The Abducens (or Sixth Cranial Nerve) rises in the medulla oblongata and supplies the external rectus muscle of the eye, which draws the eyeball outward. Research Abducens
The adrenal glands are a pair of glands above the kidneys which secrete adrenaline and other hormones. Each adrenal gland consists of an inner part called the medulla and an outer part called the cortex. The adrenal medulla is the source of epinephrine, also called adrenaline, and norepinephrine, which affect a number of body functions; for example, they stimulate cardiac action, increase the blood pressure, and affect constriction and dilation of blood vessels and musculature. All these actions help the organism deal with acute emergencies more effectively and efficiently. The adrenal cortex elaborates a group of hormones known as glucocorticoids, which include cortisone and hydrocortisone, and the mineralocorticoids, which include aldosterone and other hormonal substances that are essential to the maintenance of life and to adaptation to stress. Adrenal secretions regulate the salt and water balance of the body, influence the blood pressure, affect lymphatic tissue, influence the mechanisms of the immune system, and regulate carbohydrate and protein metabolism. In addition to these functions, the adrenal glands also elaborate male and female hormones. Research Adrenal Glands
The autonomic nervous system is responsible for the self-controlling aspects of the body's nervous network, and is under the control of the cerebral cortex, the hypothalmus, and the medulla oblongata. Working in tandem with the central nervous system, the autonomic nervous system features two subsystems which regulate body functions such as involuntary smooth muscle movement and heart rate. These two subsystems are called the sympathetic and parasympathetic nervous system, and their functions operate in opposition to one another, delicately balancing the bodily functions which they control. The sympathetic nervous causes fight or flight responses in moments of stress or stimulus, such as increased heart rate, saliva flow, and perspiration. The parasympathetic system counterbalances these effects by slowing the heart rate, dilating blood vessels, and relaxing involuntary smooth muscle fibres. Viewed individually, the sympathetic nervous system, also referred to as the thoracolumbar system, features a series of nerves which branch out of the spinal cord between the first thoracic vertebra and the second lumbar vertebra. These nerve fibres join into a long trunk of fibres, called the sympathetic trunk, on each side of the spinal cord. Along the sympathetic trunk are enlarged clusters of nerve fibres, called ganglia.
From these ganglia, a number of nerve fibres extend throughout the body's tissues. Many of these nerves create additional ganglia, such as the celiac ganglia and the mesenteric ganglia. The sympathetic nerves are responsible for contracting involuntary smooth muscle fibres, viscera, and blood vessels, speeding up the heart rate, and dilating the bronchial tubes in moments of stress. The parasympathetic nervous system, also referred to as the craniosacral system, features ganglia in the midbrain, in the medulla oblongata, and in the sacral region. The first two, the cranial ganglia of the parasympathetic system, give pass impulses to the facial, oculomotor, glossopharyngeal, and vagus nerves. The sacral group of parasympathetic nerves originate at the second, third, and fourth vertebrae and extend nerves to the bladder, the distalcolon, the rectum, and the genitals. The nerves of the parasympathetic nervous system are responsible for conserving and restoring energy in the body following a sympathetic response to stress. Research Autonomic Nervous System
The brain is the primary component of the nervous system, occupying the cranial cavity. Without its outermost protective membrane, the dura mater, the brain weighs an average of 1.4 kilograms, comprising about 97% of the entirecentral nervous system. The brain is connected to the upper end of the spinal cord (which connects through the foramen magnum of the skull) and is responsible for issuing nerve impulses, processing nerve impulse data, and engaging in the higher order thought processes. The brain is divided into three parts: the large cerebrum, the smaller cerebellum, and the brainstem leading to the spinal cord. The brainstem is also descriptively divided into the medulla oblongata, the midbrain, and the pons. The right hemisphere of the brain is a part of the cerebrum. The cerebrum, or forebrain, forms the bulk of the brain, formed of a large mass of white and grey neural fiber in the upper cranium. It is responsible for the higher thought processes (memory, judgement, reason), processing sensory data, and with initiating willful motor processes, such as voluntary muscle flexion. The cerebrum is composed of two lateral halves, or hemispheres, which feature a number of folds (gyri) and furrows (sulci) and which are connected in the middle at the medulla. Containing about a trillion neurons, the human brain is the most complex mechanism known, and its many functions are still largely a mystery. Research Brain
