Bradley is deeply relaxed and his muscles are not moving at all. This suggests that, for Bradley's motor neurons

A) sodium ions are concentrated inside the neurons and potassium ions are concentrated outside the neurons.
B) sodium ions and potassium ions are both concentrated inside the neurons.
C) sodium ions and potassium ions are both concentrated outside the neurons.
D) sodium ions are concentrated outside the neurons and potassium ions are concentrated inside the neurons.

Deep relaxation and lack of muscle movement are indicative of a low level of activity in motor neurons, which are responsible for controlling muscle movement. This low level of activity is caused by a decrease in the concentration of sodium ions outside the neuron and an increase in the concentration of potassium ions inside the neuron, creating a negative charge within the neuron. This state is known as hyperpolarization, which results in the inhibition of motor neuron activity and, consequently, muscle relaxation. Therefore, choice D, which states that sodium ions are concentrated outside the neurons and potassium ions are concentrated inside the neurons, best explains the physiological state of Bradley's motor neurons during deep relaxation.