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Lecture 2
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  • What is the resting membrane potential (RMP) and its typical range?

    • The electrical potential difference across the plasma membrane when a cell is not stimulated
    • Typical range: -40 mV to -90 mV
    membrane rmp

  • What is an action potential?

    A rapid, all-or-none electrical signal generated by ion flow across the neuronal membrane responsible for transmitting information along the axon.

    neuron actionpotential

  • Name the three key factors that contribute to the resting membrane potential.

    • Unequal ion distributions (e.g., high K+ inside, high Na+ outside)
    • Selective membrane permeability (more permeable to K+ at rest)
    • Sodium-potassium pump (Na+/K+-ATPase) maintaining gradients
    rmp factors

  • List the main steps of synaptic transmission from presynaptic action potential to postsynaptic change.

    • Action potential arrives at axon terminal
    • Voltage-gated Ca2+ channels open and Ca2+ enters
    • Synaptic vesicles fuse and release neurotransmitters
    • Neurotransmitters bind postsynaptic receptors causing membrane potential change
    synapse transmission

  • What is the stoichiometry of the sodium-potassium pump (Na+/K+-ATPase) and its effect on charge?

    • Pumps 3 Na+ out and 2 K+ in per ATP hydrolysed, contributing to a net negative charge inside the cell
    pump nak

  • What is the typical value of the resting membrane potential (RMP) in most neurons?

    About -70 mV

    membrane rmp

  • Define equilibrium potential (Eion) for an ion.

    • The membrane potential that exactly balances the electrochemical gradient so there is no net movement of that ion
    equilibrium nernst

  • Name three main factors that establish and maintain the resting membrane potential.

    • Unequal ion distributions (e.g., [Na+]out > [Na+]in, [K+]in > [K+]out)
    • Selective membrane permeability via ion channels
    • Na+/K+-ATPase pump activity (3 Na+ out, 2 K+ in)
    rmp ionchannels

  • State the Nernst equation for calculating an ion's equilibrium potential.

    • Eion = (RT / zF) * ln([ion]out / [ion]in)
    nernst equation

  • What is an Excitatory Postsynaptic Potential (EPSP)?

    A depolarization of the postsynaptic membrane that makes the neuron more likely to fire an action potential, often caused by Na+ influx.

    epsp synapse

  • According to the text, what sign is the equilibrium potential predicted to have for K+ and for Na+?

    • K+: negative (because K+ is high inside)
    • Na+: positive (because Na+ is high outside)
    nernst ions

  • What is an Inhibitory Postsynaptic Potential (IPSP)?

    A hyperpolarization of the postsynaptic membrane that makes the neuron less likely to fire an action potential, often caused by Cl- influx or K+ efflux.

    ipsp synapse

  • Why is the actual membrane potential usually less negative than EK in real cells?

    • Because the membrane is not completely impermeable to Na+ (Na+ moves in) and there is K+ leakage; combined Na+ and K+ movements depolarise the membrane
    goldman permeability

  • What are the main phases of an action potential?

    • Depolarization: rapid Na+ influx (rising phase)
    • Repolarization: Na+ inactivation and K+ efflux (falling phase)
    • Hyperpolarization (undershoot): membrane becomes more negative
    • Return to resting potential
    actionpotential phases

  • What permeability values are given for an example cell in the text (P for K+, Na+, Cl-)?

    • P(K+) = 1, P(Na+) ≈ 0.05, P(Cl-) ≈ 0.45
    permeability goldman

  • Why does Na+ move into the cell when Na+ channels open?

    Because the driving force is inward: concentration gradient (higher extracellular Na+) plus an electrical gradient attracting positive ions into the negatively charged cell.

    ionmovement na

  • What are the main gating types of ion channels listed in the text?

    • Voltage-gated channels
    • Ligand-gated channels
    • Mechanically-gated channels
    • Temperature-gated channels
    ionchannels gating

  • Define depolarizing and hyperpolarizing in terms of membrane potential.

