What are examples of impermeant molecules?
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Ions, Glucose, Amino acids
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What are examples of impermeant molecules?
Ions, Glucose, Amino acids
What does the α subunit bind in primary active transport?
ATP, 3 Na+, and 2 K+
What is the main factor that affects the rate of diffusion for lipid-soluble molecules?
Lipid solubility.
What is the Nernst equation?
EMP (mV) = ±61 log (Ci / Co)
What is the principle of sodium channel operation?
The channel conducts 'all or none,' meaning it is either open or closed.
What is primary active transport?
Molecules are 'pumped' against an electrochemical gradient at the expense of energy (ATP).
What type of energy is used in primary active transport?
Direct use of energy (ATP).
What is the role of carrier proteins in the membrane?
To transport specific molecules across the membrane.
What do membrane proteins provide to a membrane?
Specificity and function.
How do water-soluble molecules cross the cell membrane?
Water-soluble molecules cross the cell membrane via channels or other transport proteins.
What would happen if a membrane were permeable only to K+?
K+ would diffuse down its concentration gradient until the electrical potential across the membrane countered diffusion.
What ions are conducted through the sodium channel?
Na+ (sodium ions)
Why can a membrane channel be permeable to potassium but not to sodium, even though the potassium molecule is larger?
Carbonyl oxygens in the selectivity channel strip water molecules from the potassium molecule but not from the sodium molecule, allowing only potassium ions to permeate.
What are examples of permeant molecules?
Urea, Glycerol
What type of transport is described as electrogenic but contributes less than 10% to the membrane potential?
Primary active transport
What is the function of antiporters in secondary active transport?
Antiporters transport substances in the opposite direction of a 'driver' ion like Na+.
What type of enzyme is Na+-K+ ATPase?
An antiporter enzyme located on the plasma membrane of all animal cells.
What does the Goldman-Hodgkin-Katz equation describe about the resting membrane potential?
The resting membrane potential is closest to the equilibrium potential for the ion with the highest permeability.
What is another name for facilitated diffusion?
Carrier-mediated diffusion.
What ions does Na+-K+ ATPase pump and in which direction?
It pumps sodium ions out of cells and pumps potassium ions into cells against electrochemical gradients.
What limits the rate of diffusion in facilitated diffusion?
The Vmax of the carrier protein.
What critical role does Na+-K+ ATPase play in cells?
It regulates osmotic balance by maintaining Na+ and K+ balance.
What drives secondary active transport?
The energy stored in the electrochemical gradient of another molecule (usually Na+).
What role do carbonyl oxygens play in the selectivity of the potassium channel?
They strip water molecules from the potassium molecule, enabling it to permeate through the channel.
What characteristic do permeant molecules have?
Relatively high lipid solubility
How do lipid-soluble molecules move across cell membranes?
Lipid-soluble molecules move readily across cell membranes, and the rate of diffusion depends on lipid solubility.
What is the role of ion channels in the membrane?
To allow specific ions to pass through the membrane.
What determines transport through ungated channels?
Size, shape, and charge of the channel and ion.
What are the two types of gated channels?
Voltage-gated channels and chemical-gated channels.
When will negatively charged molecules stop entering the cell?
When the intracellular electrical potential is equal in magnitude but opposite in direction to the concentration force.
What is osmosis?
Osmosis is the net diffusion of water from pure water toward a water/salt solution.
What is the Nernst potential (equilibrium potential)?
The theoretical intracellular electrical potential that would be equal in magnitude but opposite in direction to the concentration force.
What technique is used to study sodium channel operation?
Patch Clamp
In which direction does water move during osmosis?
Water moves down its concentration gradient, from pure water toward a water/salt solution.
What type of energy is used in secondary active transport?
Indirect use of energy.
What is the function of Ca2+ ATPase?
It maintains a low cytosolic Ca2+ concentration.
What effect do permeant particles like urea and glycerol have on cell volume?
They cause only transient changes in cell volume.
What is the structure of mobile ion carriers?
They have a hydrophobic exterior and a hydrophilic interior.
What ions are involved in simple diffusion through leak channels as shown in the image?
Na+ (Sodium) and K+ (Potassium).
What is the equilibrium potential for sodium (ENa)?
+61 mV
What triggers the opening of voltage-gated sodium channels?
The membrane potential becoming less negative and reaching the threshold.
