Question
If schizophrenia is caused by an overabundance of the neurotransmitters dopamine and serotonin in the synapses of some areas of the brain, which drug action could work in treating the symptoms?
A. Release of cholinesterase into the synaptic cleft
B. Increased re-uptake of dopamine and serotonin by presynaptic neurons
C. Increased permeability of the presynaptic neuron to sodium
D. Blockage of dopamine and serotonin receptors on presynaptic neurons
▶️Answer/Explanation
Answer: B. Increased re-uptake of dopamine and serotonin by presynaptic neurons
Explanation:
Schizophrenia symptoms are associated with high levels of dopamine and serotonin in certain brain regions. A drug that increases the re-uptake of these neurotransmitters would help reduce their excessive presence in the synapses, thereby potentially alleviating some symptoms. This process would essentially “clear” the synapse by pulling neurotransmitters back into the presynaptic neuron, reducing their action.
Other options are incorrect:
A. Incorrect. Cholinesterase breakdown of acetylcholine is unrelated to dopamine or serotonin.
C. Incorrect. Sodium ion permeability influences action potentials but is not directly related to the regulation of neurotransmitters like dopamine or serotonin.
D. Incorrect. This would block dopamine and serotonin receptors, but it does not address the underlying issue of excess neurotransmitter release.
Question
Neurons transmit electrical impulses. Which statement describes part of this process?
A. \(\mathrm{K}^{+}\)ions are pumped out of the cell to depolarize the membrane.
B. Ion channels let \(\mathrm{K}^{+}\)diffuse into the cell to depolarize the membrane.
C. \(\mathrm{Na}^{+}\)ions are pumped into the cell to repolarize the membrane.
D. Ion channels let \(\mathrm{Na}^{+}\)diffuse into the cell to depolarize the membrane.
▶️Answer/Explanation
Answer: D. Ion channels let \(\mathrm{Na}^{+}\)diffuse into the cell to depolarize the membrane.
Explanation:
- During an action potential, depolarization occurs when sodium ions (Na⁺) diffuse into the neuron through ion channels, causing the inside of the cell to become more positive compared to the outside.
- This influx of sodium ions is a key step in the depolarization process of the neuron, leading to the transmission of the electrical impulse along the axon.
Let’s break down why the other options are incorrect:
A. Potassium ions (
) are pumped out of the cell, but this occurs during repolarization, not depolarization.
B. Potassium ions (
) do not diffuse into the cell to depolarize it. In fact, potassium ions typically diffuse out of the cell during repolarization to restore the resting potential.
C. Sodium ions (
) are pumped out of the cell during the resting state to maintain a concentration gradient, but they are not pumped into the cell during repolarization. Repolarization is achieved by the outflow of potassium ions.
Question
Atropine drops are used by opticians to dilate the pupil, so that a thorough examination of the retina can be performed. Atropine binds to acetylcholine receptors in synapses.
What is the effect of atropine binding in synapses?
A. Inhibits the binding of acetylcholine at the presynaptic membrane
B. Inhibits the release of acetylcholine from the presynaptic neuron
C. Prevents binding of acetylcholine at the postsynaptic membrane
D. Prevents transport of acetylcholine through the postsynaptic membrane
Answer/Explanation
Answer: C. Prevents binding of acetylcholine at the postsynaptic membrane
Explanation:
What does atropine do in the synapse?
Atropine is a competitive antagonist of acetylcholine. It binds to acetylcholine receptors on the postsynaptic membrane, especially muscarinic receptors, and blocks acetylcholine from binding. This prevents the usual effect of acetylcholine, such as triggering muscle contraction (including in the iris of the eye). As a result, muscles like the iris sphincter relax, causing pupil dilation (mydriasis).
Evaluating the options:
A. Incorrect – The presynaptic membrane is where acetylcholine is released, not where it binds. Atropine doesn’t act here.
B. Incorrect – Atropine does not inhibit acetylcholine release from the presynaptic neuron. It only blocks its action after it’s released.
C. Correct – Atropine binds to acetylcholine receptors on the postsynaptic membrane, preventing acetylcholine from binding and activating the receptor.
D. Incorrect – Neurotransmitters like acetylcholine do not get transported through the postsynaptic membrane. They bind to receptors on the surface to trigger a response.