Neuroscience Chapter on Synaptic Potentials

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Questions and Answers

What type of channels open when an excitatory transmitter binds to its receptors during EPSP?

Ligand gated Na+ or Ca++ channels (correct)

Ligand gated Cl- channels

Voltage gated Na+ channels

Ligand gated K+ channels

Which mechanism involves the summation of multiple EPSPs in quick succession?

Linear summation

Cumulative summation

Spatial summation

Temporal summation (correct)

What is the maximum duration of an IPSP?

10 ms

5 ms

1.5 ms

3 ms (correct)

What happens to the post synaptic membrane when the sum of EPSPs is significantly greater than IPSPs?

The membrane depolarizes to firing level. Signup and view all the answers

What is the consequence of presynaptic inhibition in the presynaptic neuron?

Decreased calcium entry Signup and view all the answers

Which of the following correctly describes the Grand Post Synaptic Potential (GPSP)?

The net outcome of all EPSPs and IPSPs in a single post synaptic neuron. Signup and view all the answers

What type of channel activity is associated with the hyperpolarization seen in an IPSP?

Opening of K+ or Cl- channels Signup and view all the answers

Which statement correctly describes presynaptic facilitation?

It involves the release of excitatory neurotransmitters like serotonin. Signup and view all the answers

What is the ionic basis of EPSP involving the influx of ions?

Influx of Na+ or Ca++ ions Signup and view all the answers

What causes fatigue in synaptic transmission?

Exhaustion of synaptic vesicles and inactivation of receptors Signup and view all the answers

How does synaptic plasticity adjust the function of a synapse?

By increasing or decreasing neurotransmitter release based on demand Signup and view all the answers

What characterizes short-term facilitation during synaptic transmission?

Continuous discharge due to accumulation of Ca++ Signup and view all the answers

What is the primary mechanism behind habituation in synaptic transmission?

Gradual inactivation of Ca++ channels Signup and view all the answers

What describes the synaptic delay during transmission?

It is typically around 0.5 m.sec. Signup and view all the answers

What role does phosphorothrylation of proteins in K+ channels play during depolarization?

It induces prolonged depolarization by closing K+ channels Signup and view all the answers

What is the relationship between the number of synapses in a reflex arc and central delay?

The number of synapses equals central delay divided by 0.5 Signup and view all the answers

What is the main ionic basis of post-tetanic potentiation in synaptic transmission?

Weakening of the Ca++ pump leading to accumulation of Ca++ Signup and view all the answers

Which of the following describes sensitization in synaptic transmission?

An augmented post synaptic response due to a noxious stimulus Signup and view all the answers

Study Notes

Synaptic Potentials

Excitatory Postsynaptic Potential (EPSP):
- Partial depolarization of the postsynaptic membrane.
- Reaches maximum after 1-1.5 ms.
- Duration: 2-5ms.
- Ionic Basis: Excitatory neurotransmitter binds to receptors, opening ligand-gated Na⁺ (or Ca²⁺) channels. Influx of Na⁺ (or Ca²⁺) causes a small depolarization and brings the membrane closer to threshold.
- Summation is necessary to reach threshold. Temporal summation occurs when presynaptic neuron stimulates repeatedly, closely timed EPSPs summate.
Inhibitory Postsynaptic Potential (IPSP):
- Partial hyperpolarization of the postsynaptic membrane.
- Reaches maximum after 1.5-2 ms.
- Duration: 3 ms.
- Ionic Basis: Inhibitory neurotransmitter binds to receptors, opening ligand-gated Cl⁻ (or K⁺) channels. Influx of Cl⁻ (or efflux of K⁺) causes hyperpolarization, moving the membrane further from threshold.
- IPSPs can also be caused by the closure of Na⁺ or Ca²⁺ channels.
- Similar to EPSPs, IPSPs can summate temporally and spatially.
Grand Postsynaptic Potential (GPSP):
- Sum of all EPSPs and IPSPs occurring at the same time in one postsynaptic neuron.
- Four possible outcomes:
  - Balance: EPSPs = IPSPs, no significant change.
  - Facilitation: EPSPs > IPSPs (membrane does not reach firing level).
  - Action Potential: EPSPs >> IPSPs (membrane reaches firing level).
  - Inhibition: IPSPs > EPSPs (hyperpolarization).

Action Potential vs. Postsynaptic Potential

Feature	Action Potential	Postsynaptic Potential
All-or-none law	Obeys all-or-none law	Does not obey all-or-none law
Graded	Cannot be graded	Graded
Summation	Cannot be summated	Summated
Propagation	Propagated	Not propagated
Refractory period	Absolute refractory period (1 ms)	No absolute refractory period
Effect of anesthesia	Blocked by anesthesia	Not blocked by anesthesia
Duration	1 ms	20 ms

Presynaptic Potentials

Presynaptic Inhibition:
- Third neuron releases inhibitory neurotransmitter (e.g., GABA).
- Possible mechanisms:
  - Closure of Ca²⁺ channels in the presynaptic neuron.
  - Opening of K⁺ or Cl⁻ channels.
- Reduced Ca²⁺ influx decreases neurotransmitter release.
- Slow onset, lasting minutes to hours.
Presynaptic Facilitation:
- Third neuron releases excitatory neurotransmitter (e.g., serotonin).
- Increases neurotransmitter release.
- Possible mechanism:
  - Serotonin → cAMP → phosphorylation of K⁺ channels. Closed K⁺ channels and prolonged depolarization.
  - Prolonged depolarization increases Ca²⁺ channel activation, resulting in more transmitter release.

Synaptic Transmission Characteristics

Forward Direction: Impulses flow from pre- to postsynaptic neuron.
Synaptic Delay: Time taken for an impulse to cross a synapse (0.5 ms). It depends on the number of synapses.
Fatigue: Decreased impulse discharge rate from postsynaptic neuron due to repetitive stimulation. Causes include depletion of synaptic vesicles and receptor inactivation.

Synaptic Plasticity

Ability of synapse to change function according to demand.
Short-term Inhibition (Habituation):
- Gradual loss of response to repeated stimuli.
- Mechanism: gradual inactivation of Ca²⁺ channels, reducing intracellular Ca²⁺, and neurotransmitter release.
Short-term Facilitation (Post-tetanic Potentiation):
- Brief intense stimulation leads to increased neurotransmitter release, longer-lasting response.
- Mechanism: accumulation of Ca²⁺ in the presynaptic terminal due to weakened Ca²⁺ pumps, leading to continuous transmitter release. This is involved in memory formation.

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Description

Explore the intricacies of excitatory and inhibitory postsynaptic potentials in this quiz. Understand the ionic basis of these processes and their significance in neural communication. Test your knowledge on EPSPs and IPSPs, their characteristics, and how they contribute to synaptic transmission.