Question

A particular disease of the nervous system specifically involves the Ca²⁺ ion channels at the chemical synapses of motor neurons where neurotransmitter is stored and released. In other words, this disease affects the
A. Axon terminals of the presynaptic cell and release of acetylcholine.
B. Axon terminals of the postsynaptic cell and the release of K⁺ ions.
C. Electric synapses.
D. Axon terminals of the presynaptic cell and release of K⁺ ions.

Answer 1

Hint:
Ion channels are macromolecular pores in cell membranes that are selectively permeable to ions, i.e., Na⁺, K⁺, Ca²⁺, and Cl^–. These pores control ion flux into and out of the cell and can trigger biochemical reactions in response to a change in intracellular ion balance.

Complete answer:
Ion channels are divided into three subfamilies based on the stimulus to which they respond: voltage-gated, ligand-gated, and mechanosensitive.
Voltage-gated channels respond to a change potential of the cell membrane. They are usually highly selective for a specific ion, i.e., Na⁺, K⁺, Ca²⁺, or Cl^–. Ligand-gated channels include acetylcholine, glutamate, GABA, glycine, serotonin, ATP, proton, and FMRF amide-sensitive receptors. Some ion channels are mechanosensitive, responding to changes in mechanical forces on the cell membrane.
Ion channels are essential for the brain as well as other functions of the body. Abnormal ion channels can be caused by several mechanisms and these abnormalities are expected to cause dysfunction and disease. If the disease acts on a chemical synapse where the neurotransmitter is stored and released, it is affecting the axon terminals of the presynaptic cell. Ca²⁺ channels are involved in regulating the release of acetylcholine by allowing Ca²⁺ to enter the presynaptic cell and promoting the fusion of acetylcholine-containing vesicles to the membrane.
Hence the correct answer is Axon terminals of the presynaptic cell and the release of acetylcholine.

Option ‘A’ is correct

Note:
Ion channels are found in all cellular membranes. Their functions include establishing resting membrane potential, producing and shaping electrical signals, gating the flow of Ca²⁺ ions which serve as intracellular messengers, controlling cell volume, and regulating ion flow across epithelial cells of secretory and resorptive tissues.