animal phys exam 4: electrophysiology of neurons

what is electrophysiology

study of cellular mechanisms for producing electrical potentials and currents

what are the different electrical signals in neurons

• plasma membrane of a neuron is polar

• one side is positive (ECF)

• one side is negative (ICF)

What does ICF mean

it’s the net negative charge within a cell due to anions as well as negatively charged proteins, nucleic acids and phosphates, has lots of cations (K+)

what does ECF mean

it is not as negatively charged as ICF and has lots of Na+

how is the plasma membrane polarized

the charge differential between ICF and ECF

what determines the charge of the plasma membrane

concentration of Na+ and K+ in the ECF and ICF which is dependent on the sodium potassium pump- 3Na+ out for every 2K+ in to get a negative resting membrane potential

how are neurons stimulated

electrical signals created by altering the permeability of the membrane to ions/opening or closing ion channels that allow ions to flow down concentration gradients and create electrical signals

what are the different ways channels are stimulated to open

• voltage-gated channels

• ligand-gated channels

• mechanical forces

• heat

• light

what are voltage-gated channels

they open and close in response to changes in membrane potential and are found primarily along the axon, and can generate and propagate the action potential

what are ligand-gated channels

they open when a specific chemical (ligand) binds to the channel and are found primarily on dendrites and soma, and can mediate synaptic communication by responding to neurotransmitters

what are the five steps to stimulating a neuron (local potentials)

• stimulation begins at dendrite

• Na+ enters at the dendrite

• change in membrane potential at dendrite

• membrane potential changes in neighboring plasma membrane (ripple effect)- local potential

• current spreads to soma and then to trigger zone

what are the four characteristics of local potentials

• graded

• decremental

• reversible

• stimulatory or inhibitory

what does graded mean for local potentials

magnitude varies based on stimulus strength, the more intense the magnitude the more Na+ channels open and the more Na+ enters the cell

what does decremental mean for local potentials

the more spread out the local potentials are the weaker they are and Na+ leaks out and drive K+ out

what does reversible mean for local potential

if the stimulation ceases then Na+ diffuses out and resting membrane potential is restored

what does stimulatory or inhibitory mean for local potentials

some local potentials depolarize cells and others hyperpolarize cells

what does action potential do

they cause a dramatic change in membrane polarity produced by voltage-gated ion channels and only occurs when there is a high enough density of voltage-gated channels- all or nothing response

when can the soma not generate action potentials

50 to 70 gates per mm²

when can the trigger zone generate action potential

350 to 500 gates per mm²