How does the inhibition of Na+-K+ ATPase by glycosides affect the Na+ electrochemical gradient?
It decreases the Na+ electrochemical gradient.
What are the given concentrations of Na_o and Na_i in the example?
Na_o = 142 mM and Na_i = 14 mM
What is one of the factors that affect the net rate of diffusion?
Concentration difference (C_o - C_i).
What is the general rule for the conduction velocity of myelinated fibers?
Fiber diameter (in mm) x 4.5 = velocity in m/s.
What is the function of the selectivity filter in K+ channels?
The selectivity filter ensures that only K+ ions can pass through the channel, maintaining the membrane's permeability to K+.
What do most synapses involve?
Transmitter substances.
What are the three types of stimuli that can cause ion channels to 'gate'?
Changes in membrane potential (voltage-gated channels), occupation of receptor (ligand-gated or receptor-operated channels), and mechanical forces (mechanosensitive channels).
What is the state of the membrane during rest in the context of action potential propagation?
The membrane is polarized with a negative charge inside and a positive charge outside.
How does the action potential propagate along the membrane?
The local current spreads, opening more Na+ channels and depolarizing adjacent sections of the membrane.
What happens to ATP during the active transport of Na+ and K+?
ATP is converted to ADP (Adenosine Diphosphate).
What is the net driving force on any ion?
The net driving force on any ion is the difference in millivolts between the membrane potential (Vm) and the equilibrium potential for that ion (Eion).
What is excitability in the context of membrane potentials?
Excitability refers to the ability of a cell to respond to stimuli and generate action potentials.
What is the permeability coefficient of water in an artificial lipid bilayer?
10^-2 cm/sec
What is temporal summation?
Temporal summation is the successive epsp's from the same synapse.
What is diffusion in the context of cell membrane transport?
Diffusion occurs down a concentration gradient through the lipid bilayer or involves a protein 'channel' or 'carrier' and requires no additional energy.
What is the formula for the Potassium Nernst Potential (E_K)?
E_K = -61 x log(K_i / K_o)
What is a ligand?
A ligand is any substance that binds to a receptor.
What happens when multiple stimuli are applied to a neuron?
The responses summate, resulting in a summed response.
What is an action potential?
A regenerating depolarization of membrane potential that propagates along an excitable membrane.
What happens when Na+-K+ ATPase is inhibited by ouabain?
Cells swell and burst.
Where is H+ ATPase found?
In parietal cells of gastric glands (HCl secretion) and intercalated cells of renal tubules (controls blood pH).
What is the relationship between membrane permeability and the time course of a change in cell volume?
Higher membrane permeability results in more transient changes in cell volume.
Why is the lipid bilayer a barrier to water-soluble substances?
Because the lipid bilayer is hydrophobic, preventing water-soluble substances from passing through easily.
What is one benefit of saltatory conduction in terms of signal transmission?
Increased velocity.
What is required to elicit an action potential during the relative refractory period?
A greater than normal stimulus.
What is the consequence of increased intracellular Ca++ levels in cardiac cells?
Increased intracellular Ca++ levels enhance cardiac contractility.
What role does potassium (K+) play in the transcellular transport of glucose and amino acids (AA)?
Potassium (K+) is transported into the epithelial cell from the extracellular fluid to maintain the sodium-potassium balance.
What limits the maximum rate of facilitated diffusion?
The maximum rate of facilitated diffusion is limited by Vmax.
How does the rate of diffusion change with increasing concentration gradient in facilitated diffusion?
In facilitated diffusion, the rate of diffusion increases with the concentration gradient but eventually reaches a maximum rate (Vmax).
How do cardiac glycosides increase cardiac contractility?
By increasing intracellular Ca2+ concentration.
What does Syndrome of Inappropriate ADH Secretion (SIADH) lead to?
Water retention, hyponatremia, and excretion of concentrated urine.
What happens to the net diffusion rate if the concentration difference (C_o - C_i) increases?
The net diffusion rate increases.
What is the resting membrane potential for astrocytes?
-80 to -90 mV
What is the role of sphingomyelin in myelination?
It decreases membrane capacitance and ion flow 5,000-fold.
What is the name of the interruptions in the myelin sheath?
Node of Ranvier.
What is the sequence of events in the propagation of an action potential?
Rest, local depolarization (stimulation), and propagation (current spread).
What type of disease is Multiple Sclerosis (MS)?
