neuro -bioelectrical signaling

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Questions and Answers

What primarily composes the plasma membrane?

Carbohydrates and minerals

Lipids and proteins (correct)

Proteins and nucleic acids

Lipids and carbohydrates

Which of the following is NOT one of the basic functions of membrane proteins?

Signal transduction

Attachment/recognition

Transport

Genetic replication (correct)

What characteristic of the plasma membrane allows it to act as a barrier to polar molecules?

Two-dimensional structure

High protein content

Hydrophilic nature

Hydrophobic core (correct)

What is the typical electrical charge inside a cell?

Electronegative Signup and view all the answers

Which model describes the dynamic nature of the plasma membrane?

Fluid mosaic model Signup and view all the answers

How do lipid molecules behave within the plasma membrane?

Diffuse rapidly through the membrane plane Signup and view all the answers

What type of membrane proteins do NOT interact with the hydrophobic core of membranes?

Peripheral membrane proteins Signup and view all the answers

What term describes the net rate of diffusion of a substance through the membrane?

Membrane permeability Signup and view all the answers

Which factor does NOT affect membrane permeability?

Vesicle density Signup and view all the answers

What is the primary energy source for active transport mechanisms?

ATP Signup and view all the answers

What is a characteristic of uniporters in active transport?

Transport only one solute at a time Signup and view all the answers

Which statement about the Na+/K+ ATPase is correct?

It directly uses ATP to move ions Signup and view all the answers

What is the role of protein channels in membrane transport?

Increases transport rate with greater channel density Signup and view all the answers

Which type of transport uses stored electrochemical gradient energy?

Secondary active transport Signup and view all the answers

What is the primary function of exocytosis?

Secretion of substances to the extracellular environment Signup and view all the answers

What characteristic is associated with competitive inhibitors in active transport?

They bind to the transporter but do not activate it Signup and view all the answers

What does membrane potential refer to?

The electrical charge difference across the cell membrane Signup and view all the answers

What maintains the balance of ions across the membrane?

Active pumps Signup and view all the answers

Which is NOT a type of ion channel mentioned?

Temperature-gated Signup and view all the answers

What is the equilibrium potential of Sodium (Na+) in extracellular fluid?

+55 mV Signup and view all the answers

What effect does a small change in ion concentration have on membrane potential?

Induces large changes Signup and view all the answers

Which ion has the highest extracellular concentration in skeletal muscle fibers?

Sodium (Na+) Signup and view all the answers

What does a resting membrane potential indicate?

Electrical charge separation across a membrane Signup and view all the answers

Which ion is typically more concentrated intracellularly compared to extracellularly in mammalian neurons?

Potassium (K+) Signup and view all the answers

Which type of channel opens or closes in response to binding with a ligand?

Ligand-gated Signup and view all the answers

What is the equilibrium potential of Potassium (K+) in a squid neuron?

-75 mV Signup and view all the answers

What is the Nernst equation used to calculate?

Equilibrium potential for ions Signup and view all the answers

At what voltage is sodium in equilibrium in a typical neuron, given the concentrations stated?

+67 mV Signup and view all the answers

What is the resting membrane potential (RMP) of a skeletal muscle cell?

-65 mV Signup and view all the answers

What does hyperpolarization refer to in terms of membrane potential?

The cell becoming more negative Signup and view all the answers

Which of the following is NOT a component of the Nernst equation?

Resting potential (RMP) Signup and view all the answers

What does ENa represent when discussing sodium ions?

The reversal potential for sodium Signup and view all the answers

How does a positive voltage inside the cell affect Na+ ions?

Promotes influx into the cell Signup and view all the answers

The parameters PK, PNa, and PCl in the equation for EREV represent what concept?

Cell permeability to respective ions Signup and view all the answers

What is the significance of the ratio of lipids to proteins in plasma membranes?

It affects the fluidity and functionality of the membrane. Signup and view all the answers

What characteristic of integral membrane proteins differentiates them from peripheral membrane proteins?

Integral proteins possess hydrophobic regions that span the membrane. Signup and view all the answers

How does the fluid mosaic model describe the plasma membrane?

The membrane exhibits fluidity, with proteins and lipids moving within its layer. Signup and view all the answers

What functionality is primarily associated with receptors in plasma membranes?

