**Core Concept**
GLUT 4 receptors are a subtype of glucose transporter proteins that play a crucial role in insulin-mediated glucose uptake in muscles and adipose tissue. They are responsible for facilitating the entry of glucose into these cells in response to insulin signaling.

**Why the Correct Answer is Right**
GLUT 4 receptors are primarily found in muscle cells (skeletal and cardiac) and adipocytes, where they are responsible for insulin-stimulated glucose uptake. When insulin binds to its receptor on the surface of these cells, it triggers a signaling cascade that ultimately leads to the translocation of GLUT 4 receptors to the cell surface, where they can facilitate glucose uptake. This process is essential for maintaining blood glucose levels within a normal range and for the proper functioning of these cells.

**Why Each Wrong Option is Incorrect**
* **Option A:** While GLUT 1 is widely distributed in various tissues, it is not the primary glucose transporter in muscle and adipose tissues.
* **Option B:** GLUT 2 is primarily found in the liver and pancreas, where it plays a role in glucose sensing and regulation of glucose metabolism.
* **Option C:** GLUT 3 is found in neurons and is responsible for basal glucose uptake in these cells, but it is not the primary glucose transporter in muscle and adipose tissues.

**Clinical Pearl / High-Yield Fact**
GLUT 4 dysfunction is associated with insulin resistance and type 2 diabetes mellitus, highlighting the importance of this glucose transporter in glucose homeostasis and insulin signaling.

**Correct Answer: C. Adipocytes and muscle cells.**