Neuron Anatomy Quiz
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Questions and Answers

What is the role of mitochondrial function at the synapse?

  • To mediate the fusion of vesicles.
  • To facilitate neurotransmitter binding.
  • To produce neurotransmitters.
  • To provide ATP for synaptic functions. (correct)

    • Which type of receptors are characterized by rapid action?

  • Neurotransmitter receptors.
  • Ionotropic receptors. (correct)
  • Reuptake transporters.
  • Metabotropic receptors.

    • What mediates the fusion of synaptic vesicles with the presynaptic membrane?

  • SNARE proteins. (correct)
  • Neurotransmitter-degrading enzymes.
  • Reuptake transporters.
  • Neurotransmitter receptors.

    • Which process is primarily responsible for the degradation of neurotransmitters in the synaptic cleft?

    <p>Metabolism by degrading enzymes.</p> Signup and view all the answers

    Which statement best describes metabotropic receptors?

    <p>They result in amplified responses.</p> Signup and view all the answers

    Which neurotransmitter is primarily inhibitory in the central nervous system?

    <p>Glycine</p> Signup and view all the answers

    What role does glutamate serve in the central nervous system?

    <p>Excitatory neurotransmitter</p> Signup and view all the answers

    Which category of neurotransmitters does acetylcholine belong to?

    <p>Monoamines</p> Signup and view all the answers

    Which of the following is classified as a gaseous neurotransmitter?

    <p>Nitric oxide</p> Signup and view all the answers

    Which amino acid neurotransmitter has an excitatory role but is less widespread than glutamate?

    <p>Aspartate</p> Signup and view all the answers

    What is the primary function of the synaptic terminal?

    <p>To release neurotransmitters into the synaptic cleft</p> Signup and view all the answers

    Which of the following structures is involved in the transmission of action potentials?

    <p>Axon</p> Signup and view all the answers

    What role do synaptic vesicles play in synaptic transmission?

    <p>Storing neurotransmitters for release</p> Signup and view all the answers

    How do excitatory postsynaptic potentials differ from inhibitory postsynaptic potentials?

    <p>Excitatory potentials increase the likelihood of action potentials; inhibitory decrease it</p> Signup and view all the answers

    What is the primary characteristic of an action potential?

    <p>It is an all-or-nothing electrical signal</p> Signup and view all the answers

    What is the function of neurotransmitters in the central nervous system?

    <p>To act as chemical messengers between neurons</p> Signup and view all the answers

    What occurs during the process of synaptic neurotransmission?

    <p>Synaptic vesicles release neurotransmitters into the synaptic cleft</p> Signup and view all the answers

    What mechanism allows the summation of postsynaptic potentials to lead to action potential generation?

    <p>Cumulative effect of excitatory and inhibitory inputs</p> Signup and view all the answers

    What effect does the larger diameter of an axon have on action potential conduction?

    <p>It allows for more efficient current flow due to reduced resistance.</p> Signup and view all the answers

    What happens to the action potential when potassium ions (K+) leave the neuron?

    <p>The action potential is degraded.</p> Signup and view all the answers

    What role does myelin play in the conduction of action potentials?

    <p>It insulates the axon, speeding up transmission.</p> Signup and view all the answers

    Why do leaky channels allow for more potassium (K+) to exit the neuron?

    <p>Due to a stronger attraction to the negative extracellular charge.</p> Signup and view all the answers

    What can be expected from an axon with a diameter of 6 µM compared to one with 15 µM?

    <p>The 15 µM axon is more efficient in carrying action potentials.</p> Signup and view all the answers

    Which cells are responsible for myelinating axons in the central nervous system?

    <p>Oligodendrocytes</p> Signup and view all the answers

    What would be the consequence of opening ion channels during an action potential?

    <p>It would cause a delay in the conduction of the action potential.</p> Signup and view all the answers

    How does myelin affect the speed of reflex movements such as the knee jerk response?

    <p>Myelin speeds up the transmission of action potentials.</p> Signup and view all the answers

    What triggers the release of neurotransmitters at the presynaptic neuron?

