L 3 SYTBTIC TRANSMATION
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L 3 SYTBTIC TRANSMATION

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Questions and Answers

What is the resting membrane potential (RMP) of a typical neuron?

  • -60 mV
  • -100 mV
  • -70 mV (correct)
  • -80 mV

    • What occurs when sodium channels open in a neuron that is at resting membrane potential?

  • An influx of Na+ leads to depolarization (correct)
  • K+ ions exit the cell causing hyperpolarization
  • The membrane potential remains unchanged
  • The membrane potential becomes more negative

    • What is the effect of opening potassium channels in a neuron at resting membrane potential?

  • There is no movement of ions across the membrane
  • The membrane potential reaches action potential threshold
  • The membrane potential becomes less negative (depolarization)
  • The membrane potential potential becomes more negative (hyperpolarization) (correct)

    • Which of the following ions contributes to the maintenance of the resting membrane potential?

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

    What role does the Na+/K+ ATPase play in neuronal function?

    <p>It maintains Na+ and K+ gradients across the membrane</p> Signup and view all the answers

    What is the term used for a decrease in membrane potential that is associated with excitation?

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

    The imbalance of excitation and inhibition in neurons can potentially lead to what?

    <p>Diseases or disorders</p> Signup and view all the answers

    Which ions primarily determine the electrochemical gradients across a neuron's membrane?

    <p>Sodium and Potassium</p> Signup and view all the answers

    What is the primary mechanism through which neurotransmitters are inactivated in the synaptic cleft?

    <p>They are inactivated or degraded by enzymes.</p> Signup and view all the answers

    Which of the following neurotransmitters is the major excitatory neurotransmitter in the brain?

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

    What distinguishes metabotropic receptors from ionotropic receptors?

    <p>Metabotropic receptors involve G-protein coupled signaling pathways.</p> Signup and view all the answers

    What role do astrocytes play in the lifecycle of glutamate?

    <p>They express transporters that remove glutamate from the synaptic cleft.</p> Signup and view all the answers

    Which neurotransmitter is synthesized from tryptophan?

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

    What is a characteristic of GABA receptors in the central nervous system?

    <p>GABAA receptors open Cl- channels.</p> Signup and view all the answers

    Which of the following neurotransmitters is associated with mediating long-term potentiation?

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

    What type of transporters are utilized for neurotransmitter uptake into glial cells?

    <p>Excitatory amino acid transporters</p> Signup and view all the answers

    Which receptor type is associated with slow synaptic transmission?

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

    How are neuropeptides typically different from classical neurotransmitters?

    <p>They have a longer duration of action.</p> Signup and view all the answers

    What initiates the release of neurotransmitters at the axon terminal?

    <p>Action potential reaching the axon terminal</p> Signup and view all the answers

    Which neurotransmitter is primarily involved in the regulation of muscle contraction?

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

    What is the main function of autoreceptors in the neuronal signaling process?

    <p>They regulate the neuron's own release of neurotransmitter.</p> Signup and view all the answers

    Which ion is primarily associated with the action of NMDA receptors?

    <p>Ca2+</p> Signup and view all the answers

    What occurs during an excitatory post-synaptic potential (ePSP)?

    <p>Influx of positively charged ions leads to depolarization.</p> Signup and view all the answers

    What role do voltage-gated sodium channels (VGSCs) play during an action potential?

    <p>They open to allow Na+ influx, resulting in depolarization.</p> Signup and view all the answers

    What defines the absolute refractory period of a neuron?

    <p>No stimulus can trigger another action potential regardless of intensity.</p> Signup and view all the answers

    What is the function of myelin in neuronal communication?

    <p>To act as an electrical insulator enhancing transmission speed.</p> Signup and view all the answers

    What triggers the exocytosis of neurotransmitters in the presynaptic terminal?

    <p>Localised calcium entry following depolarization of the axon terminal.</p> Signup and view all the answers

    What is the primary consequence of spatial summation in the nervous system?

    <p>It allows multiple presynaptic terminals to influence the postsynaptic neuron.</p> Signup and view all the answers

    Which statement best explains the 'all or none' principle of action potentials?

    <p>Once the action potential threshold is reached, the potential's strength remains consistent.</p> Signup and view all the answers

    Which neurotransmitter is generally considered to have an inhibitory effect?

    <p>GABA (γ-amino-butyric acid)</p> Signup and view all the answers

    What primarily differentiates temporal summation from spatial summation?

    <p>Temporal summation is based on the frequency of stimuli from a single neuron.</p> Signup and view all the answers

    What is the role of neurotransmitter auto-receptors?

    <p>They monitor neurotransmitter levels and modulate presynaptic release.</p> Signup and view all the answers

    What initiates the restoration of resting membrane potential after an action potential?

