The Divisions of the Nervous System

The nervous system is made up of the brain and the spinal cord

The peripheral nervous system (PNS) relays messages from the environment to the central nervous system (CNS), via sensory neurons, and from the CNS to effectors, via motor neurons.

The PNS is further subdivided into the autonomic nervous system (which controls involuntary, vital functions of the body, such as maintaining heart rates and breathing rates) and the somatic nervous system (which receives information from sensory receptors belonging to each of the 5 senses, and results in effectors being stimulated by the CNS, via motor neurons).

The autonomic nervous system is also subdivided into the sympathetic and parasympathetic branches.

These branches work as a part of an antagonistic pair during the 'rest and digest' response, and are crucial in producing the physiological arousal needed to maintain the fight or flight response.

For example, the sympathetic nervous system increases heart rate, breathing rate, causes vasoconstriction and pupil dilation, whilst the parasympathetic nervous system decreases heart rate, breathing rate, causes vasodilation and pupil constriction.