    • Depolarizing: making the membrane potential less negative (more positive)
    • Hyperpolarizing: making the membrane potential more negative
    membrane polarization

  • What is the driving force that makes Na+ move into a cell when Na+ channels open?

    • The driving force is the sum of the inward concentration gradient and the inward electrical gradient for Na+
    drivingforce sodium

  • How does the Na+/K+-ATPase pump move ions across the membrane?

    It moves 3 Na+ out of the cell and 2 K+ in per cycle.

    pump nak

  • Define depolarisation and hyperpolarisation of the membrane potential.

    • Depolarisation: membrane potential becomes less negative (more positive)
    • Hyperpolarisation: membrane potential becomes more negative
    depolarisation hyperpolarisation

  • Illustration: What concept does this image demonstrate about membrane potential changes?

    The image demonstrates depolarising (membrane becomes less negative) and hyperpolarising (membrane becomes more negative) relative to a resting potential of -70 mV. depolarising and hyperpolarising diagram

    image polarization

  • Illustrate depolarising vs hyperpolarising changes (image as illustration).

    Depolarising vs hyperpolarising diagram - Shows: resting potential ≈ -70 mV; making membrane potential more positive = depolarising; more negative = hyperpolarising

    illustration polarisation

  • Illustration: What does this image show about measuring membrane potential?

    It shows measurement using a microelectrode and reference electrode with an amplifier, displaying the potential difference and a resting potential at -70 mV. measuring membrane potential

    image measurement

  • What experimental method is described for measuring membrane potential?

    • Use a microelectrode inside the cell and a reference electrode outside; measure potential difference with an amplifier (resting ≈ -70 mV)
    measurement technique

  • What is the 'absolute refractory period' during an action potential?

    No stimulus, however strong, can elicit another action potential because voltage-gated Na+ channels are inactivated; occurs during depolarization and most of repolarization.

    neurophysiology refractory

  • Summarise the core concept linking ionic gradients, permeability and action potentials from the study notes.

    • Membrane potential arises from ionic gradients plus selective permeabilities; gated ion channels convert these gradients into action potentials
    summary core

  • What defines the 'relative refractory period'?

    A stronger-than-usual stimulus is required to reach threshold because voltage-gated Na+ channels are returning to resting state while voltage-gated K+ channels are still open; occurs during hyperpolarization.

    neurophysiology refractory

  • What is an action potential?

    A rapid, transient, all-or-none electrical signal that travels along the membrane of excitable cells and is initiated when membrane potential reaches a threshold.

    neurophysiology action_potential

  • What is 'propagation of an action potential'?

    The movement of an action potential along the axon.

    neurophysiology propagation

  • Which ion channel event causes the depolarization phase of an action potential?

    Opening of voltage-gated Na+ channels causes rapid increase in membrane potential (depolarization).

    action_potential depolarization

  • What is 'continuous conduction'?

    Action potential propagates step-by-step along the axon membrane and occurs in unmyelinated axons.

    propagation axon

  • What causes the repolarization phase of an action potential?

    Inactivation of voltage-gated Na+ channels and opening of voltage-gated K+ channels causes repolarization.

    action_potential repolarization

  • What is 'saltatory conduction' and one key advantage?

    Action potentials 'jump' between nodes of Ranvier in myelinated axons; it is faster and more energy-efficient than continuous conduction.

    propagation myelination

  • Why does membrane potential briefly become more negative than resting potential (hyperpolarization)?

    Because voltage-gated K+ channels close slowly, allowing extra K+ efflux that makes the membrane potential more negative.

    action_potential hyperpolarization

  • What is 'synaptic integration' in a postsynaptic neuron?

    The process by which a postsynaptic neuron integrates multiple synaptic inputs to determine whether to fire an action potential.

    synapse integration

  • What primarily generates the resting membrane potential (RMP)?

    Selective membrane permeability to K+ (via leak channels) and outward K+ movement down its concentration gradient, plus the Na+/K+ pump.

    resting_potential membrane_potential

  • What is 'temporal summation' of postsynaptic potentials?