    <p>Inactivation of voltage-gated sodium channels.</p> Signup and view all the answers

    What effect does myelin sheath have on the conduction of action potentials?

    <p>It increases the speed of conduction by enabling saltatory conduction.</p> Signup and view all the answers

    Which of the following ions primarily contribute to the hyperpolarization of the postsynaptic membrane during an inhibitory post-synaptic potential (iPSP)?

    <p>Chloride ions (Cl-)</p> Signup and view all the answers

    What is the primary purpose of the Na+/K+ pump in a neuron?

    <p>To restore the resting membrane potential and concentration gradients.</p> Signup and view all the answers

    Which of the following ions plays a crucial role in initiating neurotransmitter release at the presynaptic terminal?

    <p>Calcium (Ca²⁺)</p> Signup and view all the answers

    Where are synaptic vesicles containing neurotransmitters primarily located?

    <p>Presynaptic terminal</p> Signup and view all the answers

    What type of channel on the postsynaptic membrane is involved in synaptic transmission?

    <p>Ligand-gated receptor-channel</p> Signup and view all the answers

    What process terminates the action of neurotransmitters in the synaptic cleft?

    <p>All of the above</p> Signup and view all the answers

    Which ion's movement into the postsynaptic neuron typically results in excitatory postsynaptic potential (EPSP)? A) Sodium (Na⁺) B) Potassium (K⁺) C) Chloride (Cl⁻) D) Calcium (Ca²⁺)

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

    Which event directly triggers the exocytosis of neurotransmitters from synaptic vesicles in the presynaptic terminal?

    <p>Calcium (Ca²⁺) entry</p> Signup and view all the answers

    Which of the following types of calcium channels is involved in synaptic neurotransmitter release?

    <p>N-type and P-type</p> Signup and view all the answers

    What role does synaptotagmin play in synaptic transmission?

    <p>Functions as a calcium sensor, facilitating vesicle fusion</p> Signup and view all the answers

    Which group of proteins is essential for the fusion of synaptic vesicles with the presynaptic membrane?

    <p>SNARE proteins</p> Signup and view all the answers

    After release into the synaptic cleft, neurotransmitters can bind to which receptors to regulate further release from the presynaptic neuron?

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

    Which process is primarily responsible for terminating the neurotransmitter's action in the synaptic cleft?

    <p>Reuptake or enzymatic degradation</p> Signup and view all the answers

    What directly induces the fusion of synaptic vesicles with the presynaptic membrane during neurotransmitter release?

    <p>Calcium (Ca²⁺) influx</p> Signup and view all the answers

    Which protein acts as the primary calcium sensor that facilitates vesicle fusion with the presynaptic membrane?

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

    Which of the following proteins is part of the SNARE complex, essential for vesicle fusion at the synapse?

    <p>Snap25</p> Signup and view all the answers

    Which protein is involved in synaptic vesicle trafficking and fusion, and is not directly part of the SNARE complex?

    <p>SV2A</p> Signup and view all the answers

    What role does the SNARE complex play in synaptic vesicle exocytosis?

    <p>Anchoring and fusing vesicles with the presynaptic membrane</p> Signup and view all the answers

    Which of the following neurotransmitters is generally considered excitatory?

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

    Which neurotransmitter is primarily inhibitory in the central nervous system (CNS)?

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

    Where does neurotransmitter synthesis typically begin in the neurotransmitter lifecycle?

    <p>Axon terminal from precursor molecules</p> Signup and view all the answers

    What is the role of autoreceptors in the presynaptic cell?

    <p>They inhibit excessive neurotransmitter release.</p> Signup and view all the answers

    Which of the following steps in the neurotransmitter lifecycle could be a target for pharmacological intervention? (Select all that apply)

    <p>All of the above</p> Signup and view all the answers

    Which neurotransmitter is primarily excitatory and associated with major cognitive functions such as learning and memory?

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

    Which of the following is an example of a neurotransmitter precursor that is an amino acid taken into the neuron by selective transporters?

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

    Where are neurotransmitter-synthesizing enzymes typically produced before being transported to the axon terminal?

    <p>Cell body</p> Signup and view all the answers

    Which type of neurotransmitter receptor is involved in fast synaptic transmission by directly allowing ions to flow through upon ligand binding?

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

    What type of receptor is also known as a G-protein coupled receptor (GPCR) and is involved in slower synaptic transmission?

    <p>Metabotropic receptor</p> Signup and view all the answers

    Which of the following best describes the function of metabotropic receptors in neurotransmission?

    <p>They activate G-proteins that can modify ion channel function or initiate intracellular signaling.</p> Signup and view all the answers

    Which of the following statements is true regarding ionotropic and metabotropic receptors?

