Nervous System

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Somatic motor neurons innervate skeletal muscles and are under voluntary control. Individuals taking anti-psychotic medications should consult with their physicians prior to using any products containing stevia. This now causes the electrical impulse to be regenerated. What is the CNS? Take the quiz Name That Thing Test your visual vocabulary with our question challenge! Your central nervous system is composed of your brain and spinal cord and serves as the collection point for nerve impulses.

What are some disorders of the nervous system?

Brain and Nervous System

Any time one appears, it can instantly ruin your day. You need to be careful when trying to get rid of toothache. It could be a sign of something more serious. Osteoporosis is a silent disease that slowly deteriorates the bones. The damage it causes can be irreversible, but it is possible to prevent its appearance by consuming foods that are rich in calcium and maintaining a balanced diet.

The hardening of our arteries is an inevitable part of aging. Arteriosclerosis is noticed earlier in some people than in others. However, the truth is that as you age, more and more arteries will harden, so its important to treat arteriosclerosis. Information travels along these circuits via electrical signals. All neurons have a center portion called a cell body and 2 extensions called dendrites and axons.

Dendrites receive signals from other neurons and transmit electrical charges to the cell body. Axons transmit the electrical charges away from the cell body. When the current reaches the end of the axon, the axon releases chemicals called neurotransmitters. Neuro-transmitters pass the signal to the dendrites of other neurons, or to muscles or glands.

Neurons in the peripheral nervous system combine to form pairs of spinal nerves and pairs of cranial nerves. The spinal nerves arise from the spinal cord and extend axons outward into the front and hind legs and to the bladder, anus, and tail.

These nerves subdivide into smaller nerves that cover the entire surface and interior of the body. The main wires in the system are long slender processes from neurones, and these processes are called axons. There are many axons in the nerve cord, but most are small, however, five are especially large and easily seen under the microscope - these are the giant axons.

These are axons with very large diameters. The dorsal giant axons is the widest, with a diameter of about 50 micrometres. An axon is rather like an electrical wire, and just as electricity flows more easily and faster along a wide wire than along a narrow wire which provides more resistance to the flow of electricity so the nervous signal flows faster along giant axons. The nervous signal is positive electricity, consisting of the flow of positively charged ions, whereas electricity in electrical wires is negative electricity, consisting of the flow of negatively charged electrons.

These giant axons are used to carry the fastest signals along the nerve cord, and these are emergency signals that initiate escape reflexes. The larger dorsal giant axon conducts signals the fastest and in the direction from aft to fore only.

This sends signals from the rear of the worm forwards, such that if something unexpected touches the rear of the worm, a rapid signal is sent forwards along the nerve cord, causing the longitudinal muscle sin each segment to rapidly contract, shortening the worm rapidly in an attempt to escape from a would-be predator or other threat.

The two dorso-lateral giant axons connect with each other and send signals from the front end to the rear, in case the worm has to make a rapid retreat perhaps contracting into its burrow to escape a curious bird. The giant axons are made up of a number of cylindrical cells all connected end-to-end. The junctions between neighbouring cells contain fast electrical synapses nexuses that allow the electrical signal to rapidly travel from one cell to another on its way down the axon.

Sensory systems The CNS is a series of tiny but powerful! This sends out nerves, such as the segmental nerves, to the muscles and sensors of the worm. The job of the CNS is to analyse the incoming sensory information from the various sensors and determine a course of action and then send out the appropriate instructions to the muscles.

One type of important sensor are photoreceptors light sensors. Earthworms have no eyes although many other worms do, eyes are not so useful when you spend most of your life buried in soil or crawling about at night. However, worms do have light sensors in the form of specialised nerve endings called light cells of Hess. These sensors occur in most parts of the worm's skin, but they are concentrated in certain areas. They are more concentrated on the back and sides of the worm, though a few do occur on the ventral surface at the front end 1st segment of the worm.

They are also much more concentrated toward the front end of the worm, being most numerous in the prostomium the front-most lobe which is not a true segment and dwindling in density in the first three segments and are very few in number past the third segment.

There are also quite a few on the rear-most segment of the worm, including its ventral surface. Note that the front and back ends of the worm are often lifted up above the ground and so having some light sensors underneath the front and back ends, as well as one the sides and back, makes sense. So, the prostomium is the main light-sensing region of the worm.

The prostomium is innervated by a pair of branching nerves from the cerebral ganglia. These branches from the subepidermal and intermuscular plexuses.

Some of the fine branches in the subepidermal plexus end in photoreceptors light-sensitive cells.

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