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 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 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
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. By serving as this liason between the different parts of the brain, the pons is able to facilitate coordination between the functions of the two sides of the body as well as those of the face and jaw. The origins of the fifth through eighth cervical nerves are associated with the pons. Research Pons
The spinal cord is one of the primary portions of the central nervous system, serving as a medium for signals to be sent from the brain to the structures of the body, and received from them in return. Extending from the medulla oblongata, through the foramen magnum in the base of the skull, to the base of the vertebral column, the spinal cord is about half of a centimeter in diameter, and is slightly flattened. The spinal cord itself passes through the vertebral canal created by the vertebral arches, and sends out roots and branches. These structures contain bundles of nerve fibres which extend all the way down the body, innervating even the skin of the tips of the toes. The spinal cord features both efferent and afferent nerve pathways, so that nerves may be transmitted to the body's structures as well as received from them.
Paired sets of nerves branch out from the spinal cord along the vertebral column, with the lowest of these forming the sacral plexus of nerves. The sympathetic nerves travel alongside the spinal cord in the sympathetic nerve trunk, which features periodic clusters of nerves, called ganglia, which deal with specific organ groups. The spinal cord floats in a spinal fluid which protects and nourishes it and, as with the brain, is covered by a meningeal membrane composed of three layers: the pia mater, the arachnoid, and the dura mater. Damage to the spinal cord results in inability to transmit and receive nerve impulses to and from the specific area supplied by the damaged section of the spinal cord, and all sections below it, resulting in paralysis and numbness. Inflammation of the spinal covering is a condition called spinal meningitis. Research Spinal Cord
The vagus nerve is the tenth cranial nerve, branching off of the medulla oblongata and extending upward and downward into the abdomen. An important nerve, the vagus divides into several branches which innervate vital structures in the body. These include the auricular, bronchial, cardiac (inferior and superior), celiac, oesophageal, gastric, hepatic, laryngeal (recurrent and superior), meningeal, pharyngeal, and pyloric branches. Research Vagus Nerve
The vertebral canal is a tunnel formed by the juxtaposition of the individual vertebral arches in the vertebral column. This canal supports and protects the spinal cord as it runs from the medulla oblongata inside the skull to the base of the spine. Research Vertebral Canal
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Abducens
