What is the function of the endoplasmic reticulum in neurons?

• A. ER stores lipids
• B. ER is not present in neurons
• C. ER generates energy
• D. Rough ER is for protein synthesis; smooth ER is for protein transport

Answer: (D)

In neurons, the endoplasmic reticulum has two distinct forms with different roles. Rough ER, studded with ribosomes, is the site where proteins destined for membranes, receptors, or secretion are synthesized. These proteins enter the secretory pathway and are processed as they move toward their final destinations, such as the plasma membrane or synaptic vesicles. Smooth ER, which lacks ribosomes, handles lipid synthesis for membrane components and also plays a major role in intracellular calcium storage and release, which is crucial for controlling neurotransmitter release and synaptic signaling. Energy production is not a function of the ER—that’s the job of mitochondria. So the key idea is that rough ER makes proteins and smooth ER handles lipids and calcium; transport of proteins occurs via vesicular trafficking after synthesis.