Transducing signals from external stimuli. Signup and view all the answers

What is the electrical charge of the inside of a typical cell at rest?

-60 mV Signup and view all the answers

Which of the following statements is true regarding membrane permeability?

Increased temperature typically enhances membrane permeability. Signup and view all the answers

Which factor does NOT affect membrane permeability?

Concentration of intracellular sodium Signup and view all the answers

What is one of the roles of gated channels in the plasma membrane?

Opening or closing in response to specific stimuli. Signup and view all the answers

What process is involved in transporting substances from the interior to the exterior of a cell?

Exocytosis Signup and view all the answers

What component primarily contributes to the spontaneous formation of the plasma membrane?

Hydrophobic fatty acids. Signup and view all the answers

What characterizes active transport in cell membranes?

Requires energy sourced from ATP Signup and view all the answers

Which type of transporter only transports one solute at a time?

Uniporter Signup and view all the answers

What type of energy is used by primary active transport?

Chemical potential energy Signup and view all the answers

Which active transport mechanism uses the electrochemical gradient of another solute?

Secondary active transport Signup and view all the answers

Which statement about exocytosis is true?

It recycles endocytosis products to the membrane. Signup and view all the answers

What characterizes P-type ATP-driven pumps?

They phosphorylate themselves in the transport cycle. Signup and view all the answers

What occurs when the membrane potential reaches 0 mV?

The electrical charge is balanced on both sides of the membrane. Signup and view all the answers

Which ion has the highest equilibrium potential in a squid neuron?

Calcium (Ca2+) Signup and view all the answers

How does a small change in ion concentration affect membrane potential?

It induces large changes in membrane potential. Signup and view all the answers

What type of ion channel is opened by a mechanical stimulus?

Mechanically-gated channel Signup and view all the answers

What maintains the resting membrane potential in a cell?

Active transport mechanisms. Signup and view all the answers

What characterizes the balance of ions at equilibrium?

There is no net movement of ions. Signup and view all the answers

What happens during bioelectrical signaling through gated channels?

Gates can open or close based on specific signals. Signup and view all the answers

What does the Nernst equation calculate for a specific ion?

The equilibrium potential for that ion Signup and view all the answers

Which ion concentration is higher extracellularly in a mammalian neuron compared to intracellularly?

Sodium (Na+) Signup and view all the answers

At what voltage is sodium in equilibrium in a typical neuron when given the stated concentrations?

+67 mV Signup and view all the answers

What is the equilibrium potential of Chloride (Cl−) in a squid neuron?

-41 mV Signup and view all the answers

What is the effect of hyperpolarization on a neuron's membrane potential?

It decreases the neuron's excitability Signup and view all the answers

What primarily influences the opening of ligand-gated ion channels?

Binding of a specific ligand. Signup and view all the answers

What is the typical resting membrane potential (RMP) of a skeletal muscle cell?

-65 mV Signup and view all the answers

What does the EREV equation consider in determining the reversal potential?

Weighted mean of all ion effects Signup and view all the answers

What is the role of the charge on the atom (z) in the Nernst equation?

To represent the type of ion being measured Signup and view all the answers

What does a positive voltage inside the cell indicate for sodium ions?

Sodium ions will move into the cell Signup and view all the answers

What mathematically determines the Nernst equilibrium potential for sodium (Na+)?

$RT imes [Na]_o$ over $[Na]_i$ Signup and view all the answers

Study Notes

Plasma Membranes

Forms sheet-like structures that are 2 layers thick (60 – 100 Å)
Consists mainly of lipids and proteins with a 1:4 to 4:1 ratio
Has mitochondria and the plasma membrane itself
Some membranes contain carbohydrates
Hydrophilic (water-loving) and hydrophobic (water-fearing)
Forms a barrier to the flow of polar molecules
Has specific functions related to proteins:
- Channels
- Pumps
- Energy transducers
- Receptors
Inside of a cell is typically electronegative and approximately -60 mV
Considered a fluid structure with "two dimensional solutions of oriented proteins and lipids"
Lipid molecules diffuse rapidly through the membrane in the plane
Lipids and proteins do not
Fluid mosaic model dictates that membranes are not rigid
Membrane protein features include:
- Transport
- Attachment
- Signal transduction
Membrane proteins are larger than lipids
Some membrane proteins are immobile
Features of the plasma membrane include:
- Receptors
- Channels
- Cell identity
- Enzymes
- Gated channels
- CAMs (Cell Adhesion Molecules)
The structure of the plasma membrane is a thin film of lipid and protein molecules
The plasma membrane is considered a dynamic and fluid structure

