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
Cardiac muscle is red-coloured involuntary muscle that contracts automatically and rhythmically, like a smooth muscle, but is striated and multinucleated, like skeletal muscle. The muscle is fast- acting and powerful. It is under the control of the autonomic nervous system and continuously contracts and relaxes throughout life. Research Cardiac Muscle
The nervous system of the human anatomy is responsible for sending, receiving, and processing nerve impulses. All of the body's muscles and organs rely upon these nerve impulses to function. Three systems work together to carry out the mission of the nervous system: the central, the peripheral, and the autonomic nervous systems. The nervous system may be basically classified as comprised of the central nervous system and the peripheral nervous system. The central nervous system is responsible for issuing nerve impulses and analyzing sensory data, and includes the brain and spinal cord. The peripheral nervous system is responsible for carrying nerve impulses to and from the body's many structures, and includes the many craniospinal nerves which branch off of the brain and spinal cord. The autonomic nervous system is composed of the sympathetic and parasympathetic systems and is responsible for regulating and coordinating the functions of vital structures in the body. Of all of these components, the brain is the primary component of the nervous system, occupying the cranial cavity and comprising 97% of the nervous system. The brain is connected to the
upper end of the spinal cord and is responsible for issuing nerve impulses, processing nerve impulse data, and engaging in the higher order thought processes. Research Nervous System
Smooth-muscle cells are not attached to the skeleton, but are found in the walls of the blood vessels, the digestive tract, and in the dermal layer of the skin. They react slowly to stimuli from the autonomic nervous system and perform actions such as forcing food through the intestines, transporting urine to the kidneys and pumping blood through blood vessels. The muscle is non-striated and consist of spindle-shaped, uni-nuclear cells that are not bound together, as in skeletal muscle. Like skeletal muscle, smooth muscle has fibrillae but without cross striations. The muscles are involuntary, and are slow-acting, untiring, and weak in action. Research Smooth Muscle
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Autonomic Nervous System
