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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 “hardwired”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