The resting membrane potential Flashcards
Sensory neuron
carries info about the 5 sense
interneuron
is in the spinal cord, activate a motor neuron
motor neuron
causes muscle to contract, impacts other body reactions
how can a interneuron not send a motor neuron in response to a sensory neuron
brain sends a signal down a neuron in the spinal cord that release inhibitory neurotransmitter onto the interneuron
Ions
Single atoms/molecules that have unequal numbers of protons and electrons, they have a net electrical charge
Cations
positive charge
Anions
negative charge
Most relevant ions
Na+ and K+, Ca^2+, Cl-
Salts
Chemical compounds made of ions bound together, such there is a 0 net charge, table salt = potassium chloride, can be dissolved in water
Diffusion
Molecules dissolved in water want to all equal space out from each other, they will flow down the concentration gradient, from high to low, until the distribution is equal (equilibrium)
Electricity
Electrical current = flow of charged particles
Electrical potential
= Voltage = force that moves particles away from the same charged particles away from the same charge and towards the opposite charge
Electrical conductance
= ability of charge to move through a substance, opposite of resistance
Ohm’s law
I=gV
I= current
g= conductance
V= potential
Resting membrane potential, how does it acquire that negative voltage?
The inside of the cell contains neg charged proteins, K+ is pumped INTO the cell, Na+ and Ca^2+ is pumped out, K+ flows down the concentration gradient out of the cell through selective channels in the membrane, Net outflow of positive charge contributes to a negative membrane potential, the potential reaches “steady state” due a balance of concentration gradients and electrical potential
During action potential
Na+ and Ca^2+ flow in
Typical ion concentrations
Not shown: organic anions (negatively charged proteins) inside the cell, more potassium inside, more sodium, calcium , and chloride outside, each has an equilibrium potential
Ion pumps
The sodium-potassium pump expends ATP to pump sodium out and potassium in, against their concentration gradients
Ion pumps, how much is pumped in and out
every 2 K+ pulled in, 2 Na+ get pushed out, contributing to the negative charge
Also a calcium pump
push calcium out, the mitochondria and endoplasmic reticulum also pull calcium out of the cytosol
Potassium channels
most permeable to K+, which passively flows out of the cell, down its concentration gradient, establishing a negative resting potential, the resting potential would be equilibrium potential for K+ (Ek=-80mV) but some Na+ leaks in, so the resting potential is roughly -65mV
Importance of potassium
The relatively low K+ concentration outside the cell, and in the blood in CRITICAL, the blood-brain barrier helps maintain extracellular K+ concentration in the brain, as do astrocytes, Mutations of the K+ channel lead to poorly functioning neurons
What happens if the extracellular K+ concentration becomes too high? Does the membrane potential goes up or down?
K+ ions pumped into the cell no longer have a reason to flow outward, so the cell’s membrane potential rises, becoming less negative (depolarized)
resting potential
ions are charged atoms, here dissolved in fluid, pumps establish concentration gradients (Na+ and Ca^2+ out and K+ in), selective channels allow K+, positively charged to flow out, the balance of electrical force and concentration gradients settle at -65 mV.
2 forces that push sodium into the cell when sodium channels open
Electrostatic pressure and diffusion
Electrostatic pressure
like charges repel, opposites attract, Na+ wants to go towards the negative inside the cell
Diffusion
ions want to be spread out from other ions of the same element, so the move down their concentration gradients. Sodium is more concentrated outside the cell, so it wants to get inside
