pnb 2774 exam 2

coulomb's law

opposite charges attract, like charges repel

insulator

membranes typically prevent charge passage (membrane channels allow ions to go through membrane)

conductor

membranes can allow charge passage

active/passive behaviors

membrane electrical behavior (channels opening and closing, pumps, membrane behaving like components of a circuit) is responsible for signaling in neurons, muscles, and other cell types

membrane potential (Vm)

the potential inside the cell (typically negative) relative to the "reference" potential outside the cell (always assumed to be relatively 0)

normal resting potential

-70Vm

K+ leak channels

help maintain a resting negative membrane potential (Vm)

K+ efflux

makes Vm more negative

resting largely maintained by

activity of K+ leak channels

Nernst potentials

the calculated values for various ions, given the concentrations, there chargers, and a temp of 37 C

Equilibrium potential (Eion x)

the electrical potential (voltage, Vm) at which the diffusional flow of an ion one way is balanced by electrostatic attraction in the other

Equilibrium potential

the membrane potential at which a given ion type's net flux is zero

Nernst potential

describes the membrane potential that a single ion would produce if the membrane were permeable to only that ion

reversal potential

the membrane potential at which the flux of a given ion type REVERSES from inward to outward

Depolarization

changing membrane potential to be more positive

hyperpolarization

changing membrane potential to be more negative

repolarization

returning membrane potential towards rest potential

equilibrium

an unchanging state that remains so without manipulation

steady state

an unchanging state that remains so only by constant input/output

Goldman-Hodgin-Katz (GHK) equation

steady state

1 multiple choice option

GHK equation

predicts membrane potential that results from the contribution of all ions that are membrane permeant (can cross the membrane)

multiple ion case

Vm is somewhere between the most negative Ex (usually Ek) and most positive Ex(usually Ena)

one ion case

GHK reduces to Nernst, Vm approximates Ex of the most permeant ion

neurons

nerve cells that are capable of initiating and conducting electrical activity throughout the body

neuroglia

cells that support the neurons

function of nerve cells

communication and control of body functions

dendrites

receive incoming signals: passive, graded synaptic potentials (input signal)

cell body

"integrated" multiple incoming signals via summation (integrator)

axon

carriers the output signal, and "all or none" action potential (output signal)

graded potentials (active/passive behavior)

passive or electronic like a cable

action potentials (active/passive behavior)

active; self regenerating

graded potentials distance

degrade with distance and time

action potentials distance

no decrement with distance: they maintain the same amplitude

graded potentials duration

variable amplitude and variable duration, hyper or depolarizing sign

action potentials duration

all or non: fixed duration (ms)

graded potential threshold

sub-threshold no AP

action potential threshold

supra-threshold

graded and action potential common features

voltage changes in membrane, propagate down axons/dendrites, transient events

action potential

an all or none wave of elevated potential that will result in some action in part of the cell

actions

vesicle release, muscle contraction, signal propagation

ion permeabilities with negative voltage

Pk dominates for repolarization and after hyperpolarization

the neuron needs needs the after-hyperpolarization phase to:

unblock Na+ channels, close K+ channels, reset ionic gradients, return to rest

absolute refractory period

no level of stimulus can trigger an AP

relative refractory period

a greater stimulus, may trigger an AP

propagation

AP propagates as a result of local circuit current flow

unmyelinated axon AP step 1

membrane is very depolarized, nearby membrane patches are also depolarized

unmyelinated axon AP step 2

the neighboring patch of membrane then goes through the AP steps, AP moves forward

unmyelinated axon AP step 3

sections that just finished the AP are refractory. they are resistant to depolarization because Na+ channel needs time to recover

unmyelinated axon AP step 4

each segment goes through all steps of AP, regenerative

regenerative

each segment goes through full AP due to opening of voltage gated Na+ channels

Myelin "sheath"

10-160 concentric wrappings of glial membranes around axon

distance between nodes

from a few hundred um- several mm

myelin results in

saltatory conduction (jumping)

myelination

can increase the speed of conduction by a factor of 100

myelinated axon

AP's jump from node to node

synapse

the basic structural mechanism of communication between neurons or to effector cells (muscle, heart, gland)

electrical synapse

direct electrical signals

chemical synapse

chemical nuerotransmitters

electrical synapse signaling

bi-direction signaling

chemical synapse signaling

anterograde(forward direction) signaling: pre to post synaptic

electrical synapse 2

second cell mirrors first one, gap junctions

chemical synapse 2

presynaptic vesicles hold NT's, postsynaptic receptors, postsynaptic receptors

vesicle exocytosis

fusion with membrane (requires Ca2+)

vesicle endocytosis

recycling (by several paths)

SNARes

pre-synaptic membrane proteins involve in vesicle fusion. (priming/fusion molecules)

v-SNARes

vesicular SNARes, many kinds, key one is synaptotagmin: Ca2+ sensor

t-SNARes

target SNARes (terminal membrane)

Botulinum Toxin (botox)

cleaves SNARes, result less NT released, muscle flaccidity

ligand gated ion channel synaptic transmission

fast <100ms

G protein coupled receptor synaptic transmission

slow >100ms

ligand ion channels

opens ion channels

GPCR ion channels

opens or closes ion channels

ligand protein

receptor and channel part of same protein

GPCR protein

receptor and channels are separate proteins

ligand amplification

little amplification (1 or 2 NT opens one channel)

GPCR amplification

a lot of amplification (1 NT may affect many channels)

ligand receptor type

ionotropic receptor

gpcr receptor type

metabotropic receptor (2nd messengers)

chemical synapse is a point

of junction between cells

binding of NT to post synapse causes

receptors to open (increases permeability of ions that receptor prefers)

response is determined by

receptor

1 multiple choice option

Generalization of synaptic transmission

opening of NT receptor drives Vm towards Ex for that channel. Depending on Ex, the effect may be inhibitory or excitatory

hyperpolarizing

Ex

Depolarizing

Ex>Vrest

inhibitory

Ex

excitatory

Ex>threshold

If membrane is only permeable to Na+, Ena=

+61mV

if membrane is only permeable to K+, Ek=

-93mV

graded potentials

ions with greater permeability have greater influence on Vm. The larger the influence of an ion X, the closer Vm will be to Ex

EPSP

membrane more positive to rest

IPSP

membrane more negative to rest

Passive decay

graded potentials decrease in strength as they spread out from the point of origin

spatial summation

two (or more) roughly simultaneous PSP's from different locations sum up across space

postsynaptic inhibition

an inhibitory presynaptic neuron prevents an action potential from firing

temporal summation

two(or more) non simultaneous PSP's from the same location (usually) sum up over time

threshold

a state where the neuron can engage in a runaway feedback loop leading to a spike in the potential (action potential)

No summation (temporal)

two subthreshold graded potentials will not imitate an AP if they are further apart in time

Summation causing AP (temporal)

two subthreshold potentials arrive at the trigger zone within a short period of time, they may sum and initiate an action potential

termination of action

diffusion away from synapse, re-uptake by pumps and transporters, cleavage by enzymes

excitability

outside stimuli can initiate electrical charges in the muscle fiber, leading to contraction