C4- synapses
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Questions and Answers

Axo-somatic connectivity refers to the axon connecting to dendrites.

False (B)

The presence of spines on dendrites is essential for the formation of synapses.

True (A)

Axo-axonic connectivity is the most common type of synaptic interaction.

False (B)

Neurons integrate synaptic inputs predominantly at the axon hillock.

<p>True (A)</p> Signup and view all the answers

Dendrites are solely responsible for generating action potentials in neurons.

<p>False (B)</p> Signup and view all the answers

The architecture of synaptic contacts plays a crucial role in processing incoming messages.

<p>True (A)</p> Signup and view all the answers

Multiple synapses from a single axon can lead to increased precision in signal transmission.

<p>True (A)</p> Signup and view all the answers

Graded potentials occur exclusively in the axon of a neuron.

<p>False (B)</p> Signup and view all the answers

GAP junctions consist of two separate membranes that fully merge together.

<p>False (B)</p> Signup and view all the answers

The only difference between channels and GAP junctions is that GAP junctions are paired channels.

<p>True (A)</p> Signup and view all the answers

In the snail aplysia, stimulating the tail leads to the release of ink as part of a defensive mechanism.

<p>True (A)</p> Signup and view all the answers

The synaptic delay in the transmission of impulses is approximately 1 second.

<p>False (B)</p> Signup and view all the answers

Ions flow through GAP junctions only through active transport mechanisms.

<p>False (B)</p> Signup and view all the answers

The release of neurotransmitters occurs after the opening of calcium voltage gated channels.

<p>True (A)</p> Signup and view all the answers

The amount of neurotransmitter released by one action potential is highly variable and not well-defined.

<p>False (B)</p> Signup and view all the answers

Calcium concentration is significantly higher inside the cytoplasm than outside under resting conditions.

<p>False (B)</p> Signup and view all the answers

Micro-domains of calcium increase are crucial for the release of vesicles during synaptic transmission.

<p>True (A)</p> Signup and view all the answers

The overall concentration of calcium ions in the synapse determines vesicle release.

<p>False (B)</p> Signup and view all the answers

The active zone of the presynaptic membrane has no geometrical precision in vesicle release.

<p>False (B)</p> Signup and view all the answers

The amplitude of the graded potential is affected by the amount of neurotransmitter released.

<p>True (A)</p> Signup and view all the answers

Calcium channels ensure that there is an equal distribution of calcium ions inside and outside the cell.

<p>False (B)</p> Signup and view all the answers

Pumps are responsible for increasing the intracellular concentration of calcium ions.

<p>False (B)</p> Signup and view all the answers

Calcium ions play a minor role in synaptic transmission due to their brief activation time.

<p>False (B)</p> Signup and view all the answers

Calcium ($Ca^{2+}$) acts as a chemical mediator during neurotransmitter release.

<p>False (B)</p> Signup and view all the answers

The equilibrium potential of calcium is approximately +130mV.

<p>True (A)</p> Signup and view all the answers

The postsynaptic potential can only be excitatory.

<p>False (B)</p> Signup and view all the answers

The neurotransmitter (NT) is released via a process called endocytosis.

<p>False (B)</p> Signup and view all the answers

Calcium enters the presynaptic cell through voltage-gated channels during depolarization.

<p>True (A)</p> Signup and view all the answers

The binding of neurotransmitters to receptors on the postsynaptic membrane does not influence ion channel activity.

<p>False (B)</p> Signup and view all the answers

Calcium binds to cytoskeletal proteins, aiding in the movement of vesicles.

<p>True (A)</p> Signup and view all the answers

Receptors on the postsynaptic membrane are uniformly distributed across the entire membrane.

<p>False (B)</p> Signup and view all the answers

The postsynaptic current alters the excitability of the presynaptic cell.

<p>False (B)</p> Signup and view all the answers

The neurotransmitter's effect can vary based on the type of receptor it binds to.

<p>True (A)</p> Signup and view all the answers

Gap junctions enable simultaneous activation of a large number of cells due to their ability to transmit signals rapidly.

