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Tot i 3107 108 undergo further branching, each branch ending in an axon terminal. These terminals are responsible for transmitting chemical signals from the neuron to the cells contacted by the axon terminals. However, the axons of some neurons release their chemical messengers not from the axon terminals, but from the series of bulging areas along the axon known as varicosities.
The axons of some neurons are covered by a fatty membranous sheath myelin, formed by nearby supporting cells that wrap their plasma membranes around the axon. Myelin speeds up passage of the electric signals along the axon. As in other types of cells, a neuron's cell body contains the nucleus and ribosomes and thus has the genetic information and machinary necessary for protein synthesis. In order to maintain the structure and functions of the cell processes, particularly when they are long, diverse organelles and materials must be moved to them from the cell body, where they are made. This is termed axon transport
Neurons can be divided into three functional classes; afferent neurons, efferent neurons, and interneurons. Afferent neurons (sensory neurons) convey information from the tissues and organs of the body into the brain and spinal chord; efferent neurons (motor neurons) transmit electric signals from the brain and spinal cord to the muscle or gland cells termed as effector cel interneurons connect the afferent and efferent neurons (Figure 2).
Stimuli and Action Potential
The concept of stimulus denotes every change in the surroundings of the organism or part of it (organ, tissue, cell) leads to a reaction. More specifically at cellular level, a stimulus is a short lasting change in the surrounding areas of the cell resulting in an electrical action of the cell membrane.
In response to the stimulus an action potential arises. An action potential is an electrical current which is transmitted through the cell membrane. Nerve cells (neurons) are sensitive to various stimuli. Due to their having long process (nerve fibres), nerve cells are extremely suitable to transmit stiinuli. The nerve fibres could be seen as the electrical wires of the body.'
Na+ (Sodium) Influx, K+ (Potassium) Efflux
The propagation of electrical signals is a result of changes in ion concentrations inside and outside the cell membrane. When a nerve cell is at rest (polarized neuron), the concentration of K+ ions in the intracellular milieu is greater than immediately outside. The same is true for Nations; there are more 106 AM ||||||||||||||||||||||||||||||||II V
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