lecture 5: local potentials

Question 1

if an ion channel event results in an increase in sodium conductance, what happens ?

Answer 1

• the cells sodium permeability increases
• electrical and chemical gradients both favour entry of sodium
• sodium carriers positive charge into the cell
• entry of positive charge reduces the inside negativity of the membrane
• the membrane becomes slightly less negative
  = depolarisation, typically an excitatory local potential

Question 2

local potential features

Answer 2

• small: typically of the order of a few mV
• graded: vary in size and duration in relation to the strength and duration of the stimulus
• localized : occur close to the size of their initiation but do not get actively conducted away from that site
• decremental : decrease in size with distance away from the site of initiation
• either depolarizing or hyperpolarizing
• capable of summation (means they can add together which results in a bigger voltage change)

Question 3

how does the magnitude of a local potential change as the distance away from the site of initiation increases

Answer 3

the magnitude of a local potential decreases with distance away from the site of its initiation

Question 4

passive or electrotonic spread

Answer 4

• a local potential may arise at a point on the cell membrane
• the localized conductance change results in a change in transmembrane voltage at that point
• the localized change dissipates exponentially within the cell, over a distance determined by the cell properties

Question 5

temporal summation

Answer 5

local potentials that occur close together in time

Question 6

spatial summation

Answer 6

if the local potentials arise in close physical proximity

Question 7

why are local potentials important

Answer 7

• they are the typical precursors of the non decaying conducted events (action potentials) that constitute rapid long distance neural communication around the body
• sensory stimuli, from both the outside world and within the body trigger local potentials
• the fact that local potentials can be excitatory or inhibitory, that they summate over time and distance, and that they are the precursors of action potentials means that they are crucial to the nervous system’s ability to integrate information

Question 8

where do local potentials arise

Answer 8

synapses: on dendrites and cell body of neurons

Question 9

sites of sensory reception

Answer 9

• skin
• sensory organs (eg: eyes, ears, tongue)
• internal organs (eg: muscle spindles, blood vessels)

Question 10

what causes local potentials

Answer 10

• opening of ion channels

Question 11

local potentials def

Answer 11

small, transient changes in membrane potential caused by an ion channel gating event. they exist as a change in membrane potential in the cell, either making the cell more negative or less negative