cell excitability

active transport

transport is conducted against a concentration/electrical gradient

what type of transport requires energy?

active transport

what are the types of active transport?

1. primary active transport

2. secondary active transport

active transport will use energy…

directly or indirectly

passive transport

transport is only driven by concentration gradient

active transport is

saturable

what are the types of passive transport?

1. simple passive transport

2. facilitated passive transport

what type of passive transport is NOT saturable?

simple diffusion

what type of passive transport is saturable?

facilitated diffusion

why is simple diffusion not saturable?

does not have a transporter

summarize the mechanism of primary active transport

substrate binds to carrier protein which allows them to pass through membrane and be released on opposite side

summarize the mechanism of secondary active transport

the carrier and substrate bind to a transport protein that passes them through the membrane and is released at the opposite side

diffusion

movement of a molecule down a concentration gradient from high to low

osmosis

net movement of water across a semipermeable membrane

what is important to emphasize about an ideal osmosis?

requires only the movement of pure water across the membrane without any movement of solute particles across the semipermeable membrane

ion channels

pore-forming proteins that allow the flow of ions across membranes

leak ion channels

open or non-open gated channels

what is the simplest type of ion channel?

leak ion channel

ligand-gated ion channels

open when a chemical ligand, such as a neurotransmitter, binds to the protein

voltage channels

open and close in response to changes in the membrane potential

mechanically gated channels

open in response to the physical deformation of the receptor

what would an example of a mechanically gated channel be?

sensory receptors of touch and pressure

symport

proteins that move two molecules in the same direction across the membrane

antiport

protein that moves two molecules across the bilayer in opposite directions

what would an example of a mechanically-gated ion channel be?

baroreceptors

what is the name of the leak ion channels?

non-gated ion channels

what causes the voltage seen in the cell membrane experiment?

difference between the reference electrode and cytoplasm

electroneutrality principle

the total number of positive and negative charges in the extracellular and the intracellular fluid is equal

if the cell membrane is electrically neutral, what accumulation of charge will the extracellular side have?

positive

if the cell membrane is electrically neutral, what accumulation of charge will the intracellular side have?

negative

efflux

out of the cell

influx

into the cell

what does the ion concentration gradient cause in the membrane?

efflux of potassiuminflux of sodium into the cell

what is the membrane potential based on?

a difference in positive charges

what occurs during the sodium-potassium pump?

3 sodium ions move out of the cell and 2 potassium ions move into the cellsome potassium leaks back out of the cell, drive by chemical gradient

why is the sodium-potassium pump considered negative even though it involves cations?

there is a overall net loss of 1 positive charge from when you began; you started with 3 sodium ions then at the end you only have 2 potassium ions

why is the exchange of electrical charges between the extracellular and intracellular compartments by the sodium-potassium pump is considered electrogenic?

exhanges more postive charges OUT of the cell

what would it mean if the electrical charges of the cell are at equilibrium?

the cell is dead

when does diffusion of ions based on chemical gradient stop?

when the counteracting electrical gradient equals the chemical gradient

what is the charge of the potassium valence ion in reference to Nernst equation?

1

what is the charge of the sodium valence ion in reference to Nernst equation?

1

what is the charge of the chlorine valence ion in reference to Nernst equation?

-1

what is the typical value of resting membrane potential?

-90/-70mV

what is the extracellular concentration of potassium?

4 mmol/L

what ion is the main contributor to resting membrane potential?

potassium

what does depolarization do to the cell?

increases cell excitibility

depolarization

the membrane potential (INSIDE THE CELL) is less negative

what does hyperpolarization do to the cells?

silences/depresses them

hyperpolarization

the membrane potential (INSIDE THE CELL) is more negative

what happens to Vm in depolarization?

decreases (for example it goes from -70mV to -60mV)

what happens to Vm during hyperpolarization?

increases (for example goes from -70mV to -80mV)

in terms of action potential what does it mean if the membrane is depolarized?

going from negative to positive

in terms of action potential what does it mean if the membrane is polarized?

going from positive to negative

what are the steps of action potential?

