Ions, Glucose, Amino acids
ATP, 3 Na+, and 2 K+
Lipid solubility.
EMP (mV) = ±61 log (Ci / Co)
The channel conducts 'all or none,' meaning it is either open or closed.
Molecules are 'pumped' against an electrochemical gradient at the expense of energy (ATP).
Direct use of energy (ATP).
To transport specific molecules across the membrane.
Specificity and function.
Water-soluble molecules cross the cell membrane via channels or other transport proteins.
K+ would diffuse down its concentration gradient until the electrical potential across the membrane countered diffusion.
Na+ (sodium ions)
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.
Urea, Glycerol
Primary active transport
Antiporters transport substances in the opposite direction of a 'driver' ion like Na+.
An antiporter enzyme located on the plasma membrane of all animal cells.
The resting membrane potential is closest to the equilibrium potential for the ion with the highest permeability.
Carrier-mediated diffusion.
It pumps sodium ions out of cells and pumps potassium ions into cells against electrochemical gradients.
The Vmax of the carrier protein.
It regulates osmotic balance by maintaining Na+ and K+ balance.
The energy stored in the electrochemical gradient of another molecule (usually Na+).
They strip water molecules from the potassium molecule, enabling it to permeate through the channel.
Relatively high lipid solubility
Lipid-soluble molecules move readily across cell membranes, and the rate of diffusion depends on lipid solubility.
To allow specific ions to pass through the membrane.
Size, shape, and charge of the channel and ion.
Voltage-gated channels and chemical-gated channels.
When the intracellular electrical potential is equal in magnitude but opposite in direction to the concentration force.
Osmosis is the net diffusion of water from pure water toward a water/salt solution.
The theoretical intracellular electrical potential that would be equal in magnitude but opposite in direction to the concentration force.
Patch Clamp
Water moves down its concentration gradient, from pure water toward a water/salt solution.
Indirect use of energy.
It maintains a low cytosolic Ca2+ concentration.
They cause only transient changes in cell volume.
They have a hydrophobic exterior and a hydrophilic interior.
Na+ (Sodium) and K+ (Potassium).
+61 mV
The membrane potential becoming less negative and reaching the threshold.
It decreases the Na+ electrochemical gradient.
Na_o = 142 mM and Na_i = 14 mM
Concentration difference (C_o - C_i).
Fiber diameter (in mm) x 4.5 = velocity in m/s.
The selectivity filter ensures that only K+ ions can pass through the channel, maintaining the membrane's permeability to K+.
Transmitter substances.
Changes in membrane potential (voltage-gated channels), occupation of receptor (ligand-gated or receptor-operated channels), and mechanical forces (mechanosensitive channels).
The membrane is polarized with a negative charge inside and a positive charge outside.
The local current spreads, opening more Na+ channels and depolarizing adjacent sections of the membrane.
ATP is converted to ADP (Adenosine Diphosphate).
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).
Excitability refers to the ability of a cell to respond to stimuli and generate action potentials.
10^-2 cm/sec
Temporal summation is the successive epsp's from the same synapse.
Diffusion occurs down a concentration gradient through the lipid bilayer or involves a protein 'channel' or 'carrier' and requires no additional energy.
E_K = -61 x log(K_i / K_o)
A ligand is any substance that binds to a receptor.
The responses summate, resulting in a summed response.
A regenerating depolarization of membrane potential that propagates along an excitable membrane.
Cells swell and burst.
In parietal cells of gastric glands (HCl secretion) and intercalated cells of renal tubules (controls blood pH).
Higher membrane permeability results in more transient changes in cell volume.
Because the lipid bilayer is hydrophobic, preventing water-soluble substances from passing through easily.
Increased velocity.
A greater than normal stimulus.
Increased intracellular Ca++ levels enhance cardiac contractility.
Potassium (K+) is transported into the epithelial cell from the extracellular fluid to maintain the sodium-potassium balance.
The maximum rate of facilitated diffusion is limited by Vmax.
In facilitated diffusion, the rate of diffusion increases with the concentration gradient but eventually reaches a maximum rate (Vmax).
By increasing intracellular Ca2+ concentration.
Water retention, hyponatremia, and excretion of concentrated urine.
The net diffusion rate increases.
-80 to -90 mV
It decreases membrane capacitance and ion flow 5,000-fold.
Node of Ranvier.
Rest, local depolarization (stimulation), and propagation (current spread).
An immune-mediated inflammatory demyelinating disease of the CNS.
An IPSP is a hyperpolarization of the post-synaptic cell that depresses excitability.
It involves the use of an electrochemical gradient (usually for sodium).
Urea
Water has a much higher permeability (10^-2 cm/sec) compared to glucose (10^-8 cm/sec).
No action potentials are generated.
Active transport occurs against a concentration gradient, involves a protein 'carrier', and requires energy (ATP).
Receptors are often named and classified largely by reference to the ligand.
No, they do not induce refractoriness.
The frequency of APs encodes information, while the amplitude of AP is constant.
No, it is not always seen.
No, adding more carriers does not affect Vmax.