The brain stem operates automatically to control vital body functions such as breathing and blood pressure. It is a eight centimeter long stalk of nerve cells and fibres that joins the upper part of the spinal cord with the brain. The medulla oblongata is the lowest part of the brain stem and serves as the site of connection between the brain and the spinal cord. The pons is located in the brainstem, vertically between the midbrain and the medulla oblongata, and sagittally between the cerebellum and the pituitary gland. It is responsible for serving as a bridge between the cerebrum, the cerebellum, and the medulla oblongata. The brain stem is an extension of the spinal cord and acts as a highway for messages traveling from other parts of the brain to the spinal cord. The spinal cord and the brain form the central nervous system (CNS), which controls all of the body's basic functions such as breathing, the rate of your heart beat, and body temperature. Research Brain Stem
The calyces are the recesses in the internal medulla of the kidney which enclose the renal pyramids. They are used to subdivide the sections of the kidney anatomically, with distinction being made between major calyces and minor calyces. Research Calyces
The twelve cranial nerves innervate the muscles and skin of the head, neck, and, in the case of the vagus, sacral, and spinal accessory nerves, many other important structures throughout the body. These nerves originate in the pons, the forebrain, medulla oblongata, and the uppermost part of the spinal cord, between the first few cervical vertebrae.
The first four include the olfactory (1st), which innervates the nasalmucous layer and allows the sense of smell, the optic (2nd) which innervates the retina and allows the sense of sight, the oculomotor (3rd) which innervates the pupil and cilia of the eye, and the trochlear (4th) which innervates the superior oblique eyemuscles. The next cranial nerve is the trigeminal (5th) which has three divisions: the ophthalmic (eye), maxillary (upper palate and face), and mandibular (jawbone, tongue, and auriculotemporal region). The sixth, seventh, and eighth nerves are the abducens (lateral rectus of eye), the facial (face and earmuscles), and the acoustic (outer and inner ear structures), respectively. The ninth cranial nerve is the glossopharyngeal, which innervates the pharynx, tongue, and tympanus of the ear. The tenth cranial nerve, the vagus, has many branches which innervate a number of important structures, including the heart, lungs, and stomach. The eleventh cranial nerve is the accessory spinal nerve, which innervates structures of the neck and throat, including the pharynx and the cervical lymph glands. The twelfth cranial nerve is the hypoglossal nerve, which innervates the tongue. Research Cranial nerve
The medulla oblongata is the lowest part of the brainstem and serves as the site of connection between the brain and the spinal cord. Located just above the foramen magnum in the skull and in front of the cerebellum, the
medulla oblongata contains a number of nerve centers which are responsible for controlling involuntary processes such as the heartbeat, breathing, and body temperature regulation. It is only about 2.5 centimeters wide and comprises less than one percent of the weight of the central nervous system. In spite of its small size, though, it is integral in the transmission of nerve impulses between the spinal cord and the higher brain. Many of the nerve fibres which pass through the medulla oblongata cross over, so that many impulses from the right side of the brain control functions on the left side of the body and vice-versa. Research Medulla Oblongata
Physotigmine is an alkaloid derived from the Calabar Bean. It has little effect on the cerebrum, but acts strongly on the vital centres in the medulla, and on the spinal cord where it produces feebleness of muscular movement, and slightly affects sensation. It was used in medicine where it was given to relieve tetanus and to antagonise the action of atropine and to relieve ocular tension. Research Physotigmine
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Pith