    <p>Ionotropic receptors are involved in fast synaptic transmission, whereas metabotropic receptors are involved in slower synaptic transmission with potential long-term effects.</p> Signup and view all the answers

    Which of the following neurotransmitter precursors is a by-product of cellular metabolism?

    <p>α-Ketoglutarate</p> Signup and view all the answers

    Which of the following accurately describes the process through which neurotransmitters are synthesized?

    <p>They are synthesized locally in the axon terminal.</p> Signup and view all the answers

    Which type of receptor is directly involved in altering the activity of second messenger systems or gene expression in the postsynaptic cell?

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

    Which protein type primarily mediates the delayed effects triggered by neurotransmitter binding to metabotropic receptors?

    <p>G-proteins</p> Signup and view all the answers

    What is a key distinction between ionotropic and metabotropic receptors in terms of synaptic transmission?

    <p>Ionotropic receptors are involved in fast synaptic transmission, while metabotropic receptors are involved in slower and often more prolonged signaling.</p> Signup and view all the answers

    Which of the following neurotransmitters is synthesized from the amino acid tyrosine?

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

    A neuron releases neurotransmitter molecules into the synaptic cleft. Which step follows neurotransmitter release in the synaptic process?

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

    What type of receptor does glutamate primarily bind to in the postsynaptic cell for fast excitatory responses?

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

    Which enzyme is responsible for the breakdown of acetylcholine in the synaptic cleft?

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

    Which of the following mechanisms allows neurotransmitters to be reused by the presynaptic neuron? (Select one)

    <p>Reuptake by transporter proteins in the presynaptic membrane</p> Signup and view all the answers

    Which transporter is responsible for removing glutamate from the synaptic cleft by uptake into glial cells?

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

    Which of the following best describes the role of glial cells in neurotransmitter inactivation?

    <p>They take up and metabolize certain neurotransmitters from the synaptic cleft.</p> Signup and view all the answers

    Which neurotransmitter is primarily inactivated by reuptake through the GABA transporter (GAT1)?

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

    Which of the following is NOT a primary method of neurotransmitter inactivation?

    <p>Conversion into an inactive form by postsynaptic enzymes</p> Signup and view all the answers

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

    <p>They may be lost and do not participate in further synaptic signaling.</p> Signup and view all the answers

    Which neurotransmitter inactivation mechanism is primarily involved in the recycling of neurotransmitters for future synaptic release?

    <p>Reuptake by the presynaptic neuron</p> Signup and view all the answers

    Which of the following neurotransmitters is classified as a catecholamine?

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

    Which neurotransmitter is both an amino acid and an inhibitory neurotransmitter in the central nervous system?

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

    Which neurotransmitter is considered excitatory and is the primary excitatory neurotransmitter in the brain?

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

    Which of the following neurotransmitters is classified as an indolamine?

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

    Which neurotransmitter is primarily associated with the neuromuscular junction in the peripheral nervous system?

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

    What class of neurotransmitters do dopamine, noradrenaline, and adrenaline belong to?

    <p>Biogenic amines</p> Signup and view all the answers

    Which neurotransmitter is known for its role in regulating mood, appetite, and sleep, and is often targeted by antidepressant medications?

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

    Which amino acid neurotransmitter is primarily inhibitory in the brain?

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

    Which neurotransmitter functions in both the CNS and PNS and is typically excitatory, particularly at the neuromuscular junction?

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

    Histamine acts as a neurotransmitter in the brain and is part of which neurotransmitter class?

    <p>Biogenic amines</p> Signup and view all the answers

    Which neurotransmitter functions in both the CNS and PNS and is typically excitatory, particularly at the neuromuscular junction?

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

    Which enzyme is responsible for converting glutamine to glutamate in the neuron?

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

    After release into the synaptic cleft, glutamate is taken up by which type of cell for recycling?

    <p>Astrocytes (glial cells)</p> Signup and view all the answers

    Which receptor types does glutamate bind to on the postsynaptic membrane to initiate a response?

    <p>NMDA and AMPA receptors</p> Signup and view all the answers

    Which cell enzyme converts glutamate to glutamine in glial cells for transport back to the presynaptic neuron?

    <p>Glutamine synthetase</p> Signup and view all the answers

    Which of the following is an effect of glutamate binding to NMDA receptors?

    <p>Depolarization due to calcium (Ca²⁺) influx</p> Signup and view all the answers

    Glutamate can also bind to metabotropic receptors (mGluRs) on the postsynaptic neuron. These receptors are primarily involved in:

    <p>Modulation of ionotropic receptor activity</p> Signup and view all the answers

    In the glutamate-glutamine cycle, which of the following occurs first in the presynaptic terminal?