An immune-mediated inflammatory demyelinating disease of the CNS.
What is an inhibitory post-synaptic potential (IPSP)?
An IPSP is a hyperpolarization of the post-synaptic cell that depresses excitability.
What is secondary active transport?
It involves the use of an electrochemical gradient (usually for sodium).
Which substances have a permeability coefficient of 10^-4 cm/sec in an artificial lipid bilayer?
Urea
How does the permeability of water compare to that of glucose in an artificial lipid bilayer?
Water has a much higher permeability (10^-2 cm/sec) compared to glucose (10^-8 cm/sec).
What happens when no action potentials reach the threshold in synaptic responses?
No action potentials are generated.
What is active transport in the context of cell membrane transport?
Active transport occurs against a concentration gradient, involves a protein 'carrier', and requires energy (ATP).
How are receptors often named and classified?
Receptors are often named and classified largely by reference to the ligand.
Do local potentials induce refractoriness?
No, they do not induce refractoriness.
How is information encoded in action potentials?
The frequency of APs encodes information, while the amplitude of AP is constant.
Is hyperpolarization always seen after an action potential?
No, it is not always seen.
Does adding more carriers affect the Vmax in facilitated diffusion?
No, adding more carriers does not affect Vmax.
What is membrane potential (V_m)?
A charge difference across the membrane.
What is the Na+ equilibrium potential (ENa)?
The electrical potential that counters net diffusion of Na+.
Which has higher membrane permeability, urea or glycerol?
Urea has higher membrane permeability than glycerol.
What is the function of channel formers like gramicidin A?
They form ion-permeable pores in the cell membrane.
What is the absolute refractory period?
A period during which an action potential (AP) is not possible due to voltage inactivation of Na channels.
What is the typical range for the resting membrane potential (Vm)?
-90 to -70 mV
What type of channels do Na+ and K+ use for simple diffusion?
Leak channels.
What enzyme do glycosides (e.g., digoxin) inhibit?
Na+-K+ ATPase.
What happens to the voltage-gated sodium channel when the membrane potential reaches the threshold?
The gate opens, allowing sodium ions to flow into the cell.
How are action potentials initiated?
By depolarization, and they can be induced in nerve and muscle by extrinsic (percutaneous) stimulation.
What would the membrane potential (Vm) be if the membrane were permeable only to Na+?
+61 mV
What is the general rule for the conduction velocity of unmyelinated fibers?
Square root of fiber diameter = velocity in m/s.
How does the Na+-K+ pump contribute to ion balance in the cell?
The Na+-K+ pump actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, using ATP.
What are the properties of ion channels?
They have conducting states and non-conducting states, and the transition between states is called 'gating'.
What type of ion channels initiate action potentials?
Ligand-gated or receptor-operated channels (ROCs).
How many potassium ions are pumped into the cell by the sodium-potassium pump?
Two potassium ions (2 K+).
Which way do the ions diffuse when permeability increases?
Ions diffuse in the direction of their electrochemical gradient.
Does an action potential change in magnitude as it propagates?
No, it is propagated unchanged in magnitude.
What happens to the post-synaptic cell during hyperpolarization?
The post-synaptic cell is hyperpolarized, which depresses excitability and is inhibitory.
What results from increases in membrane permeability?
EPSPs (excitatory post-synaptic potentials) and IPSPs (inhibitory post-synaptic potentials) result from increases in membrane permeability.
Give an example of a symporter in secondary active transport.
Na+ and glucose (Na+ gluc).
What is spatial summation?
Spatial summation is the overlapping of epsp's from distant synapses.
Does diffusion require additional energy?
No, diffusion does not require additional energy.
Which substances are considered ligands?
Acetylcholine, Norepinephrine, Epinephrine, Serotonin (5-HT), Dopamine, Glycine, Glutamate, Adenosine.
What is the membrane potential approaching during the upstroke of an action potential?
The membrane potential approaches E_Na.
What happens to Na+ permeability during the downstroke of an action potential?
Na+ permeability decreases due to the inactivation of Na+ channels.
Why are these potentials called 'electrotonic' or 'local' potentials?
Because the effect is 'local' to the stimulus.
What determines the permeability of the axon membrane to ions?
The number of open channels.
What is the membrane potential during the deactivation of the K+ channel?
-90 mV.
How much energy does Na+-K+ ATPase require in a typical cell and in neurons?
