Which one of the following is NOT released by sympathetic preganglionic neurons?
Serotonin
Sympathetic Preganglionic Neuron Neurotransmitters
Sympathetic preganglionic neurons are part of the autonomic nervous system. These neurons originate in the spinal cord and project to sympathetic ganglia. The primary neurotransmitter released by the vast majority of sympathetic preganglionic neurons at their synapse with postganglionic neurons is acetylcholine (ACh).
However, some neurons can also co-release other substances, often peptides, which can modulate the effects of ACh or have their own distinct effects on the postganglionic neuron.
Analyzing the Options
Let's look at the neurotransmitters listed in the options:
- Neurotensin: This is a neuropeptide found in various parts of the nervous system, including some autonomic pathways.
- Enkephalin: These are opioid peptides that can function as neurotransmitters or neuromodulators. They are found in different neuronal populations, including some involved in autonomic regulation or synapses.
- Serotonin: Also known as 5-hydroxytryptamine (5-HT), Serotonin is a monoamine neurotransmitter heavily involved in functions in the central nervous system (like mood, sleep, appetite) and the enteric nervous system. While it plays roles in regulating autonomic output centrally or peripherally, it is not typically released by sympathetic preganglionic neurons.
- Substance P: This is a neuropeptide known for its role in pain transmission, but it is also found in other parts of the nervous system, including some autonomic and sensory neurons.
Why Serotonin is NOT Released by Sympathetic Preganglionic Neurons
While peptides like Neurotensin, Enkephalin, and Substance P can sometimes be found co-localized or released alongside primary neurotransmitters in various parts of the nervous system, including potentially some complex autonomic circuits or afferent fibers associated with sympathetic reflexes, Serotonin (5-HT) is not a characteristic neurotransmitter released by the cell bodies or terminals of sympathetic preganglionic neurons originating in the intermediolateral cell column of the spinal cord and synapsing in the sympathetic ganglia.
The principal neurotransmitter released by these preganglionic neurons is acetylcholine, acting on nicotinic receptors on the postganglionic neurons. Serotonin's primary sites of synthesis and release are different neuronal populations in the brainstem (raphe nuclei) and the enteric nervous system.
Therefore, among the given options, Serotonin is the substance that is NOT released by sympathetic preganglionic neurons.
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?
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 release of which neurotransmitter from the rods of retina is reduced when light strikes its outer segment?
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:
