Neurons

As we earlier discussed in our day to day physical activities the coordinating fun ction of our muscles to do those activities is a necessity.Have you ever considered how the muscles involved in those physical activities?When we consider this we can see that there is a scientific system to activate and coordinate the muscle to perfrom those activities.In this process it necessary for the body to transmit messages to eneble the muscles to produce the complex movements for  successful physical activity.Such messages are transmitted through specialized cells called neurons. Neurons are the basic elements of the nervous system.They are the cells that are specialized for communicating information.It is estimated that they are 100 -200 billion neurons in the brain itself (Feldman,1993)

Neurons have a basic structure of

     Cell body

     One axon

     One or more dendrites

     Cell body

The cell body or (soma) is the bulbous portion of the neuron containing the cell nucleus. The cell body 

(soma) makes use of nutrients to supply energy for the neuronal activity.

Axons

Axons are the long tube like extensions which starts from the cell body. Axons caarry informations away from the cell body. The axon’s main job is to send signals to the dendrites of another neuron. Each neuron has only one axon , but the axon may have branches, which are called terminal buttons,through which messages are relayed to other cells.dendrites  are clusters of fibers at one end of a neuron that receive messages from other neurons.

Myelin Sheath

Myelin Sheath is the protective coating Which covers the axon tube.The Myelin Sheathis made up of speicalized cells of fats and protein.In addition to providing protection for the axon ,the myelin sheath serves to increase the speed of electrical impulses travel through the axons.

”Those neurons that carry the most important and urgently required information have the greatest conceration of myelin.If your hand touches a hot stove ,the information regarding the pain is passed through neurons in the hand and arms that contain a relatively large quantity of myelin,speeding the message of pain to the brain.In certain diseases such as multiple sclerosis ,the myelin sheath surrounding the axon deterirates exposing the parts of the axon that are normally covered.The result is a kind of short circuit that causesa disturbance in message between the brain and muscles and result is symptoms such as the inability to walk and vision difficulties etc”

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Firing of neurons for sending signals

According to the availability of signals or electrical impulses the neuron fires or activates.

At a given moment a neuron either fires or does not fire.There is nothing in between stage.This is called “All o None Law”;principle that is the state of neurons which are either (firing)or off (resting).When they are off ,it is called resting stage and in this stage there is a negative electrical charge of about 70 milivolts within the neuron.

Action potential

When a message arrives for a neuron,the cell walls in the neuron allow positively charge ions to rush in suddenly.These positive ions cause changes in the cell from negative to positive and in this stage an electrical nerve impulses known as an “action potential” travels down the neuron.

Absolute refractory period

Just after an action potential has passed,the neuron cannnot be fired again immediately.This stage is known as “Absolute refractory period”.In this rcovery period the neuron cannnot fire or trigger,although it receives messages

Relative refractory period

This is the period during which the neuron returns to its resting state and is ready to be fired once again.

Synapses

The human body is more spohisticated than a radio or any other such apparatus.There is not structural connection between two neurons instead there is a chemical connection between them known as Synapse,through which message pulses to the other neuron.

The Synapse is the gap between neurons through which chemical messages are communicated.The gaps actually exist between axon and dendrite of another neuron.

Neurotransmitters

The gap between the axon and the dendrite is bridged by chemicals called neurotransmitters.The terminal button at the end of the axon holds synaptic vesicles.When the signal (message)reaches the end of the axon,the vesicle discharge a chemical called a neurotransmitter.

Neurotransmitters are chemicals that are used to relay ,amplify and modulate electrical signals between a neuron and another neuron cell.The neurotransmitters from the axon fit into receptors of the dendrite on the next neuron.They will then either excite the cell or make it fire or inhibit it and stop it in doing so.

Some of the major neurotransmitters are acetylcholine,dopamine,epinephrine,nor epinephrine,serotonin,glycine and glutamic acid.In addition to functioning either as an exciter or inhibitor.

Neurotransmitters make behavioural disorders when there is a deficiency.For exsample followings are the 

behavioural disorders due to deficiency of specific neurotransmitters.

       Dopamine           -  Uncontrollable termor

       Serotonin            -  Depression

       Norepinephrine  -  Depression 

       Acetylcholine     -  Paralysis ,Violent Muscle Contraction Dementia

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