About 1/5 of a typical cell’s energy and up to 2/3 of a neuron’s energy.
How does passive diffusion of potassium (K+) and sodium (Na+) contribute to membrane potential?
Passive diffusion of K+ and Na+ leads to a charge difference across the membrane, contributing to the development of a negative membrane potential.
What is the function of H+ ATPase?
It concentrates H+ ions up to 1 million-fold.
What are ionophores?
Lipid-soluble molecules (usually synthesized by microorganisms) that transport inorganic ions across the lipid bilayer and mediate passive transport.
Where do action potentials (APs) occur during saltatory conduction?
At the nodes (Nodes of Ranvier).
What is the relative refractory period?
A period during which a greater than normal stimulus is required to elicit an action potential (AP).
In which direction does K+ move during simple diffusion through leak channels?
From inside to outside the cell.
Why is the resting membrane potential (Vm) so close to the equilibrium potential for potassium (EK)?
The membrane is far more permeable to K+ than Na+.
What is the formula for the Sodium Nernst Potential (E_Na)?
E_Na = -61 x log(Na_i/Na_o)
What is the result of decreased activity of Na+/Ca2+ antiporters due to glycosides inhibiting Na+-K+ ATPase?
Increased intracellular Ca2+ concentration.
What condition is characterized by decreased ADH secretion or responsiveness to ADH?
Central or nephrogenic diabetes insipidus.
What does the symbol 'D' represent in the context of diffusion?
'D' represents the diffusion coefficient.
What is the ratio of Na+ to K+ ions transported by the Na+-K+ pump?
The Na+-K+ pump transports 3 Na+ ions out of the cell and 2 K+ ions into the cell.
What are the two types of synapses?
Excitatory and Inhibitory.
What is the function of myelin?
Myelin insulates axons to increase the speed of electrical transmission.
What is the resting membrane potential for photoreceptor cells in the light?
-70 mV
What is the net driving force on K+ ions?
20 mV
Where is sodium (Na+) pumped in the sodium-potassium pump process?
Sodium (Na+) is pumped out of the cell.
How does a subthreshold potential change propagate?
It is not propagated but decremental with distance.
What is depolarization?
Depolarization is the process of the membrane potential becoming less negative (moving towards 0 mV).
What is the threshold in the context of action potential generation?
The threshold is the membrane potential level that must be reached for an action potential to be generated.
What is the role of Na+ in secondary active transport?
Na+ acts as a 'driver' ion in symporters, facilitating the transport of other substances.
What is the general trend of permeability coefficients for substances in an artificial lipid bilayer?
Permeability decreases from water to ions like Cl-, K+, and Na+.
What is the difference in conduction velocity between non-myelinated and myelinated axons?
Myelinated axons conduct impulses faster than non-myelinated axons.
What is required for active transport to occur?
Active transport requires energy (ATP).
What would the membrane potential (Vm) be if the membrane were permeable only to K+?
The membrane potential (Vm) would be -94 mV
What are 'physiological' ligands?
Physiological ligands are ligands provided by the body, such as Acetylcholine and Norepinephrine.
What happens to K+ permeability during the upstroke of an action potential?
K+ permeability increases due to the opening of K+ channels.
What occurs when subthreshold stimuli are applied to a neuron?
The membrane potential does not reach the threshold voltage, and local currents flow but the membrane potential slowly returns to the resting value.
What happens to the transported molecule during facilitated diffusion?
It binds to the carrier protein, undergoes a conformational change, and is then released.
Which ions are primarily involved in creating the membrane potential?
Potassium (K+) and Sodium (Na+).
What would happen if a membrane were permeable to only Na+?
Na+ would diffuse down its concentration gradient until the potential across the membrane countered diffusion.
What are the two types of ionophores?
Mobile ion carriers and channel formers.
Name two gases that can diffuse through the lipid bilayer.
CO2 and O2.
What limits the maximum frequency of action potentials (APs)?
Refractory periods.
How do cardiac glycosides like Digoxin increase cardiac contractility?
Cardiac glycosides increase cardiac contractility by inhibiting the Na+/K+ ATPase pump, leading to an increase in intracellular Na+ levels. This, in turn, reduces the activity of the Na+/Ca++ exchanger, resulting in increased intracellular Ca++ levels, which enhances cardiac contractility.
What is the process called when Na+ and K+ move through leak channels?
