The release of which neurotransmitter from the rods of retina is reduced when light strikes its outer segment?
Glutamate
Rods and Neurotransmitter Release in the Retina
The retina contains photoreceptor cells called rods and cones, responsible for detecting light. Rods are particularly sensitive to low light levels and are crucial for scotopic (night) vision. These cells communicate with other neurons in the retina by releasing neurotransmitters.
Neurotransmitter Release from Rods in Dark vs. Light
In the dark, rod cells are in a relatively depolarized state. This depolarization keeps voltage-gated calcium channels open, leading to the continuous release of a specific neurotransmitter from their synaptic terminals.
When light strikes the outer segment of a rod cell, it triggers a biochemical cascade:
- Light activates the photopigment rhodopsin.
- Activated rhodopsin activates a G protein called transducin.
- Transducin activates an enzyme called phosphodiesterase.
- Phosphodiesterase breaks down cyclic GMP (cGMP).
In the dark, high levels of cGMP keep certain sodium channels in the outer segment open, maintaining the depolarized state. When light causes cGMP levels to fall, these sodium channels close. This leads to the hyperpolarization of the rod cell membrane.
This hyperpolarization closes the voltage-gated calcium channels at the synaptic terminal. With less calcium influx, the release of the neurotransmitter is reduced.
Identifying the Neurotransmitter Reduced by Light
The neurotransmitter released by rod (and cone) photoreceptors in the dark is Glutamate. When light strikes the rods, causing hyperpolarization, the release of Glutamate from these cells is significantly reduced.
Therefore, the release of Glutamate from the rods of the retina is reduced when light strikes its outer segment.
Considering Other Neurotransmitters
Let's look at the other options:
- Acetylcholine: While present in the retina, Acetylcholine is typically associated with amacrine cells, not the primary neurotransmitter released by photoreceptors.
- GABA: Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system, including the retina, often associated with amacrine and horizontal cells. It is not the neurotransmitter released by photoreceptors.
- Glycine: Glycine is another inhibitory neurotransmitter found in the retina, associated with amacrine cells. It is not the primary neurotransmitter released by photoreceptors.
Based on the physiological process of photoreceptor signaling, Glutamate is the neurotransmitter whose release is modulated by light in rods (and cones).
Important Questions from Nervous system
Which one of the following synaptic vesicle proteins is involved in tethering of the vesicle to the cytoskeletal system in the nerve terminus?
In the nervous system, the action potential is generated at the axon hillock in physiological conditions and it is conducted to the terminal end of axon. The location specific origin of action potential and its direction-specific conduction are explained by a researcher in the following proposed statements:
A. The membrane of axon hillock has highest threshold for the generation of action potential
B. The membrane of axon hillock contains large numbers of voltage-gated Na+ channels and that makes it more excitable
C. The propagating action potential in the middle of the axon cannot generate another action potential in the direction of cell body since a large fraction of voltage-gated Na+ channels in the preceding portion is voltage inactivated
D. As the number of voltage-gated Na+ channels is less in the preceding portion of axonal membrane, the propagating action potential in the middle of the axon cannot generate another action potential in the direction of cell body.
Which one of the following combinations represents both correct explanations?
Which one of the following is NOT released by sympathetic preganglionic neurons?
The time taken by synaptic vesicles to travel from the soma of a motor neuron in the spinal cord to its neuromuscular junction in a person’s foot by fast axon transport is about‐
The explanations for increased conduction velocity of action potentials in a myelinated nerve fibre (MNF) as compared to that of a non‐myelinated fibre (NNF) of same diameter are suggested below:
A. Much higher number of ions traverse a unit length of an MNF membrane compared to that of an NNF during conduction of action potential as the ionic currents are restricted to the membrane at the Nodes of Ranvier
B. The energy expenditure required to maintain ionic gradient after conduction of action potential in an MNF is higher than that of an NNF
C. The action potentials of MNF do not have a hyperpolarizing effect like that of an NNF
D. The relative refractory period is not extended in an MNF like that of an NNF
E. The axolemma at the nodes of Ranvier lacks K+ ion channels
F. MNFs are metabolically less efficient than NNFs
Choose all correct statements from the following options:
