Question

The diagram shows the sequence of events occurring as an action potential arrives at a synapse. What are the substances moving across the membranes?

	1	2	3	4	5
A.	K+	Na+	Ach	Ca2+	K+
B.	K+	Na+	K+	Ca2+	Ach
C.	Na+	K+	Ca2+	Ach	Na+
D.	Na+	K+	Na+	Ach	Ca2+

Answer 1

Hint:
The functional and structural units of the nervous system are known as neurons. Generally, neurons are known as nerve cells. It transmits information in the form of electrical impulses.

Complete answer:
Neurons communicate with each other at junctions which are known as synapses. One neuron sends a message to a target neuron of another cell with the help of a synapse. Electrical and chemical synapses are two types of synapses. The electrical synapse communicates with the help of a chemical messenger while in the electrical synapse ions flow directly between cells.
At the chemical synapse, an action potential or nerve impulse activates the presynaptic neuron to release neurotransmitters. The pre-synaptic membrane is depolarised due to the entry of sodium ions (1) as the action potential reaches the synapse. With the exit of potassium ions (2) the membrane is subsequently repolarised. The arrival of the action potential causes calcium channels in the membrane to open, thus calcium ions rush into the synaptic knob (3). This causes the synaptic vesicles to fuse with the pre-synaptic membrane, releasing acetylcholine into the synaptic cleft (4). On the postsynaptic membrane, acetylcholine binds to specific receptor sites, opening ion channels and causing sodium ions to enter (5), depolarising the membrane.
Hence the correct answer is 1. Na⁺ 2. K⁺ 3. Ca²⁺ 4. Ach⁺ 5. Na⁺..

Option ‘C’ is correct

Note:
Electric synapse can conduct the nerve impulses faster than the chemical synapse.