Membrane Proteins

Perform 4 basic functions:
- Transport
- Enzyme activity
- Signal transduction
- Attachment/recognition
Integral membrane proteins are transmembrane proteins that are hydrophobic and non-polar
Hydrophilic, polar amino acids are located on the surface of integral membrane proteins
Peripheral membrane proteins do not interact with the hydrophobic core of membranes
Peripheral membrane proteins are held to the membrane surface
These can include:
- Cytoskeleton

Molecular Gradients & Membrane Permeability

Membrane permeability (P) is the net rate of diffusion of a given substance through each unit area of the membrane for a unit concentration difference on either side.
Factors affecting membrane permeability include:
- Membrane thickness
- Lipid solubility
- Number of protein channels
- Temperature
- Molecular weight of diffusing substance

### Exocytosis

Responsible for:
- Transporting membrane components
- Recycling endocytosis products
- Secretion:
  - Moving substances from the interior to the exterior of a cell
  - Examples:
    - White blood cells
    - Neurons
    - Mucus

Active Transport

Refers to moving ions uphill
Requires energy which can be from:
- Metabolic (ATP)
- Ion gradient
Resembles enzyme-substrate interactions
Some active transport transporters ARE enzymes
Characteristics of active transport include:
- Substrate
- Binding site on transporter
- Specific affinity
- Presence of competitive and non-competitive inhibitors

Types of Transporters

Uniporter: Transports only 1 solute (molecule or ion)
Symporter (co-transporter): Transport of 1 solute COUPLED to the transport of a SECOND solute.
Antiporter (exchanger): Transport of 1 solute COUPLED to the transport of a SECOND solute.

Primary Active Transport

Uses stored chemical energy.
ATP is directly used to move ions.
Example: Na+/K+ ATPase

Secondary Active Transport

Uses stored chemical energy.
Harnesses stored electrochemical gradient energy.

ATP-Driven "Pumps"

P-type pumps:
- Phosphorylate themselves during the cycle
- Ion pumps
- Spend ATP during the cycle
- Example: SERCA
F-type pumps:
- Turbine-like proteins.
- Found in:
  - Bacteria (plasma membrane)
  - Mitochondria (inner membrane)
- Produce ATP

Cell Membrane

Membrane potential is the electrical energy separation across the cell membrane.
The membrane potential can be used to do work such as moving ions across the membrane.
A membrane potential of 0 mV indicates an equal amount of electrical charge on both sides of the membrane.
Equilibrium is a combination of electrical and concentration gradients.
Equilibrium suggests an even balance of ions with no NET movement.
Key points for membrane potential:
- A small change in ion concentration can induce large changes in the membrane potential.
- The difference in electrical charges is close to the membrane.
- Active pumps maintain the balance of ions.

Bioelectrical Signaling

Bioelectrical signals are produced via gated channels through facilitated transport.
Proteins in the membrane contain gates.
Types of ion channels:
- Voltage-gated: The electrical environment determines the opening or closing of the gate.
- Ligand-gated: A ligand (molecule) binds to the ion channel which opens or closes the gate.
- Mechanically-gated: Requires application of a "stretch" to open or close the gate; this is often found in stretch receptors.

