Synaptic Transmission Quiz
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Questions and Answers

What type of summation occurs when graded potentials arrive simultaneously from different synapses?

  • Spatial summation (correct)
  • Convergent summation
  • Temporal summation
  • Dendritic summation

    • Which statement about EPSPs is correct?

  • EPSPs have a specific threshold that must be reached.
  • EPSPs can only occur when the membrane is hyperpolarized.
  • EPSPs are graded in magnitude and can summate. (correct)
  • EPSPs cause an efflux of K+ ions.

    • Which of the following ions primarily causes hyperpolarization in postsynaptic inhibition?

  • K+ influx
  • Cl- influx (correct)
  • Na+ influx
  • Ca2+ influx

    • What is the primary role of calmodulin in neurotransmitter release?

    <p>It activates a protein kinase that promotes fusion and exocytosis of vesicles. (B)</p> Signup and view all the answers

    What role does presynaptic inhibition play in neurotransmitter release?

    <p>It inhibits the release of neurotransmitters. (A)</p> Signup and view all the answers

    What is the primary mechanism of neurotransmitter release from a presynaptic neuron?

    <p>Exocytosis triggered by calcium ion influx (B)</p> Signup and view all the answers

    Which of the following statements about temporal summation is true?

    <p>It occurs when EPSPs occur closely in time. (D)</p> Signup and view all the answers

    Which type of channel opens during an excitatory postsynaptic potential (EPSP)?

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

    What role do gap junctions play in electrical synapses?

    <p>They allow direct electrical depolarization between cells. (B)</p> Signup and view all the answers

    If the membrane potential in a postsynaptic cell reaches the threshold at the axon hillock, what occurs next?

    <p>A new action potential is generated. (C)</p> Signup and view all the answers

    Which of the following best describes the synaptic cleft?

    <p>The space that separates the presynaptic and postsynaptic membranes. (B)</p> Signup and view all the answers

    Which of the following is a function of substance P?

    <p>Helps perceive pain. (C)</p> Signup and view all the answers

    How does the amount of neurotransmitter released at the synaptic cleft vary?

    <p>It depends on the frequency of action potentials arriving at the terminal. (B)</p> Signup and view all the answers

    What is the effect of an inhibitory postsynaptic potential (IPSP) on the postsynaptic membrane?

    <p>It hyperpolarizes the membrane by opening potassium channels. (D)</p> Signup and view all the answers

    Which statement correctly distinguishes between EPSP and IPSP?

    <p>EPSP increases the likelihood of a postsynaptic action potential, while IPSP decreases it. (D)</p> Signup and view all the answers

    What is the primary function of acetylcholine (ACh) at neuromuscular junctions?

    <p>Transmit excitatory signals for muscle contraction (B)</p> Signup and view all the answers

    What effect does a muscarinic ACh channel have on postsynaptic cells?

    <p>Can lead to either hyperpolarization or depolarization (C)</p> Signup and view all the answers

    What is true about the structure of nicotinic ACh channels?

    <p>Formed by five polypeptide subunits with two ACh binding sites (B)</p> Signup and view all the answers

    Which statement about Acetylcholinesterase (AChE) is accurate?

    <p>It is responsible for inactivating ACh and terminating its action. (D)</p> Signup and view all the answers

    What is the significance of convergence in neuronal pools?

    <p>It allows for multiple impulses to be sent to a single neuron. (A)</p> Signup and view all the answers

    Study Notes

    Synaptic Transmission

    • Synapse is a functional connection between a neuron (presynaptic) and another cell (postsynaptic)
    • Electrical and chemical synapses exist
    • Electrical synapses are rare in the nervous system
    • Synaptic transmission at chemical synapses occurs via neurotransmitters (NTs)

    Learning Objectives

    • Compare convergence and divergence in neural arrangement and understand their significance
    • Describe the transmission of impulses at the synapse
    • Distinguish excitatory (EPSP) and inhibitory (IPSP) postsynaptic potentials

    Synapse = Cell-to-Cell Conduction

    • A functional connection between a neuron (presynaptic) and another cell (postsynaptic)
    • Electrical and chemical synapses exist
    • Electrical synapses are rare in the nervous system
    • Synaptic transmission at chemical synapses is via neurotransmitters

    Electrical Synapse

    • Depolarization flows from presynaptic to postsynaptic cell through channels called gap junctions
    • Formed by connexin proteins
    • Very fast conduction
    • Found in smooth and cardiac muscles, brain, and glial cells

    Chemical Synapse

    • Synaptic cleft separates terminal bouton of presynaptic from postsynaptic cell
    • Pre-synaptic terminal releases neurotransmitters
    • Synthesis of neurotransmitters
    • Ca²⁺ influx triggers release of neurotransmitters
    • NTs are in synaptic vesicles
    • Vesicles fuse with bouton membrane, releasing NT by exocytosis
    • Neurotransmitter diffuses across synaptic cleft
    • Amount of NT released depends upon frequency of AP
    • Postsynaptic cell has specific receptors for the neurotransmitter

    Synaptic Transmission 1

    • Presynaptic neuron brings impulse to the synapse to stimulate or inhibit a postsynaptic neuron
    • This is synaptic transmission
    • Action potentials travel down the axon to depolarize the bouton
    • Voltage-gated Ca²⁺ channels open; Ca²⁺ diffuses inward
    • Triggers exocytosis of vesicles, releasing NTs
    • First activating calmodulin, then protein kinase
    • Phosphorylating regulatory proteins promotes vesicle fusion and exocytosis
    • NT release is rapid because vesicles are docked at release sites before APs arrive
    • Neurotransmitters diffuse across the synaptic cleft, binding to specific receptors