    <p>Glutamine is converted into glutamate</p> Signup and view all the answers

    Which of the following statements best describes glutamate?

    <p>It is the major excitatory neurotransmitter in the brain.</p> Signup and view all the answers

    Excessive glutamate signaling can lead to which of the following? (Select one)

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

    Which cells are primarily responsible for glutamate inactivation in the synaptic cleft?

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

    Which type of glutamate receptor is directly involved in mediating long-term potentiation (LTP)?

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

    Which ion(s) are NMDA receptors permeable to?

    <p>Ca²+, Na+, and K+</p> Signup and view all the answers

    Which of the following glutamate receptors is not an ionotropic receptor?

    <p>mGluR (metabotropic glutamate receptor)</p> Signup and view all the answers

    How many types of metabotropic glutamate receptors (mGluRs) exist?

    <p>8</p> Signup and view all the answers

    Which glutamate receptor subtype is known for fast synaptic transmission?

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

    What is GABA primarily known for in the central nervous system (CNS)?

    <p>It acts as the primary inhibitory neurotransmitter.</p> Signup and view all the answers

    Which ion does GABA primarily allow to flow into the cell when it binds to its receptor?

    <p>Cl⁻</p> Signup and view all the answers

    What effect does GABA binding have on the postsynaptic neuron?

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

    Which of the following statements about GABA receptors is correct?

    <p>GABAA receptors mediate fast synaptic transmission.</p> Signup and view all the answers

    What is the mechanism of inactivation for GABA in the synaptic cleft?

    <p>Reuptake by presynaptic neurons or astrocytes</p> Signup and view all the answers

    Which of the following is a common therapeutic target for epilepsy treatments?

    <p>Enhancing GABA activity</p> Signup and view all the answers

    Which type of GABA receptor is involved in metabotropic signaling?

    <p>GABAB receptor</p> Signup and view all the answers

    What physiological response does GABA induce when it binds to GABAA receptors?

    <p>Inhibitory postsynaptic potential (iPSP)</p> Signup and view all the answers

    What are neuropeptides primarily known for in neurotransmission?

    <p>They are frequently co-released with small-molecule neurotransmitters.</p> Signup and view all the answers

    Which of the following is an example of a neuropeptide?

    <p>Substance P</p> Signup and view all the answers

    What is the primary mechanism of inactivation for neuropeptides?

    <p>Enzymatic degradation</p> Signup and view all the answers

    How do neuropeptides differ from classical neurotransmitters in their response time?

    <p>Neuropeptides mediate slower responses.</p> Signup and view all the answers

    What is the primary CNS function of dopamine (DA)? A) Mood regulation B) Inhibition C) Reward and motivation D) Pain perception

    <p>Reward and motivation</p> Signup and view all the answers

    Which neurotransmitter is primarily associated with the inhibition of neuronal activity?

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

    Which neurotransmitter receptor subtype is involved in synaptic plasticity and learning?

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

    What CNS pathology is primarily associated with excessive glutamate signaling?

    <p>Alzheimer's disease</p> Signup and view all the answers

    Which neurotransmitter is linked to mood, appetite, and sleep regulation?

    <p>Serotonin (5-HT)</p> Signup and view all the answers

    What is the primary function of noradrenaline (norepinephrine) in the CNS?

    <p>Attention and arousal</p> Signup and view all the answers

    What is the primary function of dendrites in a neuron?

    <p>Receive incoming signals</p> Signup and view all the answers

    What occurs during depolarization of the neuronal membrane?

    <p>Influx of Na+ ions</p> Signup and view all the answers

    Which of the following ions is primarily responsible for establishing the resting membrane potential (RMP)?

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

    What is the primary effect of myelination on neuronal action potentials?

    <p>Facilitates saltatory conduction</p> Signup and view all the answers

    During action potential propagation, which channels open first when the threshold is reached?

    <p>Voltage-gated Na+ channels</p> Signup and view all the answers

    What is an excitatory postsynaptic potential (ePSP) primarily associated with?

    <p>Influx of positively charged ions</p> Signup and view all the answers

    What is the role of Substance P in the nervous system?

    <p>Neurotransmitter peptide</p> Signup and view all the answers

    What is the main function of the refractory period in neuronal signaling?

    <p>Prevents back-propagation of action potentials</p> Signup and view all the answers

    Which neurotransmitter is primarily inhibitory and often targets GABA receptors?

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

    What does the term 'summation' refer to in the context of synaptic transmission?

    <p>The combined effect of multiple postsynaptic potentials leading to an action potential.</p> Signup and view all the answers

    If a neuron is depolarized to -50 mV, what is the likely outcome?

    <p>An action potential will not be generated because the threshold was not reached.</p> Signup and view all the answers

    What effect does an increase in inhibitory neurotransmitter activity have on the likelihood of generating an action potential?

