The nervous system is made up of special cells called neurons and a network of nerves. They transmit messages all over the body. The two parts of the nervous system are the central nervous system and the peripheral nervous system. The central nervous system includes the brain, spinal cord, and nerves. The peripheral nervous system is made up of sensory neurons, ganglia which are groups of neurons, and nerves connecting to other nerves and the central nervous system.
Neurons are bundles of fibers. They branch out to every part of the body from the brain and the spinal cord. The fibers are called axons. These axons cause chemicals or neurotransmitters to be released at a synapse or junction. There are over one hundred neural connections in the human brain. People who are more creative have more connections over three distinct parts of the brain.
The nervous system makes provision for a rapid response to stimuli in the environment. The purpose of this response is to counteract any adverse effects, as when a person quickly withdraws his hand from a hot stove to prevent a burn. Responses can include secretions from glands or contraction of muscle cells to provide protection from danger.
A synapse gives a signal to the neuron or cell. The fastest signal in the body occurs at 276 mph. It travels along an alpha motor neuron in the spinal cord. Sensory neurons, as in touching and smelling, transmit feedback to the central nervous system about what is going on in a person's environment. Motor neurons send signals to get muscles and glands working. The nerve cells themselves are taken care of by glial cells. Glial comes from the Greek word for glue.
Tests can be done to diagnose conditions in the nervous system. A fluoroscopy is a special x-ray which can see motion in the body, such as blood flowing. An EEG measures the brain's electrical activity. An MRI and CAT scan are other tests which can diagnose problems with the nervous system. A needle can be inserted into the spinal cord to draw out fluid for testing for infections or other conditions. This is called a spinal tap.
The most common problem involving the nervous system is chronic pain. Seizures occur from epilepsy because of abnormal electrical discharges from the brain. Movement is affected by a progressive nerve disease called Parkinson's disease. The body's own immune system attacks the lining of the nerves and causes Multiple Sclerosis. A motor neuron disease called ALS (amyotrophic lateral sclerosis) weakens muscles and slowly continues to decrease motor function. Nerve cells in the brain degenerate due to an inherited condition called Huntington's disease. Alzheimer's disease impairs mental functions, especially memory.
Other disorders can affect the nervous system. In a stroke, blood flow to the brain is blocked or there is bleeding on the brain. TIAs are mini-strokes which do not last very long but have the same symptoms as a stroke. A subarachnoid hemorrhage involves bleeding in the brain in the space between the brain and the membrane which surrounds it. Infections like encephalitis, meningitis, and polio also can have an impact on the nervous system.
A neurologist studies the nervous system. His branch of medicine is called neurology. Physiatrists work to help restore function in patients whose nervous system has been injured or has experienced disease. A person who performs surgery involving the nervous system is a neurosurgeon.
Invertebrates have a type of nervous system described as diffuse. Invertebrates have no brain. The nerves form a big net throughout the body. Organisms without a nervous system are not capable of complex behavior.
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