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Maike Eagin
Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon, within the nerve, is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium. Nerve cells (often called neurons) are further classified as sensory, motor, or mixed nerves.
Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres.[2] Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.
Specific terms are used to describe nerves and their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to innervate that section of the body or organ. Other terms relate to whether the nerve affects the same side ("ipsilateral") or opposite side ("contralateral") of the body, to the part of the brain that supplies it.
The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, and the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud. When one of the growth processes finds the regeneration tube, it begins to grow rapidly towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is very slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect.[6]
A nerve conveys information in the form of electrochemical impulses (as nerve impulses known as action potentials) carried by the individual neurons that make up the nerve. These impulses are extremely fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, where the message is converted from electrical to chemical and then back to electrical.[2][1]
The nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body.[7] In vertebrates it consists of two main parts, the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain, brainstem and spinal cord. The PNS consists mainly of nerves, which are enclosed bundles of the long fibers or axons, that connect the CNS to all remaining body parts.
Nerves that transmit signals from the CNS are called motor or efferent nerves, while those nerves that transmit information from the body to the CNS are called sensory or afferent. Spinal nerves serve both functions and are called mixed nerves. The PNS is divided into three separate subsystems, the somatic, autonomic, and enteric nervous systems. Somatic nerves mediate voluntary movement.
The autonomic nervous system is further subdivided into the sympathetic and the parasympathetic nervous systems. The sympathetic nervous system is activated in cases of emergencies to mobilize energy, while the parasympathetic nervous system is activated when organisms are in a relaxed state. The enteric nervous system functions to control the gastrointestinal system. Both autonomic and enteric nervous systems function involuntarily. Nerves that exit from the cranium are called cranial nerves while those exiting from the spinal cord are called spinal nerves.
Multiple sclerosis is a disease associated with extensive nerve damage. It occurs when the macrophages of an individual's own immune system damage the myelin sheaths that insulate the axon of the nerve.
A pinched nerve occurs when pressure is placed on a nerve, usually from swelling due to an injury, or pregnancy and can result in pain, weakness, numbness or paralysis, an example being CTS. Symptoms can be felt in areas far from the actual site of damage, a phenomenon called referred pain. Referred pain can happen when the damage causes altered signalling to other areas.
Neurologists usually diagnose disorders of nerves by a physical examination, including the testing of reflexes, walking and other directed movements, muscle weakness, proprioception, and the sense of touch. This initial exam can be followed with tests such as nerve conduction study, electromyography (EMG), and computed tomography (CT).[8]
In organisms of radial symmetry, nerve nets serve for the nervous system. There is no brain or centralised head region, and instead there are interconnected neurons spread out in nerve nets. These are found in Cnidaria, Ctenophora and Echinodermata.
Modern research has not confirmed William Cullen's 1785 hypothesis associating mental states with physical nerves,[13] although popular or lay medicine may still invoke "nerves" in diagnosing or blaming any sort of psychological worry or hesitancy, as in the common traditional phrases "my poor nerves",[14]"high-strung", and "nervous breakdown".[15]
With nerve damage there can be a wide array of symptoms. Which ones you may have depends on the location and type of nerves that are affected. Damage can occur to nerves in your brain and spinal cord. It can also occur in the peripheral nerves, which are located throughout the rest of your body.
In some instances, people with nerve damage will have symptoms that indicate damage to two, or even three, different types of nerves. For instance, you might experience weakness and burning of your legs at the same time.
It is estimated that about 20 million Americans suffer from peripheral nerve damage. This type of damage becomes increasingly common with age. Up to 70% of people with diabetes have some nerve damage.
In many instances, nerve damage cannot be cured entirely. But there are various treatments that can reduce your symptoms. Because nerve damage is often progressive, it is important to consult with a doctor when you first notice symptoms. That way you can reduce the likelihood of permanent damage.
A pinched nerve occurs when too much pressure is applied to a nerve by surrounding tissues, such as bones, cartilage, muscles or tendons. This pressure can cause pain, tingling, numbness or weakness.
A pinched nerve can occur in many areas of the body. For example, a herniated disk in the lower spine may put pressure on a nerve root. This may cause pain that radiates down the back of the leg. A pinched nerve in the wrist can lead to pain and numbness in the hand and fingers, known as carpal tunnel syndrome.
Self-care measures such as rest and pain relievers available without a prescription may resolve the symptoms of a pinched nerve. See your healthcare professional if symptoms last for several days and don't respond to self-care.
In carpal tunnel syndrome, a variety of tissues may be responsible for compression of the carpal tunnel's median nerve in the wrist. It can be caused by swollen tendon sheaths within the tunnel, enlarged bone that narrows the tunnel, or a thickened and degenerated ligament.
If a nerve is pinched for only a short time, there's often no permanent damage. Once the pressure is relieved, nerve function returns. However, if the pressure continues, chronic pain and permanent nerve damage can occur.
Materials and methods: Fifty participants in the randomized, double-blind SUmiT (Sham Effectiveness in Treatment of Overactive Bladder Symptoms) Trial who met the primary effectiveness end point after 12 weekly percutaneous tibial nerve stimulation treatments were enrolled in this prospective study to assess long-term outcomes with percutaneous tibial nerve stimulation. STEP (Sustained Therapeutic Effects of Percutaneous Tibial Nerve Stimulation) Study patients were prescribed a fixed schedule 14-week tapering protocol followed by a personal treatment plan aimed at sustaining overactive bladder symptom improvement. Overactive bladder and quality of life questionnaires were completed every 3 months and 3-day voiding diaries were completed every 6 months.
Conclusions: Most STEP participants with an initial positive response to 12 weekly percutaneous tibial nerve stimulation treatments safely sustained overactive bladder symptom improvement to 3 years with an average of 1 treatment per month.
Nerve agents are chemicals that affect the nervous system. The health effects are similar to those produced by some pesticides. The main nerve agents are the chemicals sarin (GB), soman (GD), tabun (GA) and VX. These agents are man-made and have been manufactured for use in chemical warfare. These agents are known to be present in military stockpiles of several nations, including the United States.
A nerve uses chemical signals to transmit messages to organs and tissues in the body. Nerve agents block normal functioning of these chemicals at nerve endings. The nerve then sends too many signals. This constant signaling of the nerve can cause overload in parts of the body.
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