Aqueduct of the midbrain: A canal that communicates between the third and fourth ventricles in a system of four communicating cavities within the brain that are continuous with the central canal of the spinal cord.
The four ventricles consist of the two lateral ventricles, the third ventricle and the fourth ventricle:
Lateral ventricles: The lateral ventricles are in the cerebral hemispheres. Each lateral ventricle consists of a triangular central body and four horns. The lateral ventricles communicate with the third ventricle through what is called the interventricular foramen (opening).
The third ventricle is a median (midline) cavity in the brain that is bounded by the thalamus and hypothalamus on either side. Anteriorly (in front) the third ventricle communicates with the lateral ventricles and posteriorly (in back) the third ventricle communicates with the aqueduct of the midbrain (also called the aqueduct of Sylvius).
The fourth ventricle is the most inferior (lowest) of the four ventricles of the brain. It extends from the aqueduct of the midbrain to the central canal of the upper end of the spinal cord with which it communicates by the two foramina (openings) of Luschka and the foramen (opening) of Magendie.
The ventricles are filled with cerebrospinal fluid, which is formed by structures called choroid plexuses located in the walls and roofs of the ventricles.
- Aqueous humor
Aqueous humor: In medicine, humor refers to a fluid (or semifluid) substance. Thus, the aqueous humor is the fluid normally present in the front and rear chambers of the eye. It is a clear, watery fluid that flows between and nourishes the lens and the cornea; it is secreted by the ciliary processes. The humors […]
- Arabidopsis thaliana
Arabidopsis thaliana: A plant belonging to the mustard family. Arabidopsis was the first plant genome to be sequenced, and is a popular tool for understanding the molecular biology of many plant traits, including flower development and light sensing. See also: Arabidopsis thaliana genome.
- Arabidopsis thaliana genome
Arabidopsis thaliana genome: All of the genetic information contained in Arabidopsis thaliana, a plant belonging to the mustard family. The genomes of particular nonhuman organisms such as Arabidopsis have been studied for a number of reasons including the need to improve sequencing and analysis techniques. These nonhuman genomes also provide powerful sets of data against […]
Arachnodactyly: Long spider-like fingers and toes, a frequent finding in Marfan syndrome, a heritable disorder of connective tissue. “Arachnodactyly” is derived from the Greek “arachne” (spider) and “daktylos” (finger). The Greek word was derived from the name “Arachne,” a maiden in Greek mythology whom the goddess Athena turned into a spider after the girl, a […]
Inflammation of the middle layer of membranes covering the brain and spinal cord. Arachnoiditis can occur as a complication of procedures such as myelograms, spinal operations, epidural steroid injections, and injury to the spine.