Nerve Cells & Neural Signaling pt 1 Flashcards
define resting membrane potential; what variable is used to denote this?
electrical potential (voltage) of a cell across the membrane (inside vs. outside); Vm
what is the resting membrane potential range for all cells; neurons; what does negative indicate?
- -5 to -100mV
- -70mV
the negative indicates that the inside of the cell is negatively charged compared to the outside
how do neurons communicate
generation of electrical signals, which shows in the form of changes in membrane potentials; some of these changes trigger release of neurotransmitters that carry the signal to the other cell
what is the reason(s) for difference in charge on each side of plasma membrane
- membrane permeability
- action of Na+/K+ pumps
- negatively charged molecules inside the cell
what terms can we use for “the difference in charge”
- potential difference
- membrane potential
how does the sodium/potassium pump work
creates concentration gradients for Na+ and K+ ions by moving 3 Na+ out and 2 K+ in for every 1 ATP molecule hydrolyzed
(Nah nah nah, kk) –> Net +1 out
What is the concentration for the inside and outside of cell for Na+
high outside, low inside (chemical driving force pushes Na+ into cell)
What is the concentration for the inside and outside of cell for K+
low outside, high inside (chemical driving force pushes K+ out of cell)
fixed anions are negatively charged at cytoplasmic pH. what are examples of these?
- cellular proteins
- phosphate groups of ATP and other organic molecules
what is the effect of fixed anions on distribution of cations
- unequal distribution of charges
- negative charge inside cell attracts cations
- as cations increase (to a limit) the concentration gradient favours their diffusion out of the cell
define equilibrium potential
membrane potential that would stabilize ions at their concentrations
What is the Nernst equation
Ex = (61/z)log(x0/x1)
- Ex = equilibrium potential in mV for ion X
- x0 = concentration of ion outside cell
- x1 = concentration of ion inside cell
- z = valence of ion (+1 for sodium or potassium)
in neurons (and other cells) at rest, neither sodium nor potassium is at equilibrium. why is this?
electrochemical forces act on both ions
- Na+ leak ins and K+ leak outs
- leaks create membrane potential but also slowly change concentrations in cell
- sodium/potassium pump returns ions to maintain gradients and also contributes to negative intracellular environment
what are the types of electrical signals
graded and action potentials
what are the types of gated channels
- voltage
- ligand (chemically)
- mechanically
why does membrane potential change due to gated channels
- open or close in response to stimuli
- affect movement of ions
- ion movement leads to electrical signal
how can we describe changes in membrane potential
- resting potential (reference point)
- depolarization
- repolarization
- hyperpolarization
define graded potentials
- small
- communicate over short distances
- initiated by a stimulus (stronger = larger change in Vm)
- small change in membrane potential
- decremental
- short distance travel
define action potentials by size and how they communicate
- large
- communicate over long distances
what stimuli produce graded potentials
- chemicals like neurotransmitters
- sensory stimuli like touch and light
how do graded potentials spread
electrotonic conduction (spread of voltage by passive charge movement)
what is the purpose of graded potentials
- determines whether action potential will occur
- action potential will generate if neuron is depolarized to threshold
what is threshold
level of depolarization needed to elicit action potential
what does excitatory depolarization do
bring Vm closer to threshold
what does inhibitory hyperpolarization do
take Vm away from threshold
what does the direction of change in potential depend on
- neuron
- stimulus
- specific ion channels that open/close in response to stimulus
define temporal summation
describes how graded potentials can sum
- same stimulus
- repeated close together in time
define spatial summation
describes how graded potentials can sum
- different stimuli
- overlap in time
