Sympathetic Nervous System

Question 1

What type of effectors are sympathetic?

Answer 1

Endocrine & Exocrine glands
Smooth Muscle
Cardiac Muscle

Question 2

What chemical is released at the ganglion? And what receptor does it bind to after the synapse?

Answer 2

Acetylcholine (ACh)

Binds to Nicotinic Receptors

Question 3

What chemical is released at the effectors? And what receptor does it bind to after the synapse?

Answer 3

Noradrenaline (NA)

Binds to adrenoceptors

In other animals the postganglionic neurone could secrete ACh to be bound to muscarinic receptors similar to PNS (only in sweat glands and skeletal muscle)

Another exception to the rule is at the Adrenal Medulla where there is no postganglionic nerve but instead Noradrenaline and Adrenaline is secreted into the blood by Chromaffin cells

Question 4

How is Noradrenaline synthesised?

Answer 4

Occurs in an adrenergic varicosity from the enzyme Tyrosine

Some NA is broken down by MAO enzyme

Question 5

What receptors do NA bind to?

Answer 5

• Bind to Alpha and Beta receptors on the postsynaptic cell

- Bind to Alpha2 receptors on the varicosity to cause auto inhibition

Question 6

What type of recpetors are adrenoceptors?

Answer 6

Metabotropic receptors.

Creates transmembrane domains (usually 7).

Question 7

Where are each adrenoceptors found?

Answer 7

• All adrenoceptors found on postsynaptic membrane

- ONLY Alpha2 found on presynaptic membrane

Question 8

What are the agonists to adrenoceptors?

Answer 8

Noradrenaline
Adrenaline
Isoprenaline

Question 9

How can you determine which receptors are present?

Answer 9

Based on potencies of the agonists
-If order of potency is
NA>A>ISO then alhpa1 receptors are present
-If the order of potency is ISO>A>NA then beta adrenoceptors are present

Question 10

How can the sympathetic control of pupil diameter be achieved

Answer 10

Noradrenaline acts on Alpha adrenoceptors on the radial muscle. This causes the radial muscle to contract which pulls out, causing the pupil diameter to increase (MYDRIASIS)

Question 11

What are the sympathetic cotransmitters?

Answer 11

Neuropeptide Y (NPY)
Adenosine 5'-Triphosphate (ATP)

Question 12

How do the sympathetic cotransmitters help?

Answer 12

NPY is mainly a neuromodulator which prevents NA & ATP release prejunctionally but increase NA action postjunctionally

ATP has direct action to P2 receptors but can also act as a neuromodulator at P1 receptors to prevent NA release

They all act together to cause vasoconstriction in blood vessels