    <p>It decreases the likelihood of generating an action potential.</p> Signup and view all the answers

    Which of the following statements is true regarding action potentials?

    <p>They are all-or-none responses initiated above a specific threshold.</p> Signup and view all the answers

    What is the primary function of the Na+/K+ ATPase pump in neurons?

    <p>It restores resting membrane potential by exchanging Na+ and K+ ions.</p> Signup and view all the answers

    During which phase of an action potential do voltage-gated Na+ channels close?

    <p>Repolarization phase</p> Signup and view all the answers

    What happens to a neuron during hyperpolarization?

    <p>It decreases the likelihood of generating an action potential.</p> Signup and view all the answers

    What characterizes the absolute refractory period in neurons?

    <p>The neuron is completely unable to respond to any stimulus.</p> Signup and view all the answers

    Which type of ion channel is activated when neurotransmitters bind to receptors during synaptic transmission?

    <p>Ligand-gated ion channels</p> Signup and view all the answers

    What role do calcium ions (Ca²+) play in synaptic transmission at the synaptic terminal?

    <p>They trigger the release of neurotransmitters into the synaptic cleft.</p> Signup and view all the answers

    What is the main purpose of the nodes of Ranvier in neuron signaling?

    <p>To facilitate saltatory conduction of action potentials.</p> Signup and view all the answers

    Which event directly follows the depolarization phase during action potential propagation?

    <p>Voltage-gated Na+ channels close and voltage-gated K+ channels open.</p> Signup and view all the answers

    Which ion is primarily responsible for the depolarization phase of an action potential?

    <p>Na⁺</p> Signup and view all the answers

    What process is triggered by the influx of Ca²⁺ ions at the presynaptic terminal?

    <p>Exocytosis of synaptic vesicles</p> Signup and view all the answers

    During the repolarization phase of an action potential, which ion primarily contributes to the outward current?

    <p>K⁺</p> Signup and view all the answers

    What is the typical equilibrium potential for potassium (K⁺) in a neuron?

    <p>-90 mV</p> Signup and view all the answers

    What happens to the membrane potential when a ligand-gated Na⁺ channel opens in a resting neuron?

    <p>It becomes less negative (depolarizes).</p> Signup and view all the answers

    What drives the entry of Na⁺ into a neuron when voltage-gated Na⁺ channels are opened?

    <p>Concentration gradient and electrical gradient favoring Na⁺ influx</p> Signup and view all the answers

    What is the impact on membrane potential during the influx of Cl⁻ ions when GABA binds to its receptor?

    <p>Membrane potential hyperpolarizes.</p> Signup and view all the answers

    What effect does a -2 mA current have on a resting neuron with a potential of -70 mV?

    <p>It will hyperpolarize.</p> Signup and view all the answers

    What is the primary mechanism by which a drug that blocks voltage-gated sodium channels affects action potentials?

    <p>It prevents action potentials from occurring.</p> Signup and view all the answers

    Which ion has the highest concentration inside a typical resting neuron?

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

    What effect does opening ligand-gated K⁺ channels have on the membrane potential?

    <p>The membrane hyperpolarizes.</p> Signup and view all the answers

    During which phase of an action potential are sodium channels inactivated and potassium channels opened?

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

    What occurs when a neuron is depolarized to the threshold potential?

    <p>Sodium (Na⁺) channels open.</p> Signup and view all the answers

    What is the typical equilibrium potential for sodium (Na⁺) in a neuron?

    <p>+60 mV</p> Signup and view all the answers

    How does an increase in extracellular K⁺ concentration affect neuronal excitability?

    <p>It decreases the resting membrane potential.</p> Signup and view all the answers

    Which type of current predominates during the repolarization phase of an action potential?

    <p>Outward potassium current</p> Signup and view all the answers

    Study Notes

    Neuron Anatomy

    • Neurons are the basic units of the nervous system, responsible for communication.
    • They have distinct parts:
      • Cell body (soma): Contains the nucleus and other organelles.
      • Dendrites: Branching structures that receive incoming signals from other neurons.
      • Axon: A long, slender projection that propagates action potentials away from the cell body.
      • Synaptic terminals: Specialized structures at the end of the axon that release neurotransmitters, converting electrical signals into chemical ones.

    Electrochemical Gradients and Membrane Potential

    • The membrane potential is the difference in electrical charge across the plasma membrane of a neuron.
    • This difference is maintained by ion concentration gradients and ion charge gradients.
    • Resting membrane potential (RMP): The membrane potential of a neuron at rest, typically around -70mV.
      • This negativity is due to the higher concentration of potassium ions (K+) inside the cell and sodium ions (Na+) outside the cell.
      • Sodium-potassium pump (Na+/K+ ATPase): Maintains the concentration gradients by actively transporting Na+ out of the cell and K+ into the cell.
      • Leak channels: Allow for a small, passive movement of ions across the membrane, contributing to the RMP.