    Synaptic Transmission 2

    • NT (ligand) diffuses across cleft
    • Binds to receptor proteins on postsynaptic membrane
    • Opening chemically-regulated ion channels
    • Depolarizing membrane causes EPSPs (excitatory postsynaptic potentials)
    • Hyperpolarizing membrane causes IPSPs (inhibitory postsynaptic potentials)
    • These are graded potentials

    Synaptic Transmission 3

    • EPSPs and IPSPs summate
    • If membrane potential (MP) in postsynaptic cell reaches threshold at axon hillock, a new action potential (AP) is generated
    • Axon hillock has many voltage-gated channels and is where APs are initiated

    Synaptic Transmission 4

    • Action potentials are conducted by axons
    • Opens voltage-gated Ca²⁺ channels
    • Release of excitatory neurotransmitters
    • Opens chemically gated channels
    • Inward Na⁺ diffusion causes depolarization (EPSP)
    • Localized, decremental conduction of EPSP
    • Opens voltage-gated Na⁺ and then K⁺ channels
    • Conduction of action potentials

    Synaptic Potentials

    • Synaptic potentials are graded and can depolarize or hyperpolarize the receiving cell membrane
    • EPSP (excitatory postsynaptic potential) opens Na⁺ channels, depolarizing the membrane
    • IPSP (inhibitory postsynaptic potential) opens K⁺ channels, hyperpolarizing the membrane

    Synaptic Inhibition

    • Presynaptic inhibition: one neuron synapses onto axon or bouton, inhibiting release of another neuron's neurotransmitter
    • Postsynaptic inhibition: GABA and glycine produce IPSPs, dampening EPSPs, making it harder to reach threshold
    • K⁺ efflux or Cl⁻ influx causes hyperpolarization

    Neurotransmitters

    • Acetylcholine (ACh): autonomic ganglion, stimulates muscle contractions
    • Monoamines: norepinephrine, epinephrine, dopamine, serotonin
    • Amino acids: glycine, glutamic acid, GABA
    • Peptides: enkephalins, substance P

    Neuropeptides

    • Neurons in the CNS synthesize neuropeptides
    • Act as neurotransmitters or neuromodulators
    • Enkephalins bind to opiate receptors, relieving pain
    • Beta-endorphin binds to opiate receptors, lasting longer
    • Substance P helps perceive pain

    Major Neurotransmitters

    • Acetylcholine is a major neurotransmitter in the peripheral nervous system

    Acetylcholine (ACh)

    • Most widely used NT
    • Used in brain and ANS, used at all neuromuscular junctions
    • Has nicotinic and muscarinic receptor subtypes
    • These can be excitatory or inhibitory

    Ligand-Gated Channels

    • Contain both a NT receptor site and an ion channel
    • Open when ligand (NT) binds to its receptors

    Nicotinic ACh Channel

    • Formed by 5 polypeptide subunits
    • 2 subunits contain ACh binding sites
    • Opens permitting diffusion of Na⁺ and K⁺
    • Inward flow of Na⁺ dominates, producing EPSPs

    G Protein-Coupled Channels

    • NT receptor is not part of the ion channel
    • Is a 1 subunit membrane polypeptide
    • Activates ion channel indirectly through G-proteins

    Muscarinic ACh Channel

    • Binding of 1 ACh activates G-protein cascade, affecting gated K⁺ channels
    • Opens some, causing hyperpolarization
    • Closes others, causing depolarization

    Acetylcholinesterase (AChE)

    • Inactivates ACh, terminating its action; located in the cleft

    Integration of Signals

    • Interneurons are organized into neuronal pools (groups of neurons that work together)
    • Convergence: a single neuron receives impulses from two or more fibers; allows collection and processing of information
    • Divergence: an impulse from one neuron stimulates two or more fibers, amplifying response

    Convergent Pathway

    • Many presynaptic neurons converge to influence a smaller number of postsynaptic neurons

    Divergent Pathway

    • One presynaptic neuron branches to affect a larger number of postsynaptic neurons

    Summation: Convergent Integration

    • Graded potentials are below threshold
    • Graded potentials arrive at the trigger zone, summating to create an AP
    • Spatial summation
    • Temporal summation
    • Summation can be EPSP or IPSP

    EPSP

    • Graded in magnitude
    • Have no threshold
    • Na⁺ or Ca²⁺ influx causes depolarization
    • Summate
    • Have no refractory period

    Temporal Summation

    • EPSPs fade quickly but closely-timed EPSPs sum before they fade

    Spatial Summation

    • EPSPs fade quickly over time and distance
    • EPSPs from different synapses occur in postsynaptic cell at the same time

    Postsynaptic Inhibition

    • GABA and glycine produce IPSPs
    • IPSPs dampen EPSPs, making it harder to reach threshold
    • Presynaptic inhibition: one neuron synapses onto an axon or bouton, inhibiting the release of a neuron's neurotransmitter
    • K⁺ efflux or Cl⁻ influx causes hyperpolarization

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    Description

    Test your knowledge on synaptic transmission and the functional connections between neurons. Explore electrical and chemical synapses, and understand the concepts of excitatory and inhibitory postsynaptic potentials. This quiz will challenge your understanding of neural arrangements and the significance of synapses.

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