Biopsychology: The PNS – Somatic and Autonomic Nervous Systems

The role of the peripheral nervous system (PNS) is to relay messages (nerve impulses) from the CNS (brain and spinal cord) to the rest of the body.

The PNS consists of two main components:

1) the somatic nervous system and

2) the autonomic nervous system

The somatic nervous system facilitates communication between the CNS and the outside world. The somatic nervous system is made up of sensory receptors that carry information to the spinal cord and brain, and motor pathways that allow the brain to control movement. Therefore, the role of the somatic nervous system is to carry sensory information from the outside world to the brain and provide muscle responses via the motor pathways.

The autonomic nervous system plays an important role in homeostasis, which maintains internal processes like body temperature, heart rate and blood pressure. The autonomic nervous system only consists of motor pathways and has two components: 1) the sympathetic nervous system and 2) the parasympathetic nervous system.

The sympathetic nervous system is typically involved in responses that prepare the body for fight or flight. Impulses travel from the sympathetic nervous system to organs in the body to help us prepare for action when we are faced with a dangerous situation. For example, our heart rate, blood pressure and breathing rate increase, while less important functions like digestion, salivation and the desire to urinate are suppressed.

The role of the parasympathetic nervous system is to relax the body, and return us to our ‘normal’ resting state. Consequently, the parasympathetic nervous system slows down our heart rate and breathing rate, and reduces our blood pressure. Furthermore, any functions that were previously slowed down during a fight or flight reaction are started again (e.g. digestion).