Ion Distribution

Na⁺: Extracellular concentration is 145 mM, intracellular concentration 12 mM, equilibrium potential +67 mV
K⁺: Extracellular concentration is 4 mM, intracellular concentration 155 mM, equilibrium potential -98 mV
Ca²⁺: Extracellular concentration is 1.5 mM, intracellular concentration 100 nM, equilibrium potential +129 mV
Cl⁻: Extracellular concentration is 123 mM, intracellular concentration 4.2 mM, equilibrium potential -90 mV

Resting Membrane Potential

The electrical charge separation across a membrane.
Can be found in both neurons and muscle cells.
Can vary from -80 mV to -60 mV depending on the cell.
Represents the difference in charge between the cytosol and extracellular fluid.
Depolarization: The cell is no longer polarized.
Repolarization: Returning to the resting membrane potential after depolarization; this often involves K⁺ leaving the cell.
Hyperpolarization: When the membrane potential is more negative than the resting membrane potential.
There are two types of biological signals:
- Graded potentials
- Action potentials

The Nernst Equation

An equation used to calculate the equilibrium potential of a given ion.
The Nernst equation was developed by Walther Hermann Nernst:
- June 25, 1864 to November 18, 1941
- Won the Nobel Prize in Chemistry in 1920 for his work in thermochemistry.
Equation:
- EN = RT/zF ln [S]₂/[S]₁
  - R = constant (8.3145 J·mol⁻¹·K⁻¹)
  - Z = charge on the atom, S (valence)
  - F = Faraday’s constant (9.6485 x 10⁴ C·mol⁻¹)
  - EN = voltage difference across a membrane to hold that ion in equilibrium.
  - S₂ = concentration of the ion outside the cell
  - S₁ = concentration of the ion inside the cell

Nernst Equation - Example

Example - Na⁺:
- ENa⁺ = RT/F ln [Na⁺]o/[Na⁺]i
  - o = outside the cell
  - i = inside the cell
  - RT/F = 26.73 mV (at 37°C)
  - [Na⁺]o = 145 mM
  - [Na⁺]i = 12 mM
- Calculate ENa⁺

Nernst Equilibrium

ENa⁺ = +67 mV
EK⁺ = -98 mV
This means that the Na⁺ equilibrium requires a voltage difference of +67 mV on the inside of the cell to hold the Na⁺ concentration at 145 mM outside and 12 mM inside.

Key Concepts & Nernst Equilibrium

Opposites attract, likes repel (polarity)
If the inside of the cell is positive, what is the effect on Na⁺?
If the inside of the cell is negative, what is the effect on K⁺?
What exists for a muscle cell?

Resting Membrane Potential - Muscle Cells

In skeletal muscle cells, the resting membrane potential is -65 mV.

Goldman-Hodgkin-Katz equation

This is a method to calculate the reversal potential for a membrane (ER) in a situation where there is more than one permeable ion.
Equation:
- EREV = RT/F ln (PK⁺[K⁺]o + PNa⁺[Na⁺]o + PCl⁻[Cl⁻]i) / (PK⁺[K⁺]i + PNa⁺[Na⁺]i + PCl⁻[Cl⁻]o)
  - EREV = reversal potential (zero current potential).
  - P = permeability of the cell membrane for that ion.
EREV can be used to approximate the resting membrane potential.
The ratio of K⁺ to Na⁺ permeability is approximately 0.086 in a sodium channel.
The ratio of H⁺ to Na⁺ permeability is approximately 252 in a sodium channel.

Plasma Membranes

Forms sheet-like structures, typically two layers thick (60 – 100 Å)
Composed mainly of lipids and proteins, with a ratio of 1:4 to 4:1
Exhibits hydrophilic and hydrophobic properties, creating a barrier to the flow of polar molecules
Features protein-function specificity: channels, pumps, energy transducers, and receptors
Possesses a polarized structure, with the inside of a cell typically having a negative charge (approximately -60 mV)
Exhibits fluidity due to the rapid diffusion of lipid molecules through the membrane in the plane
Adheres to the Fluid Mosaic Model, suggesting its dynamic nature and the presence of mobile membrane proteins

Membrane Proteins

Perform four basic functions: transport, enzyme activity, signal transduction, and attachment/recognition
Integral membrane proteins are transmembrane and consist of both hydrophobic and hydrophilic amino acids
Peripheral membrane proteins are associated with the membrane surface and do not interact with the hydrophobic core

Membrane permeability (P)

Indicates the net rate of diffusion of a substance through a unit area of the membrane with a unit concentration difference on either side
Influenced by factors such as membrane thickness, lipid solubility, the number of protein channels, temperature, and the molecular weight of the substance

Exocytosis

Functions in various cellular processes such as the transport of membrane components, the recycling of endocytosis products, and secretion
Involves the movement of materials from the cell interior to the exterior
Essential for various cell types including white blood cells, neurons, and mucus-producing cells

Active transport

Refers to the movement of ions against their concentration gradients, requiring energy from either metabolic sources (ATP) or ion gradients
Possesses characteristics similar to enzyme-substrate interactions, with some transporters functioning as enzymes

Active transport - Types of Transporters

Uniporter: Transports a single solute.
Symporter (co-transporter): Transports one solute coupled with the transport of another solute.
Antiporter (exchanger): Transports one solute coupled with the transport of another solute.

