PHYSIO FINAL

A 27-year-old woman undergoes surgery for mandibular reconstruction. During the procedure, succinylcholine is administered, and she develops fasciculations followed by paralysis. Succinylcholine mimics acetylcholine (ACh) at the neuromuscular junction. At the muscle end plate, ACh normally causes opening of:

• Na+ channels and depolarization toward the Na+ equilibrium potential

• K+ channels and depolarization toward the K+ equilibrium potential

• Na+ and K+ channels and depolarization to a value halfway between the Na+ and K+ equilibrium potentials

• Na+ and K+ channels and hyperpolarization to a value halfway between the Na+ and K+ equilibrium potentials

A 35-year-old man with alcohol withdrawal is treated with a benzodiazepine, which enhances GABA-A receptor activity. This receptor causes inhibitory post-synaptic potentials (IPSPs) by:

• Depolarizing the postsynaptic membrane by opening Na+ channels

• Depolarizing the postsynaptic membrane by opening K+ channels

• Hyperpolarizing the postsynaptic membrane by opening Ca2+ channels

• Hyperpolarizing the postsynaptic membrane by opening Cl− channels

A patient ingests a toxin that irreversibly blocks presynaptic voltage-gated Ca²⁺ channels at the neuromuscular junction. Which effect is expected?

• No depolarization of the postsynaptic membrane

• Enhanced acetylcholine (ACh) release

• Inhibition of acetylcholinesterase

• Increased miniature end-plate potentials (MEPPs)

A research group is studying vesicle docking in neurons. They note a protein that binds SNAREs acting as a clasp to stabilize the ternary complex during fusion. Which protein plays this role?

• Syntaxin

• Synaptotagmin

• Sec-1

• Complexin

During a neurobiology exam, a student is asked to identify which of the following is not part of the ternary SNARE complex.

• SNAP-25

• Synaptotagmin

• Synaptobrevin

• Syntaxin

A 6-year-old boy’s cultured neurons are stimulated, and intracellular Ca2+ decreases after vesicle fusion. The calcium sensor dissociates, leading to:

• Alpha-SNAP binds to the SNARE complex to disassemble it

• NSF binds to the SNARE complex to disassemble it

• SNAP-25 is recycled

• Synaptobrevin is recycled

A 40-year-old woman receives cosmetic BoTox for jawline slimming. The specific toxin used in clinical practice inhibits vesicle-associated membrane protein (VAMP). Which toxin is responsible?

• Botulinum A

• Botulinum B

• Botulinum C1

• Botulinum H

A hunter in the Amazon is struck by a poisoned arrow containing curare. He develops flaccid paralysis because curare prevents:

• Calcium channel opening

• Release of neurotransmitters

• Binding of neurotransmitters to post-synaptic receptor

• Breakdown of neurotransmitter

A farmer bitten by a green mamba develops muscle hyperexcitability due to dendrotoxin. This toxin impairs repolarization by:

• Blocking voltage-gated sodium channels, promoting depolarization

• Blocking voltage-gated sodium channels, promoting hyperpolarization

• Blocking voltage-gated potassium channels, promoting depolarization

• Blocking voltage-gated potassium channels, promoting hyperpolarization

A neuroscientist measures an increased number of vesicle quanta released per stimulus at the NMJ after rapid stimulation. This transient increase in synaptic strength is best described as:

• Facilitation

• Potentiation

• Spatial summation

• Temporal summation