SLP RS 102: Synapse

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Questions and Answers

What is the primary mechanism through which excitation occurs in postsynaptic cells?

Decrease of calcium conductance

Opening of chloride channels

Increase of potassium conductance out of the neuron

Opening of sodium channels (correct)

Which mechanism leads to inhibition in a postsynaptic neuron?

Opening of chloride channels (correct)

Opening of sodium channels

Decrease in potassium efflux

Increase in calcium influx

Which substance is usually classified as excitatory?

Glycine

Dopamine

Glutamate (correct)

GABA

What effect does increasing the resting membrane potential have on neuronal excitability?

It makes the neuron less excitable Signup and view all the answers

How does the conduction through potassium channels affect excitation?

Increases potassium efflux, resulting in increased negativity Signup and view all the answers

What is the role of receptor enzymes in neuronal inhibition?

To inhibit cellular metabolic functions Signup and view all the answers

Which of the following changes increases the likelihood of excitation?

Increased sodium conductance Signup and view all the answers

What defines the resting membrane potential in neurons?

Always negative Signup and view all the answers

What triggers the release of neurotransmitters from presynaptic terminals?

Influx of calcium ions Signup and view all the answers

What is the role of inhibitory receptors in the postsynaptic membrane?

To provide restraint on nervous action Signup and view all the answers

How do excitatory postsynaptic potentials (EPSPs) differ from inhibitory postsynaptic potentials (IPSPs)?

EPSPs increase the likelihood of an action potential, whereas IPSPs decrease it. Signup and view all the answers

What is the primary ion involved in the triggering of neurotransmitter release at presynaptic terminals?

Calcium Signup and view all the answers

Which explanation correctly describes the role of the axon hillock?

It generates action potentials after summation of inputs. Signup and view all the answers

What does spatial summation refer to?

The simultaneous activation of multiple synapses on a neuron. Signup and view all the answers

Which state of a neuron corresponds to when it is less likely to generate an action potential?

Inhibited state Signup and view all the answers

What best defines an excitatory postsynaptic potential (EPSP)?

It decreases the membrane potential, moving it closer to threshold. Signup and view all the answers

What is the normal intraneuronal potential of a resting neuron?

-65 millivolts Signup and view all the answers

Which ions are primarily involved in the different states of neuronal function?

Sodium ions, potassium ions, and chloride ions Signup and view all the answers

What causes a neuron to enter an excited state?

Sodium ion influx Signup and view all the answers

What is the minimal change in voltage that signifies an excitatory postsynaptic potential (EPSP)?

20 millivolts Signup and view all the answers

What process is required for a single presynaptic terminal to significantly increase neuronal potential?

Simultaneous discharge of many terminals Signup and view all the answers

How does a neurotransmitter work when secreted into the synaptic cleft?

It increases the membrane's permeability to sodium ions Signup and view all the answers

Which potential must an EPSP reach to elicit an action potential in the postsynaptic neuron?

-55 millivolts Signup and view all the answers

What does temporal summation involve?

Discharges of the same neuron in rapid succession Signup and view all the answers

What role do chloride ions play in synaptic transmission?

They inhibit synaptic transmission by introducing negative charges. Signup and view all the answers

What happens to a neuron when it is facilitated?

Its membrane potential is closer to the threshold for firing. Signup and view all the answers

What is the primary reason a single presynaptic terminal usually fails to excite a neuron?

The amount of transmitter released is insufficient to reach firing threshold. Signup and view all the answers

Which statement correctly describes an excitatory post-synaptic potential (EPSP)?

An EPSP is a gradual depolarization of the postsynaptic membrane. Signup and view all the answers

What is 'spatial summation' in the context of neuronal firing?

The ability to sum effects from multiple excitatory inputs at different locations. Signup and view all the answers

What causes excitation in neurons?

Opening of voltage-gated sodium channels. Signup and view all the answers

What occurs during 'temporal summation'?

A single terminal's rapid, successive discharges summate to reach threshold. Signup and view all the answers

Which type of synapse is most commonly found in the nervous system?

Chemical synapse using neurotransmitters. Signup and view all the answers

What effect does an IPSP have on the postsynaptic membrane potential?

