Ventral Health Dictionary

Relating to the front of the body. In human anatomy, the term is synonymous with ventral.... anterior

A winged-like expansion of cuticular integument of nematodes; an expansion at the oesophageal region called “cervical alae”, e.g. in Toxocara species, or at the posterior end called “caudal alae” and in the larval stages of some nematodes the expansion may extend almost entire lateral aspects of the body, these expansions are called “lateral alae”. In Oxyuridae, e.g. Enterobius vermicularis, the cuticle at the anterior end expands dorso-ventrally into “cephalic alae”.... ala

In nematodes, an opening of the alimentary system on the ventral side at the posterior end of the female nematodes.... anus

A common opening of the alimentary and reproductive systems of male nematodes, normally situated on the ventral side at the posterior end of the body.... cloaca

These are swellings on the dorsal roots of spinal nerves just proximal to the union of the dorsal and ventral nerve roots. They are situated in the inter-vertebral foramina and contain the cell bodies of sensory neurones. (See SPINAL COLUMN; SPINAL CORD.)... dorsal root ganglia

An opening of the excretory system, normally situated on the ventral side at the anterior part of the body (e.g. in trematode miracidia).... excretory pore

A cuticular thickening of the ventral wall of the spicular pouch in nematodes. Both gubernaculum and telamon are for guiding the spicules out of the body. Shape and size and number of the spicules, gubernaculum and telamon are also used for identification of the nematodes.... telamon

An opening of the female reproductive system, may be situated at the anterior, middle or posterior parts and on the ventral side of the body according to groups of nematodes.... vulva

Relating to the back, located on or near the back, or describing the uppermost part of a body structure when a person is lying face-down. The opposite of dorsal is ventral.... dorsal

adj. relating to the crown of the head or of a tooth. The coronal plane divides the body into dorsal and ventral parts (see illustration overleaf).... coronal

n. an anatomical division of the forebrain, consisting of the epithalamus, thalamus (dorsal thalamus), hypothalamus, and ventral thalamus (subthalamus). See brain.... diencephalon

adj. (in anatomy) extending from the back (dorsal) surface to the front (ventral) surface.... dorsoventral

the early embryo before the formation of *somites. It is a flat disc of tissue bounded dorsally by the amniotic cavity and ventrally by the yolk sac. The formation of the *primitive streak and *archenteron in the embryonic disc determines the orientation of the embryo, which then becomes progressively elongated.... embryonic disc

n. (in anatomy) a process, outgrowth, or extension of an organ or other structure. It is often paired. In the spinal cord crescent-shaped areas of grey matter (seen in cross section) are known as the dorsal and ventral horns.... horn

a congenital abnormality in which the pancreas develops in two parts draining separately into the duodenum, the small ventral pancreas through the main ampulla and the larger dorsal pancreas through an accessory papilla. In rare instances this is associated with recurrent abdominal pain, probably due to inadequate drainage of the dorsal pancreas. Diagnosis is made by CT imaging, magnetic resonance cholangiopancreatography (MRCP), or *ERCP.... pancreas divisum

combining form denoting 1. ventral. 2. the abdomen.... ventro

(vitelline sac) the membranous sac, composed of mesoderm lined with endoderm, that lies ventral to the embryo. It is one of the *extraembryonic membranes. Its initially wide communication with the future gut is later reduced to a narrow duct passing through the *umbilicus. It probably assists in transporting nutrients to the early embryo and is one of the first sites where blood cells are formed.... yolk sac

This is the lower portion of the CENTRAL NERVOUS SYSTEM which is situated within the SPINAL COLUMN. Above, it forms the direct continuation of the medulla oblongata, this part of the BRAIN changing its name to spinal cord at the foramen magnum, the large opening in the base of the skull through which it passes into the spinal canal. Below, the spinal cord extends to about the upper border of the second lumbar vertebra, where it tapers o? into a ?ne thread, known as the ?lum terminale, that is attached to the coccyx at the lower end of the spine. The spinal cord is thus considerably shorter than the spinal column, being only 37– 45 cm (15–18 inches) in length, and weighing around 30 grams.

In its course from the base of the skull to the lumbar region, the cord gives o? 31 nerves on each side, each of which arises by an anterior and a posterior root that join before the nerve emerges from the spinal canal. The openings for the nerves formed by notches on the ring of each vertebra have been mentioned under the entry for spinal column. To reach these openings, the upper nerves pass almost directly outwards, whilst lower down their obliquity increases, until below the point where the cord ends there is a sheaf of nerves, known as the cauda equina, running downwards to leave the spinal canal at their appropriate openings.