    <p>Arrival of an action potential</p> Signup and view all the answers

    Which ion channels open when the membrane depolarizes?

    <p>Calcium ion channels</p> Signup and view all the answers

    What role do calcium ions play in neurotransmitter release?

    <p>They activate vesicular release in the presynaptic terminal</p> Signup and view all the answers

    What occurs to the ion channels after the membrane repolarizes?

    <p>They close</p> Signup and view all the answers

    During neurotransmitter release, where are the vesicles located?

    <p>In the presynaptic terminal</p> Signup and view all the answers

    What is the primary effect of the action potential on the presynaptic neuron?

    <p>It opens voltage-gated calcium channels</p> Signup and view all the answers

    Which of the following statements about calcium ions during neurotransmission is true?

    <p>Calcium ions enter the synapse following an action potential</p> Signup and view all the answers

    What happens to neurotransmitter release if calcium ion influx is inhibited?

    <p>Neurotransmitter release is decreased or stops</p> Signup and view all the answers

    How does the presynaptic neuron facilitate neurotransmitter release?

    <p>By allowing calcium ions to enter upon action potential arrival</p> Signup and view all the answers

    Which process describes the release of neurotransmitters in response to calcium ions?

    <p>Vesicular release</p> Signup and view all the answers

    Which of the following functions is NOT associated with acetylcholine?

    <p>Mood regulation</p> Signup and view all the answers

    What type of receptors do serotonin (5-HT) primarily interact with?

    <p>G-protein coupled receptors</p> Signup and view all the answers

    Which neurotransmitter is associated with the control of sodium ion influx through nicotinic receptors?

    <p>Acetylcholine</p> Signup and view all the answers

    Which category of receptors includes both alpha and beta types?

    <p>Adrenergic receptors</p> Signup and view all the answers

    Which of the following neurotransmitters is primarily involved in wakefulness and inflammatory responses?

    <p>Histamine</p> Signup and view all the answers

    What occurs to potassium ions during an action potential when the outside of the neuron becomes more negative than the inside?

    <p>Potassium ions leave the neuron.</p> Signup and view all the answers

    Which ion is primarily responsible for triggering the activation of voltage-gated sodium channels during an action potential?

    <p>Sodium ions (Na+)</p> Signup and view all the answers

    What type of ion enters the neuron when ligand-gated sodium ion channels are opened?

    <p>Sodium ions (Na+)</p> Signup and view all the answers

    What is the impact of positive charge influx through sodium ion channels on the neuron's membrane potential?

    <p>It causes depolarization of the neuron.</p> Signup and view all the answers

    During the process of action potential generation, where does sufficient sodium ion diffusion lead to activation?

    <p>Axon hillock</p> Signup and view all the answers

    What primarily establishes the membrane potential in a resting neuron?

    <p>The differing concentrations of ions on each side of the membrane</p> Signup and view all the answers

    Which ion concentration is higher inside the neuron at rest?

    <p>Potassium ions (K+)</p> Signup and view all the answers

    In the context of resting neurons, what prevents ions from crossing the membrane?

    <p>The absence of open ion channels</p> Signup and view all the answers

    What is the role of voltage-gated ion channels in the axon?

    <p>To initiate action potentials by allowing ion flow</p> Signup and view all the answers

    How do electrochemical gradients influence ion movement across the membrane?

    <p>They drive ions from areas of higher to lower concentration</p> Signup and view all the answers

    What is primarily balanced by the distribution of Na+ and K+ ions in a resting neuron?

    <p>The charge difference across the membrane</p> Signup and view all the answers

    Which structure within the axon provides structural support and transport?

    <p>The cytoskeleton</p> Signup and view all the answers

    Which of the following does NOT contribute to the resting state of a neuron?

    <p>Increased permeability to sodium ions</p> Signup and view all the answers

    Which process is not a method for terminating the action of neurotransmitters after their release?

    <p>Binding to postsynaptic receptors</p> Signup and view all the answers

    What is primarily responsible for transporting neurotransmitters back into the presynaptic terminal?

    <p>Specific transporter proteins</p> Signup and view all the answers

    Which statement about neurotransmitter reuptake is true?

