Parasympathetic nervous system

Question 1

What is the main role of the parasympathetic NS?

Answer 1

Keeps body energy low:

• Blood pressure, heart rate + respiratory rates = low- has inhibitory effect on many tissues and organs
• But gastrointestinal activity high

= rest and digest

Question 2

Name one example of a parasympathetic nerve and what does it innervate?

Answer 2

Vagus nerve in cranial region
- innervates many different tissues e.g. heart, lungs, pancreas etc

Question 3

Name an example of a ganglion in the parasympathetic NS and where is it located?

Answer 3

Ciliary ganglion- located in cranial region behind the eye

Question 4

What is the neurotransmitter involved at the pre + post ganglionic neuron for parasympathetic NS?

Answer 4

acetylcholine = ACh

Question 5

Name the 2 receptors that ACh acts on and where are they found?

Answer 5

Nicotinic - post-synaptic membrane on post ganglionic neuron

Muscarinic- post synaptic membrane on effector cell

Question 6

Describe the parasympathetic neuroeffector pathway

Answer 6

1. Long preganglionic neuron in cranial/sacral region- ACh released
2. Acts on nicotinic receptors on post-ganglionic neuron
3. Variscosities then release ACh which act on muscarinic receptors on effector to produce a reponse

Question 7

Where is ACh synthesised?

Answer 7

Terminal boutons of pre-ganglionic neuron

Varicosities of post-ganglionic neuron

Question 8

Describe how ACh is sythesised and what happens when an action potential is triggered?

Answer 8

1. Made from acteyl CoA + choline, involving choline acetyltransferase (enzyme)
2. Packaged into vesicles
3. AP = ACh released into synaptic cleft
4. ACh binds to cholinergic receptors on post-synaptic membrane
5. ACh removed via acetylcholinesterase- some choline taken back up by terminal/varicosity for reuse

Question 9

Explain 2 differences between nicotinic and muscarinic receptors in the parasympathetic NS

Answer 9

Nicotinic:
- Located at ganglia on post-ganglionic neuron
= ionotropic receptor = acts as ion channels- when opend they allow for an influx of ions

Muscarinic
- Located at effector tissues
= metabotropic = G-coupled receptors to 2nd messengers
- Different types of muscarinic receptors

Question 10

Name the 3 main types of muscarinic receptors in the parasympathtic NS and where are they located + what are they involved in?

Answer 10

M1 = gut- increased gastric acid secretion
M2 = cardiac- reduces cardiac activity
M3 = glandular = secretion
smooth muscle = constriction

Question 11

Describe the structure of a nicotinic receptor and where does ACh bind to?

Answer 11

= protein spanning entire cell membrane with an intracellular region and an extracellular region- comprised of 5 protein subunits

ACh binds to extracellular portion

Question 12

Describe the structure of a muscarinic receptor and where does ACh bind and what happens?

Answer 12

Composed of single protein that has 7 different transmembrane domains with some parts in intracellular parts and some in extracellular

ACh binds to extracellular part = shape change = intracellular part bind to G proteins = ion influx/enzyme activation = response

Question 13

Name 4 different classes of parasympathetic drugs and how do they affect the the PNS

Answer 13

Parasympathomimetic/cholinomimetic agonists = mimic effects of parasympathetic NS- so enhances PNS

Parasympatholytic/muscarinic antagonists = blocks PNS receptors- reduces PNS

Cholinesterase inhibitors (ACHEI) = blocks action of acetylcholinerase = prevents uptake = enhances PNS

Ganglionic blocking drugs/nicotinic antagonists = blocks sympathetic + parasympathetic NS

Question 14

Name 2 examples of tissues/organs innervated by parasympathetic NS

Answer 14

Heart
Eye

Question 15

Name 2 examples of tissues/organs innervated by parasympathetic NS

Answer 15

Heart
Eye

Question 16

Describe the role of parasympathetic NS in controlling the heart

Answer 16

1. Long preganglionic neuron (=vagus nerve) forms synapse with post ganglionic neuron in heart
2. ACh released and binds to nicotinic receptors
3. Postganglionic nerves releases ACh which acts at M2 muscarinic receptors
4. Decreases heart function

Question 17

What 3 parts of the heart are M2 receptors located

Answer 17

SA node (pacemaker)
Atrial muscle
AV node

Question 18

Describe a clinical use of parasympathetic drugs for the heart

Answer 18

Cardiac arrest
- atropine = muscarinic antagonist- used for resuscitation

Question 19

Describe the role parasympathetic NS in controlling pupil diameter

Answer 19

1. Pre-synaptic neuron forms synapse within ciliary ganglion
2. ACh released and binds to nicotinic receptors
3. Post-synaptic neuron forms synapse with circular muscle
4. ACh released and binds tp M3 receptors = causes circular muscle to contract = pupil constriction/miosis

Question 20

Whats the difference between mydriasis and miosis?

Answer 20

mydriasis = pupil dilation
miosis = pupil constriction

Question 21

Describe the role of the PNS in focussing the eye

Answer 21

1. Ciliary muscle determines whether sensory ligaments expand or contract for focused or distant vision
2. PNS innervates ciliary muscle = muscle contracts and moves inwards = suspensory ligaments relax = lens fattens- so can focus on near vision = accomodation

Question 22

What is a side effect of mydriatic drugs?

Answer 22

Cycloplegia = paralysis of ciliary muscles = loss of accomodation

Question 23

Define: accomodation of the eye

Answer 23

ability of the eye to change focus from distant to near objects

Question 24

Describe some clinical uses of miotic drugs

Answer 24

• Rapid pupil closure after surgery
• Glaucoma = build up of fluid which adds pressure to eye
  Pupil constriction = promotes fluid drainage
• Anticholinesterases increases pupil constriction also

Question 25

Name a parasympathetic cotransmitter and what does it work with?

Answer 25

Vasoactive Intestinal polypeptide = 28 amino acid peptide
Works with ACh when there is a high frequency stimulation