Brainstem structures

This article takes a detailed look at the structures of the brain and what function various parts serve.

From the outside, the most obvious parts of the brain are

  • The two wrinkled cerebral hemispheres in the left and right halves of the upper brain (together called the cerebrum)
  • The cerebellum, a smaller section attached to the lower back portion of the cerebrum
  • The brainstem, which extends down from the center of the brain and in front of the cerebellum, to merge with the top of the spinal cord.

Looking at the brain from the side (see Figure 2) tells us something about why certain functions are located where they are in the system.

Figure 2. The brain seen from the side.

The brainstem is often thought of as the most primitive region of the brain because evolutionary studies have shown it to be the first area to develop in complex animals. The brainstem controls our most basic functions, many of which happen without our thinking about them at all.

Three structures make up the brainstem:

  • The medulla, which controls breathing, swallowing, blood pressure, and heart rate
  • The pons (Latin for “bridge”), which links the cerebellum to the cerebrum
  • The midbrain, which governs rudimentary vision and hearing

Running down the length of the brainstem is the reticular formation, which is responsible for wakefulness or arousal. If a brain tumor distorts the reticular formation, a comalike state can occur.

There are twelve pairs of cranial nerves. Each cranial nerve exists as a pair, one nerve for the left side of the body and the other nerve for the right side. Most of them originate in the brainstem. They are identified by numbers (I through XII). These nerves control important things such as swallowing, facial movement, the senses (vision, taste, and hearing), and neck and shoulder muscles.

Major nerves carrying information to and from the rest of the body pass through the brainstem. The nerve axons cross over in the medulla so that the left side of the brain controls the right side of the body, and vice versa. Tumors on one side of the brain may well affect movement and sensation on the opposite side of the body. (An exception is in the cerebellum, where a side of the brain sends signals to the same side’s arm and leg.)

Above the midbrain is the diencephalon, which includes the thalamus and hypothalamus. The hypothalamus is a regulatory center involved in many important functions, such as hormone secretion (including that of the nearby pituitary gland), the autonomic nervous system, eating, sleeping, temperature, emotion, and sexual behaviors. Sitting above the hypothalamus, the thalamus serves as an information processor for much of what goes to and from the brain.

The cerebellum is the lower back of the brain, beneath the cerebral hemispheres and separated from them by a fold of dura mater called the tentorium. It is about one eighth the size of the cerebrum. The cerebellum is involved in fine motor coordination and balance, continually and automatically making allowances that let the body maintain its balance. If a tumor grows in the cerebellum, a person may stagger (ataxic gait) or make jerky movements. The person may be unable to judge distances or make his or her hands do what he or she wants them to do.

The cerebrum is the part of the brain that developed most recently in evolutionary terms and is enormous in proportion to the rest of the brain in humans. It is the part of the brain involved in sensory input, thinking, reasoning, learning, and memory—the functions we associate with intelligence. The cerebrum is proportionately larger in animals that seem to be able to take in sensory information and analyze it in some way. But only in humans is it so massive and complex.

The cerebrum is made up of right and left cerebral hemispheres, with a large groove called the cerebral fissure separating the two sides. Deep inside the brain, in the middle, is the corpus callosum, a bundle of nerve fibers connecting the halves of the brain, allowing information to move back and forth between the two sides.

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What is the Visible Human Project?

The Visible Human Project is an effort to create a detailed data set of cross-sectional photographs of the human body, in order to facilitate anatomy visualization applications. !

how much did the national library of medicine's project, the visible human project, cost?

The Visible Human Project data-gathering cost $1.4 million (£707,842), the project was started in 1991, and took 2.5 years to find the ideal specimens.

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