A charge difference across the membrane.
The electrical potential that counters net diffusion of Na+.
Urea has higher membrane permeability than glycerol.
They form ion-permeable pores in the cell membrane.
A period during which an action potential (AP) is not possible due to voltage inactivation of Na channels.
-90 to -70 mV
Leak channels.
Na+-K+ ATPase.
The gate opens, allowing sodium ions to flow into the cell.
By depolarization, and they can be induced in nerve and muscle by extrinsic (percutaneous) stimulation.
+61 mV
Square root of fiber diameter = velocity in m/s.
The Na+-K+ pump actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, using ATP.
They have conducting states and non-conducting states, and the transition between states is called 'gating'.
Ligand-gated or receptor-operated channels (ROCs).
Two potassium ions (2 K+).
Ions diffuse in the direction of their electrochemical gradient.
No, it is propagated unchanged in magnitude.
The post-synaptic cell is hyperpolarized, which depresses excitability and is inhibitory.
EPSPs (excitatory post-synaptic potentials) and IPSPs (inhibitory post-synaptic potentials) result from increases in membrane permeability.
Na+ and glucose (Na+ gluc).
Spatial summation is the overlapping of epsp's from distant synapses.
No, diffusion does not require additional energy.
Acetylcholine, Norepinephrine, Epinephrine, Serotonin (5-HT), Dopamine, Glycine, Glutamate, Adenosine.
The membrane potential approaches E_Na.
Na+ permeability decreases due to the inactivation of Na+ channels.
Because the effect is 'local' to the stimulus.
The number of open channels.
-90 mV.
About 1/5 of a typical cell’s energy and up to 2/3 of a neuron’s energy.
Passive diffusion of K+ and Na+ leads to a charge difference across the membrane, contributing to the development of a negative membrane potential.
It concentrates H+ ions up to 1 million-fold.
Lipid-soluble molecules (usually synthesized by microorganisms) that transport inorganic ions across the lipid bilayer and mediate passive transport.
At the nodes (Nodes of Ranvier).
A period during which a greater than normal stimulus is required to elicit an action potential (AP).
From inside to outside the cell.
The membrane is far more permeable to K+ than Na+.
E_Na = -61 x log(Na_i/Na_o)
Increased intracellular Ca2+ concentration.
Central or nephrogenic diabetes insipidus.
'D' represents the diffusion coefficient.
The Na+-K+ pump transports 3 Na+ ions out of the cell and 2 K+ ions into the cell.
Excitatory and Inhibitory.
Myelin insulates axons to increase the speed of electrical transmission.
-70 mV
20 mV
Sodium (Na+) is pumped out of the cell.
It is not propagated but decremental with distance.
Depolarization is the process of the membrane potential becoming less negative (moving towards 0 mV).
The threshold is the membrane potential level that must be reached for an action potential to be generated.
Na+ acts as a 'driver' ion in symporters, facilitating the transport of other substances.
Permeability decreases from water to ions like Cl-, K+, and Na+.
Myelinated axons conduct impulses faster than non-myelinated axons.
Active transport requires energy (ATP).
The membrane potential (Vm) would be -94 mV
Physiological ligands are ligands provided by the body, such as Acetylcholine and Norepinephrine.
K+ permeability increases due to the opening of K+ channels.
The membrane potential does not reach the threshold voltage, and local currents flow but the membrane potential slowly returns to the resting value.
It binds to the carrier protein, undergoes a conformational change, and is then released.
Potassium (K+) and Sodium (Na+).
Na+ would diffuse down its concentration gradient until the potential across the membrane countered diffusion.
Mobile ion carriers and channel formers.
CO2 and O2.
Refractory periods.
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.
Simple diffusion.
It detects changes in membrane potential and triggers the opening of the channel.
In simple diffusion, the rate of diffusion increases linearly with the concentration gradient.
+61 mV
The diameter of the fiber. Larger diameter fibers conduct faster than smaller ones.
Due to the presence of K+ 'leak' channels and the selectivity filter that allows K+ ions to pass through easily.
-85 to -95 mV
Schwann cells.
Voltage-gated channels.
To pump sodium (Na+) out of the cell and potassium (K+) into the cell.
ATP (Adenosine Triphosphate).
No, summation is not possible.
Overshoot refers to the membrane potential becoming positive, moving above 0 mV.
The lower record is from the postsynaptic cell.
Non-myelinated axons show continuous conduction, while myelinated axons show saltatory conduction.
Protein 'channels' or 'carriers' facilitate the movement of substances through the cell membrane during diffusion.
Nicotine stimulates nicotinic (nACh) receptors.
The membrane potential approaches E_K.
The speed of transmission depends on fiber size and whether it is myelinated. Information of lesser importance is carried by slowly conducting unmyelinated fibers.
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.
Potassium (K+) diffuses out of the cell.
The concentration gradient of Na+.
Water and water-soluble substances such as ions, glucose, H2O, and urea.
Channel formers transport 1000 times more ions per unit time than mobile ion carriers.
Due to voltage inactivation of Na channels.
