Neuroscience Chapter on Synapses
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Questions and Answers

What is the primary function of a synapse?

  • To regulate the metabolic rate of neurons.
  • To transmit information between neurons or between a neuron and another cell. (correct)
  • To produce neurotransmitters within neurons.
  • To provide structural support to neurons.

Which type of cell listed can be a postsynaptic cell in the peripheral nervous system?

  • Adipocyte
  • Muscle cell (correct)
  • Osteocyte
  • Epithelial cell

What characterizes an electrical synapse?

  • Slower signal transmission compared to chemical synapses.
  • Reliance on neurotransmitters to transmit signals.
  • Direct connection between neurons via gap junctions. (correct)
  • Use of a synaptic cleft that is 20-40 nanometers wide.

What role do calcium ions play in chemical synapses?

<p>They trigger the release of neurotransmitters from synaptic vesicles. (B)</p> Signup and view all the answers

Which of the following best describes the width of the synaptic cleft in a chemical synapse?

<p>20-40 nm (B)</p> Signup and view all the answers

What is formed between cells through gap junctions?

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

What is the name of the entire postsynaptic structure in a chemical synapse?

<p>Motor end plate (B)</p> Signup and view all the answers

In electrical communication, what is nerve conduction based on?

<p>An ion balance (C)</p> Signup and view all the answers

Which of the following neurotransmitters is primarily responsible for initiating muscle contractions?

<p>Acetylcholine (C)</p> Signup and view all the answers

What is the primary difference in signal transmission between electrical and chemical synapses?

<p>Electrical synapses transmit signals faster than chemical synapses. (D)</p> Signup and view all the answers

Where are T-SNARE proteins located?

<p>On the target cell or organelle membrane (C)</p> Signup and view all the answers

What is the role of synaptotagmin in the SNARE complex?

<p>It senses calcium ions ($Ca^{2+}$), enhancing SNARE complex assembly. (D)</p> Signup and view all the answers

Which of the following conditions is caused by the blockage of neurotransmitter release at the neuromuscular junction?

<p>Botulism (C)</p> Signup and view all the answers

What is the initial step in the merging process facilitated by SNARE proteins?

<p>V-SNARE and T-SNARE proteins locking together. (B)</p> Signup and view all the answers

Which of the following is a V-SNARE protein that binds with syntaxin and SNAP-25 to form the 'SNARE complex'?

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

In a chemical synapse, what directly causes the synaptic delay?

<p>The diffusion time for neurotransmitters across the synaptic gap (A)</p> Signup and view all the answers

What is the direct consequence of the action potential reaching the presynaptic terminal?

<p>Opening of voltage-gated $Ca^{+2}$ channels and $Ca^{+2}$ influx. (A)</p> Signup and view all the answers

Which of the following accurately describes the role of SNARE proteins in neurotransmitter release?

<p>They mediate the fusion of synaptic vesicles with the presynaptic membrane. (D)</p> Signup and view all the answers

What is the immediate effect of acetylcholine (ACh) binding to nicotinic ACh receptors (nAChRs) on the postsynaptic cell?

<p>Opening of a nonselective cation channel permeable to both $Na^+$ and $K^+$. (D)</p> Signup and view all the answers

What determines the quantity of acetylcholine released into the synaptic cleft?

<p>The amount of $Ca^{+2}$ influx into the presynaptic terminal. (C)</p> Signup and view all the answers

How is the motor end plate potential classified?

<p>Graded potential. (C)</p> Signup and view all the answers

What triggers the opening of voltage-gated $Na^+$ channels in the subneural parts of the postsynaptic membrane?

<p>The accumulation of EPPs to reach the threshold potential. (A)</p> Signup and view all the answers

Which of the following neurotransmitters is primarily responsible for inhibitory neurotransmission in the CNS?

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

Which of the following plays an important role in learning and memory?

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

Which of the following is the primary mechanism of action of botulinum toxin?

<p>Preventing synaptic vesicles from releasing neurotransmitters from nerve endings to muscle cells. (A)</p> Signup and view all the answers

Which of the following SNAP-25 is destroyed by?

