**Core Concept**
The **pars nervosa**, also known as the posterior pituitary, is a part of the pituitary gland that plays a crucial role in the storage and release of hormones. The predominant cells in this region are involved in the transmission of signals from the hypothalamus to the posterior pituitary.

**Why the Correct Answer is Right**
The correct answer is related to the type of cells responsible for this function. The **pituitary** is divided into two main parts: the anterior pituitary and the posterior pituitary. The posterior pituitary, or **pars nervosa**, is composed mainly of **pituitary**, or specialized glial cells called **pituicytes**, and axons of hypothalamic neurons. However, the most predominant cells are actually the **pitucytes** and the axon terminals of the hypothalamic neurons, but among the given options, **pitucytes** are the most relevant.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the predominant cell type in the **pars nervosa**.
**Option B:** This option is also incorrect as it is not the primary cell type found in the **pars nervosa**.
**Option C:** This option is not the correct answer as the **pars nervosa** is not primarily composed of this cell type.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** This is not the correct answer as the **pars nervosa** is mainly composed of another type of cell.

**Clinical Pearl / High-Yield Fact**
The **pars nervosa** plays a critical role in the regulation of water balance in the body through the release of **antidiuretic hormone (ADH)**, also known as **vasopressin**.

**Correct Answer Line**
**Correct Answer: D. Pituicytes.**