## **Core Concept**
Electrical synapses, also known as gap junctions, allow for direct communication between neurons through the exchange of ions and small molecules. This type of synapse is characterized by its ability to facilitate bidirectional transmission of signals.

## **Why the Correct Answer is Right**
The correct answer, **D. Unidirectional transmission**, is a property not associated with electrical synapses. Electrical synapses are known for their ability to transmit signals in both directions, which is essential for coordinating activities among groups of neurons. This bidirectional capability is a hallmark of electrical synapses, contrasting with chemical synapses, which typically transmit signals in one direction.

## **Why Each Wrong Option is Incorrect**
- **Option A: Bidirectional transmission** - This is a characteristic of electrical synapses. They allow ions and small molecules to pass directly from one cell to another, enabling bidirectional communication.
- **Option B: Presence of gap junctions** - Electrical synapses are indeed characterized by the presence of gap junctions, which are channels that directly connect the cytoplasm of two cells, allowing for the exchange of ions and small molecules.
- **Option C: Lack of synaptic delay** - Electrical synapses typically have little to no synaptic delay because the signal transmission occurs through direct ion flow, not through the release and uptake of neurotransmitters.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that electrical synapses are crucial in certain types of neurons where synchronized activity is required, such as in the retina and in some areas of the brain. Unlike chemical synapses, electrical synapses do not involve neurotransmitter release and can transmit signals in both directions.

## **Correct Answer:** D. Unidirectional transmission.