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Chapter 48: Problem 6

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell \(X\) and an EPSP in postsynaptic cell Y. A likely explanation is that (A) the threshold value in the postsynaptic membrane for cell \(\mathrm{X}\) is different from that for cell \(\mathrm{Y}\). (B) the axon of cell \(\mathrm{X}\) is myelinated, but that of cell \(\mathrm{Y}\) is not. (C) only cell Y produces an enzyme that terminates the activity of the neurotransmitter. (D) cells X and Y express different receptor molecules for this particular neurotransmitter.

Short Answer

Expert verified
The correct answer is (D).

Step by step solution

01

Understanding IPSP and EPSP

IPSP stands for Inhibitory Postsynaptic Potential, which makes the postsynaptic neuron less likely to generate an action potential. EPSP stands for Excitatory Postsynaptic Potential, which makes the postsynaptic neuron more likely to generate an action potential. Thus, IPSP and EPSP have opposite effects on the postsynaptic cell.
02

Analyze the Differences Between Cells X and Y

Given that cell X experiences an IPSP and cell Y experiences an EPSP for the same neurotransmitter, the cause must lie in the differences between the two cells in how they respond to the neurotransmitter.
03

Evaluate Option A

Option A states that the threshold value in the postsynaptic membrane for cell X is different from that for cell Y. However, IPSP and EPSP are determined by the type of ion channels that open, not the threshold value.
04

Evaluate Option B

Option B states that the axon of cell X is myelinated, but that of cell Y is not. Myelination affects the speed of action potential transmission but not whether a cell produces an IPSP or EPSP.
05

Evaluate Option C

Option C states that only cell Y produces an enzyme that terminates the activity of the neurotransmitter. This would affect how long the neurotransmitter exerts its effect, but not whether it causes an IPSP or EPSP.
06

Evaluate Option D

Option D states that cells X and Y express different receptor molecules for this particular neurotransmitter. This is a likely explanation as different receptors can mediate either an IPSP or EPSP depending on the ion channels they control.
07

Conclusion

After evaluating all the options, the most likely explanation is that cells X and Y express different receptor molecules for this particular neurotransmitter. This difference in receptor types leads to different postsynaptic potentials (IPSP or EPSP) in each cell.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

IPSP
IPSP stands for Inhibitory Postsynaptic Potential. When a neurotransmitter binds to its receptor on the postsynaptic neuron, it can open ion channels that allow negatively charged ions to flow into the cell. This inflow makes the inside of the neuron more negative compared to the outside, which is called hyperpolarization. Hyperpolarization reduces the likelihood that the neuron will reach the threshold needed to trigger an action potential. Key points about IPSP include:
  • It makes the postsynaptic neuron less likely to fire.
  • It involves the opening of ion channels like those for chloride (Cl-) ions.
  • It is an essential part of balancing excitatory signals in the brain, preventing excessive neuronal firing.
By understanding IPSP, we can appreciate how neuronal circuits avoid overstimulation, maintaining the balance necessary for proper brain function.
EPSP
EPSP stands for Excitatory Postsynaptic Potential. It occurs when a neurotransmitter causes positively charged ions, such as sodium (Na+), to enter the postsynaptic neuron. This inflow makes the inside of the neuron less negative, a process called depolarization. Depolarization brings the membrane potential closer to the threshold needed to generate an action potential. Key aspects of EPSP include:
  • It makes the postsynaptic neuron more likely to fire an action potential.
  • It typically involves the opening of sodium channels, which allows Na+ ions to enter the cell.
  • It plays a crucial role in synaptic transmission, enabling neurons to communicate effectively.
Understanding EPSP helps to illuminate how neurons send excitatory signals to one another, forming the basis of neural communication.
Postsynaptic Receptors
Postsynaptic receptors are proteins located on the membrane of the postsynaptic neuron. These receptors bind neurotransmitters released from the presynaptic neuron, causing a reaction in the postsynaptic cell. The type of receptor and the resultant ion channels it activates will dictate whether the postsynaptic potential is inhibitory (IPSP) or excitatory (EPSP). Important points on postsynaptic receptors include:
  • They are specific to certain neurotransmitters, like serotonin, dopamine, or glutamate.
  • Different receptors can produce either an IPSP or EPSP, depending on the neurotransmitter and the type of ion channel they open.
  • They are critical in determining the overall response of the postsynaptic cell.
Knowing about postsynaptic receptors is key to understanding how neurons interpret and respond to signals received.
Neuronal Communication
Neuronal communication involves the transmission of signals between neurons through synapses. This process is fundamental to how the brain and nervous system function. Communication between neurons usually occurs through the release of neurotransmitters at the synaptic cleft. Here鈥檚 how this process works:
  • The presynaptic neuron releases neurotransmitters.
  • These neurotransmitters cross the synaptic cleft and bind to receptors on the postsynaptic neuron.
  • Depending on the type of receptor and the ion channels it controls, the binding can cause either an IPSP or an EPSP.
This process allows the brain to perform complex tasks, from simple reflexes to advanced cognitive functions. By understanding neuronal communication, we grasp how neurons integrate various signals to produce coherent responses.

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Most popular questions from this chapter

Which of the following is the most direct result of depolarizing the presynaptic membrane of an axon terminal? (A) Voltage-gated calcium channels in the membrane open. (B) Synaptic vesicles fuse with the membrane. (C) Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft. (D) An EPSP or IPSP is generated in the postsynaptic cell.

Why are action potentials usually conducted in one direction? (A) Ions can flow along the axon in only one direction. (B) The brief refractory period prevents reopening of voltagegated Na \(^{+}\) channels. (C) The axon hillock has a higher membrane potential than the terminals of the axon. (D) Voltage-gated channels for both \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{+}\) open in only one direction.

Ouabain, a plant substance used in some cultures to poison hunting arrows, disables the sodium-potassium pump. What change in the resting potential would you expect to see if you treated a neuron with ouabain? Explain.

If a drug mimicked the activity of GABA in the CNS, what general effect on behavior might you expect? Explain.

This diamond-back rattlesnake (Crotalus atrox) alerts enemies to its presence with a rattle-a set of modified scales at the tip of its tail. Describe the roles of gated ion channels in initiating and moving a signal along the nerve from the snake's head to its tail and then to the muscle that shakes the rattle.
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