Voluntary actions:

• Example: writing, walking, drinking
• Interpretation of information in the cerebrum
• According to our own will
• Effector: skeletal muscle
• Involves somatic nervous system
• Involve processes of analysis, integration, and interpretation of information

Involuntary actions:

• Example: heartbeat, sneezing, blood pressure
• Interpretation of information in the medulla oblongata
• Occurs automatically without notice
• Effector: smooth muscle, cardiac muscle, and glands
• Do not involve processes of analysis, integration and interpretation of information
• Involves the autonomic nervous system

Spinal reflex action involved skeletal muscle as an effector:

• This action is an involuntary action controlled by the spinal cord and responds quickly and spontaneously toward the external stimulus
• The nerve impulse is sent from receptors to the spinal cord and from the spinal cord to effectors
• The pathway passed by the nerve impulse in a reflex action is known as the reflex arc

Reflex arc of knee jerk (involve two types of neurones):

• Stimulus: the tendon below the kneecap is knocked
• Sensory receptors: stretch out the quadriceps muscle (stretch receptor) and triggers a nerve impulse
• Sensory neurone: sends nerve impulses to the spinal cord
• Motor neurone: receives the nerve impulse from the sensory neurone and send it to the effector
• Effector: quadriceps muscle contracts
• Response: leg kicks forward

Reflex arc involving three neurones:

• Stimulus: Finger touches fire.
• Sensory receptor: Skin (heat receptor) detects the heat and nerve impulse is triggered.
• Sensory neurone: Send nerve impulse to relay neurone.
• Relay neurone (in the spinal cord): Strech out the quadriceps muscle.
  • Receives nerve impulse from the sensory neurone and send it to the motor neurone.
• Motor neurone: Receives nerve impulse from relay neurone and transmits it to the effector.
• Effector: Biceps contract, triceps relax.
• Response: Hand pulls away from fire.