1. resting membrane potential

2. depolarizing stimulus

3. membrane depolarizes to reach the threshold; voltage gated channels begin to open

4. influx of sodium depolarizes the cell

5. gates of sodium channel close (30mV) and slower potassium ion channels open

6. efflux of potassium; start of repolarizing cell

7. potassium channels remain open, transient hyperpolarization

8. voltage-gated potassium channels close, less potassium leaking from cell

9. cell returns to resting ion permeability and resting membrane potential

what are steps 3 and 4 dependent on in the event of action potential?

voltage-gated ion channels

how would lidocaine influence action potential?

blocks opening of sodium channel meaning steps 3 and 4 would not occur

threshold

what change must be reached for action potential to occur

local/graded potential

if the depolarization does not reach the threshold

overshoot

when depolarized membrane reverses its polarity at its peak due to inactivation of sodium channels than reactivation of potassium polarization

what ion transport causes an axon's repolarization phase of the action potential?

efflux of potassium

what are the two basic electrical signal types on the cell membrane?

1. graded potential

2. action potential

graded potentials

travel over short distances and lose strength as they travel through the cell

action potentials

brief, large depolarizations that travel long distances through a neuron without losing strength

what ion can modulate the function of the sodium voltage-gated channels?

calcium

you have a small dog that has just gone through birth that presents tremors and shaking. You run a blood test and notice that there are high levels of calcium present. What is the cause of the dogs symptoms?

hypocalcemia

how does high levels of calcium in the cell membrane influence the cell?

cell becomes more excited because sodium gated channels remain open allowing more sodium to enter the cell

what is the consequence of a channelopathy that interferes with the closure of the inactivation gate in sodium voltage-gated channels of a stimulated excitable cell?

depolarization phase is prolonged

absolute refractory period

period of ongoing action potential during which no stimulus can initiate another action potential

relative refractory period

follows the absolute refractory period during which a strong stimulus can initate another action potential

why are refractory periods important in the heart?

ensures that there is a synchronized electrical signal followed by a mechanical signal

all-or-none principle

any depolarization of the cell membrane of an excitable cell either has not effect or results in a full action potential

action potentials are…

uniform in one kind of cell

what is an example of a channelopathy in horses?

hyperkalemic periodic paralysis

what breed does hyperkalemic periodic paralysis affect?

Quarterbred horses

what are the three ways to identify the potassium chemical gradient?

1. using numbers

2. using dots

3. using the blue triangle that represents the strength of the concentration gradient

what does not change in the potassium chemical gradient?

directionality does not change; always leaks intracellular fluid

what happens to gradient strength of the cell membrane if you have a higher concentration of potassium in the extracellular fluid?

strength decreases

what happens to the concentration gradient strength if you have a lower potassium concentration in the extracellular fluid?

strength increases

how is the extracellular compartment of the cell membrane influenced by hyperkalemia?

more potassium is outside the cell

how is the gradient affected by hyperkalemia?

and the gradient is now smaller; this results in positive charges remaining in the cell rather then leaving

what does hyperkalemia lead to in the cell?

this will depolarize the cell leading to cell excitability

how is the extracellular compartment of the cell influenced by hypokalemia?

less potassium will reach outside the cell

how is the gradient effected in the cell membrane during hypokalemia?

gradient will be very big allowing several positive charges to leave and make the intracellular compartment more negative

hyperpolarization will make the cell…

less excitable

if you have a resting membrane value of -94mV then you do a blood test and calculate a value of -75mV, would it be hyperkalemia or hypokalemia?

hyperkalemia (depolarization of cell = more excitable)

if you have a resting membrane value of -94mV then you do a blood test and calculate a value of -112mV, would it be hyperkalemia or hypokalemia?

hypokalemia (hyperpolarization = cells less excitable)

what determines the distribution of electrical charges around the cell membrane of excitable cells?

1. electrochemical gradients for different ions

2. semi permeability of the cell membrane