<p>Botulinum toxin A-E (D)</p> Signup and view all the answers

A patient presents with severe muscle contractions and spastic paralysis. Which toxin is most likely responsible for these symptoms?

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

Why is honey not recommended for babies?

<p>It may contain botulinum spores, which can produce toxins in the baby's digestive system. (D)</p> Signup and view all the answers

Which of the following proteins is destroyed by Botulinum toxin C?

<p>Syntaxin (D)</p> Signup and view all the answers

What is the primary defect in Lambert-Eaton Syndrome (L-E Syndrome)?

<p>Autoantibodies destroy voltage-gated $Ca^{2+}$ channels, reducing acetylcholine release. (A)</p> Signup and view all the answers

Which of the following best describes how tetanus toxin affects neuronal function?

<p>It blocks the release of inhibitory neurotransmitters from interneurons, leading to overactivity of motor neurons. (D)</p> Signup and view all the answers

How does Curare cause muscle relaxation?

<p>By blocking acetylcholine receptors on muscle cells (C)</p> Signup and view all the answers

What is the primary mechanism by which curare leads to muscle paralysis?

<p>Preventing muscle contraction by blocking acetylcholine receptors. (D)</p> Signup and view all the answers

What is the effect of an IPSP on the postsynaptic neuron's membrane potential?

<p>It causes hyperpolarization, making the membrane potential more negative. (B)</p> Signup and view all the answers

Which of the following neurotransmitters is most likely to produce an EPSP?

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

If the total postsynaptic potential in a neuron is high in IPSP, how will this affect the neuron?

<p>It will be inhibited, reducing the likelihood of an action potential. (A)</p> Signup and view all the answers

What is the term for the process where many presynaptic neurons send signals to one single postsynaptic neuron?

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

Which of the following describes the immediate effect of curare on acetylcholine levels in the synaptic cleft?

<p>Increased levels due to prevention of binding to receptors (C)</p> Signup and view all the answers

Which of the following accurately describes the effect of opening potassium ($K^+$) and chloride ($Cl^−$) channels on the postsynaptic membrane?

<p>Hyperpolarization and IPSP production (A)</p> Signup and view all the answers

Which of the following events is characteristic of EPSP?

<p>Influx of sodium ($Na^+$) ions into the cell (D)</p> Signup and view all the answers

Flashcards

Synapse

A specialized junction where communication occurs between neurons or between a neuron and another cell (muscle or gland).

Electrical Synapse

A type of synapse where electrical signals directly pass between neurons through specialized protein channels called gap junctions.

Chemical Synapse

A synapse where chemical messengers called neurotransmitters are released from one neuron to another across a tiny gap called the synaptic cleft.

Neuromuscular Junction

A synapse where a neuron communicates with a muscle cell, triggering muscle contraction.

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Presynaptic Cell

The neuron that releases neurotransmitters at a synapse.

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Postsynaptic Cell

The neuron or cell that receives neurotransmitters at a synapse.

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Axodendritic Synapse

A synapse where the axon of a neuron connects to the dendrite of another neuron.

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Axosomatic Synapse

A synapse where the axon of a neuron connects to the cell body (soma) of another neuron.

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Synaptic Transmission

The arrival of an action potential (AP) at the presynaptic terminal triggers a series of events leading to the release of neurotransmitters.

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Calcium Influx

The presynaptic neuron's membrane depolarizes, opening voltage-gated calcium (Ca+2) channels, allowing Ca+2 to flow into the presynaptic terminal and increase intracellular Ca+2 concentration.

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Vesicle Fusion

Synaptic vesicles containing neurotransmitters fuse with the presynaptic membrane due to the interaction of SNARE proteins (V-SNAREs and T-SNAREs).

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Neurotransmitter Release

Neurotransmitters are released into the synaptic cleft through exocytosis, the process of fusing the vesicle membrane with the presynaptic membrane.

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Neurotransmitter Binding

Neurotransmitters bind to specific receptors on the postsynaptic membrane, triggering a response in the postsynaptic neuron.

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Glutamate

The most common excitatory neurotransmitter in the central nervous system (CNS).

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GABA

The main inhibitory neurotransmitter in the CNS.

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Neurotransmitters

Chemicals used by nerve cells to communicate with each other. They are stored in synaptic vesicles and released into the synaptic cleft.

