Lecture 10 + 11 - The Resting Cell Membrane and Changing it

Question 1

What is the resting membrane potential ?

Answer 1

the electrical potential difference across the cell membrane at rest
provides the basis for cell signaling

the cell membrane is not permeable to ions - so we need gated ion channels - when opened ions will flow rapidly down their electrochemical gradient

Question 2

what are the values for the 4 key resting potentials to remeber ?

Answer 2

Cardiac myocytes -80mV
Neurones -70mV
Skeletal muscle myocytes -90mV
Smooth muscle myocytes -50mV

Question 3

how is the resting potential maintained

Answer 3

K+ channels that are OPEN at REST form the main make up of the resting potential

when the diffusion of K+ out of the membrane matches (equlibirum) with K+ flow inward from the Electrical gradient we are at rest

membrane potential arises because the membrane is selectively permeable to K+

there is some movement of Na+ and Ca2+ and Cl- inward that slightly reduces membrane potential (net)

Question 4

How do we measure the resting potential ?

Answer 4

a membrane potential is the electrical charge that exists across a membrane

we use a Microelectrode (glass pippete filled with conducting solution attached to a volt meter) - that penetrates the cell memebrane and measures the membrane potential

Question 5

Find your group work and other resources to use the Nernst equations a few times

Answer 5

do it !

Question 6

Define Depolarization

Answer 6

A decrease in the size of the membrane potential from its normal value - the cell interior will become less negative

-70mV to -50mV

Question 7

Define Hyperpolarization

Answer 7

An increase in the size of the membrane potential from its normal value - the cell interior will become more negative

-70mV to -90mV

Question 8

why / how do membrane potentials arrive ?

Answer 8

we have a semi permeable membrane - does not let ions pass the membrane without using controllable ion channels

it is a result of selective ion permeability
if we change selectivity of the membrane between ions we will change the membrane potential

if we increase membrane permeability to a particular ion then that moves the potential to wards the equilibrium potential for that ion

Question 9

what happens when we open K+ or Cl- ion channels ?

what happens when we opoen Na+ or Ca2+ ion channels ?

Answer 9

K+ will move out of cell and Cl- will move into cell and cause hyper polarization - gain of negative charge
Na+ and Ca2+ will move into cell cause depolarization - the cell gains positive charge

Question 10

explain how real cells have imperfect selectivity

Answer 10

real cells have channels open for more than one ion

so each ion makes a contribution to the membrane potential depending on how permeable that ion is (how many open channels there are)

Question 11

explain the nicotinic Ach receptor

Answer 11

these are found at the neuromuscular junction - neurones release ach into the synapse

ach binds to receptors on the muscle membrane - gated receptors open to let in MAINLY Na+
but some K+ will also pass through, however anions will not pass through

Na+ influx into muscle cell moves it close to the action potential and resulting muscle contraction

Question 12

outline the types of gating in GATED pores

Answer 12

Ligand gating -
lingand binds to open/close the channel
channels at synapse respond to extracellular transmitters (ach)

Voltage Gating
Channel will open or close in response to a change in the membrane potential - such as action potentials

Mechanical Gating
Channel will open or close in response to membrane deformation
mechanoreceptors - such as hair cells

Question 13

outline the how synaptic transmission works

what can it occur between (dont learn just think logically)

Answer 13

nerve - nerve
nerve - muscle
nerve - gland
sensory cell - nerve

transmitter release from the presynaptic cleft to act on a receptor on the postsynaptic membrane

Question 14

explain fast synaptic transmission

Answer 14

the receptor protein is also an ion channel - transmitter binding causes channel to open

excitatory synapses - open channels to cause membrane depolarisation
causes an exitatory post synaptic potential (EPSP)
longer than the action potential
permebale to Na+ and Ca2+

Inhibitory synapses - open chanels that cause hyperpolarization
Permeable to K+ or Cl-
Inhibitory post synaptic potential (IPSP)

i think IPSP and EPSP combine to cause the action potential process

Question 15

explain slow post synaptic transmission

Answer 15

receptor and channel are two separate proteins

1- Direct G protein coupling

2-Gating via an intracellular messenger cascade system - this is the SLOWEST as it has many steps

Question 16

Name two factors that can influence membrane potential

Answer 16

1. Changes in the ion concentration
   most vital is the extracellular K+ potential of 4.5mM - altered in clinical situations
   think excitability in heart - too much K+ and too excitable or membrane channels shut off after too much exposure and now person is slow and sluggish
2. Elctrogenic pumps
   Na/K ATPase - sodium pump
   provides a small contribution to the membrane potential due to a net charge of -1 in the membrane for every 3/2 movement
   it is the primary active transporter in cells, and if it did not set up the Na+ gradients MANY secondary active transporters that rely on flowing down the Na+ gradient would not work