ch 12: nervous tissue pt 3 - pumps & channels in neurons, brief intro to neuron potentials

membrane proteins that MAINTAIN a concentration gradient by moving substances AGAINST their concentration gradient are called

pumps

do pumps require cellular energy?

yes

what type of pumps do neurons have in their membranes?

sodium, potassium, calcium

protein PORES in the membrane that allow ions to move DOWN their concentration gradient are called

channels

when channels, they allow...

a specific type of ion to diffuse

what are the three types of channels?

• leaky (passive)

• chemically/ligand-gated: open when neurotransmitter binds

• voltage-gated

the neuron is split into FOUR segments. name them and describe what they're made up of

receptive: dendrite & soma

initial: axon hillock

conductive: axon & its branches

transmissive: synaptic knobs

(RICT)

where are leaky channels in the neuron?

entire neuron

where are pumps in the neuron?

entire neuron: Na+/K+

transmissive: Ca2+

where are ligand-gated/chemically-gated channels in the neuron?

only receptive; K+, Cl-, cation (both Na+ and K+)

where are voltage-gated channels in the neuron?

initial: Na+ / K+

conductive: Na+ / K+

transmissive: Ca2+

what makes Na+ voltage-gated channels unique?

they have TWO gates (activation and inactivation) instead of just one

what are the three states of the Na+ voltage-gated channel?

resting: activation gate closed, inactivation gate open = Na+ can't enter

activation: both activation and inactivation gate open = Na+ moves thru channel

inactivation: activation open, inactivation closed = Na+ can't enter

* quickly returns to resting

a "modality gated channel" opens in response to?

a specific type of sensory stimulus, ex change in temp, pressure, or light

where are modality gated channels found?

in membranes of SENSORY neurons that respond to environment changes - ex, skin respond to mechanical pressure

what is the point of leak channels & Na/K pumps along the entire plasma membrane of the neuron?

to maintain resting membrane potential

at rest, neurons are at their

resting membrane potential (RMP)

what is the most important factor in setting RMP?

K+ diffusion

due to its concentration gradient, K+ diffuses ______ of the cell at rest

out

at rest, K+ diffusion out of the cell is limited by the ___________

electrical gradient, ie the pull from the negative RMP

what would happen if only K+ leaked out?

RMP would be = [K+] is at equilibrium with the electrical gradient, ie -90mV

other than K+ diffusion, what else influences RMP?

Na+ diffusion INTO the cell; makes RMP less negative, ie -70mV instead of -90mV

other than the leak channels (both Na+ and K+), what else influences RMP?

Na+/K+ bumps, which take 3 Na+ out and 2 K+ in; contributes only about -3mV

what is actual important function of the Na+/K+ pump?

maintain concentration gradient for sodium and potassium

at rest, how are ions distributed across the neuron's plasma membrane? why?

unevenly distributed, due to the action of pumps

AT REST: in the cytosol, there is a higher concentration of which ion(s)?

K+ (and Pi + proteins)

AT REST: in the interstitial fluid, there is a higher concentration of which ion(s)?

Na+, Cl-, Ca2+

the calcium concentration gradient is where?

at the synaptic knob

at rest, the gated channels in the neuron are??

closed!

the "membrane potential" is

the electrical charge across the membrane

at rest, the cytosol is _______ compared to the interstitial fluid

negative, -70mV; can be measured with microelectrodes

voltage is the

amount of difference in electrical charge

resistance electrically is

opposition to movement of charged particles

current is

the movement of charged particles across the plasma membrane thru open channels

ohm's law

current = voltage/resistance

what is an action potential?

ALL-OR-NOTHING nerve impulse after graded potential gets us to the threshold

give a VERY BRIEF summary of what happens in the receptive segment

the neurotransmitter released by presynaptic neuron binds here; graded potentials are produced

give a VERY BRIEF summary of what happens in the initial segment

summation of graded potentials & initiation of action potential

give a VERY BRIEF summary of what happens in the conductive segment

propagation of the action potential

give a VERY BRIEF summary of what happens in the transmissive segment

action potential causes the release of neurotransmitter

image of neuron segments