Answer: Sodium (Na+).
- A Potassium (K+)
- B Calcium (Ca2+)
- C Chloride (Cl-)
- D Sodium (Na+)
Correct answer: D. Sodium (Na+)
Explanation: When Na+ channels open, sodium rushes in and the membrane depolarises, generating the action potential.
Structure of a neuron. Image: LadyofHats (Mariana Ruiz), Public Domain, via Wikimedia Commons.
Concept context
Brain, spinal cord, neurons, reflex arcs, and sense organs.