    <p>It happens via highly specific transporter proteins.</p> Signup and view all the answers

    Which of the following statements best describes the role of autoreceptors?

    <p>They are sensitive to higher concentrations of the same neurotransmitter.</p> Signup and view all the answers

    What is the role of enzymes in the synaptic cleft regarding neurotransmitters?

    <p>To degrade neurotransmitters for removal</p> Signup and view all the answers

    Which transport mechanism is utilized by transporter proteins to move neurotransmitters back into the presynaptic neuron?

    <p>Symport transport</p> Signup and view all the answers

    What happens to neurotransmitters that diffuse away from the synaptic cleft?

    <p>They are taken up by glial cells.</p> Signup and view all the answers

    Which of the following is not true about reuptake of neurotransmitters?

    <p>It uses nonspecific transport mechanisms.</p> Signup and view all the answers

    What initiates the release of neurotransmitters at the synapse?

    <p>Activation of voltage-gated calcium channels</p> Signup and view all the answers

    What happens to the ion channels after the membrane repolarizes?

    <p>They close to prevent further ion influx</p> Signup and view all the answers

    Which of the following accurately describes synaptic vesicles?

    <p>They store neurotransmitters and are activated by calcium ions</p> Signup and view all the answers

    What is the consequence of impaired calcium ion influx in the presynaptic neuron?

    <p>Decreased neurotransmitter release</p> Signup and view all the answers

    During an action potential, what primarily causes the membrane depolarization?

    <p>Sodium ion influx</p> Signup and view all the answers

    How do graded electrical potentials contribute to neurotransmitter release?

    <p>They modulate the action potential frequency in the presynaptic neuron.</p> Signup and view all the answers

    What is the main role of voltage-gated calcium ion channels at the synapse?

    <p>To allow calcium ion entry which triggers vesicular neurotransmitter release</p> Signup and view all the answers

    Which statement best describes the sequence of events at the synapse following action potential?

    <p>Calcium ions enter, promoting fusion of vesicles and neurotransmitter release.</p> Signup and view all the answers

    What characterizes the role of neurotransmitters within the synapse?

    <p>They serve as the primary messengers in neuronal signaling.</p> Signup and view all the answers

    Study Notes

    Neuron Anatomy

    • Contains a cell body (soma), dendrites, axon and synaptic terminals
    • Soma contains the nucleus and organelles
    • Dendrites are the main receptive surfaces that receive incoming signals from other neurons
    • Axon is a long projection that extends from the cell body and transmits action potentials to other cells
    • Synaptic terminals are at the end of axons and form synapses.
    • Synaptic terminals have synaptic vesicles that store neurotransmitters
    • Synaptic vesicles are small, membrane-bound sacs filled with neurotransmitters.
    • Synaptic vesicles are released into the synaptic cleft in response to an action potential
    • Synaptic clefts allow the diffusion of released neurotransmitters to the postsynaptic neuron.
    • Mitochondria provide ATP for the functions of the synapse.
    • Active Zones are specialized regions where synaptic vesicles dock and prepare for release.
    • SNARE Proteins mediate fusion of synaptic vesicles with the presynaptic membrane.

    Neurotransmitters

    • Neurotransmitters are molecules in the nervous system that transmit messages between neurons.
    • Neurotransmitters can be categorized by their structure and function.
    • Neurotransmitters are stored in synaptic vesicles.
    • Upon arrival of an action potential, neurotransmitters are released into the synaptic cleft.
    • Neurotransmitters bind to receptors on the post-synaptic neuron to initiate postsynaptic events.