    Multiple postsynaptic potentials (EPSPs or IPSPs) arrive at the same synapse in rapid succession from a single presynaptic neuron.

    summation synaptic

  • What determines an ion's equilibrium potential?

    The ion's concentration gradient across the membrane and its charge (valence), as described by the Nernst equation.

    equilibrium_potential nernst

  • What is 'spatial summation' of postsynaptic potentials?

    Multiple postsynaptic potentials (EPSPs or IPSPs) arrive at the same postsynaptic neuron simultaneously from different presynaptic neurons.

    summation synaptic

  • Why is the resting membrane potential usually less negative than the K+ equilibrium potential (E_K)?

    Because the membrane is slightly permeable to Na+ at rest, allowing Na+ entry that depolarizes the membrane relative to E_K.

    resting_potential permeability

  • What are the main classes of neurotransmitters listed?

    • Amino Acids: e.g., GABA (inhibitory), Glutamate (excitatory)
    • Amines: e.g., Dopamine, Serotonin, Norepinephrine
    • Peptides: e.g., Endorphins, Substance P
    • Other: e.g., Acetylcholine (ACh)
    neurotransmitters classification

  • What factors can change the membrane potential?

    Changes in ion concentrations, changes in membrane permeability to specific ions (opening/closing channels), and activity of ion pumps.

    membrane_potential factors

  • What is the difference between depolarizing and hyperpolarizing changes in membrane potential? (see image)

    Depolarizing: membrane potential becomes less negative (more positive). Hyperpolarizing: membrane potential becomes more negative. depolarising vs hyperpolarising

    membrane potentials

  • How is 'depolarising' vs 'hyperpolarising' described for membrane potential?

    • Depolarising: membrane potential becomes less negative (more positive).
    • Hyperpolarising: membrane potential becomes more negative.
    membrane_potential polarisation

  • How is membrane potential measured with electrodes? (image illustration)

    A microelectrode inside the cell and a reference electrode outside measure the potential difference, amplified and displayed with resting potential around -70 mV. microelectrode measuring membrane potential

    technique measurement
Study Notes

Chapter 4 — The Neuron: Key Study Notes

Overview

  • Neuronal signalling uses electrical changes across the membrane (membrane potentials) and chemical transmission at synapses to transmit information.

Synaptic transmission (how neurons connect)

  • Steps:
  • Action potential arrives at the presynaptic terminal.
  • Voltage-gated Ca\(^{2+}\) channels open; Ca\(^{2+}\) influx triggers vesicle fusion.
  • Neurotransmitters are released into the synaptic cleft and bind postsynaptic receptors.
  • Receptor binding changes postsynaptic ion permeability and membrane potential.
  • Vesicle cycle: storage → Ca\(^{2+}\)-triggered fusion → diffusion → receptor action → removal (reuptake/degradation).

Membrane potentials

  • Resting membrane potential (RMP): typical neuronal value ≈ -70 mV; results from ion concentration gradients and selective membrane permeability.
  • Main contributors: high intracellular K\(^+\), high extracellular Na\(^+\) and Cl\(^-\), ion channels, and the Na\(^+\)/K\(^+\)-ATPase which maintains gradients (\(3\ \mathrm{Na}^+\) out, \(2\ \mathrm{K}^+\) in).

Depolarising vs hyperpolarising diagram Alt text: Depolarising and hyperpolarising membrane potential diagram.

Factors that determine RMP

  • Ionic concentration gradients across the membrane (e.g., \([\mathrm{K}^+]_{\text{in}}\gg[\mathrm{K}^+]_{\text{out}}\)).
  • Membrane permeability to specific ions (open channels).
  • Electrogenic pumps (Na\(^+\)/K\(^+\)-ATPase) that consume metabolic energy.

Nernst equation (equilibrium potential for one ion)

  • General form for ion with valence \(z\): \(\(E_{\text{ion}} = \frac{RT}{zF}\ln\frac{[\text{ion}]_{\text{outside}}}{[\text{ion}]_{\text{inside}}}\)\)
  • Gives the membrane potential where net flux of that ion is zero (balance of concentration and electrical forces).

