Neuroscience: Synaptic Potentials Quiz

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Questions and Answers

What occurs due to a prolongation of depolarization in a neuron?

Increased repolarization of K+ channels

Decrease in Ca++ channel activity

Sustained opening of Ca++ channels (correct)

Release of serotonin in excess

What factor primarily contributes to synaptic delay?

Duration of neurotransmitter binding

Rate of ion exchange

Number of synapses in the reflex arc (correct)

Distance between neurons

Which mechanism leads to short term inhibition in synaptic transmission?

Inactivation of Ca++ channels (correct)

Exhaustion of synaptic vesicles

Gradual inactivation of K+ channels

Increased release of neurotransmitters

Which of the following describes synaptic plasticity?

The ability to adjust synaptic function based on demand Signup and view all the answers

What is the primary effect of post-tetanic potentiation in a synaptic response?

Continuous discharge from the post synaptic neuron Signup and view all the answers

What characterizes an Excitatory Post Synaptic Potential (EPSP)?

It results from the influx of sodium ions through ligand gated channels. Signup and view all the answers

What is indicated by a decrease in the rate of discharge of impulses due to repetitive stimulation?

Synaptic fatigue Signup and view all the answers

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

It represents the combined total of all EPSPs and IPSPs occurring simultaneously. Signup and view all the answers

What primarily leads to sensitization in synaptic transmission?

Pre synaptic facilitation from a noxious stimulus Signup and view all the answers

How does an Inhibitory Post Synaptic Potential (IPSP) affect the post synaptic membrane?

It causes hyperpolarization, moving the membrane away from the firing level. Signup and view all the answers

During synaptic transmission, what is the consequence of closing K+ channels?

Prolonged depolarization of the neuron Signup and view all the answers

What is the typical duration of synaptic delay between neurons?

0.5 milliseconds Signup and view all the answers

What is the role of presynaptic inhibition?

It involves closure of Na+ channels in the presynaptic neuron. Signup and view all the answers

Which of the following statements about fatigue in synapses is true?

Fatigue can occur due to exhausted synaptic vesicles Signup and view all the answers

What type of summation occurs when multiple EPSPs are received in rapid succession?

Temporal summation. Signup and view all the answers

Which scenario would most likely result in an action potential being generated?

EPSP significantly exceeds IPSP. Signup and view all the answers

What is the ionic basis for an EPSP?

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

What happens during presynaptic facilitation?

An excitatory transmitter is released, increasing neurotransmitter release. Signup and view all the answers

Which of the following outcomes occurs if the EPSP is greater than the IPSP but does not reach the firing level?

There is facilitation without firing. Signup and view all the answers

When does an IPSP typically reach its maximum effect?

Within 1.5 - 2 ms. Signup and view all the answers

Study Notes

Synaptic Potentials

Excitatory Postsynaptic Potential (EPSP):
- Causes partial depolarization of the postsynaptic membrane.
- Reaches maximum after 1-1.5 milliseconds.
- Lasts 2-5 milliseconds.
- Ionic basis: excitatory neurotransmitter binding to receptors opens ligand-gated Na+ (or Ca++) channels, allowing Na+ (or Ca++) influx, creating a small depolarization.
- Summation is required to reach threshold for an action potential.
- Temporal summation occurs when the presynaptic neuron is stimulated repeatedly in quick succession.
Inhibitory Postsynaptic Potential (IPSP):
- Causes partial hyperpolarization of the postsynaptic membrane.
- Reaches maximum after 1.5-2 milliseconds.
- Lasts 3 milliseconds.
- Ionic basis: inhibitory neurotransmitter binding to receptors opens ligand-gated Cl- (or K+) channels, allowing Cl- influx (or K+ efflux), creating a small hyperpolarization, moving the membrane away from the firing level.
- IPSPs can also be produced by closing Na+ or Ca++ channels.
- Summation is required to affect membrane potential.
- Temporal and spatial summation are similar to EPSPs.
Grand Postsynaptic Potential (GPSP):
- Sum of all EPSPs and IPSPs occurring at the same time in one postsynaptic neuron.
- Four possible outcomes:
  - Balance between facilitation and inhibition: no change to membrane potential.
  - Facilitation: EPSP > IPSP, no action potential.
  - Action potential: EPSP >> IPSP, membrane reaches firing level.
  - Inhibition: IPSP > EPSP, hyperpolarization.

Action Potential vs. Postsynaptic Potential

Action Potential:
- All-or-none law.
- Cannot be graded.
- Cannot be summed.
- Propagated.
- Has absolute refractory period.
- Blocked by anesthesia.
- Duration: 1 millisecond.
Postsynaptic Potential:
- Does not follow all-or-none law.
- Graded (amplitude varies).
- Can be summed.
- Not propagated.
- No absolute refractory period.
- Not blocked by anesthesia.
- Duration: 20 milliseconds.

Presynaptic Potentials

Presynaptic Inhibition:
- Third neuron (inhibitory) releases an inhibitory transmitter.
- Mechanisms:
  - Closure of Ca++ channels.
  - Opening of K+ or Cl- channels.
  - Reduced Ca++ entry into the presynaptic knob, decreasing neurotransmitter release.
- Slow development, lasting minutes to hours.
Presynaptic Facilitation:
- Third neuron (excitatory) releases an excitatory transmitter (e.g., serotonin).
- Serotonin/cAMP increases in the presynaptic knob.
- Phosphorylates a protein in K+ channels.
- Closes K+ channels, prolonging depolarization.
- Increased Ca++ influx causing sustained neurotransmitter release.

Synaptic Transmission Characteristics

Forward Direction (Unidirectional): Impulses travel from presynaptic to postsynaptic neuron.
Synaptic Delay: Time taken for an impulse to travel across a synapse, typically 0.5 milliseconds.
Fatigue: Decreased rate of impulse discharge from the postsynaptic neuron due to repetitive stimulation (exhaustion of synaptic vesicles).

Synaptic Plasticity

Short-Term Inhibition (Habituation): Gradual loss of response to a benign stimulus repeated at intervals (inactivation of Ca2+ channels reducing neurotransmitter release).
Short-Term Facilitation (Post-tetanic Potentiation): Brief, high-frequency stimulation of a presynaptic neuron; brief, intense stimulation leading to sustained release of neurotransmitter. Ionic basis is accumulation of Ca2+ in the presynaptic neuron, weakening Ca2+ pump.
Sensitization: Prolonged augmented response of the postsynaptic neuron due to application of a noxious stimulus accompanying a benign stimulus (Pre-synaptic facilitation).

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Description

Test your knowledge on excitatory and inhibitory postsynaptic potentials in neuroscience. This quiz covers the ionic mechanisms, durations, and summation types involved in synaptic transmission. Perfect for students looking to deepen their understanding of synaptic functions.