Nervous System

• The central nervous system is made up of the brain and the spinal cord, the peripheral nervous system (PNS) relays messages from the environment to the CNS, via sensory neurones, and from the CNS to effectors, via motor neurones.
• The PNS is further divided 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 and results in effectors being stimulated by the CNS, via motor neurones).
• The autonomic nervous system is also subdivided into the sympathetic and parasympathetic branches. These branches work as 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 rates, breathing rate, causes vasoconstriction and pupil dilation, whilst the parasympathetic nervous system decreases heart rate, breathing rates, causes vasodilation and pupil constriction.