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What is Acetylcholine?

Acetylcholine is a neurotransmitter that triggers muscle contractions. It's also vital for learning and memory in the central nervous system (CNS).

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Explain Electrical Synapses

Electrical synapses allow for direct electrical current flow between neurons through gap junctions. It's fast and bidirectional.

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Describe Chemical Synapses

Chemical synapses use neurotransmitters to transmit signals across a gap called the synaptic cleft. It's slower and unidirectional.

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What are V-SNAREs and T-SNAREs?

V-SNAREs are proteins on the surface of vesicles, while T-SNAREs are on the target membrane. They work together to merge the vesicle and release neurotransmitters.

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What proteins support SNARE function?

SNARE proteins, like synaptobrevin, syntaxin, SNAP-25 and synaptotagmin, coordinate vesicle fusion for neurotransmitter release.

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Explain Botulinum Toxin's Action

Botulinum toxin blocks the release of neurotransmitters from synaptic vesicles, causing muscle paralysis. It's extremely potent.

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Name conditions affecting the neuromuscular junction

Lambert-Eaton Syndrome, Botulism, Tetanus, Myasthenia Gravis, and Curare Effect are conditions affecting the neuromuscular junction leading to muscle weakness or paralysis.

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What is the neuromuscular junction?

The neuromuscular junction is a specialized synapse where a neuron communicates with a muscle cell, triggering contraction.

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Botulinum Toxin: Mechanism of Action

Botulinum toxin, produced by Clostridium botulinum, blocks muscle contraction by preventing the release of acetylcholine at the neuromuscular junction.

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Botulinum Toxin: Targets

Botulinum toxin specifically targets and degrades SNAP-25, synaptobrevin, and syntaxin, which are essential proteins involved in neurotransmitter release.

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Botulinum Toxin: Clinical Applications

Botulinum toxin is used to treat facial wrinkles, muscle spasms, migraine headaches, excessive sweating, and certain neuromuscular disorders.

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Tetanus: Mechanism of Action

Tetanus toxin prevents the release of inhibitory neurotransmitters, causing excessive muscle contraction (spastic paralysis) due to unchecked motor neuron activity.

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Tetanus: Target

Tetanus toxin specifically targets and disrupts synaptobrevin within inhibitory interneurons, leading to uncontrolled muscle contraction.

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Lambert-Eaton Syndrome: Cause

Lambert-Eaton syndrome is an autoimmune disease resulting in muscle weakness due to a reduction in acetylcholine release caused by autoantibodies attacking voltage-gated calcium channels.

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Myasthenia Gravis: Cause

Myasthenia gravis is an autoimmune disease characterized by muscle weakness due to antibodies attacking acetylcholine receptors on muscle cells, leading to impaired transmission of signals.

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Curare: Mechanism of Action

Curare, a natural compound, acts as a muscle relaxant due to its ability to block acetylcholine receptors, preventing muscle contraction.

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What is curare and how does it work?

Curare is a naturally occurring poison that blocks acetylcholine receptors at the neuromuscular junction. This prevents muscle contraction, leading to paralysis. Curare was traditionally used by South American natives to paralyze animals for hunting.

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What is a postsynaptic potential?

A postsynaptic potential (PSP) is a temporary change in the membrane potential of a postsynaptic neuron caused by the release of neurotransmitters from a presynaptic neuron.

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What is an EPSP?

An excitatory postsynaptic potential (EPSP) is a depolarization of the postsynaptic neuron's membrane, making it more likely to fire an action potential. It is caused by excitatory neurotransmitters like glutamate.

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What is an IPSP?

An inhibitory postsynaptic potential (IPSP) is a hyperpolarization of the postsynaptic neuron's membrane, making it less likely to fire an action potential. It is caused by inhibitory neurotransmitters like GABA.

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What is neural convergence?

Convergence occurs when multiple presynaptic neurons send signals to a single postsynaptic neuron. This allows for integration of inputs from different sources.

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What is neural divergence?

Divergence occurs when a single presynaptic neuron sends signals to multiple postsynaptic neurons. This allows for widespread distribution of information.

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What is synaptic facilitation?

