Which one of the following synaptic vesicle proteins is involved in tethering of the vesicle to the cytoskeletal system in the nerve terminus?
Synapsin
Synaptic Vesicle Tethering Proteins
Synaptic vesicles are tiny sacs found within the nerve terminus (also called the axon terminal) that store neurotransmitters. When a nerve impulse arrives, these vesicles fuse with the cell membrane to release the neurotransmitters into the synaptic cleft, allowing communication with the next neuron.
Before they can fuse, synaptic vesicles are often held in place near the synapse. This holding is done by anchoring or tethering them to the cytoskeleton, which is like the cell's internal scaffolding system made of proteins like actin.
Several proteins are associated with synaptic vesicles and play different roles in the process of neurotransmission:
- Synaptotagmin: This protein acts as a calcium sensor. When calcium ions enter the nerve terminus during an action potential, Synaptotagmin binds to calcium, which triggers the rapid fusion of the synaptic vesicle with the plasma membrane, leading to neurotransmitter release.
- Synapsin: Synapsin proteins (like Synapsin I, II, and III) are found on the surface of synaptic vesicles. A key function of Synapsin is to bind to the actin cytoskeleton. This binding tethers, or holds, the synaptic vesicles in a reserve pool away from the release sites. When a nerve impulse arrives and calcium levels rise, Synapsin becomes phosphorylated (modified), which reduces its binding to actin, allowing the vesicles to move towards the active zone for fusion.
- Synaptophysin: This is an integral membrane protein found in synaptic vesicles. Its exact function is still being studied, but it is thought to be involved in vesicle formation, trafficking, and possibly forming pores during fusion.
- Synaptobrevin: Also known as VAMP (Vesicle-Associated Membrane Protein), Synaptobrevin is another integral membrane protein of synaptic vesicles. It is a core component of the SNARE protein complex, which is essential for the vesicle to dock and fuse with the target membrane (the plasma membrane of the nerve terminus).
Based on these roles, the protein specifically known for tethering synaptic vesicles to the cytoskeletal system in the nerve terminus is Synapsin.
Important Questions from Nervous system
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 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:
