Question

when you touch something hot, a neuron in your finger senses the temperature. which best describes the first reaction the neuron has?
a. sodium atoms travel through the veins.
b. neurotransmitters cross a synapse.
c. a resting potential forms.
d. ions flow into the neuron.

Explanation:

• Option A: Sodium ions (not atoms) move across neuron membranes, not through veins. Veins are for blood, so A is incorrect.
• Option B: Neurotransmitters crossing a synapse happens between neurons, after the initial ion flow in the sensing neuron. So B is not the first reaction.
• Option C: A resting potential is the state before stimulation. When a neuron senses a stimulus (like heat), it moves from resting to action potential, so C is incorrect.
• Option D: When a neuron is stimulated (like touching hot), ion channels open, and ions (e.g., sodium) flow into the neuron, starting the action potential. This is the first reaction of the neuron to the stimulus.

Answer:

D. Ions flow into the neuron.