Autonomic Nervous System

Question 1

What is the autonomic nervous system?

Answer 1

Sub-section of peripheral nervous system that regulates involuntary processes from CNS to peripheral organs e.g. heart rate, digestion, respiration

Question 2

What are the 3 divisions of the ANS?

Answer 2

• Sympathetic - links CNS to peripheral organs
• Parasympathetic - links CNS to peripheral organs
• Enteric nervous system- controls GI tract

Question 3

What is the autonomic nervous system comprised of?

Answer 3

• 2 efferent (transmit away from CNS) neurones
• Pregranglionic neurons which synapse onto Postganglionic neurons- these innervate target organs

Question 4

Describe the parasympathetic nerves

Answer 4

• Have long pre-ganglionic fibre, short post- ganglionic fibre

Question 5

Where do the parasympathetic pre-ganglionic fibres arise from?

Answer 5

• Cranial nerves 3,7,9 and 10 and the sacral spinal cord 2,3,4
  Brainstem

Question 6

Where do the parasympathetic preganglionic fibres synapse with postganglionic fibres?

Answer 6

• At the head or near the wall of an organ supplied by vagus or sacral nerves
• The vagus nerve contains about 75% of all parasympathetic fibres

Question 7

What do the parasympathetic pre-ganglionic fibres release, and where does the neurotransmitter act?

Answer 7

• ACh, which acts at nicotinic (Nic) receptors

Question 8

What do the parasympathetic post-ganglionic fibres release and where does the neurotransmitter act?

Answer 8

• ACh which acts at muscarinic (Mus) receptors
• Exception is non-adrenergic-non-cholinergic (NANC) nerves which use chemicals such as nitric acid (NO)

Question 9

What are the functions of the parasympathetic nervous system?

Answer 9

• Slows heart rate and lowers blood pressure
• Vasodilates gut and stimulate gut motility and secretions
• Constricts pupil and contracts ciliary muscles to allow closer focus
• Increase secretion from salivary glands

Question 10

What are some of the organs ONLY innervated by parasympathetic nerves?

Answer 10

• Pancreas
• Secretory cells of stomach
• Lungs (though airways contain Beta adrenoceptors, modulate by circulating adrenaline released by sympathetic adrenal glands)

Question 11

Describe the sympathetic nerves?

Answer 11

• Short pre-ganglionic fibre, long post-ganglionic fibre

Question 12

Where do the sympathetic pre-ganglionic fibre arise from?

Answer 12

• Lateral horns of grey matter from T1-L2/3

Question 13

Where do the Sympathetic preganglionic fibres synapse with postganglionic fibres?

Answer 13

At paravertebral or pre vertebral ganglia. They directly synapse onto chromatin cells of adrenal medulla

Question 14

What do the sympathetic pre-ganglionic fibres release and where does the neurotransmitter act?

Answer 14

• ACh, which acts at nicotinic receptors (Nic).

Question 15

What do the sympathetic post-ganglionic fibres release and where does the neurotransmitter act? What is the exception?

Answer 15

• NA (noradrenaline), which acts at alpha or beta adrenoceptors
• Exception is sweat glands, where the nerves release ACH which acts at muscarinic receptors (Mus)

Question 16

What is the approx ratio of adrenaline to noradrenaline released by stimulation of sympathetic pre-ganglionic fibres?

Answer 16

• 80% adrenaline
• 20% noradrenaline
  Both from adrenal glands
  No post-ganglionic fibres are involved in innervation of adrenal glands

Question 17

What are some organs ONLY innervated by sympathetic nerves?

Answer 17

• Sweat glands
• Kidney
• Blood vessels

Question 18

What are the functions of the sympathetic nervous system?

Answer 18

• Increase heart rate + contractility and vasodilates coronary arteries. Constricts vessels to skin and intestines
• Causes bronchodilation and increases blood flow to lungs
• Vasodilates to skeletal muscles, relaxes ciliary muscle to lens
• Inhibits gut peristalsis and constricts intestinal and urinary sphincters
• Dilates pupils
• Increases secretions from salivary gland