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 diaphragm is the primary muscle responsible for respiration. Connected to the abdominal wall, the lumbar vertebra, the lower ribs, the sternum, and the pericardium of the heart by tendinous tissue, the thin diaphragm creates a partition between the thoracic and abdominal cavity. The
diaphragm forms a domed structure, and when the diaphragm muscle contracts, it lowers to a more flattened arrangement. This flattening causes a vacuum in the thoracic cavity and pressure in the abdominal cavity. The vacuum is filled by the expanding lung tissue and inhaled air. The pressure on the lower viscera are helpful in childbirth and in pushing fecal matter through the lower intestinal tract for expulsion. When the diaphragm relaxes to its domed structure, the air is exhaled and the lungs contract. Though the intercostal and abdominal muscles are also used in respiration, during sleep, it is primarily due to contractions of the diaphragm. The diaphragm is supplied by the inferior and superior phrenic arteries and the musculophrenic artery. It is innervated phrenic nerve. Research Diaphragm
The external oblique (obliquus externus abdominis) is a large, thin sheet of muscle that runs along the side of the torso and partly on the front. The muscle is divided into two portions; and upper thoracic portion and a lower flank portion. The thoracic portion is located along the rib cage. The lower flank portion is located along the side of the abdomen between the rib cage and the pelvis. The muscle originates from the fifth to twelfthribs and inserts in the lip of the iliac crest, inguinal ligament, and the rectus abdominis muscle. The individual ribs can be seen beneath this muscle when it is relaxed. Most of this muscle is concealed by a cushion of fat. The two portions meet at the waist. It is innervated by branches of the lower thoracic nerve and supplied branches of the lumbarartery and the intercostal arteries. This muscle assists the rectus abdominis muscle in flexing the spine when the trunk twists or turns. It also supports the abdominal organtissue. Research External Abdominal Oblique
The external oblique (obliquus externus abdominis) is a large, thin sheet of muscle that runs along the side of the torso and partly on the front. The muscle is divided into two portions; and upper thoracic portion and a lower flank portion. The thoracic portion is located along the rib cage. The lower flank portion is located along the side of the abdomen between the rib cage and the pelvis. The muscle originates from the fifth to twelfthribs and inserts in the lip of the iliac crest, inguinal ligament, and the rectus abdominis muscle. The individual ribs can be seen beneath this muscle when it is relaxed. Most of this muscle is concealed by a cushion of fat. The two portions meet at the waist. It is innervated by branches of the lower thoracic nerve and supplied branches of the lumbarartery and the intercostal arteries. This muscle assists the rectus abdominis muscle in flexing the spine when the trunk twists or turns. It also supports the abdominal organtissue. Research External Oblique
The femoral nerves branch off of the spinal cord between the second and fourth lumbarvertebrae. They extend down the leg to innervate the muscles and skin of the leg, including the thigh, knee, part of the calf, the ankle and the foot. Research Femoral Nerves
The iliocostals lumborum consists of several muscle straps that link the lumbar vertebrae and sacrum with the lower six or seven ribs. The muscle straps have a number of tendons, varying in different individuals, which insert in all angles in the lower six ribs. The muscle is innervated by dorsal branches of the lumbar and thoracic nerves and supplied by branches from the aorta. Research Iliocostalis Lumborum
The iliohypogastric nerve branches off of the spinal cord at the first lumbar vertebra. It extends to the skin which covers the pubis and the side of the gluteal region, at the waist. Research Iliohypogastric Nerve
The ilioinguinal nerves branch off of the spinal cord at the first lumbar vertebra. They extend down the abdominal wall to the groin, external genitals, and the upper thigh. Research Ilioinguinal Nerves
The iliopsoas is actually the blending of two muscles, the large, flat triangulariliacus and the fusiform psoas major. It is considered a single muscle group that begins deep in the back of the abdomen where the iliacus orignates from the iliac fossa and the psoas major originates from the bodies of the vertebrae and invertebral disks from the twelfth thoracic to the fifth lumbar and the transverse processes of the lumbarvertebrae. The muscle converges towards its insertion on the back of the femur. It is innervated by the lumbar plexus and supplied by posterior branches of the profunda femoris artery. This muscle is a powerful flexor of the hip joint. It flexes the thigh when kicking, or the pelvis and trunk when doing sit-ups. Research Iliopsoas
The internal oblique (obliquus internus abdominis) is a small, thin, deep muscle of the abdomen. It runs diagonally opposite underneath the external oblique. It has a quadrilateral form originating from the hipbone (crest of the ilium), and extending to the cartilage of the lower ribs (the tenth, elenenth, and twelfthribs). It is innervated by the lower thoracic nerves and supplied the intercostal and lumbar arteries. This muscle protects a weak point in the abdominal wall and works with the external oblique to help twist the torso. Research Internal Oblique
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Autonomic Nervous System
