neuron communication

describe neuron language

• “yes-no”

• excitatory

• inhibitory

what are humans fluid balance?

• seawater

  • water o2, electrolytes

• mammals are 2/3 water

  • humans 45-70%

what electrolyte ions are do humans have

• na+

• cl-

• K+

• ca2+

• mg2+

• a- (organic negatively charged ions

breakdown of fluid balance compartments and how they differ

• intracell = 2/3

• extracell = 1/3

  • interstitial fluid (26%) — which is between cells

  • blood plasma (7%)

• diff in location and composition

diffusion

• passive process

• high conc to low conc

electrostatic pressure — what does this mean?

• opposite charged attract

• same charges repulse

membrane potential — describe fluid

• fluid inside cell is more negative than fluid outside of the cell

• the membrane maintains a electrical gradient via polarization

• some chemicals pass more easily and freely than others

what chemicals pass more easily and freely than others

o2, co2, h20 always cross

describe various forces driving na+ and k+ at membrane

• electrostatic and diffusion drives na+ in

• electrostatic drives k+ in

• diffusion drives k+ out

characteristics of lipid bilayer?

1. impermeable to Na+

2. kept out by a force

describe sodium-potassium transporter

• na/k exchange

  • exchanges 3 sodium for 2 potassium

• keeps conc of na+ low in cell

• 40& of neuron’s energy goes to pump

describe what occurs at resting membrane potential

• little na+ can enter through gated channels

• k+ moves out on its concentration gradient

• k+ moves in on its electrostatic pressure

what is the mV of cell at rest? what occurs here?

• -70 mV

• messages constantly coming in

  • some are yes, some are no

when does cell fire?

• -40 mV

what are ion channels?

• small pore in the membrane channel made up of proteins

• specific

  • only let certain ions in or out

• voltage-gated

describe what occurs during depolarization

• sodium channels open at -40 mV

  • threshold of excitation

• potassium channels less sensitive

  • opens at ~-20 mV

  • K+ starts to leave

• peaks at +40 mV

  • na+ channels close

  • reached in ~1 msec

describe what occurs during repolarization

• once sodium channels close, k+ channels are still open

• outflow of K+ brings cell back to rest

• k+ channels start to close at -70 mV

describe refractory periods

• k+ channels are slow

  • too much k+ has left so cell TOO negative

• na/k pummp starts back up and gets cell back to resting

• na+ channels reset

• once cell back to -70, it can fire again

EPSP

• Excitatory Post-Synaptic Potential = cell is more likely to fire

IPSP - what enters and exits?

• Inhibitory Post-Synaptic Potential = cell is less likely to fire

• Cl- enters, K+ leaves = cell hyperpolarizes

spatial summation vs temporal summation

• spatial - more than one neuron fires at the same time

• temporal - one neuron fires over and over again

what is propogation

• transmission of AP down the axon

• only goes in one direction

saltatory conduction

• impulse of myelinated neurons jumps from one NoR to another

• depol at one node brings about depol at the next node

all or none law

• either occurs or doesn’t

• strength same from start to finish

rate law

• firing rate depends on the stimulus

• strong stim = more APs

• weak stim = less APs

____ is always the same, ___ can change

• amplitude

• firing rate

the ___ the axon the faster the rate of conduction

thicker

look into synaptic transmission tomorrow