Session 4.2: Changing Membrane Potential

Question 1

what different types of signalling involve a changing membrane potential

Answer 1

1. action potentials in nerve and muscle cells
2. triggering and control of muscle contraction
3. control of secretion of hormones and neurotransmitter
4. transduction of sensory information into electrical activity by receptors
5. postsynaptic actions of fast synaptic transmitters

Question 2

what is depolarisation

Answer 2

a decrease in size of the membrane potential so cell interior becomes less negative (-50mV)

Question 3

what is hyperpolarisation

Answer 3

an increase in size of membrane potential so cell interior more negative (-90mV)

Question 4

what does increasing membrane permeability of a particular ion

Answer 4

moves the membrane potential towards equilibrium potential

Question 5

how do you increase hyperpolarisation

Answer 5

opening k and cl channels

Question 6

how do you increase depolarisation

Answer 6

open na and ca channels

Question 7

what is an example of a channel that is less selective

Answer 7

at neuromuscular junctions - ACh release which bind to nicotinic acetylcholine receptors on muscle membrane
negatively charged middle of the channel so selective for cations (allow Na and K) and gated so when ACh binds causes conformational change which allows sodium ions to enter
this is selective as does not allow anions due to negatively charged residues

Question 8

what is the membrane potential across neuromuscular junction

Answer 8

0mV ( as let both sodium and potassium across, this is potential intermediate between the Ena and Ek)

Question 9

what are the different types of gated channels

Answer 9

1. ligand gated
2. voltage gated
3. mechanical gated

Question 10

what are ligand gated channels

Answer 10

open and close in response to binding of ligand and intracellular messengers
eg: at synapses that respond to transmitters

Question 11

what are voltage gated channels

Answer 11

open and close in response to changes in membrane potential

eg: action potentials

Question 12

what are mechanical gated channels

Answer 12

open or close in reponse to membrane deformation

eg: mechanoreceptors in carotic sinus stretch receptors

Question 13

what do synaptic connections occur between

Answer 13

nerve and nerve
nerve and muscle
nerve and gland
nerve and sensory

Question 14

what happens at the synpase

Answer 14

action potential - neutrotransmitter and fuses. chemical transmitter released from presynaptic cells binds to receptors on postsynaptic membrane

Question 15

how does fast synaptic transmission occur

Answer 15

when the receptor protein also acts as an ion channel, eg:sodium

Question 16

how does depolarisation occur

Answer 16

excitary transmitters open ligand gated channels

Question 17

how does an excitatory post synaptic potential form

Answer 17

sodium or calcium enter through ligand gated channels resulting in a change in memrbane potential

Question 18

what are some key features of excitatory post synaptic potentials

Answer 18

very long, longer than action potential
graded in amplitude with amount of transmitters
transmitters include acetylcholine, glutamate

Question 19

what is the purpose of excitatory post synaptic potential

Answer 19

making membrane potential less negative around threshold for opening of voltage sensitive channels which can lead to an action potential. they convert a chemical stimulus to electrical stimulus to depolarise membrane enough to open channels

Question 20

how does hyperpolarisation occur

Answer 20

inhibitory transmitters open ligand gated channels

Question 21

how does an inhibitory post synaptic potential form

Answer 21

more permeable to K+ leaving and Cl entering

Question 22

what is the purpose of an inhibitory post synaptic potential

Answer 22

so moves memrbane ptoential away from threshold for action potential so inhibited

Question 23

what are some examples of inhibitory transmitters

Answer 23

glycine, gamma-aminobutryic acid (GABA)

Question 24

how does slow synaptic transmission occur

Answer 24

the receptor and channel are seperate proteins

Question 25

what are types of slow synaptic transmission

Answer 25

1. Direct G-protein gating - protein binds to the receptor and a G protein is activated and migrates and interacts with channel to open it. this is localised and quite rapid
2. gating via an intracellular messnger - binding of to G protein which activates an enzyme which causes a signalling cascade which results in production of intracellular messenger molecules or protein kinase which acts on channel to activate it. this acts throughout cell and can undergo amplfication by cascade

Question 26

what other factors influence membrane potential

Answer 26

1. changes in ion concentration - such as extracellular k+ (usually 4.5mM) which can alter membrane excitability like in the heart
2. electrogenic pumps - such as Na/K-ATPase, one cycle = one positive charge out which leaves behind negative charge making a more negative memrbane potential

Question 27

how is the active transport of ions so important

Answer 27

sets up gradient so maintains membrane potential