Subcortical Structures and Functions


So far we have examined mostly the large, visible areas on the surface of the brain: the cerebral cortex. While this is an important part of the brain, it is only the surface. Below the cerebral cortex are a variety of other structures, called subcortical (literally "below the cortex") structures.

You need not memorize these structures for an introductory psychology class. The main idea is that there are many specialized areas below the cortex. The following table lists the most commonly accepted, classic functions attributed to major brain areas below the cerebral cortex. This list is greatly oversimplified; exceptions, controversies, and complications are left out.

FOREBRAIN
(below cerebrum)

Basal ganglia

—involved in motor control

Limbic system

—not one structure but several: hippocampus, amygdala, septum, cingulate gyrus, and others

—middle of septum is one location of "pleasure centers"

—amygdala involved in emotions, fear, defensive, and aggressive behaviors

—hippocampus interacts with temporal lobe to help establish event memory

Thalamus

—looks like two eggs or small, joined footballs

—implicated in control of sleep and attention

—a relay station; receives input from eyes, ear, spinal cord, relays information to cerebral cortex

Hypothalamus

—involved with basic functions like eating, sex, temperature control, sleep, aggression

—produces sex, growth and stress—related hormones carried down axons to pituitary gland, released from there into bloodstream to activate and organize distant body systems

MIDBRAIN

Tectum

—consists of four bumps, the colliculi

—superior (higher up) colliculi related to eye movement and localization of objects

—inferior (lower down) colliculi related to sense of hearing

Tegmentum

—includes red nucleus and substantia nigra, involved in control of movement

—contains part of reticular formation (see below)

HINDBRAIN

Cerebellum

—appears as a separate structure with a cauliflower—like appearance behind the brain

—controls fine motor movement, timing; motor memory, planning of movements, also practice—related memory and detection of errors in non—motor tasks

Reticular formation

—consists of densely packed, reticulated (netlike) cells located in central core of hindbrain

—thought to activate thalamus and cortex, therefore often called the "reticular activating system"

Pons

—connects cerebrum with cerebellum

—contains centers regulating sleep, feeding and facial expression

Medulla

—first part of the brain above the spinal cord, essentially a continuation of the cord

—controls heart and respiration rate, digestive functions, blood pressure

What is the brain stem?

The brain stem is the part of the nervous system starting where the spinal cord enters the brain, at the base of the skull. The brain stem (not the cortex!) is the "core" of the brain. It extends upward to the hypothalamus. Strictly speaking, every structure on the above list except the cerebellum is part of the brain stem. However, t he term brain stem is used most commonly to refer to part of the brain that appears as a continuation of the spinal cord into the brain: the hindbrain and lower portion of the midbrain.

What effect can be produced by small injuries in the brain stem?

The brain stem controls vital functions such as breathing and temperature regulation. Even tiny injuries to the brain stem can produce coma (long-lasting unconsciousness) or death. My wife worked in an Emergency Room, and she remembers a woman being brought by ambulance after an automobile accident, unconscious, with pupils fixed and dilated and unresponsive to light, indicating brain death. The only injury doctors could find was a small puncture wound to the brain stem.

See the Whole Brain Atlas for much more detail, including many images showing various brain structures. The URL:

<http://www.med.harvard.edu/AANLIB/home.html>


Write to Dr. Dewey at psywww@gmail.com.

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Copyright © 2007 Russ Dewey