Transmission of nerve impulses occurs over the network of cells composing the nervous tissue.
Neuroglia (A) are non-neuronal cells found that support nervous tissue. They are involved in nerve cell homeostasis. Glia are non-excitable and much smaller and more numerous than neurons.
Efferent (B) and Afferent (C) pathways are functional networks’ names based on the direction of neuronal impulse. Efferent pathways carry signals from the brain to the body parts whereas afferent signals come from body parts to the brain.
Therefore, the options A, B and C are incorrect.
Neurons (D) or nerve cells are the basic origin and conduit of all nerve impulses. The transmission of nerve impulses along a neuron from one end to the other is believed to occur as a result of electrical changes across the membrane of the neuron. The ability of a neuron to maintain polarity (charge difference) across the plasma membrane is crucial to the conduction of nerve impulse.
Therefore, option (D) is correct.