    Changes in Membrane Potential

    • Depolarization: A decrease in the negative charge inside the cell, typically caused by an influx of positive ions like sodium (Na+)
      • Depolarizations often lead to excitation.
    • Hyperpolarization: An increase in the negative charge inside the cell, typically caused by an efflux of potassium ions (K+) or an influx of negative ions like chloride (Cl-).
      • Hyperpolarizations often lead to inhibition.

    Excitation and Inhibition

    • Excitatory postsynaptic potential (ePSP): A depolarization of the post-synaptic membrane, triggered by the binding of excitatory neurotransmitters to post-synaptic receptors.
      • Occurs when positive ions like Na+ or Ca2+ flow into the cell.
    • Inhibitory postsynaptic potential (iPSP): A hyperpolarization of the post-synaptic membrane, triggered by the binding of inhibitory neurotransmitters to postsynaptic receptors.
      • When positive ions (e.g., K+) flow out of the cell or negative ions (e.g., Cl-) flow into the cell.

    Summation

    • Spatial summation: The combined effect of multiple synaptic inputs arriving at different locations on the postsynaptic neuron.
      • If the combined effect of all inputs is strong enough to reach the action potential threshold, an action potential will be generated.
    • Temporal summation: The combined effect of multiple synaptic inputs arriving close together in time at a single location on the postsynaptic neuron.
      • If the sum of the inputs reaches the action potential threshold, an action potential will be generated.

    Action Potential

    • Action potential (AP): A brief, rapid, and large change in membrane potential that travels down the axon.
      • The AP is initiated when the membrane potential reaches the action potential threshold, usually around -55mV.
    • Voltage-gated sodium channels (VGSCs): Open during depolarization, allowing Na+ to rush into the cell, further depolarizing the membrane.
    • Voltage-gated potassium channels (VGPCs): Open near the peak of depolarization, allowing K+ to flow out of the cell, repolarizing the membrane.
    • Refractory period: A brief period following an action potential during which the neuron is less likely to fire another action potential.
      • Absolute refractory period: No stimulus, regardless of its strength, can trigger another action potential.
      • Relative refractory period: Only a very strong stimulus can trigger another action potential.

    Action Potential Propagation

    • APs travel down the axon in a unidirectional manner, moving away from the cell body towards the axon terminal.
    • The depolarization of one segment of the axon triggers the opening of VGSCs in adjacent segments, causing the AP to propagate along the axon.

    Myelin

    • Myelin: A fatty sheath that insulates axons, increasing the speed of action potential conduction.
      • Oligodendrocytes: Produce myelin in the central nervous system (CNS).
      • Schwann cells: Produce myelin in the peripheral nervous system (PNS).
    • Nodes of Ranvier: Gaps in the myelin sheath where VGSCs are concentrated.
    • Saltatory conduction: The rapid jumping of APs from one node of Ranvier to the next, speeding up conduction.
    • Demyelination: Loss of myelin, often associated with diseases like multiple sclerosis, can disrupt the speed and efficiency of neural communication.

    Synaptic Transmission

    • Synapse: The junction between the pre-synaptic neuron and the post-synaptic neuron.
    • Synaptic cleft: The narrow gap between the pre-synaptic and post-synaptic membranes where neurotransmitters are released.
    • Synaptic vesicles: Small sacs within the pre-synaptic terminal that store neurotransmitters.
    • Neurotransmitters: Chemical messengers that transmit signals from one neuron to another.
    • Neurotransmitter receptors: Proteins on the post-synaptic membrane that bind to neurotransmitters, triggering a response in the post-synaptic neuron.

    Neurotransmitter Release

    • Action potential reaches the pre-synaptic terminal.
    • Depolarization opens voltage-gated Ca2+ channels.
    • Ca2+ influx triggers the fusion of synaptic vesicles with the pre-synaptic membrane, releasing neurotransmitters into the synaptic cleft.

    Neurotransmitter Actions

    • Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the post-synaptic membrane.
    • Ionotropic receptors: Directly open ion channels, leading to rapid changes in membrane potential.
    • Metabotropic receptors: Activate G-proteins, which can modulate ion channels or trigger intracellular signaling pathways, leading to slower and more complex changes in cell function.

    Neurotransmitter Inactivation

    • Enzymatic degradation: Neurotransmitters are broken down by enzymes in the synaptic cleft.
    • Reuptake: Neurotransmitters are transported back into the pre-synaptic neuron or taken up by neighboring glial cells.
    • Diffusion: Neurotransmitters can diffuse away from the synaptic cleft.