It decreases the membrane potential, making firing less likely. Signup and view all the answers

What can happen if an EPSP and an IPSP occur simultaneously?

They can completely or partially nullify each other. Signup and view all the answers

What occurs when potassium channels open in a neuron?

Potassium exits the cell, leading to hyperpolarization. Signup and view all the answers

What triggers an action potential in the context of multiple synaptic inputs?

The cumulative effect of excitatory inputs exceeds the firing threshold. Signup and view all the answers

Why is the stimulation of motor and sensory neurons during reflexes significant?

It involves the small molecule system of transmitters. Signup and view all the answers

What role do ligand-gated sodium channels play in synaptic transmission?

They mediate the effects of neurotransmitters on the postsynaptic neuron. Signup and view all the answers

In which scenario is presynaptic inhibition likely to occur?

When adjacent sensory nerve fibers inhibit one another. Signup and view all the answers

What must occur for the exocytosis of neurotransmitters to take place?

Calcium must enter the neuron through voltage-gated channels. Signup and view all the answers

Study Notes

Mechanism of Neurotransmitter Release

An action potential causes depolarization of the presynaptic membrane, opening voltage-gated calcium channels.
Calcium ions influx into the presynaptic terminal directly influences neurotransmitter release into the synaptic cleft.

Excitation of the Postsynaptic Membrane

Activated excitatory receptors lead to:
- Opening of sodium channels, allowing positive charges to flow into the postsynaptic neuron, raising membrane potential.
- Reduced conductance through potassium and chloride channels, increasing positivity inside the neuron.
- Alterations in internal metabolism that may enhance excitatory receptors or limit inhibitory ones.

Inhibition of the Postsynaptic Membrane

Inhibitory mechanisms include:
- Opening of chloride channels allows negative chloride ions to enter, increasing negativity within the neuron.
- Increased efflux of potassium ions, which also leads to a more negative internal potential.
- Activation of enzymes that decrease the number of excitatory receptors or increase inhibitory receptors.

Common Neurotransmitters

Acetylcholine: predominantly excitatory.
Norepinephrine: typically excitatory.
Dopamine: functions as an inhibitor.
Glycine and GABA: key inhibitory neurotransmitters.
Glutamate: primarily excitatory.
Serotonin: inhibitory role in pain modulation.

Neuronal States and Membrane Potentials

Neuron states include:
- Resting state: approximately -65 mV.
- Excited state: around -45 mV (due to sodium influx).
- Inhibited state: about -70 mV (following potassium efflux or chloride influx).
Changes in membrane potential correlate with ion movement: sodium influx depolarizes, while potassium and chloride movements can hyperpolarize.

Definitions and Comparisons

EPSP (Excitatory Postsynaptic Potential): Depolarization that moves potential towards threshold for action potential.
IPSP (Inhibitory Postsynaptic Potential): Hyperpolarization that moves potential away from threshold.
EPSPs differ from action potentials as they are graded and not all-or-none responses.
Spatial summation: Multiple terminals activate simultaneously, leading to EPSP accumulation.
Temporal summation: Rapid successive firings from a single terminal that build upon prior potentials.

Generation of Action Potentials

Action potentials are generated when the summed EPSPs reach the threshold at the axon hillock.
The axon hillock integrates all inputs and is crucial for determining neuronal firing.

Membrane Excitability

High threshold membranes require greater stimulation to become excited compared to low threshold membranes.
Facilitated neurons are closer to action potential threshold and respond more easily to additional excitatory inputs.

Interactive Mechanisms

Simultaneous inputs of EPSPs and IPSPs can cancel out the effects, preventing action potential generation.
Neuronal facilitation allows a neuron to be primed for easier excitation upon subsequent stimulation, enhancing responsiveness to new signals.

Learning Scenario Insight

The ease of manipulating fine beads without gloves emphasizes the significance of tactile feedback and sensation in motor control, paralleling neurophysiological processes involving synaptic transmission and receptor activation.

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Description

This quiz covers the key concepts related to synapses, including how action potentials lead to neurotransmitter release, and the mechanisms of excitation and inhibition in postsynaptic membranes. Additionally, it explores common neurotransmitters and compares the states of a neuron: resting, excited, and inhibited.