Autonomic Control of the Vasculature

Question 1

What is the Autonomic Nervous System?

Answer 1

The ANS makes routine homeostatic adjustments in physiological systems without instructions from the conscious mind.

Question 2

What is the difference between somatic and autonomic nervous system?

Answer 2

ANS- has two neurons in a chain: preganglionic (myelinated) and postganglionic (non-myelinated).

SNS- the main neurotransmitter is Ach with nicotinic acetylcholine receptor (channel linked ion receptors)

Question 3

Describe the sympathetic nervous system.

Answer 3

• Fight or Flight
• Origin: Thoracolumbar region
• Ganglia: next to spinal cord
• Neurotransmitter:
  Ach at pre-ganglionic synapse
  Noradrenaline at post-ganglionic synapse

Question 4

Describe the Parasympathetic nervous system.

Answer 4

• Rest and Digest
• Origin: Sacrocranial Outflow (C3,7,9,10) and (S2,3,4)
• Ganglia: diffuses near site of action
• Neurotransmitter:
  Ach at pre and post ganglionic synapse

Question 5

What is the function of the Baroreceptor reflex?

Answer 5

It is one of the body’s homeostatic mechanism that helps to maintain blood pressure at nearly constant levels.

Question 6

What is the Baroreceptor reflex?

Answer 6

Homeostatic mechanism -> negative feedback. 
stretch receptors (baroreceptors) present in the aortic arch and carotid sinus send signals to the medulla of the brain. 
It is mediated by the parasympathetic and sympathetic nervous system.

Question 7

What are the actions carried out by the baroreceptor reflex?

Answer 7

1. Decreases sympathetic activity
2. Increases parasympathetic activities
   - > Both of this leads to relaxation in vessel walls -> Less peripheral vascular resistance
3. Lower heart rate by increased vagus activities.

Question 8

Where are neurotransmitters stored and released?

Answer 8

NTs are stored in vesicles and released by exocytosis.

The Vesicles merge with the plasma membrane and NTs are released into the synaptic cleft.

Question 9

Why do NTs go in one direction?

Answer 9

• diffusion gradient

- receptors only exist in the post synaptic neuron and not in the axon terminals

Question 10

What makes the ‘sympathetic triad’?

Answer 10

Noradrenaline
ATP
Neuropeptide Y

• -> work together to stimulate smooth muscle contraction.
• -> small blood (resistance) vessels are greatly innervated by adrenergic hormones.

Question 11

Describe the importance of PVAT?

Answer 11

PVAT- Perivascular Adipose Tissue
- shares border with the tunica externa/adventitia wall of the blood vessel.
- This allows for possibility of cross talk
- decreased response to vasoconstrictor noradrenaline in the presence of periaortic fat
= inhibits contraction
= can promote angiotensin II formation