Reflex Action
These are the sudden, automatic response of the body which are shown for certain stimuli without the will of the person. Therefore, they are called involuntary actions or reflex actions.
The spinal cord also controls involuntary movements called reflex actions or simply Reflexes.
Reflex arcs, as shown in figure 1.5,are nerve pathways that need to cross only two synapses before producing a response. It is because the signal nerve has to travel up the spinal cord to the brain react quickly.
Fig 1.5: Reflex Action and Reflex Arc
For example, when the doctor taps your knee, your knee tissues that connect knee cap to leg muscles stretch and stimulate a sensory neuron in your leg.This sensory neuron sends an impulse to your spinal cord.
An inter neuron in the spinal cord directs the impulse to the motor neurons. That is the reason, your leg jerks when the doctor strike or tap it.
This jerk is an example of reflex action.so reflex action is an automatic, unintentional that cannot be controlled and reflex arc is the nervous pathway which carries the impulses causing reflex action.
You do not feel the pain until moment after you jerk your hand away. If you didn't have reflex arc,your hand will remain on the stove until our brain interpreted the heat detected by thermo receptors in your skin. Your hand would be badly burned before your reaction.
Primary Actions
There are two types of actions occur in our body. These are voluntary actions and involuntary actions.
- Voluntary Actions
The actions which are under the control of brain i.e, reading of book, writing, driving, and speaking etc are called voluntary actions.In a voluntary action the sensory stimuli may be conveyed directly to brain through sensory neurons or may first to the spinal cord.
From spinal cord, the information may be passed on to the brain by associative neurons. The brain comprehends the information and sends motor impulse to the specific effectors for relevant controlled response
2. Involuntary Actions
Involuntary actions are those which are directly under the control of specific parts of the brain or spinal cord. We can't do these actions with our intentions.
Examples include the heart beat, working of the digestive system etc. In a reflex actions, For example, when we accidently touch something very hot, the hand is at once withdrawn. What happens is that the sensory fiber carries the impulse to the spinal cord.
From it, message is transmitted to the muscles of arm which contract and the hand is withdrawn without the involvement of brain.
