Lesson 2 The Autonomic Nervous System

Lesson 2: The Autonomic Nervous System

Learning intentions: • Describe the role and function of the

two divisions of the ANS : sympathetic and parasympathetic

• Explain the flight or fight response

Role of ANSAutonomic means not under voluntary control (i.e. automatic, independent).

The autonomic nervous system is a network of neurons connecting the CNS to our internal muscles and organs.

It functions continuously whether we are awake, asleep, or even under a general anaesthetic. It may be the only part of the nervous system keeping a person alive when all other parts of the brain have shut down (eg. In a coma).

Automatic Nervous System

SympatheticParasympathetic

Parasympathetic

The parasympathetic nervous system serves two main functions:

1. It returns the body to a calm state by reversing the direction of the changes to physiological functions that had occurred as a result of the

action of the sympathetic nervous system.

2. It minimises energy use and keeps the internal systems of the body constantly regulated. This process is known as homeostasis.

For most of the time, the parasympathetic system is dominant because it is involved with normal everyday functioning, rather than in sudden reactions

to stressful or threatening situations. It regulates such functions as the digestion of food, the elimination of wastes, and the production of tears.

Sympathetic

The flight-fight response is an automatic reaction by the sympathetic nervous system to prepare the body for dealing with a physically or psychologically threatening situation. Normally, when placed under threat, an organism will fight or flee. In either case, its bodily resources need to be maximised for survival. Therefore, instead of using energy digesting lunch, blood and its energy giving substances (oxygen, sugar, fats) are diverted to the muscles, especially those of the limbs, since they are the ones most likely to be called upon whether the fight or flight option is chosen, if the threat is a physical one.

From the diagram above, it is clear that all the changes that occur in SYMPATHETIC AROUSAL are those that are getting the body ready for physical exertion. Because the body would suffer if it was left in that state for long, as soon as the threat is past, the PARASYMPATHETIC NERVOUS SYSTEM returns the

functions to the normal state of balance (homeostasis).

An example of the Sympathetic Nervous System in action….. It is a nice, sunny day...you are taking a nice walk in the park.

Suddenly, an angry bear appears in your path. Do you stay and fight OR do you turn and run away? These are "Fight or Flight" responses. In

these types of situations, your sympathetic nervous system is called into action - it uses energy - your blood pressure increases, your heart

beats faster, and digestion slows down.

An example of the Parasympathetic Nervous System in action… It is a nice, sunny day...you are taking a nice walk in the park.

This time, however, you decide to relax in comfortable chair that you have brought along. This calls for "Rest and Digest" responses. Now is the time for the parasympathetic nervous to work to save energy - your blood pressure decreases, your heart beats slower, and digestion can

start