Sympathetic nervous system

Question 1

What is the main function of the sympathetic NS?

Answer 1

To produce rapid reponses without conscious control

Question 2

In the sympathetic NS, where can preganglionic neurons terminate in?

Answer 2

Paravertebral chains
Prevertebral ganglia in abdominal cavity
Adrenal medulla

Question 3

In the sympathetic NS, what are the main neurotransmitters used for the pre + post ganglionic neurones and which receptors do they act on?

Answer 3

Pre = ACh- nicotinic receptors
Post = noradrenaline- adrenoceptors

Question 4

What are some other neurotransmitters used by the postganglionic neurons and what are they used for and what receptors do they act on?

Answer 4

ACh for sweat glands in skeletal muscles- muscarinic receptors
Adrenaline = main neurotransmitter involved in the fight or flight response

Question 5

Describe the synthesis of noradrenaline

Answer 5

1. Produced within the varicosities on post-ganglionic nerves
2. Produced from tyrosine with many enzymes involved including tyrosine hydroxylase
3. The noradrenaline is then packaged into vesicles ready for release when an AP is triggered

Question 6

Name the 2 main types of adrenoceptors

Answer 6

Alpha
Beta

= metatropic receptors

Question 7

How is noradrenaline removed after it has been released?

Answer 7

Uptake mechanisms- exist on both pre and post synaptic membrane
- uptake on pre can be repackaged into vesicles = transmitter economy

• enzyme monoamine oxidase (=MAO) can breakdown noradrenaline within varicosities

Question 8

What kind of receptor does noradrenaline act on, on a varicosity and what effect does this have?

Answer 8

Alpha 2 receptors to inhibit the release of noradrenaline

Question 9

What are adrenoreceptors?

Answer 9

= single protein that spans the cell membrane with 7 transmembrane domains

= G protein coupled receptors

Question 10

Describe what happens when a neurotransmitter binds to adrenoceptors

Answer 10

1. Binds to extracellular portion of receptor
2. = protein shape change
3. = intracellular regions attach to G proteins within cell
4. G proteins bring about a response inside the cell e.g. activate 2nd messenger systems, enzymes, open ion channels

Question 11

What are agonists?

Answer 11

agents that act at receptors and stimulate them to produce a response

Question 12

Where are adrenoceptors found?

Answer 12

All over the body- on most organs and tissues
- Both alpha + beta can be located on post synaptic membranes
- Mainly alpha adrenoceptors- most common = alpha 2 on presynaptic membranes

Question 13

Name 3 agonists involved in the activation of adrenoceptors

Answer 13

Noradrenaline
Adrenaline
Isoprenaline

Question 14

How are alpha and beta adrenoceptors identified?

Answer 14

AGONIST POTENCY ORDER:
Agonists act at receptors these being noradrenaline, adrenaline and isoprenaline:

• alpha adrenoceptors activated most potently by noradrenaline, then adrenaline then isoprenaline
• Beta adrenoceptors activated most potently by isoprenaline, then adrenaline then noradrenaline

Question 15

Name 3 examples of alpha 1 agonists

Answer 15

decongestant = causes blood vessels to constrict when it activates alpha 1 adrenoceptors
Glaucoma
mydriasis

Question 16

What is an antagonist?

Answer 16

= agents that block the activation of receptors

Question 17

Give an example of an alpha 1 antagonist and what does it do?

Answer 17

Anti-hypertensive = stops blood vessels from contracting

Question 18

Name an example of a beta 2 agonist and what does it do?

Answer 18

Salbutamol used to activate beta 2 adrenoceptors which opens airways for asthma

Question 19

Where are beta 1 receptors found and what do beta 1 agonists do

Answer 19

Found in the heart:
Enhance cardiac muscle contraction = promotes cardiac activity- used during cardiac arrest

Question 20

Explain what beta antagonists do

Answer 20

Beta Blockers:
Regulate heart rate by reducing contractivity

Question 21

Name some examples of places drugs can target on presynaptic membrane and how do they work

Answer 21

• Alpha 2 receptors blocked = more noradrenaline released or stimulated = reduces noradrenaline release
• Uptake inhibitors blocked = more noradrenaline released
• MAO blocked = promotes noradrenaline levels
• Block tyrosine hydroxylase = reduces noradrenaline release
• Introduce false neurotransmitter which can be packaged into vesicles, displacing noradrenaline

Question 22

What enzyme is involved in the synthesis or noradrenaline?

Answer 22

tyrosine hydroxylase

Question 23

Describe the role of the sympathetic NS in control of pupil diameter

Answer 23

1. Preganglionic cell bodies within thoracic region- axons form synapse with postganlionic nerve that innervates radial muscle/dilator pupillae in the eye
2. Sympathetic pathway activated- ACh released at preganglionic acting on nicotinic receptors on postganglonic
3. Noradrenaline is released at postganglionic neuron and acts on alpha adrenoceptors = radial muscle contraction = pupil dilation/mydriasis

Question 24

What is radial muscle?

Answer 24

= smooth muscle arranged radially

Question 25

What do sympathomimetic drugs do?

Answer 25

= mimic the actions of the sympathetic NS

Question 26

Describe some clinical uses of sympathetic drugs in the eye

Answer 26

• Mydriatic drugs for eye inspection and surgery as pupils are more dilated
• Antiglaucoma drugs:
  Glaucoma = build up of fluid in eye = more pressue
  drugs can cause vasoconstriction to reduce amount of fluid that can be secreted by cilary body = allowing for reabsorption of fluid

Question 27

Define: Glaucoma

Answer 27

= build up of fluid on the eye, increasing pressure

Question 28

Name 2 examples of sympathetic co-transmitters and what do they cause

Answer 28

Neuropeptide Y (NPY)
Adenosine 5’-triphosphate (ATP)

Both act to cause vasoconstriction