M101A

sensory neuron that is activated by an external stimulus (touch) and causes small changes to the electrical charge of the neuron

EX: in the skinl, touch acitvate picinia corpuscles (special sesnory neurons) and cause small changes to the neurons electrical charge.

Point of contact between 2 cells that pass on signals

EX: occurs between the sensory neuron and motor neuron and the motor neuorn to the qudriceps muscle.

large electrical signal that travels along a neuron to send messages over long distances

EX: motor neuron in the spinal cord generates an action potential to send messages to the muscles

action potential occur when the inside of a neuron is more positive than its usual state (depolarization)

It is triggered by the receptor potential or synaptic potential

Depolarization: If an electrical current makes the inside of a neuron more positive, it depolarizes and goes above the threhold potential, firing an action potential aka action response

Hyperpolarization: If an electrical current makes the inside of a neuron more negative, it hyperpolarizes and nothng significant occurs, only the electric charges changes aka passive response.

An action potential fires or it does not, regardless of how strong the stimulus is

A larger current does not mean a larger action potential

Increasing the current won’t increase the action potential, the amplitude is constant and it will only cause other action potentials to fire.

neurons are poor conductors because they lose electrical current as they travel down the axon due to their “leaky membrane” which causes the electrical signal to weaken over distance

Wires are efficent in transmitting electrical signals over long distanes

Neurons lose signal strength quickly (within few mm) due to membrane leakiness.

The signal decreases in neurons since the axon membrane allows electrical current to leak out, so less current is available to change the membrane potential further down the axon,

typically less than 1mm

neurons use action potential as a “booster system” that heps neurons conduct electrical signals over long distances, even though axons are poor conductors.

when the action potential is triggered along the axon, it maintains a constant amplitude without weakening allowing effective signal transmission

action potential are important for electrical signaling becuase they enable active conduction of signals, overcoming the natural leakiness of neurons, making them effective for long-distance communication in the nervous system.

1. ion concentraion differences across the membrane

2. selective permeability to certain ions

active transporters move ions into or out of cells against their concentration gradients using energy.

ion channels allow ions to pass through the membrane in the direction of their concentration gradient (high to low) and are selectively permeable to certain ions

They work in opposite ways: transporters move ions against the gradients, while channels let ions move along the gradients, generating electrical potential.

when the electrical charge of a neuron is not sending signals

by adjusting the ion concentrations in different compartments and regulating the memrbane’s permeability to ions.

intercellular fluid is water inside cells, high in potassium and low in chloride and sodium

extracellulatr fluid is outside the cell, it is hihg in sodium and chloride, low on potassium

whether a substance can cross the plasma membrane

lipis are fat and oils and molecules that do not mix well with water (non polar) but mix with oils or other non-water solvents.

1. K+, Cl-, ions don’t dissolve in lipids but can still get through the membrane since the membrane has tiny pores for theses molecules to pass (ion channels)

2. Some molecules like Urea, can enter more easily inside the cell due to their lipid solubility

ion channels are Pores in the membrane that allow some water-soluble (hydrophilic) substances like ions to cross

Only small hydrophilic molecules can fit through these pores

they use special transport mechanisms to move across the membrane aka active transporters

made up of 2 layers of lipid aka Lipid bilayer.

Also have phospholipids; the head is polar (hydrophilic) and the tail is non-polar(hydrophobic). Phospholipids naturally face the tail away from the water and the head faces toward the water region

No electrical potential (charge difference) will be measured across the membrane

a difference in K+ concentration on both sides of the membrane, inside becoming more negative when K+ moves out.

the inside will be negatively charged relative to the outside since K+ moves out, taking positive charges with it

nerve cells use pumps to accumulate K+ inside, and K+ flows out through channels generating resting membrane

K+ ions move outside due to their concentration gradient, making the outaside of the membrane more positive

The positive charge outside repels more K+ from leaving the membrtane since like charges repel each other

the point where the concentration gradient (high to low) pushing K+ out balances the electrical gradient pulling K+ back in so K+ no longer moves in or out

only a small amount of K+ moves, less than one millionth of the total K+ ions on each side

No, the concentrations of K+ and Cl- remain nearly constant, and charge seperation is only near the membrane and doesn't change the overall amount of K+ or CL- in the entire solution

Nerst equation calculates the equilibrium potential across a membrane for an ion in electrochemical equilibrium

Ex = RT/ zF ln ([X] in/[X] out)

Ex: equilibrium potential for ion X

z: valence (electrical charge) of ion

F: Faraday’s constant

Ex= 58log ([X] in/[X] out)

58 is a constant used at room temperature

ions with charge of +2 (calcium Ca2+), the constant in the Nernst equation becomes +29mV instead of 58mV

-58 mV

the potential would be +58mV at equilibrium

the membrane potential would be +29mV since Ca2+ has a charge of +2

for Cl-, tenfold concentration difference inside vs outside would result in a +58mV potential, but the direction of the charge would depend on Cl-’s negative nature.

concentration gradient and electrical potential

K+ ions move from in to out of the cell, creating negative membrane potential inside

A more negative inside will reduce K+ movememnt out of the cell since neg charge attracts positive K+ ions

at -58 mV, the membrane potential exactly balances the tenfold concentration gradient of K+

K+ will move into the cell, as the positive ions are attracted to the more negative inside

It Depends on the concentration gradients of K+ and Na+ and the relative permeability of the membrane to each ion

Goldman’s equation takes into account the concentyration gradients and permeability of multiple ions

membrane potential would be 0mV since their actions cancel each other out

The concentration of Cl- is inverted since it it negatively charges, unlike K+ and Na+

Vm = (58log) (Pk [k+] out + PNA[Na+] out + PCl [Cl-] in) / (Pk [K+] in + PNA[Na+] in + PCl [Cl-] out)

membrane is more permeable to K+ (potassium) at rest

The permeability to Na+ increases during an action potential creating a depolarization, causing Na+ to flow into the neuron, making the inside more negative

the resting membrane potential is -65 mV and K+ is the closest to equilibrium

The membrane potential goes from negative (resting state) to positive (due to Na+ flux) and back to neg (when K+ permeability is restored)

the resting membrane potential becomes less negative as external K+ concentration increases

0 mV

The slight permeability of other ions like Na+ and Cl-, which affect the resting membrane potential expecially at low K+ concentrations

he membrane more permeable to K+ than other ions and that there is more K+ inside neuron than outside

K+ channels allow K+ to leave the cell at rest and membrane transporters maintain high K+ concentration inside the neuron

The equilibriym potential for Na+ is positivem it’s important because if the membrane becomes highly permeable to Na+, the membrane potential would become positive causing an action potential

loweirng external Na+ concentration reduces botht eh rate of rise and the peak amplitude of the action potential

Linear relationship between action potential amplitude and the logarithm of the external Na+ concentration, with a slope of 58mV per tenfold change in Na+ concentration

No, lowering Na+ concentration has little effect on the resting membrane potential, indicating that Na+ permeability is low at rest

the membrane depolarizes because of a temporary increase in Na+ permeability, allowing Na+ to rush into the neuron

membrane repolarizes at Na+ permeability decreases, followed by an undershoot caused by a brief increase in K+ permeability