<p>True (A)</p> Signup and view all the answers

In the heart, myocardiocytes are connected only through chemical synapses.

<p>False (B)</p> Signup and view all the answers

Electrical synapses can only transmit ions and not metabolic peptides.

<p>False (B)</p> Signup and view all the answers

The directionality of an electrical synapse is determined solely by the presynaptic cell.

<p>True (A)</p> Signup and view all the answers

Chemical synapses lack a synaptic cleft between the pre and post synaptic membranes.

<p>False (B)</p> Signup and view all the answers

The release of neurotransmitters at chemical synapses occurs via exocytosis.

<p>True (A)</p> Signup and view all the answers

Calcium ions play a vital role in the action potential at the presynaptic terminal by opening voltage-gated channels.

<p>True (A)</p> Signup and view all the answers

Chemical synapses require a direct physical connection between neurons to transmit signals.

<p>False (B)</p> Signup and view all the answers

The presence of synaptic vesicles in the presynaptic membrane is essential for storing neurotransmitters.

<p>True (A)</p> Signup and view all the answers

Synchronous discharges can occur in electrical synapses due to the interconnectedness of neurons through gap junctions.

<p>True (A)</p> Signup and view all the answers

Flashcards

Axo-dendritic connectivity

The connection between an axon and a dendrite, where communication occurs via neurotransmitters.

Spines

Small, specialized structures on dendrites that receive signals from axons, often forming synapses.

Synapse

A specialized contact point where an axon releases neurotransmitters, and a dendrite receives them, triggering a signal.

Axo-somatic connectivity

Synaptic connections where the axon directly contacts the cell body (soma) of a neuron.

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Axo-axonic connectivity

A rare type of synapse where an axon connects to another axon, potentially influencing its signal transmission.

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Integration of incoming messages

The ability of a neuron to receive and integrate signals from multiple synapses simultaneously.

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Axon hillock

The region of a neuron where the axon originates and where all incoming signals are summed together to determine if an action potential will be fired.

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Synaptic integration

The process by which a neuron receives signals from multiple synapses and combines them to produce a response.

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Active Zone

The portion of the presynaptic membrane where vesicles are released. It's a precisely defined area that ensures a specific number of vesicles are released with each action potential.

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Quantal Release

The process involving the release of a fixed amount of neurotransmitter from a single vesicle. This amount is considered a 'quantum' of neurotransmitter release.

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Postsynaptic Potential

The change in membrane potential of a postsynaptic neuron caused by the binding of neurotransmitters released from a presynaptic neuron. It's a graded potential, meaning its amplitude and duration depend on the amount and duration of neurotransmitter release.

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Neurotransmitter Release

The process by which neurotransmitters are released from presynaptic neurons. It's triggered by action potentials and involves the influx of calcium ions that cause vesicles to fuse with the presynaptic membrane.

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Calcium Microdomain

An increase in calcium concentration within the synaptic button. This increase is localized and only occurs near the calcium channels and vesicles, allowing for efficient neurotransmitter release.

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Calcium Pumps

Specialized proteins that regulate the concentration of calcium ions within a cell. They work to remove calcium from the cytoplasm, preventing excessive calcium concentrations.

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Electrochemical Gradient

The difference in electrical charge across a cell membrane. It's essential for the movement of ions across the membrane, including calcium ions.

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Synaptic Transmission

The process by which an action potential triggers the release of neurotransmitters from a presynaptic neuron. It involves a chain of events beginning with calcium influx and ending with vesicle fusion and neurotransmitter release.

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SNARE Proteins

A type of protein that facilitates the fusion of vesicles with the presynaptic membrane, leading to the release of neurotransmitters.

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Resting Membrane Potential

The membrane potential of a neuron at rest. It's usually negative compared to the outside of the cell.

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Gap Junction

A specialized structure that allows for direct communication between two neurons, enabling the rapid flow of electrical signals across their membranes.

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Synaptic Delay

The brief delay that occurs between the arrival of a signal at the presynaptic neuron and the activation of the postsynaptic neuron.

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Aplysia Model

A model system used to study how neurons interact and communicate, often focusing on the release of ink by the sea snail Aplysia.