Simple diffusion.
What is the role of the voltage sensor in a voltage-gated sodium channel?
It detects changes in membrane potential and triggers the opening of the channel.
How does the rate of diffusion change with increasing concentration gradient in simple diffusion?
In simple diffusion, the rate of diffusion increases linearly with the concentration gradient.
What is the calculated Sodium Nernst Potential (E_Na) in the example?
+61 mV
What determines the conduction velocity of action potentials in nerve fibers?
The diameter of the fiber. Larger diameter fibers conduct faster than smaller ones.
Why is the cell membrane so permeable to K+?
Due to the presence of K+ 'leak' channels and the selectivity filter that allows K+ ions to pass through easily.
What is the resting membrane potential for skeletal muscle fibers?
-85 to -95 mV
What cells surround the nerve axon to form a myelin sheath?
Schwann cells.
What type of ion channels are involved in action potential propagation?
Voltage-gated channels.
What is the main function of the sodium-potassium pump?
To pump sodium (Na+) out of the cell and potassium (K+) into the cell.
What molecule provides the energy for the sodium-potassium pump to function?
ATP (Adenosine Triphosphate).
Can summation occur with action potentials?
No, summation is not possible.
What does overshoot mean in the context of membrane potential?
Overshoot refers to the membrane potential becoming positive, moving above 0 mV.
What does the lower record represent in synaptic responses?
The lower record is from the postsynaptic cell.
What is the primary visual difference between non-myelinated and myelinated axons in terms of impulse conduction?
Non-myelinated axons show continuous conduction, while myelinated axons show saltatory conduction.
What role do protein 'channels' or 'carriers' play in diffusion?
Protein 'channels' or 'carriers' facilitate the movement of substances through the cell membrane during diffusion.
Which receptors does nicotine stimulate?
Nicotine stimulates nicotinic (nACh) receptors.
What is the membrane potential approaching during the upstroke of an action potential?
The membrane potential approaches E_K.
What factors affect the speed of transmission of nerve cell action potentials?
The speed of transmission depends on fiber size and whether it is myelinated. Information of lesser importance is carried by slowly conducting unmyelinated fibers.
What is net diffusion?
Net diffusion is the difference between the magnitude of diffusion from side A to B and the magnitude of diffusion from side B to A.
What is the direction of potassium (K+) diffusion in relation to the cell membrane?
Potassium (K+) diffuses out of the cell.
What drives the diffusion of Na+ across the membrane?
The concentration gradient of Na+.
What substances does the lipid bilayer act as a barrier to?
Water and water-soluble substances such as ions, glucose, H2O, and urea.
How do channel formers compare to mobile ion carriers in terms of ion transport?
Channel formers transport 1000 times more ions per unit time than mobile ion carriers.
Why is an action potential not possible during the absolute refractory period?
Due to voltage inactivation of Na channels.
What is the equilibrium potential for potassium (EK)?
-94 mV
What is the direction of sodium (Na+) movement in the transcellular transport of glucose and amino acids (AA)?
Sodium (Na+) moves from the lumen into the epithelial cell and then into the extracellular fluid.
What is the effect of glycosides inhibiting Na+-K+ ATPase on intracellular Na+ concentration?
Increased intracellular Na+ concentration.
What happens to the activity of Na+/Ca2+ antiporters when Na+-K+ ATPase is inhibited by glycosides?
The activity of Na+/Ca2+ antiporters decreases.
What is Vmax in the context of facilitated diffusion?
Vmax is the maximum rate of facilitated diffusion.
How is the Sodium Nernst Potential (E_Na) calculated in the example?
E_Na = -61 log(14/142) = -61 log(0.1) = +61 mV
What happens when there is too much ADH in the body?
It leads to water retention, hyponatremia, and excretion of concentrated urine.
What is the point of communication between neurons?
Synapses.
What does the term 'gating' refer to in ion channels?
The transition between conducting and non-conducting states.
What initiates the propagation of an action potential?
Opening of Na+ channels generates local current that depolarizes adjacent membrane, opening more Na+ channels.
What happens during local depolarization in action potential propagation?
Na+ channels open, causing a local current that depolarizes the adjacent membrane.
How does an action potential respond to stimulus strength?
It is independent of stimulus strength (all or none).
What effect does increasing Na+ or K+ permeability (or extracellular concentration) have on Vm?
