responsibility:

• Tectum: Auditory and visual systems
• Tegmentum: Movement, sleep, arousal, attention, muscle tone, and reflexes

Hindbrain

The hindbrain is involved in the autonomic functions of the body such as heart rate and breathing as well as the coordination of movement. The hindbrain includes two divisions with assigned duties:

• Cerebellum: Motor movement and its coordination
• Pons: The bridge connecting the cerebellum to the rest of the brain
• Medulla: Vital functions of the body such as the cardiovascular system, breathing, and the movement of skeletal muscles

Tiptoeing back and forth from the periphery

There’s that toe again! Of the two divisions of the body’s nervous system, think of the peripheral nervous system (PNS) as a system of connections that make it possible for the brain and spinal cord to communicate with the rest of the body. Two sets of nerves are involved:

• Spinal nerves: These nerves carry neural signals both to and from the spinal cord. Sensory nerves carry information from the body to the central nervous system: For example, they carry signals from sensors in your foot when somebody steps on your foot. Motor nerves carry signals from the central nervous system to the body; they cause the muscles in your limbs to move (raising your hand).
• Cranial nerves: These nerves are involved in the muscular (motor) and sensory processes, except that they are connected directly to the brain itself, not to the spinal cord. Cranial nerves support functions occurring in your face and head, including seeing and hearing, blinking and speaking.