Final answer:
The nervous system is composed of neurons and glial cells, where neurons are the primary signaling cells and glial cells provide essential support functions.
Step-by-step explanation:
In general, the nervous system is composed of two types of cells: neurons and glial cells. Neurons are responsible for sending electrical and chemical signals, which allow for communication within the nervous system. They are the primary signaling units, and their structure typically includes dendrites, a cell body, and an axon. On the other hand, glial cells, often simply referred to as glia, serve to support neurons; they provide structural support, nutritional support, transportation of waste and nutrients, myelination, and mediate immune responses within the nervous system. Glial cells, therefore, play a vital supporting role, but it's the neurons that are primarily associated with signaling in the nervous system.
Based on this understanding, the correct answer to the question - "In general, the nervous system is composed of which two types of cells?" is option C) 2 and 4, which are neurons and glial cells, respectively.