bb quiz review

Question 1

An electrophysiologist studying synaptic transmission in the brain is recording post synaptic potentials in a rat brain slice. Upon application of an agonist to the slice (indicated by the arrow) a ligand gated ion channel was activated and the following trace recorded.

IPSP

Addition of which agonist would have produced this response?

Answer 1

GABA is the main inhibitory neurotransmitter in the brain. The GABAA receptor is a ligand gated ion channel that selectively conducts Cl− ions. Activation of this channel would therefore cause a hyperpolarisation (more negative) of the plasma membrane making it less excitable (i.e. further away from the threshold for firing an action potential). GABA also activates metabotropic glutamate receptors (i.e. GPCRs activated by GABA called GABAB receptors).

Question 2

The temperature at which bacteria need to function fluctuates with their environment. Bacteria therefore need to adjust the composition of their phospholipid bilayer membranes in order to maintain them at a relatively constant fluidity.

Which change in composition would increase the fluidity of this type of membrane?

Answer 2

more cis double bonds

Question 3

A 18 year old man is taken to the accident and emergency department after eating a large quantity of “magic” mushrooms at a music festival. He has symptoms of “SLUDGE” syndrome (Salivation, Lacrimation, Urination, Defecation, Gastrointestinal upset & Emesis) resulting from a massive discharge of his parasympathetic nervous system.

Which drug would alleviate the man’s symptoms?

Answer 3

Atropine or pralidoxime

Question 4

What current flow and ion channels are responsible for the upstroke of a neuronal action potential

Answer 4

An influx of Na+ ions through Voltage gated Na+ channels

Question 5

Compared to Drug Y, Drug X has:

Answer 5

Lower intrinsic efficacy
CORRECT. Intrinsic efficacy is the capacity of a drug to activate (or inactivate) a receptor. Because drug Y has a higher maximum response it must have a higher intrinsic afficacy

Question 6

what is A

Answer 6

full agonist

Question 7

how is information coded by action potentials

Answer 7

frequency

Question 8

cell biologist prepares an antibody that recognises an intracellular receptor.

Which receptor does the antibody recognise?

Answer 8

thyroid hormone receptor

Question 9

what does myelin sheath do

Answer 9

Question 10

A 32 year old woman is being treated in the Emergency Department for acute alcohol intoxication. The consultant explains to a student present that the effects of alcohol can be felt so quickly after consumption because ethanol is lipophilic. This lipophilicity gives it the ability to pass freely through lipid bilayers and enter the brain despite the presence of tight capillary junctions.

What other type of molecule, present in the body, shares this ability?

Answer 10

Dissolved gasses
The lipid bilayer is permeable to hydrophobic and small uncharged polar molecules only, large polar molecules and ions cross the membrane by the aid of transport proteins or ion channels.

Question 11

Whooping cough, also known as pertussis is a highly contagious infection caused by the Gram negative bacterium Bordetella pertussis. The classic symptom of the disease is a prolonged period of severe coughing fits. A component of the toxin (known as pertussis toxin) produced by this bacterium acts to ADP-ribosylate Gαi proteins locking them in their inactive GDP bound form.

What change in effector protein activity would be expected as a result of the actions of this bacterial toxin?

Answer 11

Question 12

A cell biologist prepares an antibody that recognises a ligand gated ion channel.

Which receptor does the antibody recognise?

Answer 12

Nicotinic acetylcholine receptor
CORRECT – Nicotinic Acetylcholine receptors are ligand gated ion channels. Muscarinic acetylcholine receptors are GPCRs

Question 13

A 13 year old boy has strabismus, a vision impairment where the eyes do not simultaneously align when looking at an object. In order to correct this defect a consultant ophthalmic surgeon injects Botulinum toxin into the boy’s left medial rectus muscle (an extraocular muscle) .

At what level in the neuromuscular junction does this toxin alter transmission?

Answer 13

Inhibition of vesicle fusion

CORRECT. Botulinum toxin, a product of the anaerobic bacteria Clostridium botulinum, exterts its effect by entering nerve endings and cleaving the SNARE protein SNAP-25. SNARE proteins are essential for vesicle fusion and release of neurotransmitter into the neuromuscular jucntion. Thus, Botulinum toxin inhibits the release of acetylcholine into the neuromuscular junction. In the treatment of strabismus Botulinum toxin is injected in the stronger extraocular muscle causing a temporary and partial paralysis. The treatment may need to be repeated once the paralysis wears off. However, in some cases the effects can be permanent because paralysis of the stronger muscle allows the weaker extraocular muscle time to remodel for correct function.
Neuromuscular junction

Question 14

A pharmaceutical company is developing a new inhibitor of the sodium-calcium exchanger (NCX) for protection against myocardial ischemia/reperfusion injury.

What is the normal stoichiometry of this exchanger working in forward mode?

Answer 14

3 Na+ in
1Ca2+ out

Question 15

PNS neurotransmitters

Answer 15

Question 16

A 57 year old man has a deep laceration on the palm of his right hand after falling on some broken glass. Prior to suturing and cleaning the wound a local anesthetic containing lidocaine is applied.

How does this drug temporarily block the generation of action potentials in sensory neurones?

Answer 16

Prevents the influx of Na+ ions through Voltage gated Na+ channels
CORRECT. Lidocaine binds to voltage-gated sodium channels in a 1:1 fashion and prevents the flow of sodium ions through the channel pore.

Question 17

A 27 year old woman is diagnosed with Neurocardiogenic Syncope (NCS), a condition resulting from disturbances to the function of the autonomic nervous system.

Which postsynaptic receptor is present in all preganglionic neurones at their synapse with ganglionic junctions in this division of the nervous system?

Answer 17

Nicotinic acetylcholine receptors are present in all postganglionic neurones in both the sympathetic and parasympathetic divisions of the ANS. Similar to the nicotinic acetylcholine receptors found at the neuromuscular junction, the ganglionic nAChRs are ligand gated ion channels permeable to the cations Na+ and K+. However, the subunit composition of the ganglion type nAChR differs from that of the skeletal muscle type. Binding of acetylcholine (the “ligand”) results in opening of the channel pore and flow of Na+ and K+ ions down their electrochemical gradients. Na+ ions enter the cell and K+ ions leave through the open pore but because more Na+ ions enter than K+ ions leave, there is a net inward flow of positive charge into the cell. This influx of positive charge depolarises the membrane potential (i.e. the membrane potential becomes less negative) resulting in an excitatory response which, if of sufficient magnitude, will propagate an action potential in the postganglionic neurone leading to the effector organ.

Question 18

A 2 month old boy is taken to the emergency department with severe respiratory depression. His mother had taken codeine for back pain and the doctor suspects that she may be an ultra-rapid metaboliser and has passed the metabolite of codeine (morphine) to the boy through her breast milk.

Over activity of which enzyme would make the boy’s mother an ultra-rapid metaboliser ?

Answer 18

CYP2D6