    Major Neurotransmitters

    • Acetylcholine (ACh): Plays a role in learning, memory, and muscle contraction.
    • Catecholamines:
      • Dopamine (DA): Involved in movement, reward, and motivation.
      • Noradrenaline (NA) / (Nor)epinephrine: Involved in alertness, arousal, and mood.
      • Adrenaline (A): Involved in stress response and energy mobilization.
    • Indolamines:
      • Serotonin (5-HT): Involved in mood, sleep, and appetite.
      • Histamine: Involved in alertness, immunological responses, and gastric acid regulation.
    • Glutamate (L-Glu): Major excitatory neurotransmitter.
    • γ-amino-butyric acid (GABA): Major inhibitory neurotransmitter.
    • Glycine (L-Gly): Inhibitory neurotransmitter.

    Neurotransmitter Receptors

    • Ionotropic receptors: Directly open ion channels, leading to rapid changes in membrane potential.
      • Acetylcholine (ACh): Nicotinic receptors
      • GABA: GABAA receptors
      • Glutamate: NMDA, AMPA, and Kainate receptors.
    • Metabotropic receptors: Activate G-proteins leading to slower and more complex changes in cell function.
      • Acetylcholine (ACh): Muscarinic receptors
      • Dopamine (DA): D1-like (D1, D5) and D2-like (D2, D3, D4) receptors
      • GABA: GABAB receptors
      • Glutamate: mGluR1-8 receptors
      • (Nor)adrenaline (NA) / (Nor)epinephrine: α1, α2, β1, β2 receptors
      • Serotonin (5-HT): 5-HT1, 2, 4-7 receptors
      • Others: Histamine, glycine, aspartate receptors

    Co-transmission: Neuropeptides

    • Neuropeptides: Peptide neurotransmitters often released together with small-molecule neurotransmitters.
      • Stored in dense-core vesicles.
      • Examples: Substance P (pain perception), endorphins, enkephalins, dynorphins (opioid peptides), neurotensin, neuropeptide Y, vasoactive intestinal polypeptide (VIP).
    • Neurotransmission vs. Neuromodulation:
      • Neurotransmission: Rapid communication via small-molecule neurotransmitters.
      • Neuromodulation: Slow, longer-lasting effects mediated by neuropeptides, modifying the activity of neural circuits.
    • Co-transmission: The combined action of small-molecule neurotransmitters and neuropeptides allows for flexible and nuanced responses to stimuli.

    Learning Outcomes

    • Understand the structure and function of the synapse and its role in neuronal communication.
    • Identify common neurotransmitters and their receptors in the CNS.
    • Explain the mechanisms of excitatory and inhibitory postsynaptic potentials.
    • Describe the components of an action potential and how it is generated and propagated.
    • Understand the concept of summation and how it contributes to action potential generation.
    • Explain the steps involved in synaptic neurotransmission and the role of co-transmission.

    Neuron Structure and Function

    • Dendrites: Receive incoming signals from other neurons.
    • Resting Membrane Potential (RMP): The electrical charge difference across the neuron's membrane when it's at rest, typically around -70 mV.
    • Depolarization: The process of the neuron's membrane potential becoming less negative due to an influx of positively charged ions, primarily sodium (Na⁺).
    • Excitatory Postsynaptic Potential (ePSP): A depolarization of the postsynaptic membrane, making it more likely to fire an action potential, caused by an influx of positively charged ions.
    • Refractory Period: A period following an action potential where the neuron is less likely to fire another action potential. This prevents the action potential from traveling backwards.
    • Action Potential Propagation:
      • Threshold: The minimum level of depolarization needed for an action potential to occur.
      • Voltage-gated Sodium (Na⁺) Channels: Open first when the threshold is reached, causing a rapid influx of Na⁺ ions.
      • Myelination: The insulation of axons by a fatty sheath, allowing for faster transmission of action potentials via "saltatory conduction" (jumping from one node of Ranvier to the next).

    Neurotransmitters

    • Substance P: A neurotransmitter peptide involved in pain perception.
    • Potassium (K⁺): The ion primarily responsible for establishing the resting membrane potential.
    • Serotonin: A neurotransmitter involved in mood regulation and often targeted in antidepressant therapies.

    Neuron Function and Action Potentials

    • Na+/K+ ATPase Pump: This pump is critical for restoring the neuron's resting membrane potential after an action potential. It pumps out three sodium ions (Na+) for every two potassium ions (K+) that it brings into the cell, maintaining the negative charge inside the neuron.

    • Absolute Refractory Period: During this period, the neuron is completely unable to fire another action potential, regardless of the stimulus strength. This ensures that action potentials travel in one direction along the axon.

