This antagonistic functional relationship serves as a balance to help maintain homeostasis. In this case, one stimulates and the other inhibits. Many visceral organs are supplied with fibers from both divisions. The autonomic nervous system has two parts, the sympathetic division and the parasympathetic division. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. The autonomic nervous system is a visceral efferent system, which means it sends motor impulses to the visceral organs. Because all spinal nerves have both sensory and motor components, they are all mixed nerves.
The two roots join to form the spinal nerve just before the nerve leaves the vertebral column. The cell bodies of the sensory neurons are in the dorsal root ganglion, but the motor neuron cell bodies are in the gray matter. This means there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve.Įach spinal nerve is connected to the spinal cord by a dorsal root and a ventral root. Each pair of nerves corresponds to a segment of the cord and they are named accordingly. Thirty-one pairs of spinal nerves emerge laterally from the spinal cord. Many patients also exhibit no tumor growth over a number of years when followed by yearly MRI scans.
Usually, the symptoms are mild and many patients are not diagnosed until some time after their tumor has developed. In other cases, the growth rate is more rapid and patients develop symptoms at a faster pace. In the majority of cases, these tumors grow slowly over a period of years. As the tumors enlarge, they involve surrounding structures which have to do with vital functions. The location of these tumors is deep inside the skull, adjacent to vital brain centers in the brain stem. These tumors are non- malignant, meaning that they do not spread or metastasize to other parts of the body. The remaining four nerves consist of significant amounts of both sensory and motor fibers.Īcoustic neuromas are benign fibrous growths that arise from the balance nerve, also called the eighth cranial nerve or vestibulocochlear nerve. Five other nerves are primarily motor in function but do have some sensory fibers for proprioception.
Three of the nerves are associated with the special senses of smell, vision, hearing, and equilibrium and have only sensory fibers. Most of the nerves have both sensory and motor components. The cranial nerves are designated both by name and by Roman numerals, according to the order in which they appear on the inferior surface of the brain. All of these nerves, except the vagus nerve, pass through foramina of the skull to innervate structures in the head, neck, and facial region. Twelve pairs of cranial nerves emerge from the inferior surface of the brain. A nerve may also have blood vessels enclosed in its connective tissue wrappings. Within the fasciculus, each individual nerve fiber, with its myelin and neurilemma, is surrounded by connective tissue called the endoneurium. Each bundle of nerve fibers is called a fasciculus and is surrounded by a layer of connective tissue called the perineurium. Mixed nerves contain both types of fibers.Ī connective tissue sheath called the epineurium surrounds each nerve. Motor nerves have only efferent fibers, long axons of motor neurons. Sensory nerves contain only afferent fibers, long dendrites of sensory neurons. Structure of a NerveĪ nerve contains bundles of nerve fibers, either axons or dendrites, surrounded by connective tissue.
The autonomic nervous system consists of nerves that connect the CNS to the visceral organs such as the heart, stomach, and intestines.
#The somatic nervous system skin#
The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. Acknowledgements The Peripheral Nervous System
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