    Neurotransmitter Receptors

    • Neurotransmitter receptors can be ionotropic or metabotropic:
      • Ionotropic receptors provide a rapid action and are short-lived, linked to ion channels that cause ionic flux
      • Metabotropic receptors provide a slower action and have a longer duration. They mediate short and long-term effects and amplified responses, as they act through secondary messengers, triggering a cascade of events

    Common Neurotransmitters

    • Amino Acids:
      • Gamma-aminobutyric acid (GABA): Primary inhibitory neurotransmitter in the CNS
      • Glycine: Inhibitory neurotransmitter, mainly found in the spinal cord and brainstem
      • Glutamate: Primary excitatory neurotransmitter in the CNS
      • Aspartate: Has an excitatory role but is less widespread than glutamate
    • Acetylcholine
    • Monoamines
    • Peptides
    • Purines
    • Gaseous neurotransmitters
    • Trace Amines

    Action Potential

    • Action Potential is triggered by depolarization of the membrane when the inside of the cell becomes more positive.
    • Sodium channels are opened in response to depolorization, and sodium flows into the cell, causing further depolarization
    • Potassium channels open later, and potassium flows out of the cell, repolarizing the membrane.
    • Capacitance across the membrane attracts positively charged ions, such as Sodium, outside of the cell.

    Factors Affecting Action Potential Conduction Velocity

    • Axon Diameter:
      • Larger diameter axons have less resistance and provide more efficient conduction velocity.
    • Myelination:
      • Myelination acts as insulation, speeding up the transmission along axons. It is critical for rapid reflex movements.
      • Myelin is arranged in concentric layers of lipids interspersed between protein layers
      • Oligodendrocytes produce myelin in the central nervous system (CNS)
      • Schwann cells produce myelin in the Peripheral Nervous System (PNS)
      • Multiple Sclerosis is an autoimmune disease where the myelin sheath is damaged.

    Release of Neurotransmitters

    • Release of neurotransmitters from the presynaptic terminal follows the arrival of an action potential.
    • The arrival of the action potential at the axon terminal opens voltage-gated calcium channels, allowing Calcium ions to move across the presynaptic membrane
    • Calcium entering the terminal triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft
    • Neurotransmitters diffuse across the synaptic cleft and bind to post-synaptic receptors

    Neurotransmitter Deactivation

    • Reuptake Transporters are proteins that are located on the presynaptic membrane or nearby glial cells. They reabsorb the neurotransmitter from the synaptic cleft, reducing its concentration.
    • Neurotransmitter-Degrading Enzymes, located in the synaptic cleft, metabolize neurotransmitters, reducing their concentration.

    Synaptic Transmission

    • Synaptic transmission is the process of transferring information from one neuron to another across a synapse.
    • The process involves an electrical signal (the action potential) triggering the release of neurotransmitters into the synaptic cleft, which then bind to postsynaptic receptors.
    • Synaptic transmission is crucial for communication between neurons and for the functioning of the nervous system.
    • It is crucial for all aspects of nervous system function:
      • perception of sensory input
      • generation of motor commands
      • cognitive processes
      • emotional responses

    Synaptic Plasticity

    • Synaptic Plasticity is the ability of synapses to change their strength over time. This can involve changes in the amount of neurotransmitter released, the sensitivity of receptors, or the number of synapses.
    • Synaptic plasticity is an important mechanism for learning and memory.
    • Long-term potentiation (LTP) is a process that strengthens synapses, increasing the likelihood that the postsynaptic neuron will fire in response to the presynaptic neuron. This process is thought to be important for learning and memory.
    • Long-term depression (LTD) is a process that weakens synapses, decreasing the likelihood that the postsynaptic neuron will fire in response to the presynaptic neuron. This process is thought to be important for forgetting and pruning unnecessary synapses.

    Co-transmission

    • Co-transmission occurs when two or more neurotransmitters are released from the same presynaptic terminal.
    • Co-transmission allows for a wider range of signaling possibilities and can influence the activity of post-synaptic neurons in complex ways.

