Trigger 1 : Structure of the nervous system

Question 1

What are myotomes, what do they do and where are they found?

Answer 1

• Go down the spine

- A group of muscles innervated by a single nerve

Question 2

What are dermatomes, what do they do and where are they found?

Answer 2

• A group of skin all innervated by a single spinal nerve.

- C1 has no dermatome / sensory input.

Question 3

How are the 31 spinal nerves organised?

Answer 3

By

• Cervical = Neck
• Thoracic = Thorax
• Lumbar = lower back
• Saccrum + coxyx = Tail bone

Question 4

What parts of the spinal cord are innervated by what parts of the ANS?

Answer 4

Autonomic = involuntary

Sympathetic: Thoracolumbar
Parasympathetic: Craniosacral

Question 5

What is the role of cranial nerve X?

Answer 5

It is the vagus nerve 
Innervates:
- Heart
- Stomach
- Lungs

Question 6

The somatic nervous system is…

What is the pattern of ‘innervation’ i.e. neurotransmitter…

Answer 6

• Voluntary (skeletal muscle)
• Has a motoneuron in CNS
• Neurotransmitter released = Ach (acetylcholine)
• Receptor = Nicotinic AchR (acetylcholine receptor) = ionotropic

Question 7

The sympathetic nervous system is…

What is the pattern of ‘innervation’ i.e. neurotransmitter…

Answer 7

• Involuntary = fight
• 1 short preganglionic neuron from CNS
• 1st synapse : Ach,Nicotnic AchR. Is flouted in superior cervical ganglion.
• 1 long postganlionic neuron to target organ
• 2nd synapse : Noradrenaline, Adrenoreceptor, Metabotropic receptor (GPCR)

Question 8

Adrenoreceptor receptor variation within the body…

Answer 8

• B1, Gas: Heart -> sympathetic drive, inotropy (increase in contraction), Chronotropy (increase in heart rate), lusitrophy ( relaxation);.
• B2, Gas: Bronchial tree in lungs, relaxing.
• B2/3 : Bladder -> Relaxes the bladder SM (detrusor)

Question 9

The parasympathetic nervous system is…

What is the pattern of ‘innervation’ i.e. neurotransmitter…

Answer 9

1st 
-1 long preganglionic neuron from CNS from cranial or sacral nerves. 
- Neurotransmitter : Ach
- Receptor : nicotinic AchR 
2nd 
- 1 short postganglionic neuron.
- Neurotransmitter : Ach 
- Receptor : Muscarinic acetylcholine receptor = metabotropic (GPCR)

Question 10

Musarinic receptor variation within the body…

Answer 10

• M2 (Gai) = Heart, relaxes
• M3 (Gaq)= Exocrine glands (e.g. gastric parietal cells), secretion + smooth muscle e.g. bladder detrusor (contracts), airways, GI tract.

Question 11

What does a GPCR agonist do?

Answer 11

• Binds to membrane portion of GPCR (serpentine receptor)
• Coupled to heterotrimeric G protein -> G protein, gamma+beta
• G protein -> target 1
• Gamma+beta -> target 2

Question 12

How does peeing work?

Answer 12

• Peeing is parasympathetic
• Contract bladder detrusor (ACh, M3, Musc) to squeeze bladder
• Open external sphincter = voluntary control (somatic NS)

Question 13

How would you treat incontinence?

Answer 13

Antagonise the muscarinic M3 receptors.

• Anticholinergic
• Prevent bladder detrusor muscle.

Question 14

Sympathetic control of the bladder…

Answer 14

• Relax the bladder detrusor (B2/B3 adrenergic receptors)
• Constrict internal sphincter (a1 adrenergic receptors)
• Voluntary control of external sphincter

Question 15

Therapeutics of inability to micturate + overactive bladder

Answer 15

• a1 adrenoceptor antagonist
• Relax the internal sphincter ( help micturition if blockage e.g. enlarged prostate)
• B3 adrenoceptor agonies
• Enhances bladder relaxation (e.g. overactive bladder)