Session 8 Flashcards
What are the differences between the sympathetic (SNS) and parasympathetic (PNS) nervous systems in terms of ganglionic fibres?
The PNS has long pre-ganglionic fibres, short post-ganglionic fibres, with receptors found mainly within the target tissue. These help control the ‘rest and digest’ responses in the body.
The SNS has short pre-ganglionic fibres synapsing in the sympathetic chain, with long post-ganglionic fibres. These help control ‘fight or flight’ responses in the body.
What are the different receptor types found in the autonomic nervous system?
PNS
- nicotinic AChR (pre-ganglionic)
- muscarinic AChR (post-synaptic)
SNS
- nicotinic AChR (pre-ganglionic)
- adreno-receptor (post-synaptic)
All pre-ganglionic neurons are cholinergic; PNS uses mAChR on post-synaptic neurons, SNS uses adreno-receptors (both α- and β-) on post-synaptic neurons
To which category of membrane proteins does the nicotinic Ach receptor (nAChR) belong?
A: G-protein coupled receptor B: Voltage-gated channel C: Kinase linked receptor D: Nuclear receptor E: Ligand-gated ion channel
E - Ligand-gated ion channel
RITE K(L)ING – Remember that ligand gated ion channels are a receptor type. Muscarinic AChRs and adreno-receptors are G-protein coupled receptors, the others are incorrect.
What are the common peripheral receptors found in the SNS and PNS, and add their respective G-proteins.
SNS (receptors; G-proteins) Alpha-1; Gαq Alpha-2; Gαi Beta-1; Gαs Beta-2; Gαs
PNS (receptors; G-proteins)
M1; Gαq
M2; Gαi
M3; Gαq
What are the differences between where the PNS and SNS arise from?
PNS nuclei are found in the brainstem and sacral region of the spinal cord.
SNS nuclei are found in the thoracolumbar region of the spinal cord.
A patient is admitted with a heart rate of 120bpm (normal range = 60-100). The doctor wants to give this patient a drug that will slow the heart down. Which of the following receptor antagonists would be the best choice?
A – α-1 B – M1 C – β-1 D – M2 E – β-2
C – β-1
β-1 receptor antagonists (aka ‘beta blockers’) would be the best choice as they would inhibit the Gs receptor, causing less cAMP, therefore slowing the heart rate down.
α-1 receptors are found in smooth muscle; antagonising these receptors would cause vasodilation of blood vessels to reduce blood pressure.
M1 receptors are not found in the heart so would have no effect on heart rate.
M2 receptors are found in the heart and slow the heart rate down, so antagonising this receptor will cause tachycardia and therefore have the opposite to the desired effect.
β-2 receptors are found in the lungs and therefore would have no effect on heart rate (note that antagonising this receptor would cause bronchoconstriction and cause difficulty breathing – definitely not what you want!)
Outline the steps that are involved in regulating noradrenaline (NA) release in a post-ganglionic sympathetic neuron synapse:
NA synthesised from dopamine by the enzyme (A) --> Depolarisation opens (B), increasing [Ca2+]i --> Release of neurotransmitter into the synapse (acts on adreno-receptors) --> NA in the synapse is terminated by re-uptake into the (C) by high affinity (D) transporter --> Any NA not taken up by 'Uptake 1' or 'Uptake 2' is metabolised by (E)
A – dopa decarboxylase B – VGCC C – pre-synaptic terminal D – Na-dependent E – monoamine oxidase (MAO) or COMT
A patient with Chronic Obstructive Pulmonary Disease (COPD) has come to see his GP for an annual check. He has been on a β-2 agonist to help improve his breathing, but still complains of breathlessness. The GP wants to add another inhaler that antagonises the muscarinic receptors in the lung.
What 3 possible side effects do you think the patient will complain of?
Commonly dry mouth, constipation and urinary retention (not being able to urinate)
Acronym for over-active parasympathetic system = SLUDGE (salivation, lacrimation, urinary voiding, defecation, GI symptoms e.g. diarrhoea, emesis (vomiting)).
Can also cause bradycardia, bronchoconstriction and increased sweating.
Therefore, the patient is likely to experience symptoms that are the opposite to these.
Myasthenia gravis is a condition that reduces the number of available acetylcholine receptors at the neuromuscular junction. Explain why giving an acetylcholine esterase inhibitor can be beneficial in such patients?
Acetylcholine is degraded by the enzyme acetylcholine esterase. In patients with fewer receptors, the effect of Ach can be augmented by preventing their degradation, by inhibiting this enzyme.
A patient comes to see his GP and is diagnosed with a pheochromocytoma; a rare tumour of chromaffin cells in the adrenal medulla. What symptoms do you think he would complain of?
A: Central weight gain, muscle wasting, easy bruising
B: Weight loss, tiredness, skin pigmentation
C: Tiredness, weight gain, cold intolerance
D: Headaches, palpitations, sweating
E: Weight loss, tremor, heat intolerance
D: Headaches, palpitations, sweating
This rare tumour causes excessive release of noradrenaline and adrenaline. Therefore you would expect to see features of an overactive sympathetic nervous system, such as:
Hypertension, tachycardia/palpitations, headaches, sweating, weight loss, tremor. D is the only answer to contain all of the correct features.
(for interest, A = Cushing’s syndrome, B = Addison’s Disease, C = hypothyroidism, E = hyperthyroidism)
