Questions & Answers

A diagram showing axon terminal and synapse is given. Identify correctly at least two of A-C.

A. A- Receptor, C- Synaptic vesicles
B. B- Synaptic connection, C- ${K^+}$
C. A- Neurotransmitter. B- Synaptic cleft
D. C- Neurotransmitter, B- $Ca^{++}$.

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Hint: The given diagram shows a synapse. Synapse is a junction between two neurons that allows signals to pass from one neuron to another through a neurotransmitter.

Complete step-by-step answer:
A synapse occurs between a presynaptic neuron and a postsynaptic neuron. The presynaptic neuron sends the message and the postsynaptic neuron as the receiver of the message. Synapses may be excitatory or inhibitory. The release neurotransmitter which is either an inhibitory or excitatory neurotransmitter. They cannot be both.
The parts to a synapse is given below as per the diagram:
Label A - Receptors: These are proteins to which neurotransmitters bind. They can open ion channels and excite the postsynaptic neuron.
Label B- Synaptic cleft: The synaptic cleft is a gap between the presynaptic and postsynaptic neuron. In this gap neurotransmitters are abundant.
 Label C- Synaptic vesicles: Small capsule-like structures located inside the axon terminals and they contain the neurotransmitters. They get attached to the presynaptic membrane and release the neurotransmitter in the synaptic cleft.

Thus, option A. A- Receptor, C- Synaptic vesicIes is the correct answer.

Additional information:
Neurotransmitters are substances which are released by presynaptic neurons. They make changes in the postsynaptic neuron. They may lower or raise its membrane potential.
Neurotransmitters can be excitatory that bind to receptors and cause an electrical signal to be transmitted down the cell. They may be inhibitory and may block the signal from continuing, preventing the message from being carried.

Note: A junction between two neurons or between a neuron and a target cell, like a muscle or a gland. At the synapse, an action potential is generated in sending neurons which causes the transmission of a signal to another neuron.