11 March 2014

#93 Voluntary and involuntary actions

Knee jerk is an involuntary reflex. 
Two types of action controlled by the human nervous system are: voluntary and involuntary actions. The peripheral nerves transmit both of them.  

Comparison of voluntary and involuntary actions 

Voluntary action
Involuntary action
- Conscious thought (make decision about making action).
- Free will
- Consciously control skeletal muscles
- Does not involve thought

- Not under the control of the will
- Cannot control the activities.


If we want to ask question, we raise our hands
- skeletal muscle (e.g. knee jerk)
- smooth muscles (e.g. peristalsis)
- cardiac muscles (e.g. pumping of the heart)
Respond with the benefit of experience

Respond quickly to avoid danger

Controlled by
Forebrain (Cerebrum):
- coordinates incoming information, initiates impulses sent to the effectors.
- may spontaneously initiates actions without any sensory stimulation.
- Hind-brain (cranial reflex action)  
- Spinal cord (spinal reflex action), e.g. blinking of the eyes

Speed of action

Slow response, as the cerebrum needs time to “think” before an action is carried out.

Rapid response, as the cerebrum is not involved.

Response to the same stimulus

The same stimulus may produce various responses.
E.g.  when you are hungry, you may decide to eat or not to eat, or  just need to drink water.

The same stimulus always results in the same response (stereotyped response), e.g. the knee jerk reflex.

Forebrain is responsible for voluntary actions,
hindbrain is responsible for involuntary actions.