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What is the function of electrical synapses?

Electrical synapses allow for rapid and synchronized firing of neurons. This is because neurons are connected by gap junctions, which allow for the direct flow of ions and small molecules between cells.

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What are gap junctions?

Gap junctions are specialized channels that connect the cytoplasm of adjacent cells, allowing the direct passage of ions and small molecules.

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Why is the heart considered an electrical syncytium?

The heart is an electrical syncytium because all of its muscle cells (myocardiocytes) are connected by gap junctions, allowing for coordinated contraction.

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What is the directionality of electrical synapses?

Electrical synapses are bidirectional, meaning signals can travel in both directions. This is because the channels forming the gap junction are symmetrical.

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What distinguishes a chemical synapse from an electrical synapse?

In chemical synapses, a space called the synaptic cleft separates the presynaptic and postsynaptic neurons. Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron.

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What are neurotransmitters?

Neurotransmitters are chemical messengers that transmit signals between neurons.

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What are synaptic vesicles?

Synaptic vesicles are small sacs that store neurotransmitters within the presynaptic neuron.

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What are receptors in a chemical synapse?

Receptors on the postsynaptic neuron bind to neurotransmitters, triggering a signal transduction pathway.

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Explain the process of neurotransmitter release.

The arrival of an action potential at the presynaptic terminal triggers a chain of events, including the opening of voltage-gated calcium channels, which allows calcium ions to influx into the presynaptic terminal.

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What is exocytosis?

Exocytosis is the process by which synaptic vesicles fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft.

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Calcium Influx at Synapse

Calcium ions (Ca2+) enter the presynaptic terminal through voltage-gated calcium channels, triggered by the arrival of an action potential.

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Vesicle Fusion

The influx of calcium causes synaptic vesicles, containing neurotransmitters, to fuse with the presynaptic membrane.

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Neurotransmitter Binding

Neurotransmitters in the synaptic cleft bind to specific receptors on the postsynaptic membrane.

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Postsynaptic Channel Opening/Closing

The binding of neurotransmitters to receptors opens or closes ion channels, allowing ions to flow across the postsynaptic membrane.

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Postsynaptic Potentials (EPSPs & IPSPs)

The flow of ions through postsynaptic channels generates excitatory or inhibitory postsynaptic potentials (EPSPs or IPSPs), altering the excitability of the postsynaptic neuron.

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Neurotransmitter Removal

After the neurotransmitter has done its job, it is quickly removed from the synaptic cleft by different mechanisms, ensuring that signaling is precisely controlled.

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Vesicle Recycling

The synaptic vesicle membrane is retrieved from the plasma membrane after neurotransmitter release, ensuring a continuous supply of vesicles for future signaling.

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Synaptic Precision

The chemical synapse, where neurotransmitter release occurs, is a highly precise structure. The close proximity of the membranes and the high density of receptors on the postsynaptic membrane ensure that the signal is delivered efficiently and accurately.

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Receptor Specificity

The type of receptor activated by a neurotransmitter determines the specific ion channels that open or close, leading to either excitatory or inhibitory postsynaptic potentials.

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Study Notes

Membrane Excitability: Synapses

  • Axon potential can be established at the axon hillock or terminal when a minimum intensity (rheobase) is reached.
  • Absolute refractoriness is a fixed time period that cannot be shortened.
  • Neurons have varying discharge frequencies; different brain regions have distinct neuronal properties.

Signals to Communicate

  • Action potentials originate at the axon hillock or axon endings.
  • Neurons communicate using action potentials as signals.
  • Graded potentials, if strong enough, trigger action potential at the axon hillock.
  • Sensory neurons transmit information to the spinal cord or brainstem, then communicate to the brain.

Modalities of Cellular Signaling

  • There are different types of cellular signaling, including:
    • Nonspecialized synapses:
      • Humoral: Hormones released travel and bind their target.
      • Paracrine: Local chemical messengers released affect neighboring cells.
      • Autocrine: Cells releases molecules that affect themselves.
  • Chemical synapse involves chemical release into the synaptic cleft between neurons, and the receptor cells respond to this chemical signal.
  • Electrical synapses involve a direct physical connection (gap junctions) between neurons, allowing ions to flow directly.

