Which of the following must be true about the structures of axons and muscle cells in order for nerve impulses to stimulate muscle contraction?
a- Axons and muscle cells must both have structures that make and secrete the same small molecules.
b- axons and muscle cells must both have receptors that recognize the same small molecules.
c- Axons must have structures that make and secrete molecules, and muscle cells must have receptors that recognize these molecules.
d-Muscle cells must have structures that make and secrete molecules, and axons must have receptors that recognize these molecules.
To determine the answer to this question, we need to understand the connection between axons and muscle cells and how nerve impulses stimulate muscle contraction.
In order for nerve impulses to stimulate muscle contraction, the axons, which transmit electrical signals from the brain or spinal cord to the muscle cells, need to interact with the muscle cells in a specific way. This interaction generally involves the release of neurotransmitters by the axons and the recognition of these neurotransmitters by receptors on the muscle cells.
Option a states that both axons and muscle cells must have structures that make and secrete the same small molecules. While axons do release small molecules called neurotransmitters, muscle cells do not secrete these molecules. Therefore, option a is incorrect.
Option b states that both axons and muscle cells must have receptors that recognize the same small molecules. This is partially true because axons release neurotransmitters, and muscle cells have receptors that recognize these neurotransmitters. However, this option does not consider the secretion of neurotransmitters by axons. Therefore, option b is not a complete explanation of the process.
Option c states that axons must have structures that make and secrete molecules, and muscle cells must have receptors that recognize these molecules. This option correctly explains the process. Axons produce and release neurotransmitters, while muscle cells have receptors that recognize these neurotransmitters. Therefore, option c is correct.
Option d states that muscle cells must have structures that make and secrete molecules, and axons must have receptors that recognize these molecules. This option does not accurately describe the process. Muscle cells do not secrete molecules that directly stimulate their own contraction, and axons do not have receptors to recognize such molecules. Therefore, option d is incorrect.
In conclusion, the correct answer is option c: Axons must have structures that make and secrete molecules, and muscle cells must have receptors that recognize these molecules.