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Visibly Human Health and Disease in the Human Body

The Brain and Nervous System

THE BRAIN AND NERVOUS SYSTEM The nervous system is the body’s communication and coordination network. Three systems make up the nervous system: the central nervous system, the peripheral nervous system and the autonomic nervous system.

The central nervous system is composed of the brain and spinal cord. Cranial nerves branch out from the brain and spinal nerves branch from the spinal cord to innervate all parts of the body. These branching nerves form the network of the peripheral nervous system.

The central nervous system processes sensory input from the peripheral nerves, and if the impulse from the input is strong enough, a chemical reaction takes place eliciting muscle response. The autonomic nervous system works in concert with the central and peripheral nervous systems and manages basic functions, such as blood pressure and heart rate adjustment, which function "automatically."

The human brain is a spongy three-pound mass of white and gray matter that is composed of millions of dendrocytes, which are myelinated nerve fibers and cell bodies. Brain cells communicate with another by the movement of chemical signals across gap junctions between axons of the dendrocytes.

right brain
Normal human brain, right hemisphere.
NMHM 1988.0004.03


Horizontal section of brain
Horizontal section of brain
This brain section shows all the major landmarks of brain anatomy. The open spaces comprise the ventricular system of the brain through which cerebrospinal fluid flows. 1998.0034.09
Sagittal section of head
Sagittal section of head
The cerebrum, cerebellum, and brain stem can be seen in this sagittal section of the head. The brain and spinal cord are surrounded by a dense connective tissue called the dura mater that contains the cerebrospinal fluid (CSF) which provides the brain with buoyancy and protection. This fluid also helps to stabilize the brain’s chemical and pressure environment. AFIP 2351


Hansen disease
Hansen’s disease (leprosy)
This is an amputated foot of a leprosy patient. This patient was diagnosed with borderline tuberculoid leprosy and was treated with dapsone (sulfone), rendering the disease inactive. Complications arising from peripheral neuropathy due to the disease process resulted in disabling the foot. Despite doctor’s recommendations for alternative management, the patient insisted on amputation. Leprosy is caused by the intracelluar bacterium Mycobacterium leprae that was first identified by Dr. Armauer Hansen in 1873.