12.4 - Voluntary and Involuntary Actions

The responses produced can either be voluntary or involuntary actions. Here are some of the similarities and differences between voluntary and involuntary actions.

• Similarities

  • Both require stimulation, impulse, neuron and an effector organ

• Differences

  • Voluntary action

    • Types of nervous system involved: Somatic nervous system
    • Consciousness: Yes
    • Parts of the brain involved: Regulated by the cerebral cortex
    • Effector organs involved: Skeletal muscles

  • Involuntary action

    • Types of nervous system involved: Autonomous nervous system
    • Consciousness: Not conscious
    • Parts of the brain involved: Regulated by the medulla oblongata and hypothalamus
    • Effector organs involved: Smooth muscle and glands

Figure 11 - Voluntary actions such as walking and talking are under conscious control. Voluntary control of the skeletal muscles is controlled by the cerebral cortex of the cerebrum. Information that reaches the cerebral cortex results in a perception of the external environment.

Involuntary Actions Involving Skeletal Muscles: Reflex Response

Involuntary actions that involve skeletal muscles allow immediate action that does not require conscious effort. For instance, if you accidentally touch a hot stove, the reaction is to pull the finger away immediately without having to think about it. In such situations when the responses to stimuli are involuntary , they are called reflexes. The nerve pathway involved in a reflex action is called a reflex arc.

Figure 12 - The three-neuron reflex arc, involving 3 neurons and a spinal cord.

Importance of Reflexes

• Provide a means for immediate withdrawal from dangerous stimuli.
• Coordinate rapid automatic responses without the need for instructions from the brain.
• Since only the spinal cord is involved, the brain is reserved for more complicated tasks and analytical functions.

Figure 13 - The two-neuron reflex arc, involving 2 neurons only.