Nernst equation and example calculations Alt text: Nernst equation and example for monovalent ions.

Goldman–Hodgkin–Katz (GHK) equation

  • For multiple permeant ions, membrane potential depends on permeabilities \(P\) and concentrations: \(\(E_m = \frac{RT}{F}\ln\frac{P_K[\mathrm{K}^+]_o + P_{Na}[\mathrm{Na}^+]_o + P_{Cl}[\mathrm{Cl}^-]_i}{P_K[\mathrm{K}^+]_i + P_{Na}[\mathrm{Na}^+]_i + P_{Cl}[\mathrm{Cl}^-]_o}\)\)
  • Explains why real Em is usually less negative than \(E_K\) alone (small Na\(^+\) permeability shifts Em toward less negative values).

Postsynaptic potentials (PSPs)

  • PSPs are graded (size depends on neurotransmitter amount and receptor response) and can summate.
  • Excitatory postsynaptic potential (EPSP): depolarizing, often due to Na\(^+\) influx; moves membrane closer to threshold.
  • Inhibitory postsynaptic potential (IPSP): hyperpolarizing, often due to Cl\(^-\) influx or K\(^+\) efflux; moves membrane away from threshold.

Synaptic integration and summation

  • Temporal summation: PSPS from the same synapse arrive in rapid succession and add.
  • Spatial summation: PSPS from different synapses at the same time combine.
  • The neuron fires an action potential if integrated PSPs bring the axon hillock to threshold.

Action potential (AP)

  • AP is a rapid, all-or-none depolarization that propagates along the axon to transmit information.
  • Phases and ionic basis:
  • Resting: Em ≈ -70 mV.
  • Depolarization (rising phase): voltage-gated Na\(^+\) channels open → rapid Na\(^+\) influx → Em becomes positive.
  • Repolarization (falling phase): Na\(^+\) channels inactivate; voltage-gated K\(^+\) channels open → K\(^+\) efflux → Em returns toward rest.
  • Hyperpolarization (undershoot): K\(^+\) channels close slowly, Em becomes more negative than RMP temporarily.
  • Driving force on an ion can be expressed as: \(\(\text{Driving force} = V_m - E_{\text{ion}}\)\) where \(V_m\) is membrane potential and \(E_{\text{ion}}\) is that ion's equilibrium potential.

Refractory periods

  • Absolute refractory period: during depolarization and most repolarization Na\(^+\) channels are inactivated; no stimulus can elicit another AP.
  • Relative refractory period: during hyperpolarization a stronger-than-normal stimulus can trigger an AP because some Na\(^+\) channels have recovered.

Propagation of action potentials

  • Continuous conduction: unmyelinated axons; AP is regenerated along each patch of membrane (slow).
  • Saltatory conduction: myelinated axons; APs jump between nodes of Ranvier, increasing speed and efficiency.
  • Myelin reduces membrane capacitance and increases membrane resistance, speeding conduction.

Neurotransmitters — main classes and examples

  • Amino acids: GABA (inhibitory), Glutamate (excitatory).
  • Amines: Dopamine, Serotonin, Norepinephrine.
  • Peptides: Endorphins, Substance P.
  • Other small molecules: Acetylcholine (ACh).

Quick practical points for study

  • Remember RMP ≈ -70 mV and Na\(^+\)/K\(^+\) pump stoichiometry (\(3\ \mathrm{Na}^+\) out, \(2\ \mathrm{K}^+\) in).
  • Use Nernst for single-ion equilibrium potentials and GHK for realistic Em with multiple ions.
  • Distinguish graded PSPs (local, summating) from all-or-none APs (propagating).

Key terms (flashcard-style)

  • Resting membrane potential (RMP)
  • Nernst equation and equilibrium potential
  • Goldman–Hodgkin–Katz equation
  • EPSP / IPSP
  • Absolute vs relative refractory period
  • Saltatory vs continuous conduction