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Autonomic nervous system

Learning objectives

This study unit will help you to:

  1. Understand the divisions of the nervous system. 
  2. Define the autonomic nervous system and its functions. 
  3. Learn about the two main divisions of the autonomic nervous system. 
  4. Name the location, ganglia, and nerves of each division.

Watch video

The nervous system can be divided into central and peripheral nervous systems. The peripheral nervous system is further divided into the somatic and autonomic nervous systems. 

The autonomic nervous system (ANS) is a functional division of the nervous system that controls involuntary actions of muscles, glands and internal organs (e.g. bowel movements). Together with endocrine glands, the ANS affects important body functions without the direct involvement of the cerebral cortex. In contrast, the somatic nervous system mediates voluntary responses of the body (e.g. skeletal muscle function) and it’s under the direct control of the cerebral cortex. 

The ANS can be divided according to its location (central and peripheral parts) and function. Functionally, the ANS is divided into sympathetic (SNS) and parasympathetic (PSNS) nervous systems. They usually work antagonistically in their target organs but in a well-integrated manner. It is the balance of the actions of both divisions that maintains a stable internal environment in the body.

This video tutorial will provide you with an overview of the autonomic nervous system.

Take a quiz

Now that you have watched the videos about the autonomic nervous system, solidify your knowledge by taking our quiz. 

Are you already a pro? To expand the number of topics you’ll get quizzed on, try out our custom quiz about the peripheral nervous system:

Browse atlas

Take a closer look at the sympathetic and parasympathetic nervous systems in the gallery below. 


Key facts about the sympathetic nervous system
Origin Intermediolateral columns of spinal cord T1-L2/L3
Ganglia Paravertebral ganglia (sympathetic trunk), prevertebral (collateral/preaortic) ganglia
Output nerves Periarterial carotid nerve plexuses (T1-T3): Supply head and neck
Cardiopulmonary splanchnic nerves
(T4-T6): Supply thoracic viscera
Greater, lesser, and least thoracic splanchnic nerves
(T7-T11): Supply abdominal viscera
Lumbar splanchnic nerves
(T12-L3): Supply pelvic viscera
Function Eye: Mydriasis (pupil dilatation), contraction of levator palpebrae superioris muscle (opens eyelids)
Respiratory system:
Cardiovascular system:
SA node stimulation (increasing heart rate), positive inotropic effect (increasing force of myocardial contraction), vasoconstriction of peripheral circulation
Gastrointestinal system
: Inhibition of salivation, inhibition of gastrointestinal secretion and motor activity, contraction of gastrointestinal sphincters and blood vessels
Urinary system
: Relaxation of urinary bladder, relaxation and contraction of the sphincter uretrae muscle, renin release
Genital system
: Facilitation of ejaculation
Adrenal system
: Catecholamine release from suprarenal glands
: Contraction of arrector pili muscle, sweat release
Key facts about the parasympathetic nervous system
Origin Cranial outflow: Brainstem
Sacral outflow:
S2-S4 segments of spinal cord
Ganglia Ciliary, pterygopalatine, otic, submandibular, abdominopelvic ganglia on the walls of the abdominopelvic organs
Output nerves Cranial outflow: Branches of oculomotor (CN III), facial (CN VII), glossopharyngeal (CN IX), and vagus (CN X) nerves – supply head, neck, heart, larynx, trachea, bronchi, lungs, liver, gallbladder, stomach, pancreas, kidney, small intestine, proximal large intestine
Sacral outflow:
Pelvic splanchnic nerves: supply descending colon, sigmoid colon, rectum, bladder, penis/clitoris
Function Eye: Myosis (pupil constriction), relaxes the fibrae zonulares (accommodation), facilitates the flow of tears
Respiratory system
: Bronchoconstriction, facilitates secretion of respiratory glands
Cardiovascular system:
Decreases heart rate (inhibitory effect on SA node), vasodilation of peripheral vasculature
Gastrointestinal system
: Facilitates salivation, increases secretion, peristalsis and digestion of food; facilitates secretions of intrinsic glands, pancreas and release of bile from gallbladder; relaxes sphincter muscles
Urinary system:
Facilitates contractions of urinary bladder and passage of urine
Genital system:
Stimulates erection of penis and clitoris

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