Active transport - Primary Active Transport

Directly utilizes chemical energy, primarily ATP, to move ions
Na+/K+ ATPase is a classic example of a primary active transporter

Active transport - Secondary Active Transport

Harnesses stored electrochemical gradient energy

ATP-driven "pumps"

P-type pumps: Phosphorylate themselves during their cycle and are involved in ion transport, representing primary active transport. An example is the SERCA pump (SarcoEndoplasmic Reticulum Ca++ ATPase).
F-type pumps: Turbine-like proteins involved in oxidative phosphorylation found in bacteria (plasma membrane) and mitochondria (inner membrane).

Cell membranes - Membrane potential

Represents the electrical energy separation across the cell membrane, creating the potential to do physical work
A membrane potential of 0 mV indicates an equal amount of electrical charge on both sides of the membrane
Equilibrium involves a balance of electrical and concentration gradients with no net movement of ions
Key points:
- Small changes in ion concentration can induce large changes in membrane potential.
- The difference in electrical charges are localized near the membrane.
- Active "pumps" maintain the balance of ions.

Bioelectrical Signaling - Mechanism

Relies on gated channels, facilitating transport and containing gates that open or close, affecting ion movement
Three types of ion channels:
- Voltage-gated: Influenced by the electrical environment
- Ligand-gated: Binding of a ligand (molecule) to the ion channel opens or closes its gate
- Mechanically-gated: Require a mechanical stimulus, often associated with "stretch" receptors

Ion Distribution

Ion concentrations inside and outside of skeletal muscle fibers vary significantly, with differences in concentration gradients driving the movement of ions across the membrane

Nernst Equation

Measures the equilibrium potential for an ion
Example:
- ENa = +67 mV
- EK = -98 mV

These values indicate that to hold sodium in equilibrium concentrations (145 mM outside and 12 mM inside), a voltage difference of +67 mV on the INSIDE of the cell is needed.

Resting Membrane Potential (RMP)

Represents the charge separation across the membrane in a cell, typically -80 to -60 mV
Involves a difference in concentration of ions between the cytosol and extracellular fluid
Depolarization occurs when the cell becomes less polarized, usually caused by an influx of positive ions
Repolarization refers to the process of restoring the cell's resting membrane potential
Hyperpolarization signifies an increase in the negative charge inside the cell
Two primary types of biological signals are generated:

Nernst Equation (Expanded)

Formula:
- EN = (RT/zF) ln ([S]2/[S]1)
- R = constant (8.3145 J·mol-1·K-1)
- Z = charge on the ion, S (valence).
- F = Faraday’s constant (9.6485 x 104 C·mol-1)
- EN = voltage difference across a membrane to hold that ion in equilibrium

Nernst Equation - Example: Na +

Formula:
- ENa = (RT/F) ln ([Na]o/[Na]i)
- o = outside cell
- i = inside cell
- RT/F = 26.73 mV.(at 37 deg C)
- [Na]o = 145 mM
- [Na]i = 12 mM

Nernst Equilibrium

ENa = +67 mV.
EK = -98 mV.
These values indicate that to hold sodium in equilibrium concentrations, a voltage difference of +67 mV on the INSIDE of the cell is required.

Resting Membrane Potential (RMP) - Skeletal muscle cell

The RMP in a skeletal muscle cell is typically -65 mV

Goldman-Hodgkin-Katz (GHK) Equation

GHK equation helps calculate the resting membrane potential (EREV - reversal potential):
Erev = (RT/F) ln((PK[K]o + PNa[Na]o + PCl[Cl]i) / (PK[K]i + PNa[Na]i + PCl[Cl]o))
EREV = reversal potential (zero current potential)
P = permeability of the cell to that ion
PK+ / PNa+ = 0.086 (sodium channel)
PH+ / PNa+ = 252 (sodium channel)

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Questions and Answers

What primarily composes the plasma membrane?

