The nervous system enables us to respond to our environment and coordinate our actions. If the body is to function properly, the conditions inside it must be carefully controlled.

Divisions of the nervous system

The human nervous system is made up of the following components:

  • the central nervous system (CNS) – the brain and spinal cord
  •  the peripheral nervous system (PNS) – parts of the nervous system outside the brain and spinal cord. It includes the cranial nerves, spinal nerves and their roots and branches.
The central nervous system
The brain and spinal cord are the key locations of the central nervous system where neurological information is correlated and integrated. The brain and spinal cord are both protected by a system of membranes called meninges, and are suspended in cerebrospinal fluid; they are further protected by the skull and vertebral column bones.

The peripheral nervous system can be further divided into the sensory  or afferent division which includes nerves that have a sensory function and carry impulses to the CNS for integration, and the motor or efferent division which include nerve fibers that carry impulses away from the CNS to initiate an effector. 

The somatic nervous system (SNS), which controls voluntary motor responses, and the autonomic nervous system (ANS), which controls involuntary motor responses, are the two main subdivisions of the motor division.

divisions of the nervous system
Divisions of the nervous system

Divisions of the Autonomic Nervous System

The two divisions of the autonomic nervous system are the sympathetic division and the parasympathetic division.  Many of the internal organs are regulated by the autonomic nervous system through a balance of two aspects, or divisions. In addition to the endocrine system, the autonomic nervous system plays an important role in the body’s homeostatic systems. The sympathetic nervous system is linked to the fight-or-flight reaction, while parasympathetic activity is known as “rest and digest.” The balance between the two systems is known as homeostasis. Dual innervation determines activity at each target effector. The sympathetic and parasympathetic divisions, for example, both connect to the heart. One causes an increase in heart rate, while the other causes a reduction in heart rate.

Functions of the nervous system

The nervous system controls:

  • Brain growth and development
  • Sensations (such as touch or hearing)
  • Perception (the mental process of interpreting sensory information)
  • Thought and emotions
  • Learning and memory
  • Movement, balance, and coordination
  • Sleep
  • Healing and rehabilitation
  • Stress and the body’s responses to stress
  • Aging
  • Breathing and heartbeat
  • Body temperature
  • Hunger, thirst, and digestion
  • Puberty, reproductive health, and fertility

Neuroscientists study these and other nervous system functions in both healthy and diseased states. Studying and understanding the nervous system is important because it affects so many areas of human health and well-being.