action potentials

which cations are concentrated inside and outside the membrane at resting potential?

-Cation Na+ are many outside the cell and few inside -K+ is a few outside of the cell and many inside -Ca2+ are many outside the cell and few inside

what are ion channels?

-a pore in the cell membrane that permits the passage of certain ions through the membrane when the channels are open -allows ions of a specific type to pass through the membrane -some ion channels leak, · staying open all the time and the cell membrane of a neuron contains many such channels that selectively allow potassium ion to cross the membrane, but not sodium ions

potassium ion during action potential

-a potassium atom carries a positive charge -Potassium ions move outside the membrane and sodium ions stay in, repolarizing the cell -The neuron become hyperpolarized when more potassium ions are on the outside than sodium ions are on the inside

sodium ion during an action potential

-a sodium atom carries a positive charge -When the stimulus causes the sodium channels in the neurons membrane to open it allows the Na+ ions that were outside the membrane to rush into the cell -When they enter the neuron the cells electrical potential becomes more positive

How does a neuron reach the threshold? (Explain in terms of postsynaptic potentials!)

-depolarization -When the depolarization reaches about -55 mV a neuron will fire an action potential. This is the threshold. If the neuron does not reach this critical threshold level, then no action potential will fire.

saltatory conduction

-form of conduction that is characteristic of myelinated axons, in which the action potential jumps form one node of Ranvier to the next -Myelin sheath speeds conduction and the sheath that is around the axon is interrupted by node of ranvier (small gaps space every millimeter along the axon) and since the myelin insulation resists the flow of ions across the membrane the action potential jump from node to node which is whats known as the saltatory conduction

Why are action potentials unidirectional?

-refractory periods, when the next part of the axon is firing, the previous cell has not yet reached resting potential, meaning the sodium channels cannot open -concentration gradient, electrostatic pressure

refractory phase

-return to state of resting slightly negative charge (polarization) -no amount of stimulation can cause the neurons to fire again in this stage. -has two phases absolute refractory phase and relative refractory phase

Diffusion

-spontaneous spread of molecules from an area of high concentration to an area of low concentration -get away from the tension -relates to resting membrane potential by being one of the three forces that maintains equilibrium pressure when the cell is at resting potential

Where (on the neuron) does an action potential start? Where does it end?

-the action potential starts at the axon hillock where it creates a wave along the axon -the action potential ends at the axon terminal

sodium-potassium pump

-the energetically expensive mechanism that pushes sodium ions out of a cell, and potassium ions in -active force -relates to resting membrane potential by being apart of the three forces that maintain equilibrium pressure when the cell is at resting potential

electrostatic pressure

-the propensity of charged molecules or ions to move toward areas with the opposite charge -what keeps most of the potassium inside -relates to resting membrane potential by being one of the three forces that maintains equilibrium pressure when the cell is at resting potential

Depolarization

-the reverse of hyperpolarization, the decrease in membrane potential (makes the inside of the neuron more like the outside so a neuron brings its membrane potential closer to 0) -closer to an action potential

describe the amplitude of an action potential. does this differ between action potentials?

-the size or amplitude of the action potential is independent of stimulus size -referred to as the all-or-none property of the action potential (either it fires at its full amplitude or it doesn't tire at all)

polarized cell

-when neurons are more negative on the inside than on the outside they are polarized -away from teh midpoint

action potential steps

1 - Stimulus disturbs the plasma membrane 2 - Sodium Na+ channels open, allowing Na+ to flow into the cell, lessening the polarization/difference in charge at that location 3 - This change causes nearby voltage-gated sodium channels to open, allowing more Na+ to flow into cell 4 - That area of the inside of the cell is now slightly more positive, and the outside, slightly more negative 5 - This affects other nearby voltage-gated Na+ channels and depolarization moves down the membrane = action potential 6 - These channels close and voltage-gated potassium K+ channels open, potassium flows out of the cell repolarizing the membrane 7 - Sodium-potassium pumps then restore resting potential and reestablish proper concentrations of Na+ and K+

anion

A negatively charged ion, such as protein or a chloride ion

Cation

A positively charged ion, such as potassium or sodium ion (at rest)

what is a cell membrane?

It's a double layer of fatty molecules studded with various sorts of specialized proteins

Absolute refractory phase

a brief period of complete insensitivity to stimuli

excitatory postsynaptic potential

a depolarizing potential in a neuron that is normally caused by synaptic excitation. EPSPs increase the probability that the postsynaptic neuron will fire an action potential

inhibitory postsynaptic potential

a hyperpolarizing potential in a neuron. IPSPs decrease the probability that the postsynaptic neuron will fire an action potential. Its also a result from opening of channels that permit chloride ion to enter the cell

Hyperpolarization

an increase in membrane potential (the neuron become even more negative on the inside relative to the outside) (makes it farther from 0)

postsynaptic potential (PSP)

local potential that is initiated by stimulation at a synapse which can vary in amplitude and spread passively across the cell membrane decreasing in strength with time and distance

How does the rate of action potentials affect neuronal communication?

neuronal communication can be strengthened by more action potentials!! (there is no such thing as a stronger or a weaker action potentials)

relative refractory phase

only strong stimulation can reach threshold to produce another action

equilibrium potential

point at which the movement of ions across the cell membrane is balanced, as electrostatics pressure pulling ions in one direction is offset by the diffusion force pushing them in the opposite direction

which anions are concentrated inside and outside the membrane at resting potential?

the anion Cl- are mostly concentrated outside and few inside

resting membrane potential

the electrical charge of a neuron when it is not active

afterpotential

the positive or negative change in membrane potential that may follow an action (they are related to the movement of ions)

threshold of excitation

the stimulus intensity that is just adequate to trigger an action potential in an axon