Facilitation is a process by which repeated stimulation of a synapse leads to an increase in its strength. This is because the presynaptic neuron releases more neurotransmitters or the postsynaptic neuron becomes more sensitive to neurotransmitters.

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How do EPSPs and IPSPs determine neuron firing?

The summation of EPSPs and IPSPs determines whether a postsynaptic neuron will fire an action potential. If the sum of EPSPs is greater than the sum of IPSPs, the neuron will fire. If the sum of IPSPs is greater than the sum of EPSPs, the neuron will not fire.

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Study Notes

Nervous System Physiology Essentials 3

  • This chapter covers the essentials of nervous system physiology, focusing on synapses.

Synapses

  • A synapse is the connection between two neurons, muscle cells, or gland cells.
  • The presynaptic cell is positioned before the synapse, and the postsynaptic cell is after the synapse.
  • Synapses in the central nervous system (CNS) are connections between two neurons, while synapses in the peripheral nervous system (PNS) connect neurons to muscle or gland cells.
  • The synapse between a neuron and a muscle cell is called a neuromuscular junction.

Synapse Types

  • Synapses are categorized based on structure and function.
  • Structural features: Axodendritic, axosomatic, axoaxonic.
  • Functional features: Excitatory and inhibitory.
  • Electrical and chemical synapses are the major types.

Electrical Synapses

  • Establish a direct connection between neurons, letting ions flow freely.
  • Communication happens through gap junctions, which allow direct ion flow.
  • Very rapid transmission.
  • Found in smooth muscle and heart muscle.
  • Transmission is bidirectional.

Chemical Synapses

  • More prevalent compared to electrical synapses.
  • A gap called a synaptic cleft separates the presynaptic and postsynaptic cells.
  • Neurotransmitters are released from vesicles in the presynaptic terminal across the synaptic cleft.
  • Neurotransmitters bind to receptors on the postsynaptic cell, sending signal
  • Transmission is unidirectional, slower than electrical synapses.
  • This type involves a chemical messenger.

Neurotransmitters

  • Chemical messengers that transfer signals between nerve cells.
  • Stored in synaptic vesicles.
  • Released by exocytosis upon arrival of an action potential.
  • Bind to receptors on postsynaptic membrane.
  • Examples include glutamate, GABA, acetylcholine.

Important Neurotransmitters/Conditions affecting Neurotransmission

  • Glutamate is a major excitatory neurotransmitter in the CNS and has roles in learning and memory.
  • GABA is a major inhibitory neurotransmitter in the CNS and has a role in calming effects and preventing nerve cell overstimulation.
  • Acetylcholine is essential for muscle contractions and has roles in learning and memory.
  • Various diseases and conditions, such as Lambert-Eaton Syndrome, Botulism, Tetanus, Myasthenia Gravis and Curare, can affect synaptic transmission and neuromuscular junction.

V-SNARE and T-SNARE

  • These proteins (V-SNARE and T-SNARE) play pivotal roles in exocytosis.
  • V-SNAREs are located on vesicles, while T-SNAREs are on the target cell membranes.
  • Their interaction forms a SNARE complex, mediating vesicle fusion.

SNARE Proteins

  • Synaptotagmin, syntaxin, SNAP-25, and synaptobrevin are types of SNARE proteins.
  • SNARE proteins are needed for neurotransmitter release via regulated exocytosis.

Summation

  • Temporal summation: rapid arrival of successive signals from a single presynaptic neuron.
  • Spatial summation: simultaneous stimulation from multiple presynaptic neurons.
  • These types of summation are critical for the postsynaptic neuron responding appropriately.

Facilitation

  • The temporary increase in the excitability of a neuron due to repeated stimulation.

Convergence and Divergence

  • Information gathering at a single postsynaptic neuron from several presynaptic neurons (Convergence).
  • Signal dispersal from a presynaptic neuron to several postsynaptic neurons (Divergence).

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Nervous System Physiology Essentials 3 PDF 2024-2025

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Test your knowledge of synapses with this comprehensive quiz. Explore key concepts including electrical and chemical synapses, the role of neurotransmitters, and the significance of calcium ions. Perfect for students studying neuroscience and nervous system functions.

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