The obex is the point in the human brain

Human brain

The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 at which the fourth ventricle

Fourth ventricle

The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle...

 narrows to become the central canal

Central canal

For the engineering project, see Indiana Central Canal.The central canal is the cerebrospinal fluid-filled space that runs longitudinally through the length of the entire spinal cord. The central canal is contiguous with the ventricular system of the brain...

 of the spinal cord

Spinal cord

The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...

.

The obex occurs in the caudal

Anatomical terms of location

Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...

 medulla

Medulla oblongata

The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

.

The decussating of sensory fibers

Sensory decussation

The sensory decussation or decussation of the lemniscus is a decussation or cross over of axons from the gracile nucleus and cuneate nucleus. The fibres of this decussation are called the internal arcuate fibres and are found at the superior aspect of the closed medulla superior to the motor...

 happens at this point.

Clinical significance

Hemangioblastoma

Hemangioblastoma

Hemangioblastomas are tumors of the central nervous system that originate from the vascular system usually during middle-age. Sometimes these tumors occur in other sites such as the spinal cord and retina...

has been observed in this location.
Neurological surgical intervention in the treatment of syringomyelia or hydromyelia may involve plugging the obex to prevent the transmission of cerebrospinal fluid to the central canal of the spinal cord.

External links

• Photo at aphis.usda.gov (file not found as of 2008-08-16)