Question

The dark current of the retina refers to…

inhibition of inhibitory NTs

inhibition of excitatory NTs

excitation of inhibitory NTs

excitation of excitatory NTs

Of the following neurotransmitters, which are not stored in vesicles before release by the presynaptic axon?

Amino Acids

Monoamines

Endocannabinoids

Acetylcholine

Polypeptides

Answer 1

The dark current of the retina refers to…

Answer: (B) Inhibition of excitatory NTs.

When unstimulated cyclic-nucleotide gated channels in the outer segment of the photoreceptor cell in the dark open due to binding of cGMP cause inward flow of  positively charged ions like sodium or calcium leads to depolarization to about −40 mV.

Of the following neurotransmitters, which are not stored in vesicles before release by the presynaptic axon?

Answer: (C) Endocannabinoids.

Endocannabinoids differs from canonical neurotransmitters, such as ACh, glutamate, and GABA by not stored in and released into the synapse through synaptic vesicles and also not released at the presynaptic locus. It acts in atypical retrograde fashion.