Question

The functional junction between two neurons is called
A) Synapse
B) Axon
C) Dendrite
D) None of the above

Answer 1

Hint: Dendrites are copiously branched extensions of the neuron, while axons are single, long projections. Both are involved in signalling, but one is concerned with afferent, the other with different signals.

Complete Answer:
- Neurons communicate with each other via synapses or synaptic junctions. These are places where two neuronal membranes of different neurons are on either side of the synaptic cleft. When the message that is being transmitted down one neuron reaches the end, it causes the release of molecules known as neurotransmitters into the synaptic cleft.
- The neurotransmitters cross this gap and attach to receptors on the surface of the neuron on the other side. Once this occurs, the chemical signal is once more converted into an electrical impulse propagated down the second neuron’s membrane.
- The axon is an extension which extends away from the neuronal cell body or soma, transmitting the electrical signal away to the extreme end of the neuronal cell.
- Dendrites, on the other hand, are much shorter extensions that pick up this signal and transmit it towards the neuronal cell body.
- The order or impulse transmission is: depolarisation of the dendritic membranes, down to the cell body, and finally along the axonal membrane. Transmission is unidirectional; it will not go in reverse.

The correct answer to this question is option (A).

Note: Axonal processes can be extremely long, reaching up to a few metres in length. Many of them are covered in a myelin sheath that speeds up impulse transmission and saves on energy utilisation.