Which of the following is NOT one of the basic functions of membrane proteins?

What characteristic of the plasma membrane allows it to act as a barrier to polar molecules?

What is the typical electrical charge inside a cell?

Which model describes the dynamic nature of the plasma membrane?

How do lipid molecules behave within the plasma membrane?

What type of membrane proteins do NOT interact with the hydrophobic core of membranes?

What term describes the net rate of diffusion of a substance through the membrane?

Which factor does NOT affect membrane permeability?

What is the primary energy source for active transport mechanisms?

What is a characteristic of uniporters in active transport?

Which statement about the Na+/K+ ATPase is correct?

What is the role of protein channels in membrane transport?

Which type of transport uses stored electrochemical gradient energy?

What is the primary function of exocytosis?

What characteristic is associated with competitive inhibitors in active transport?

What does membrane potential refer to?

What maintains the balance of ions across the membrane?

Which is NOT a type of ion channel mentioned?

What is the equilibrium potential of Sodium (Na+) in extracellular fluid?

What effect does a small change in ion concentration have on membrane potential?

Which ion has the highest extracellular concentration in skeletal muscle fibers?

What does a resting membrane potential indicate?

Which ion is typically more concentrated intracellularly compared to extracellularly in mammalian neurons?

Which type of channel opens or closes in response to binding with a ligand?

What is the equilibrium potential of Potassium (K+) in a squid neuron?

What is the Nernst equation used to calculate?

At what voltage is sodium in equilibrium in a typical neuron, given the concentrations stated?

What is the resting membrane potential (RMP) of a skeletal muscle cell?

What does hyperpolarization refer to in terms of membrane potential?

Which of the following is NOT a component of the Nernst equation?

What does ENa represent when discussing sodium ions?

How does a positive voltage inside the cell affect Na+ ions?

The parameters PK, PNa, and PCl in the equation for EREV represent what concept?

What is the significance of the ratio of lipids to proteins in plasma membranes?

What characteristic of integral membrane proteins differentiates them from peripheral membrane proteins?

How does the fluid mosaic model describe the plasma membrane?

What functionality is primarily associated with receptors in plasma membranes?

What is the electrical charge of the inside of a typical cell at rest?

Which of the following statements is true regarding membrane permeability?

Which factor does NOT affect membrane permeability?

What is one of the roles of gated channels in the plasma membrane?

What process is involved in transporting substances from the interior to the exterior of a cell?

What component primarily contributes to the spontaneous formation of the plasma membrane?

What characterizes active transport in cell membranes?

Which type of transporter only transports one solute at a time?

What type of energy is used by primary active transport?

Which active transport mechanism uses the electrochemical gradient of another solute?

Which statement about exocytosis is true?

What characterizes P-type ATP-driven pumps?

What occurs when the membrane potential reaches 0 mV?

Which ion has the highest equilibrium potential in a squid neuron?

How does a small change in ion concentration affect membrane potential?

What type of ion channel is opened by a mechanical stimulus?

What maintains the resting membrane potential in a cell?

What characterizes the balance of ions at equilibrium?

What happens during bioelectrical signaling through gated channels?

What does the Nernst equation calculate for a specific ion?

Which ion concentration is higher extracellularly in a mammalian neuron compared to intracellularly?

At what voltage is sodium in equilibrium in a typical neuron when given the stated concentrations?

What is the equilibrium potential of Chloride (Cl−) in a squid neuron?

What is the effect of hyperpolarization on a neuron's membrane potential?

What primarily influences the opening of ligand-gated ion channels?

What is the typical resting membrane potential (RMP) of a skeletal muscle cell?

What does the EREV equation consider in determining the reversal potential?

What is the role of the charge on the atom (z) in the Nernst equation?

What does a positive voltage inside the cell indicate for sodium ions?

What mathematically determines the Nernst equilibrium potential for sodium (Na+)?

Study Notes

Plasma Membranes

Membrane Proteins

Molecular Gradients & Membrane Permeability

Active Transport

Types of Transporters

Primary Active Transport

Secondary Active Transport