Increasing Na+ or K+ permeability (or extracellular concentration) affects the membrane potential (Vm) by altering the net driving force on the ions.
What is hyperpolarization?
Hyperpolarization is the process of the membrane potential becoming more negative than the resting potential.
What should you consider when thinking about which ions are involved in synaptic responses?
You need to consider the equilibrium potentials of the ions.
What does the upper record represent in synaptic responses?
The upper record is from the presynaptic cell.
How does myelination affect the conduction of nerve impulses?
Myelination increases the speed of nerve impulse conduction by allowing the impulse to jump between nodes of Ranvier.
How does active transport differ from diffusion?
Active transport occurs against a concentration gradient and requires energy (ATP), while diffusion occurs down a concentration gradient and does not require additional energy.
What is another name for the Potassium Nernst Potential?
The equilibrium potential
How are receptors often subdivided?
Receptors are often subdivided by reference to ligands, such as ACh into nicotinic (nACh) and muscarinic (mACh) receptors.
Where is Ca2+ ATPase present?
On the cell membrane and the sarcoplasmic reticulum in muscle fibers.
What determines the steady-state cell volume?
The concentration of impermeant particles in the extracellular fluid (e.g., Na+, K+, protein-).
Why do action potentials only occur at the nodes during saltatory conduction?
Because Na channels are concentrated at the nodes.
What is the effect of inhibiting the Na+/K+ ATPase pump on intracellular ion levels?
Inhibiting the Na+/K+ ATPase pump increases intracellular Na+ levels and reduces the activity of the Na+/Ca++ exchanger, leading to increased intracellular Ca++ levels.
What is the relationship between the rate of diffusion and the concentration gradient in simple diffusion?
The rate of diffusion is directly proportional to the concentration gradient (Co - Ci).
What is the role of the inactivation gate in a voltage-gated sodium channel?
It closes the channel after a certain period, stopping the flow of sodium ions.
What are some causes of hypernatremia (increased plasma Na+)?
Increased water loss, excessive sweat loss, central or nephrogenic diabetes insipidus (decreased ADH secretion or responsiveness to ADH).
How is net diffusion related to the concentration difference?
Net diffusion is proportional to the concentration difference (C_o - C_i).
In the context of diffusion, what do C_o and C_i represent?
C_o represents the concentration outside the membrane, and C_i represents the concentration inside the membrane.
What is the structure of ion channels?
Proteins that span the membrane and have a water-filled channel that runs through the protein.
What is an axo-dendritic synapse?
A synapse between the axon of one neuron and the dendrite of another.
What is the resting membrane potential for photoreceptor cells in the dark?
-40 mV
How many sodium ions are pumped out of the cell by the sodium-potassium pump?
Three sodium ions (3 Na+).
How is a subthreshold potential change related to stimulus strength?
It is proportional to stimulus strength (graded).
Can summation occur with subthreshold potential changes?
Yes, subthreshold potential changes exhibit summation.
Can IPSPs summate?
Yes, IPSPs can summate.
What do symporters do in secondary active transport?
They transport substances in the same direction as a 'driver' ion like Na+.
Why is the last epsp larger in the given synaptic response?
The last epsp is larger because it occurs before the previous epsp has fully decayed.
What are nodes of Ranvier?
Nodes of Ranvier are gaps in the myelin sheath along a myelinated axon where action potentials are regenerated.
What is the direction of movement for substances in active transport?
Substances move against a concentration gradient in active transport.
What does tonicity depend on?
Tonicity depends on the membrane and the solute.
What is the effect of 'local current flow' in a neuron?
It depolarizes adjacent regions of a neuron.
What is the direction of sodium (Na+) diffusion in relation to the cell membrane?
Sodium (Na+) diffuses into the cell.
What counters the diffusion of Na+ across the membrane?
The electrical potential across the membrane.
What characteristic of the lipid bilayer allows it to be a barrier to ions?
Its hydrophobic nature.
How does saltatory conduction contribute to energy efficiency in neurons?
It conserves energy.
In which direction does Na+ move during simple diffusion through leak channels?
From outside to inside the cell.
What is the concentration gradient of sodium (Na+) in the epithelial cell during the transcellular transport of glucose and amino acids (AA)?
The concentration of sodium (Na+) is high in the epithelial cell and low in both the lumen and extracellular fluid.
What is the function of the selectivity filter in a voltage-gated sodium channel?