    Neurotransmitters

    • Acetylcholine (ACh)
      • Plays a key role in both the peripheral and central nervous systems.
      • Involved in muscle contraction, arousal, attention, learning, and memory.
      • Two receptor types:
        • Nicotinic : Ion channel linked. Activated by acetylcholine, resulting in sodium ion influx.
        • Muscarinic : G-protein coupled.
    • GABA
      • Inhibitory neurotransmitter
      • GABAA receptors are ligand-gated chloride ion channels

    Monoamines

    • Catecholamines
      • Dopamine (DA)
        • Involved in mood, reward, pleasure, and motor function.
        • Five receptor types, all G-protein coupled, split into D1-like (D1 and D5) and D2-like (D2, D3, D4).
      • Noradrenaline (NA) or Norepinephrine (NE)
        • Involved in arousal, attention, mood, and stress responses.
        • Receptor types: Alpha (α1, α2) and Beta (β1, β2, β3) adrenergic receptors.
      • Adrenaline (A)
    • Indolamines
      • Serotonin (5-HT)
        • Involved in mood regulation, appetite, sleep, and learning.
        • Numerous receptor types (e.g., 5-HT1, 5-HT2), most are G-protein coupled except for 5-HT3, which is ionotropic.
      • Histamine
        • Involved in wakefulness and inflammatory responses.
        • Four receptor types: H1, H2, H3, and H4 receptors.

    The Axon

    • Process extension on neurons
    • Contains a high concentration of voltage-gated ion channels
      • Potassium Channel: Located on the Axolemma.
      • Sodium Channel: Located on the Axolemma.
      • Sodium/Potassium Pump: Located on the Axolemma.
    • The Axolemma is the membrane of the axon
    • The cytoplasm of the axon includes cytoskeleton elements that provide shape and a transport network.

    Concentration and Electrochemical Gradients

    • The Concentration Gradient: Drives ion movement across a membrane through open channels.
      • Facilitates movement from areas of higher concentration to lower concentration.
    • The Electrochemical Gradient:
      • Considers the electrical potential across the membrane.

    Excitatory and Inhibitory Synapses

    • Acetylcholine:
      • Excitatory.
      • Opens positively charged sodium ion (Na+) channels.
    • GABA:
      • Inhibitory
      • Opens negatively charged chloride ion (Cl-) channels.

    Summation and The Initiation of The Action Potential

    • Ligand-gated sodium ion channels open via chemical neurotransmitter, leading to sodium ion influx.
    • Voltage-gated sodium and potassium channels, along with calcium channels, are present from the axon hillock to the axon terminal.
    • If enough sodium ions diffuse to the axon hillock, adjacent voltage-gated sodium channels are activated.

    Release of Neurotransmitters

    • Usually follows arrival of action potential at the synapse or a graded electrical potential.
    • Release occurs at the synaptic cleft between the presynaptic and postsynaptic neurons.

    Voltage-Gated Calcium Ion Channels

    • Located in the axon terminal.
    • Open when the membrane depolarizes.
    • Close when the membrane repolarizes.
    • When open, they allow calcium ions to flow into the axon terminal.

    Vesicular Release Activated by Calcium Ions

    • Calcium ions entering the synapse trigger the release of neurotransmitters.
    • Vesicles located in the synaptic terminal contain neurotransmitters.
    • Autoreceptors are located on the presynaptic neuron, sensitive to higher concentrations of the same neurotransmitter.

    Neurotransmitter Deactivation

    • The action of neurotransmitters needs to be terminated after release to allow for further synaptic events.
    • The following pathways contribute to the inactivation of neurotransmitters:
      • Reuptake by the presynaptic neuron: Transporter protein pumps neurotransmitters back into the presynaptic neuron.
      • Inactivation/degradation by enzymes in the synaptic cleft: Enzymes break down the neurotransmitters.
      • Glial cell uptake: Glial cells absorb the neurotransmitters.
      • Diffusion: Neurotransmitters can diffuse away from the synapse.

    Neurotransmitter Reuptake

    • Specific transporter proteins located on the presynaptic terminal move most small-molecule neurotransmitters (or their metabolites) back to the presynaptic terminal for reuse.
    • Reuptake also occurs at glial cells.

    Transport and Symport

    • Transporter proteins utilize symport to transport neurotransmitters across the presynaptic neuron membrane.
    • The neurotransmitter binds to sodium ions.
    • The concentration and electrical gradient of sodium ions facilitate the movement of the neurotransmitter inward, against its own gradient.

    Neurotransmitter Degradation

    • Neurotransmitters are removed from the synaptic cleft by specific enzymes that break down their structure.
    • This allows for the postsynaptic cell to produce subsequent synaptic events.

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