Question

Beginning at the synapse of a neuron, place the events in neuronal signaling in the correct sequence. 1. Ion channels bind the ligand and open. 2. Na is pumped out of the cell, and the membrane potential is restored. 3. Acetylcholinesterase breaks down acetylcholine. 4. Na enters the postsynaptic cell, and the membrane potential changes. 5. Acetylcholine is released into the synapse. 6. Na ion channels close. 4, 5, 1, 2, 6, 3 6, 4, 3, 1, 2, 5 3, 4, 6, 1, 5, 2 1, 2, 3, 4, 5, 6 5, 1, 4, 3, 6, 2

Answer 1

Answer: 5, 1, 4, 3, 6, 2

Explanation:

The synapse is an intercellular approach between neurons or between a neuron and a muscle or glandular effector cell. At the synapse, the transmission of the nerve impulse takes place. This is initiated by a chemical discharge that causes an electrical current in the membrane of the presynaptic cell (sending cell). Then, once this nerve impulse reaches the end of the axon (the connection with the other cell), the neuron secretes a chemical compound called neurotransmitter that is deposited in the cleft or synaptic space (intermediate space between this transmitting neuron and the postsynaptic or receiving neuron). These secreted substances or neurotransmitters (noradrenaline and acetylcholine among others) are responsible for exciting or inhibiting the action of the other cell called postsynaptic cell.

The events are:

• Acetylcholine is released into the synapse (5): Acetylcholine is a neurotransmitter that is released at synapses in response to a specific stimulus. The secreted neurotransmitter acts on specialized receptor sites on the postsynaptic cell, which causes changes in the metabolism of the postsynaptic cell, modifying its cellular activity.
• Ion channels bind the ligand and open (1): The channels control the transmission between neurons because they bind neurotransmitters and open in response to a ligand. So the neurotransmitters diffuse across the cleft and bidn to receptors.

• Na enters the postsynaptic cell, and the membrane potential changes (4): Sodium channels open and allow an inward diffusion of sodium ions (Na+) from the outside to the inside. This causes the membrane potential to become less negative or more positive or to approach the threshold potential. Next, this triggers an excitatory potential (EPSP) so it causes the postsynaptic membrane to depolarize and fire an action potential. which spreads along the membrane of the post-synaptic neuron. This means an impulse is transmitted.

• Acetylcholinesterase breaks down acetylcholine (3): Acetylcholinesterase is an enzyme that breaks down the neurotransmitter so it causes the inactivation of acetylcholine into acetic acid and choline.
• Na ion channels close (6):  Na channels open and close according to different signals. The peak voltage causes them to close, and potassium channels open. So sodium ions stay inside the cell while potassium ions move outside of it. When this happens, repolarization (change in membrane potential that retunrs it to a negative value) takes place. Potassium channels remain open after the potential reaches the resting level causing hyperpolarization (the membrane potential becomes more negative) and it alters the ability of certain of ions to enter the cell.  At the end, the cell has more K+ ions on the outside.
• Na is pumped out of the cell, and the membrane potential is restored (2): The sodium-potassium pump moves sodium ions to the outside and potassium ions to the inside.