Electric Synapses

  • Electric synapses use gap junctions to create direct channels for ion flow between membranes.
  • There is no pre- or post-synaptic delay in an electric synapse.
  • Communication can be bidirectional.

Chemical Synapses

  • Chemical synapses use neurotransmitters to transmit signals across the synaptic cleft.
  • The pre- and post-synaptic membranes are separated by a space called the synaptic cleft.
  • Neurotransmitters are stored in synaptic vesicles.
  • An action potential will cause the release of neurotransmitters into the synaptic cleft.
  • Neurotransmitters bind to receptors on the post-synaptic membrane.

Model of Study: Snail Aplysia

  • Snail aplysia release ink in response to danger stimulation of their tail.
  • The number of neurons stimulated correlates with the volume of ink released.
  • Neurons that are interconnected by gap junctions cause rapid, simultaneous activation of cells.

Electric Synapses in the Heart

  • The heart is an electrical syncytium due to electrical coupling through gap junctions.
  • Gap junctions are bidirectional, meaning there's no single direction to signal flow.

Chemical Synapses: Synaptic Cleft

  • Contain neurotransmitters that will be released when stimulated by an electric nerve impulse.
  • Neurotransmitter release is triggered in the presynaptic membrane by calcium influx.

Synaptic Potentials

  • Excitatory postsynaptic potentials (EPSPs): depolarize the membrane toward threshold, potentially triggering action potentials.
  • Inhibitory postsynaptic potentials (IPSPs): hyperpolarize the membrane, making it harder to generate action potentials.

Synaptic Integration

  • Graded potentials from multiple synapses either summate or cancel, and are integrated in the post-synaptic membrane at the trigger zone.
  • Spatial summation occurs when multiple presynaptic neurons release neurotransmitters at once.
  • Temporal summation occurs when a single neuron fires multiple times rapidly.

Current to Frequency Coding

  • Action potentials are triggered when enough EPSPs summate to reach the threshold, and the frequency of these action potentials reflect the strength of the input.

Paired-Pulse Facilitation and Depression

  • Paired-pulse facilitation is an effect where subsequent postsynaptic potentials are larger if preceded by a previous AP, indicating a persisting calcium influx, increasing the likelihood of neurotransmitter release.
  • Paired-pulse depression occurs when subsequent EPSPs are smaller than previous ones, meaning calcium influx in the presynaptic cell is affected and reduced due to the depletion of the neurotransmitter vesicles.

The Targets of Neuronal Communication

  • The CNS regulates many effectors including cardiac and smooth muscles, most exocrine glands, and adipose tissue.

Clinical case: Neurotransmitter Hypothesis of Depression

  • Neurotransmitters can modulate the number of receptors on post-synaptic cells, increasing the responsiveness of the target cells to the signal.

Geometrical Connectivity

  • Synapses can be located axodendritically, axosomatically and axo-axonically, meaning synapses can occur on different neuronal regions.
  • Synaptic location plays an important role in regulating overall neuronal activity.

Receptors

  • Receptors are proteins on the postsynaptic membrane that receive neurotransmitters.
  • Ionotropic receptors are channels that open directly by neurotransmitter binding to alter the flow of ions across the membrane.
  • Metabotropic receptors are coupled to signaling cascades that ultimately alter ion channel activity.

Neurotransmitter Production and Release

  • Neurotransmitters are synthesized in the cell body and transported to the synapse.
  • The amount of released neurotransmitter/amplitude of postsynaptic potential depends on the rate of action potentials in the presynaptic terminal.
  • The release of neurotransmitters depends on the strength of calcium influx into the presynaptic terminal.

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Synapses: Membrane Excitability PDF

Description

This quiz explores key concepts in synaptic connectivity, focusing on axo-somatic and axo-axonic interactions. It discusses the importance of dendritic spines, graded potentials, and the role of synaptic architecture in neuron signaling. Test your understanding of these fundamental neuroscience principles.

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