Nervous System Overview

Lesson Overview

In this lesson, we introduce the anatomy (structure) and physiology (functions and relationships) of the nervous system.


Gain an understanding of the foundational anatomy and physiology of the nervous system.


Define the nervous system and its functions. Explain what is included in the central nervous system (CNS), peripheral nervous system, somatic and autonomic nervous systems. Explain what is associated with the sympathetic nervous system and with the parasympathetic nervous system.


  • The nervous system consists of the brain, spinal cord, neurons, nerves, meninges, cerebrospinal fluid and sensory receptors.
  • The nervous system is divided into the central nervous system and peripheral nervous system.
  • The central nervous system (CNS) is comprised of the brain and spinal cord.
  • The peripheral nervous system contains all the nerves that lie outside of the spinal cord and brain. (See more below.)
  • The nervous system includes a collection of nerves and neurons that transmit signals between different parts of the body. “It is essentially the body’s electrical wiring.” (livescience)
  • Neurons communicate via electrical signals which are converted into chemical messengers called neurotransmitters.

Brain Communicates Using Neurons

The basic working unit of the nervous system is a cell called a neuron. The human brain contains about 100 billion neurons… The brain is made up of many networks of communicating neurons. In this way, different parts of the brain can ‘talk’ to each other as well as work together to send messages to the rest of the body. – National Institutes of Health 


The nervous system:

  • Regulates certain body processes such as blood pressure and the breathing rate, and
  • Connects the brain and spinal cord with muscles and sensory receptors.

The functions of the nervous system can be categorized as 1) sensory, 2) integration and 3) motor. (Inner Body, Nervous System)

  1. The sensory function involves collecting information and passing it on to the central nervous system.
  2. Integration refers to an evaluation of the signals by the brain and spinal cord.
  3. The motor function is the carrying of signals from the CNS that can result in, for instance, moving a part of the body.

Communicating Through Your Nerves

By communicating through your nerves, your nervous system constantly monitors the internal activities of your body systems, attempting to keep them in a healthy balance called “homeostasis.” It also monitors your environment to assess if it is safe or dangerous and sends messages to your body either to relax and enjoy or act quickly to get to safety.  – Yoga for Healthy Aging 

Peripheral Nervous System

  • While the CNS is defined as the brain and spinal cord, the peripheral nervous system includes all other parts of the nervous system which communicate between the CNS and the rest of the body.
  • The peripheral nervous system contains 12 cranial nerves and 31 pairs of spinal nerves and ganglia. (
  • The peripheral nervous system is divided into the somatic (voluntary) and autonomic (typically involuntary) nervous systems.

Somatic & Autonomic Systems

  • The somatic nervous system controls conscious bodily activities such as moving the arm.
  • The autonomic nervous system (ANS) governs the typically automatic functions, including breathing, heart rate and the endocrine (hormone) system.
  • The autonomic nervous system (ANS) is an area of particular focus for understanding how yoga practices reduce negative effects of chronic stress and improve health and wellness. The ANS is divided into the sympathetic and parasympathetic nervous systems, only one of which is activated at any time.

Sympathetic & Parasympathetic Systems

The sympathetic nervous system triggers the stress response. When stress is perceived to be excessive or threatening, a physiological reaction called the Fight or Flight Response occurs. See much more: Stress & Relaxation.

The parasympathetic nervous system controls the Relaxation Response and the Rest and Digest state (which indicates full parasympathetic activation when the body’s vital signs are in their calm state, and the immune, repair, and digestive systems are operating). See much more: Stress & Relaxation.

See also the Enteric Nervous System, made up of nerves found in the gut lining and sometimes called the “second brain.”