Autonomic Nervous System

Question 1

Define the ANS

Answer 1

The autonomic nervous system (ANS) is a network of nerves and ganglia that controls involuntary physiologic actions and maintains internal homeostasis and stress responses

Question 2

Describe functions of the sympathetic and parasympathetic nervous systems

Answer 2

Sympathetic:
* Fight flight
• It is the emergency system
• It prepares the body to put out energy and to protect it from effects of injury
It shuts the gut down, speeds up the heart, increases blood pressure, dilates the pupils of the eyes, makes more glucose available in the blood for energy

Parasympathetic:
* Rest and digest
• It is the “housekeeping” division
• It usually acts in opposition to the sympathetic system
It activates the gut for digestion, slows the heart rate, decreases the blood pressure, etc.

Question 3

What is the anatomical basis for division of the SNS and PSNS?

Answer 3

Sympathetic:

• Pre- G neurons arise from the thoracic and lumbar regions of the spinal cord
• Pre-ganglionic neurons are short. They are cholinergic = acetylcholine is the neurotransmitter
• Post ganglionic neurons are long. They are adrenergic = epinephrine and norepinephrine are neurotransmitters

Parasympathetic:
* The preganglionic neurons arise from the brain stem and the sacral region of the spinal cord
• Parasympathetic pre-ganglionic neurons are long, while post-ganglionic neurons are short
* Pre and post ganglionic parasympathetic neurons release acetylcholine

Question 4

Name the major neurotransmitters that are released by:

• preganglionic autonomic neurons
• postganglionic sympathetic neurons
• postganglionic parasympathetic neurons
• adrenal medullary cells

Answer 4

Preganglionic autonomic neurons:
Acetylcholine

Postganglionic sympathetic neurons:

• Epinephrine
• Norepinephrine

Postganglionic parasympathetic neurons:
* Acetylcholine

Adrenal medullary cells:
• Secrete hormones instead of NTMs
* It converts the amino acid tyrosine, into the catecholamines; epinephrine, norepinephrine, anddopamine

Question 5

Name the major neurotransmitters that are released by:

• preganglionic autonomic neurons
• postganglionic sympathetic neurons
• postganglionic parasympathetic neurons
• adrenal medullary cells

Answer 5

Preganglionic autonomic neurons:
Acetylcholine

Postganglionic sympathetic neurons:

• Epinephrine
• Norepinephrine

Postganglionic parasympathetic neurons:
* Acetylcholine

Adrenal medullary cells:
• Secrete hormones instead of NTMs
* It converts the amino acid tyrosine, into the catecholamines; epinephrine, norepinephrine, anddopamine

Question 6

Describe the types of receptors on autonomic ganglia and on various target organs

Answer 6

• Post-ganglionic neurons (Sympathetic and Parasympathetic systems): Nicotinic receptors

• Nicotinic receptors are ionitropic receptors: they work as ion channels
• When Acetylcholine binds to a nicotinic receptor, it opens it up and allows Na+ ions to enter neuron. This leads to action potential
• Effector organs connected to SNS: adrenergic receptors
• Effector organs connected to PSNS: muscarinic receptors
• When muscarinic receptors are stimulated, it causes a decrease in the heart rate, a decrease in heart contractility and a decrease in the size of the bronchioles

Adrenergic and Muscarinic receptors are Metabotropic receptors. Metabotropic receptors link to G protein that acts via intracellular second messengers

Question 7

Understand how anaesthetics and anaphylaxis are treated with drugs that act on the ANS

Answer 7

• Epinephrine activates both α- and β-adrenoceptors
• It is secreted together with norepinephrine by the adrenal medulla in response to stress
• Local anaestheticscause dilatation of blood vessels
• The addition of a vasoconstrictor such asadrenaline/epinephrine to thelocal anaestheticpreparation diminisheslocalblood flow, slowing the rate of absorption and thereby prolonging theanaestheticeffect
• Anaphylaxis: Epipen, adrenaline acts quickly to open up the airways, reduce swelling and raise the blood pressure