Nervous response

When you hand got pricked by a sharp needle, you withdraw your hand away quickly from the needle or you try to move the needle away.

The above is a typical example of a nervous response.

What is a nervous response?

In a nervous response, there must be:

• a stimulus (plural: stimuli) detected by receptors (pain receptors on fingers detect pain)
• a response performed by effectors
  • voluntary (we know we are doing this action e.g. move the needle away to a safe place) OR
  • involuntary / reflex (actions performed without our knowing at that instant e.g. moving hand quickly away, pupil decreasing in size under strong light )
• a nervous system links the receptors to the effectors

In short, the nervous system coordinates the different parts of the body, to bring about responses to stimulus.

Points to note:

1) Threshold intensity

Not all stimuli can cause a reaction in the end. Some of them are too weak or too short in duration. In more scientific terms, the stimuli need to be able to reach the threshold intensity --- strong in intensity or long in duration to illicit an action potential.

2) Action potential

Do not be intimidated by this word. Action potential is the same as impulse.
"Potential" refers to the difference in amount of charges between the outside and inside of a nerve fibre. (~difference in potential between the two ends of a battery)

A stimulus evokes the generation of an "action potential", a temporary change in amount of charges which travels down the nerve fibre. (~signal travelling down a telephone wire)

3) Generator potential

Generator potential is different from action potential. Generator potential does not travel along the nerve fibre. You may consider it to be a localized change in the concentration of various types of electrolytic charges. This is involved in the functioning of rods.

You may need many generator potentials to add together to cause a nerve impulse (action potential) to fire off ----- summation.

4) Our brain

Our brain can be divided into many regions. One of these is the cerebrum for coordinating voluntary actions. The reflex centres (e.g. in the medulla oblongata) are for involuntary / reflex actions.

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