ANS - The Sympathetic SYSTEM

The Autonomic Nervous System

The autonomic nervous system (ANS) regulates the functions of our internal organs (the viscera) such as the heart, stomach and intestines. The ANS is part of the peripheral nervous system and it also controls some of the muscles within the body. We are often unaware of the ANS because it functions involuntarily and reflexively. However, some people can be trained to control some functions of the ANS such as heart rate or blood pressure. The ANS is most important in two situations:• In emergencies that cause stress and require us to "fight" or take "flight" (run away)• In non emergencies that allow us to "rest" and "digest."

REST AND DIGEST

TAKE FLIGHT

The ANS regulates:• Muscles• - in the skin (around hair follicles; smooth muscle)

- around blood vessels (smooth muscle)- in the eye (the iris; smooth muscle)- in the stomach, intestines and bladder (smooth muscle)- of the heart (cardiac muscle)

• Glands• The ANS is divided into three parts:a) The sympathetic nervous systemb) The parasympathetic nervous systemc) The enteric nervous system

The Sympathetic Nervous System

As we notice in the picture, the sympathetic nervous system originates in the spinal cord. Specifically, the cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and lumbar spinal cord. Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another neuron (post-ganglionic neuron) in the ganglion. A few preganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post-ganglionic neuron then projects to the "target" - either a muscle or a gland.

The fight or flight responseSituation: It is a nice, sunny day...I’m going on a nice walk in the woods. Suddenly, a fierce boar appears in front of me.

What shall I do? Stay and fight OR run away? These are "Fight or Flight" responses. In these types of situations, the sympathetic nervous system is called into action - it uses energy - so blood pressure increases, heart beats get faster, and digestion slows down.

Neurotransmitters

The synapse in the sympathetic ganglion uses acetylcholine as a neurotransmitter; the synapse of the post-ganglionic neuron with the target organ uses the neurotransmitter called norepinephrine.

Acetylcholine

• Acetylcholine (often abbreviated ACh) is the most common neurotransmitter. It is located in both the central nervous system (CNS) and the peripheral nervous system (PNS).• Acetylcholine was the first neurotransmitter to be identified. It was discovered by Henry Hallett Dale in 1914 and its existence was later confirmed by Otto Loewi. Both individuals were awarded the Nobel Prize in Physiology in 1936 for their discovery.

Norepinephrine

Norepinephrine is both a neurotransmitter and a hormone. It is a catecholamine (a) produced by the (b) adrenal glands using (c) dopamine as a starting point. • (a) Catecholamines are a type of hormone known to strongly affect blood pressure by acting on the blood vessels and the heart. They are made from the amino acid tyrosine. Illness and certain types of cancers can increase the level of catecholamines in the body, leading to elevations in blood pressure and heart rate. • (b) The adrenal glands are small, triangle- or pyramid-shaped organs found near the top of each kidney. There are two adrenal glands - one on each side of the body. The adrenal glands produce a variety of hormones involved in stress reactions, blood pressure regulation, and the handling of vitamins and minerals. Certain types of adrenal gland problems can cause an increase in hormone release, leading to elevated blood pressure, rapid heart beat, or high/low levels of minerals and/or nutrients.• (c) Dopamine is a body chemical that plays important roles at several locations in the body.Dopamine levels are high in the brain, where it is necessary for: - Learning - Mood regulation - Information processing/integrationDopamine can also be given intravenously as a medication. In this capacity, it acts as a stimulant on the cardiovascular system and results in increased heart rate, increased blood pressure, and increased blood flow. Dopamine given this way does not affect the brain. Dopamine is the root chemical the body uses to synthesize catecholamines.

The parasympathetic nervous system

In the picture the cell bodies of the parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves III, VII, IX and X form the preganglionic parasympathetic fibers. The preganglionic fiber from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse. This synapse uses the neurotransmitter called acetylcholine. From this ganglion, the post-ganglionic neuron projects to the target organ and uses acetylcholine again at its terminal.

The rest and digest response

Situation: It is a bright, summer day...John is playing on the sand with Richard, his son, while Margie, his wife, is sitting on a beach towel in total relax. After some time, John decides to sit on a chair to relax, too. This calls for "Rest and Digest" responses. Now it is the time for the parasympathetic nervous to work to save energy. This is when blood pressure can decrease, pulse rate can slow, and digestion can start.

The restless activity of ANS

It should be noted that the autonomic nervous system is always working. It is NOT only active during "fight or flight" or "rest and digest" situations. Rather, the autonomic nervous system acts to maintain normal internal functions and works with the somatic nervous system. The enteric nervous system is a third division of the autonomic nervous system. It is a meshwork of nerve fibers that innervate the viscera (gastrointestinal tract, pancreas, and gall bladder).

The Enteric Nervous System

Summing up: the effects of sympathetic and parasympathetic stimulation

Structure Sympathetic Stimulation Parasympathetic Stimulation

Iris (eye muscle) Pupil dilation Pupil constriction

Salivary Glands Saliva production reduced Saliva production increased

Oral/Nasal Mucosa Mucus production reduced Mucus production increased

Heart Heart rate and force increased Heart rate and force decreased

Lung Bronchial muscle relaxed Bronchial muscle contracted

Stomach Peristalsis reduced Gastric juice secreted; motility increased

Small Intestine Motility reduced Digestion increased

Large Intestine Motility reduced Secretions and motility increased

Liver Increased conversion ofglycogen to glucose

Kidney Decreased urine secretion Increased urine secretion

Adrenal medulla Norepinephrine andepinephrine secreted

Bladder Wall relaxedSphincter closed

Wall contractedSphincter relaxed

Two effects of the sympathetic/parasympatetic stimulations

a) DILATED PUPIL(an effect of the sympathetic

stimulation)

b) SALIVA PRODUCTION INCREASED(an effect of the parasympathetic

stimulation)

LICEO SCIENTIFICO STATALE«G. GALILEI»

PescaraA.S. 2014-15

UDA CLIL: The Sympathetic/Parasympathetic

Systems and Humour

English Teacher: Miscia RobertaClass: III A