Module 3: Lecture 1 Flashcards
what separates the intra and extra cellular fluid?
the plasma membrane
- restricts the flow of molecules (bilipid membrane, not just anything can cross it)
is a water molecule able to cross a bilipid membrane?
no
are ions water soluble?
yes
do ions have attractive forces?
yes between them
what would the ions in the extracellular and intracellular fluid do if there was not a membrane?
they would just mix
what is the membrane potential?
the restriction of ions in the membrane and the difference of charges in the ICF and ECF due to the difference of ions between them
- preventing ions from freely diffusing into their lower concentration space
what does saying “the membrane has been polarized” mean?
there is a separation of charge across the membrane
ex. -4 inside the cell and +6 inside the cell gives us a difference of 10
what is the fundamental basis for cellular communication in nervous and muscle tissues?
when we allow ions to somehow mix and traverse across the membrane
- the separation of charge that allows your nervous system to communicate
the plasma membranes of all living cells are polarized _________.
electrically
- separates charge to form a ‘membrane potential’
what are the key factors regarding membrane potential?
- it is defined by the separation of charge
- difference in the relative number/concentration of cations and anions in the ICF and ECF (dictates the degree or magnitude of the membrane potential)
- difference in permeability of key ions
- therefore: ion movement (membrane potential) is influenced by both ion concentration and membrane permeability
- membrane potential is measured as volt or millivolt
what is the basis of cellular communication?
- restricting the movement of ions st rest because of the cell membrane
- when we allow the charges to mix, we can use the mixing to perform work
what is the fundamental basis that allows your nervous system to communicate?
- separation of charge of the cell/plasma membrane
what is membrane potential measured by?
Volt or millivolt (mV)
the movement of ions across a membrane are determined by?
- concentration gradient (high to low)
- electrical gradient (opposites attract, similar charges repulse)
- combined effects = the electrochemical gradient
whether the ion moves across the membrane or not depends on?
whether the membrane is permeable to that ion
- cell membranes are very restrictive to the flow of ions across it
what makes a membrane have a ‘potential’?
when there is an unequal distribution of electrical forces
- hence, a membrane potential has been generated
- exists because of an unequal + and - on both sides
in biological cells, there are many ions in the ICF and ECF, but there is a greater concentration of ions located?
in a thin layer along the outer and inner surface of a cell membrane
is the membrane itself charged?
no
why are the ECF and ICF neutral?
because the net charge of cations is balanced by the net charge of anions
- there is only potential at the membrane and there is no other membrane in the fluid other than that one so there is no separation of charge(they just attract one another and mix)
the magnitude of the potential (mV) depends on?
the number of opposite NET charges that are separated
- ex. difference between -8 and +8 is 16 which is greater than -3 and +3 which is 6. the membrane with 16 has a greater magnitude of potential, more net difference of the charge
what makes a membrane potential exist?
an unequal distribution of positive and negative ions
do all cells have a membrane potential?
yes
how can our nerve cells and our skeletal muscle cells utilize the charge potential of the membrane?
to communicate with one another by very rapid and transient charges
what are the two different cell types on whether they can utilize the cellular potential?
- non-excitable cells
- excitable cells
- they have a ‘resting membrane potential’ that is relatively constant
what are excitable cells?
- nerve or muscle cells that can produce rapid and transient changes in their resting membrane potential when excited (called electrical signal (communicaton))
what are key ions in membrane potential?
- sodium (Na+)
- potassium (K+)
- negatively charged intracellular proteins (A-)
do we have more sodium ions in extra or intracellular fluid at rest?
extracellular
do we have more potassium ions in extra or intracellular fluid at rest?
intracellular
where are negatively charged intracellular proteins more concentrated, ICF or ECF? and why can’t they flow down their concentration gradient at rest?
- ICF
- because they have no permeability; they are only going to be contributing to the membrane potential within the inside of the cell
is the cell membrane more permeable to potassium or sodium at rest?
potassium (50-75x more than sodium)
a lot more potassium can _____ the cell than sodium can ____ the cell at rest for a nerve cell
- leave
- enter
since ions like Na and K are water-soluble, they cannot diffuse across the lipid-rich plasma membrane. so how do they pass through the membrane?
they can move through ion channels
- they are protein channels embedded into the bilipid membrane that allow the ions to traverse across it
- PASSIVE channels. NOT active transport
- sometimes referred to as Leak channels
why are protein channels also called leak channels?
because they are kind of like a water tap that is always leaking ions through it
are protein (leak) channels selective?
- yes
- you have sodium leak channels and potassium leak channels
what happens to the charge of the ICF and ECF when potassium ions move out of ICF and into ECF?
ICF becomes more negative and ECF becomes more positive
why is the ICF more negatively charged than the ECF?
because the membrane is impermeable to large proteins (A-) so they don’t leave the cell
when are the electrical gradients and the concentration gradients completely balanced? (equilibrium potential)
when there is no further NET movement of K+
- when the inward electrical gradient exactly counterbalances the outward concentration gradient
what pushes potassium into the cell and what pushes potassium out of the cell?
out of the cell: the concentration (chemical) gradient
into the cell: the electrical gradient (A- ions make the inside more negative so that potassium will be attracted to the inside)
what has happened once the potassium equilibrium potential of -90mV has been reached?
- the plasma membrane has a potential
- no net movement of K+ across the membrane
- a large concentration of K+ still exists inside the cell
INSIDE the cell, relative to the outside of the cell, at equilibrium what is the membrane potential? (potassium equilibrium potential)
-90mV
why do we talk about the inside of the cell as -90mV rather than the outside being +90mv?
- random convention so we all utilize the same language
- we always reference the inside of the cell with respect to the outside of the cell
what is the -90mV dictated by?
- the intracellular protein membrane potentials
- key- the concentration differences
how do we measure the -90mV of a cell?
with a micro-voltmeter measuring with one electrode inside the cell and the other one outside
how do we measure the -90mV?
the Nernst equation:
E= 61 log Co/Ci
E= equilibrium constant for the ion in mV
61= constant
Co= concentration of the ion outside the cell
Ci= concentration of the ion inside the cell
what is the equilibrium potential for sodium?
+65mV