    • Ligand-gated Ion Channels: Neurotransmitters bind to these channels during synaptic transmission, triggering their opening. This allows specific ions to flow across the membrane, leading to either depolarization or hyperpolarization of the postsynaptic cell.

    • Action Potential Propagation: After depolarization, voltage-gated Na+ channels close, and voltage-gated K+ channels open. This allows K+ to flow out of the cell, repolarizing the membrane and initiating the refractory period.

    • Nodes of Ranvier: These gaps in the myelin sheath along the axon are crucial for saltatory conduction. This type of conduction allows action potentials to jump from one node to the next, significantly increasing their speed of propagation.

    Synaptic Transmission

    • Calcium Ions (Ca²+) Play a vital role in neurotransmitter release. When an action potential reaches the synaptic terminal, Ca²⁺ ions enter the terminal through voltage-gated Ca²⁺ channels. This influx of Ca²⁺ triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft.

    • Hyperpolarization: This state makes it less likely for a neuron to fire an action potential by increasing the membrane potential further away from the threshold.

    • Neurotransmitters: Glycine is a primary inhibitory neurotransmitter that typically targets GABA receptors.

    Synaptic Integration

    • Summation: The combined effect of multiple postsynaptic potentials (PSPs) can determine whether a neuron will fire an action potential.

    • Excitatory Postsynaptic Potentials (EPSPs): Depolarize the postsynaptic neuron, increasing the likelihood of an action potential.

    • Inhibitory Postsynaptic Potentials (IPSPs): Hyperpolarize the postsynaptic neuron, decreasing the likelihood of an action potential.

    Action Potential Threshold

    • Threshold: If a neuron is stimulated to -50 mV, an action potential will not be generated because the threshold for firing has not been reached. A strong enough stimulus is needed to overcome the threshold and trigger an action potential.

    Action Potentials

    • During depolarization, sodium ions (Na⁺) move into the neuron, creating an inward current.
    • During repolarization, potassium ions (K⁺) move out of the neuron, creating an outward current.
    • The equilibrium potential (Nernst potential) for potassium (K⁺) in a neuron is typically -90 mV.
    • Calcium ions (Ca²⁺) trigger the release of neurotransmitters at the presynaptic terminal through exocytosis.

    Membrane Potential

    • Opening ligand-gated Na⁺ channels causes the membrane potential to become less negative (depolarize).
    • The driving force for Na⁺ entry when voltage-gated Na⁺ channels open is both the concentration gradient and electrical gradient.
    • Influx of Cl⁻ ions when GABA binds to its receptor causes the membrane potential to hyperpolarize.
    • A current of -2 mA applied to a neuron at rest (-70 mV) will cause the membrane potential to hyperpolarize.

    Sodium-Potassium Pump

    • The Na⁺/K⁺ pump maintains the resting membrane potential by pumping K⁺ into the cell and Na⁺ out, maintaining their concentration gradients.

    Ion Effects

    • Influx of K⁺ ions into a neuron due to a drug causes the neuron to hyperpolarize.

    Action Potentials and Sodium Channels

    • Blocking voltage-gated sodium channels prevents action potentials from occurring
    • Sodium channels are responsible for the rapid depolarization phase of an action potential

    Resting Membrane Potential

    • Potassium (K⁺) has the highest concentration inside a typical resting neuron
    • The resting membrane potential is typically around -70 mV

    Neurotransmitter Effects on Membrane Potential

    • Opening ligand-gated potassium channels results in hyperpolarization of the membrane

    Action Potential Phases

    • Repolarization is characterized by sodium channel inactivation and potassium channel opening
    • Repolarization brings the membrane potential back towards the resting potential

    Threshold Potential and Action Potentials

    • Reaching the threshold potential triggers the opening of sodium channels, leading to an action potential

    Sodium Equilibrium Potential

    • The equilibrium potential for sodium (Na⁺) in a neuron is typically around +60 mV

    Extracellular Potassium Concentration and Neuronal Excitability

    • Increased extracellular potassium concentration decreases the resting membrane potential, making neurons less excitable

    Repolarization Current

    • Outward potassium current is responsible for the repolarization phase of an action potential

    Neurotransmitter Role in Synaptic Transmission

    • Neurotransmitters bind to receptors on the postsynaptic neuron, initiating ionic currents
    • These ionic currents can either excite or inhibit the postsynaptic neuron

    Chloride Ion Influx and Synaptic Signalling

    • An influx of chloride (Cl⁻) ions in a postsynaptic neuron leads to hyperpolarization, thus inhibiting neuronal firing

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    Description

    Explore the intricate anatomy of neurons, the fundamental units of the nervous system. Understand the structure and function of key components like the cell body, dendrites, and axon, along with the essential concepts of electrochemical gradients and resting membrane potential.

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