Introduction to the ANS

Question 1

What does the ANS control?

Answer 1

The ANS alters the diameter of blood vessels, it can affect the airways, mobilise sugars from stores of glycogen and lipids, allows us to urinate when we need to, move food through our body and defecate when we need to, it controls all the secretion including sweating and saliva production.

Question 2

What is the structure of the ANS?

Answer 2

• A connection between the central nervous system and peripheral organs.
  
  • Largely outside of voluntary control
  • Two neurone system
  • Consists of two systems:
    ○ Sympathetic (fight or flight)
    ○ Parasympathetic (rest and digest)
  • Often have opposing effects on a tissue
  • BUT some tissues have a single nerve supply

Question 3

How do the ganglions differ between the PNs and the SNs?

Answer 3

• If we look at the parasympathetic nervous system we have a first nerve that then releases acetylcholine.
  
  • This region where the acetylcholine is releases is called the ganglion.
  • The second nerve will be activated and in the case of the parasympathetic nerve, acetyl choline will be released.
  • In the sympathetic nervous system we have a vey short pre-ganglionic fibre, but again, acetylcholine is released which is picked up by the receptors and stimulates the post-ganglionic fibre that now releases noradrenaline.
  • This is the standard for most sympathetic nerves
  • The exception is the sweat gland, a sympathetic nerve, but releases acetylcholine instead of noradrenaline.
  • Another slight exception is the adrenal gland, where acetylcholine is released from the first fibre and then it interacts with adrenal cells.

Question 4

Where are the parasympathetic nerves located?

Answer 4

• Cranial nerve III (OCULOMOTOR)
  ○ Pupil
  
  • Cranial nerve VII (FACIAL)
    ○ Submaxillary, sublingual and lacrimal glands
  • Cranial nerve IX (GLOSSOPHARYNGEAL)
    ○ Parotid glands
  • Cranial nerve X (VAGUS)
    ○ Heart, kidneys, bronchi and GI tract to colon
  • Sacral nerves
    ○ Remainder of GI tract, bladder and genitalia

Question 5

Where are the sympathetic nerves located?

Answer 5

• Paravertebral chain of ganglia (~25)
  
  • Prevertebral ganglia near aorta
  • Superior cervical paravertebral ganglia
    ○ Pupil, facial glands, head circulation
  • Middle and inferior paravertebral ganglia
    ○ Heart and lungs
  • Remaining paravertebral ganglia
    ○ Sweat glands, pilomotor (hair) muscles., blood vessels of skeletal muscle and skin
  • Prevertebral ganglia
    ○ GI tract

Question 6

What is the difference between sympathetic and parasympathetic nerves? (summary)

Answer 6

Sympathetic nervous system-FFF
Thoraco-lumbar overflow
Short pre-ganglionic fibres
Noradrenaline is main terminal messenger

Parasympathetic nervous system- R&D
Sacro-cranial outflow
Long pre-ganglionic fibres
Acetylcholine is the main terminal messenger