Voluntary and Involuntary Actions

• Two types of action controlled by the human nervous system are:

(a)voluntary action

(b)involuntary action

• The peripheral nerves transmit both voluntary and involuntary actions.

Voluntary action

Nature of the control of action

• Involves thought

and free will

• Allows us to consciously

control our skeletal

muscles

Voluntary action is controlled by:

• Cerebrum (fore-brain) which:

(a)coordinates incoming information and then initiates impulses which are sent to the effectors.

(b)may spontaneously initiates actions without any sensory stimulation.

Receptors involved:

• An action may be initiates by the stimulation of a receptor,or by the conscious will of the brain itself

Inborned or learned actions• Voluntary actions are learned

Role of voluntary action:

• To respond with the benefit of experience

Parts of the nervous system involved:

• Reflex arc structures • Interneurons(ascending and descending

fibres )in the spinal cord • Always involved the cerebrum

Speed of action:

• Slow response,as the

cerebrum needs time

to “think”before an

action is carried out.

• Eg. ) if we want to ask

question, we raise our

hands.

Response to the same stimulus:

• The same stimulus may produce various responses.

• Eg.) when you are hungry,you may decide to eat or not to eat, or just need to drink water.

Involuntary action

Nature of the control of action

• Does not involve thought

• Not under the control of the will

• Cannot control the activities

• examples; pumping of the heart and peristalsis

Controlled by:

• Spinal cord(spinal reflex action)

• Hind-brain(cranial reflex action) example blinking of the eyes

Parts of the nervous system involved:

• Reflex arc:afferent neurones(from receptors)to intermediate neurones in spinal cord and out through efferent neurones (to effectors)

• Hind-brain(in cranial reflex action)

Receptors involved:

• A receptor is always involved

Inborned or learned actions

• Reflex actions are inborn (already “hard-wired”at birth

Role of involuntary action:

• To respond quickly to avoid danger

Speed of action:

• Rapid response,as the cerebrum is not involved

Response to the same stimulus:

• The same stimulus always results in the same response(stereotyped response),example as in the knee jerk

Examples of involuntary action:

• Involuntary action(reflex action)involving skeletal muscle:

(a)knee jerk

• Involuntary action involving:

(a)smooth muscles

(b)cardiac muscles

(c)glands,example,normal blood pressure