-94 mV
Sodium (Na+) moves from the lumen into the epithelial cell and then into the extracellular fluid.
Increased intracellular Na+ concentration.
The activity of Na+/Ca2+ antiporters decreases.
Vmax is the maximum rate of facilitated diffusion.
E_Na = -61 log(14/142) = -61 log(0.1) = +61 mV
It leads to water retention, hyponatremia, and excretion of concentrated urine.
Synapses.
The transition between conducting and non-conducting states.
Opening of Na+ channels generates local current that depolarizes adjacent membrane, opening more Na+ channels.
Na+ channels open, causing a local current that depolarizes the adjacent membrane.
It is independent of stimulus strength (all or none).
Increasing Na+ or K+ permeability (or extracellular concentration) affects the membrane potential (Vm) by altering the net driving force on the ions.
Hyperpolarization is the process of the membrane potential becoming more negative than the resting potential.
You need to consider the equilibrium potentials of the ions.
The upper record is from the presynaptic cell.
Myelination increases the speed of nerve impulse conduction by allowing the impulse to jump between nodes of Ranvier.
Active transport occurs against a concentration gradient and requires energy (ATP), while diffusion occurs down a concentration gradient and does not require additional energy.
The equilibrium potential
Receptors are often subdivided by reference to ligands, such as ACh into nicotinic (nACh) and muscarinic (mACh) receptors.
On the cell membrane and the sarcoplasmic reticulum in muscle fibers.
The concentration of impermeant particles in the extracellular fluid (e.g., Na+, K+, protein-).
Because Na channels are concentrated at the nodes.
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.
The rate of diffusion is directly proportional to the concentration gradient (Co - Ci).
It closes the channel after a certain period, stopping the flow of sodium ions.
Increased water loss, excessive sweat loss, central or nephrogenic diabetes insipidus (decreased ADH secretion or responsiveness to ADH).
Net diffusion is proportional to the concentration difference (C_o - C_i).
C_o represents the concentration outside the membrane, and C_i represents the concentration inside the membrane.
Proteins that span the membrane and have a water-filled channel that runs through the protein.
A synapse between the axon of one neuron and the dendrite of another.
-40 mV
Three sodium ions (3 Na+).
It is proportional to stimulus strength (graded).
Yes, subthreshold potential changes exhibit summation.
Yes, IPSPs can summate.
They transport substances in the same direction as a 'driver' ion like Na+.
The last epsp is larger because it occurs before the previous epsp has fully decayed.
Nodes of Ranvier are gaps in the myelin sheath along a myelinated axon where action potentials are regenerated.
Substances move against a concentration gradient in active transport.
Tonicity depends on the membrane and the solute.
It depolarizes adjacent regions of a neuron.
Sodium (Na+) diffuses into the cell.
The electrical potential across the membrane.
Its hydrophobic nature.
It conserves energy.
From outside to inside the cell.
The concentration of sodium (Na+) is high in the epithelial cell and low in both the lumen and extracellular fluid.
It ensures that only sodium ions can pass through the channel.
They have a threshold voltage, usually 15 mV positive to the resting potential.
Yes, action potentials do not summate; information is coded by frequency, not amplitude.
Large water ingestion, Syndrome of Inappropriate ADH Secretion (SIADH).
They allow K+ ions to move across the cell membrane, contributing to its high permeability to K+.
-50 to -60 mV
-60 to -70 mV
Every 1-3 mm.
Mechanosensitive channels.
135 mV
Potassium (K+) is pumped into the cell.
Repolarization is the process of the membrane potential returning towards the resting potential after depolarization.
They are classified as symporters or antiporters.
An epsp is an electrotonic response that decays with an exponential time course.
Saltatory conduction is the process by which nerve impulses jump from one node of Ranvier to the next in myelinated axons.
Substances move down a concentration gradient in diffusion.
Osmolarity is merely another measure of concentration.
Na+ permeability increases due to the opening of Na+ channels.
A bigger stimulus results in a bigger response.
Depolarization will be greatest at the point of stimulation and will fall exponentially with distance.
It is capable of generating action potentials.
Depolarization.
K+ permeability increases due to the opening of K+ channels.
It is conducted without decrement, meaning it is an 'active' membrane event.
Specific ions.
Negatively charged amino acids.
There is increased K+ conductance due to the delayed closure of K+ channels.
+10 mV.
Only Ca ions; they are important in synaptic transmission.
Muscle contraction and secretion (e.g., epinephrine from chromaffin cells of the medulla).
Approximately 60 m/s.
The membrane potential rapidly depolarizes.
Because they are too large.
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.
Approximately 30 mmho/cm².
Depolarization.
K+ (potassium) channel.
It undergoes inactivation.
Activation (opening of the channel when the membrane is depolarized) and deactivation (closure of the channel when the membrane repolarizes).
Voltage-gated ion channels.
Because it is pulled away from its water shell by negatively charged amino acids.
The membrane potential repolarizes.
Channels that are selective only for cations (Na, K, and Ca) over anions (e.g., Cl-).
Transitions between different states of the channel protein.