It ensures that only sodium ions can pass through the channel.
What characterizes action potentials as all-or-none events?
They have a threshold voltage, usually 15 mV positive to the resting potential.
Do action potentials have constant amplitude?
Yes, action potentials do not summate; information is coded by frequency, not amplitude.
What are some causes of hyponatremia (decreased plasma Na+)?
Large water ingestion, Syndrome of Inappropriate ADH Secretion (SIADH).
What role do K+ 'leak' channels play in cell membrane permeability?
They allow K+ ions to move across the cell membrane, contributing to its high permeability to K+.
What is the resting membrane potential for smooth muscle fibers?
-50 to -60 mV
What is the resting membrane potential for neurons?
-60 to -70 mV
How often is the myelin sheath interrupted along the nerve axon?
Every 1-3 mm.
What type of ion channels are important for hearing?
Mechanosensitive channels.
What is the net driving force on Na+ ions?
135 mV
Where is potassium (K+) pumped in the sodium-potassium pump process?
Potassium (K+) is pumped into the cell.
What is repolarization?
Repolarization is the process of the membrane potential returning towards the resting potential after depolarization.
How are protein cotransporters classified?
They are classified as symporters or antiporters.
What is an excitatory postsynaptic potential (epsp)?
An epsp is an electrotonic response that decays with an exponential time course.
What is saltatory conduction?
Saltatory conduction is the process by which nerve impulses jump from one node of Ranvier to the next in myelinated axons.
What is the direction of movement for substances in diffusion?
Substances move down a concentration gradient in diffusion.
What is osmolarity a measure of?
Osmolarity is merely another measure of concentration.
What happens to Na+ permeability during the upstroke of an action potential?
Na+ permeability increases due to the opening of Na+ channels.
How are local potentials graded?
A bigger stimulus results in a bigger response.
What happens to depolarization when stimulation is restricted to a small area of the membrane?
Depolarization will be greatest at the point of stimulation and will fall exponentially with distance.
What does it mean for a membrane to be excitable?
It is capable of generating action potentials.
What initiates an action potential?
Depolarization.
What happens to K+ permeability during the downstroke of an action potential?
K+ permeability increases due to the opening of K+ channels.
What does it mean for an action potential to propagate?
It is conducted without decrement, meaning it is an 'active' membrane event.
What are ion channels usually selectively permeable to?
Specific ions.
What lines the sodium channels and helps pull the sodium ion away from its water shell?
Negatively charged amino acids.
What occurs after the hyperpolarization of the membrane following an action potential?
There is increased K+ conductance due to the delayed closure of K+ channels.
At what membrane potential does the Na+ channel activation occur?
+10 mV.
What ions do 'Ca channels' pass and why are they important?
Only Ca ions; they are important in synaptic transmission.
What are some cellular responses initiated by action potentials in non-nervous tissues?
Muscle contraction and secretion (e.g., epinephrine from chromaffin cells of the medulla).
What is the typical velocity of an action potential?
Approximately 60 m/s.
What happens to the membrane potential during the upstroke of an action potential?
The membrane potential rapidly depolarizes.
Why are unhydrated potassium ions unable to diffuse through the sodium channel?
Because they are too large.
What are the basic characteristics of an action potential?
All-or-none event (need to reach threshold), constant amplitude (do not summate), initiated by depolarization, involve changes in permeability, and rely on voltage-gated ion channels.
What is the conductance of the Na+ channel at its peak activation?
Approximately 30 mmho/cm².
What triggers most voltage-gated ion channels to open?
Depolarization.
Which ion channel undergoes deactivation according to the graph?
K+ (potassium) channel.
What happens to the Na+ channel after activation?
It undergoes inactivation.
What are the two gating transitions in ion channels?
Activation (opening of the channel when the membrane is depolarized) and deactivation (closure of the channel when the membrane repolarizes).
What type of ion channels do action potentials rely on?
Voltage-gated ion channels.
Why can the smaller unhydrated sodium ion diffuse through the sodium channel?
Because it is pulled away from its water shell by negatively charged amino acids.
What happens to the membrane potential during the downstroke of an action potential?
The membrane potential repolarizes.
What are 'non-selective cation channels'?
Channels that are selective only for cations (Na, K, and Ca) over anions (e.g., Cl-).
What do the terms 'gate' and 'gating' refer to in ion channels?
Transitions between different states of the channel protein.