The cord is a cylinder, about the thickness of the little ?nger. It has two slightly enlarged portions, one in the lower part of the neck, the other at the last dorsal vertebra; and from these thickenings arise the nerves that pass to the upper and lower limbs. The upper four cervical nerves unite to produce the cervical plexus. From this the muscles and skin of the neck are mainly supplied, and the phrenic nerve, which runs down through the lower part of the neck and the chest to innervate the diaphragm, is given o?. The brachial plexus is formed by the union of the lower four cervical and ?rst dorsal nerves. In addition to nerves to some of the muscles in the shoulder region, and others to the skin about the shoulder and inner side of the arm, the plexus gives o? large nerves that proceed down the arm.

The thoracic or dorsal nerves, with the exception of the ?rst, do not form a plexus, but each runs around the chest along the lower margin of the rib to which it corresponds, whilst the lower six extend on to the abdomen.

The lumbar plexus is formed by the upper four lumbar nerves, and its branches are distributed to the lower part of the abdomen, and front and inner side of the thigh.

The sacral plexus is formed by parts of the fourth and ?fth lumbar nerves, and the upper three and part of the fourth sacral nerves. Much of the plexus is collected into the sciatic nerves, the largest in the body, which go to the legs.

The sympathetic system is joined by a pair of small branches given o? from each spinal nerve, close to the spine. This system consists of two parts, ?rst, a pair of cords running down on the side and front of the spine, and containing on each side three ganglia in the neck, and beneath this a ganglion opposite each vertebra. From these two ganglionated cords numerous branches are given o?, and these unite to form the second part – namely, plexuses connected with various internal organs, and provided with numerous large and irregularly placed ganglia. The chief of these plexuses are the cardiac plexus, the solar or epigastric plexus, the diaphragmatic, suprarenal, renal, spermatic, or ovarian, aortic, hypogastric and pelvic plexuses.

The spinal cord, like the brain, is surrounded by three membranes: the dura mater, arachnoid mater, and pia mater, from without inwards. The arrangement of the dura and arachnoid is much looser in the case of the cord than their application to the brain. The dura especially forms a wide tube which is separated from the cord by ?uid and from the vertebral canal by blood vessels and fat, this arrangement protecting the cord from pressure in any ordinary movements of the spine.

In section the spinal cord consists partly of grey, but mainly of white, matter. It di?ers from the upper parts of the brain in that the white matter (largely) in the cord is arranged on the surface, surrounding a mass of grey matter (largely neurons – see NEURON(E)), while in the brain the grey matter is super?cial. The arrangement of grey matter, as seen in a section across the cord, resembles the letter H. Each half of the cord possesses an anterior and a posterior horn, the masses of the two sides being joined by a wide posterior grey commissure. In the middle of this commissure lies the central canal of the cord, a small tube which is the continuation of the ventricles in the brain. The horns of grey matter reach almost to the surface of the cord, and from their ends arise the roots of the nerves that leave the cord. The white matter is divided almost completely into two halves by a posterior septum and anterior ?ssure and is further split into anterior, lateral and posterior columns.

Functions The cord is, in part, a receiver and originator of nerve impulses, and in part a conductor of such impulses along ?bres which pass through it to and from the brain. The cord contains centres able to receive sensory impressions and initiate motor instructions. These control blood-vessel diameters, eye-pupil size, sweating and breathing. The brain exerts an overall controlling in?uence and, before any incoming sensation can affect consciousness, it is usually ‘?ltered’ through the brain.

Many of these centres act autonomously. Other cells of the cord are capable of originating movements in response to impulses brought direct to them through sensory nerves, such activity being known as REFLEX ACTION. (For a fuller description of the activities of the spinal cord, see NEURON(E) – Re?ex action.)

The posterior column of the cord consists of the fasciculus gracilis and the fasciculus cuneatus, both conveying sensory impressions upwards. The lateral column contains the ventral and the dorsal spino-cerebellar tracts passing to the cerebellum, the crossed pyramidal tract of motor ?bres carrying outgoing impulses downwards together with the rubro-spinal, the spino-thalamic, the spino-tectal, and the postero-lateral tracts. And, ?nally, the anterior column contains the direct pyramidal tract of motor ?bres and an anterior mixed zone. The pyramidal tracts have the best-known course. Starting from cells near the central sulcus on the brain, the motor nerve-?bres run down through the internal capsule, pons, and medulla, in the lower part of which many of those coming from the right side of the brain cross to the left side of the spinal cord, and vice versa. Thence the ?bres run down in the crossed pyramidal tract to end beside nerve-cells in the anterior horn of the cord. From these nerve-cells other ?bres pass outwards to form the nerves that go direct to the muscles. Thus the motor nerve path from brain to muscle is divided into two sections of neurons, of which the upper exerts a controlling in?uence upon the lower, while the lower is concerned in maintaining the muscle in a state of health and good nutrition, and in directly calling it into action. (See also NERVE; NERVOUS SYSTEM.)... spinal cord