electrode potentials

Question 1

membrane potential

Answer 1

the potential difference between the inside and outside the cell
-inside -outside
-outside usual;ly define by 0

Question 2

how to experimentally measure membrane potential

Answer 2

• fill a micro electrode(fine glass pipette) with a conducting solution (KCL)
  -then penetrate the microelectrode into the cell membrane to measure membrane potential

Question 3

depolarization

Answer 3

A decrease in the size of the membrane potential from its normal value. Cell interior becomes less negative e.g. a change from – 70 mV to – 50 m

Question 4

hyperpolarization

Answer 4

An increase in the size of the membrane potential from its normal value. Cell interior becomes more negative e.g. a change from – 70 mV to – 90 mV

Question 5

what to consider when setting up membrane potentials

Answer 5

-concentration gradient(chemical gradient)
-charge gradient (electrical forces)

Question 6

what is setting up a resting potential dependent on

Answer 6

• concentration gradient the concentration of ions inside and outside of the cell affects the movement of ions
  -sodium-potassium pump is responsible for setting up membrane potential.

Question 7

equilibrium potential

Answer 7

-there is no net movement of ions across a membrane the concentration gradient and charge gradient are equal
-thought of as opposite forces so when the outward diffusion gradient exceeds the inward charge gradient ions move out of the cell

Question 8

calculating equilibrium potential for K+

Answer 8

• nernest equation, write on cheatsheet

Question 9

how do we calculate real membrane potentials

Answer 9

• use the GHK equation
  -because real membrane have channels open for more than one type of ion and the contribution of each ion depends on how permeable the membrane is to that ion

Question 10

excitatory synapses

Answer 10

• Excitatory transmitters open ligand-gated channels that cause membrane depolarization
• Can be permeable to Na+, Ca2+ or sometimes cations in general
• The resulting change in membrane potential is called an excitatory post-synaptic potential (EPSP)
  -action potential generated

Question 11

Inhibitory synapses

Answer 11

• Inhibitory transmitters open ligand-gated channels that cause hyperpolarization
• Can be permeable to K+ or Cl-
• The resulting change in membrane potential is called an inhibitory post-synaptic potential (IPSP)
  -no action potential

Question 12

what are action potentials for?

Answer 12

• passing information along axons causing the release of neurotransmitters or hormones
  -have different thresholds in different body parts

Question 13

how do we know the direction ions will move in?

Answer 13

• concentration gradient= ions will usually move from an area of high concentration to an area of low concentration
  -electrical charge is also considered to know which side ions will be attracted to and which side repulsion will occur

Question 14

action potential threshold in axon

Answer 14

plus thirty

Question 15

action potential threshold in skeletal muscle

Answer 15

plus forty

Question 16

action potential threshold in the sino-atrial node

Answer 16

plus thirty

Question 17

action potential threshold in cardiac ventricle

Answer 17

plus thirty

Question 18

resting potential

Answer 18

• sodium-potassium pump moves 3 sodium ions out and 2 potassium ions in by active transport
  -sodium ion channels are closed and potassium ion channels are open allowing facilitated diffusion
  -therefore, the membrane is more permeable to potassium ions
• therefore the membrane is polarised.( more positive outside than inside)
  -resting potential= -70

Question 19

how action potential is intiated

Answer 19

stimulus causes sodium ion channels to open so sodium ions diffuse into the cell. (membrane is more permeable to sodium)
-when the potential difference reaches -55v, positive feedback occurs so more sodium ion channels open and more sodium ions diffuse into the cell.
-depolarisation occurs (inside more positive than outside). reaches+40v

Question 20

recovery after an action potential

Answer 20

-repolarisation = sodium ion channels close and potassium channels open. potassium diffuses out of the cell bringing the potential difference back to more positive than inside.
-there is a potential difference overshoot. making the cell hyperpolarised
-original potential difference is returns and resting potential is maintained by the sodium-potassium pump
- reactionary period= recovery period. after action potential neurones cant be excited straight away

Question 21

basic structure of NA+ channels

Answer 21

-complex arrangement of proteins that forms a transmembrane pore through which sodium ions can pass in response to changes in the cell membrane potential.
-primary structural component is the alpha subunit, which is responsible for ion conduction and gating.
-It consists of four homologous domains (I to IV), and each domain has six transmembrane segments (S1 to S6).
-Voltage sensors are present in the S4 segment of each domain and play a crucial role in responding to changes in the membrane potential

Question 22

basic structure of K+ channels

Answer 22

-have a tetrameric structure, consisting of four alpha subunits.
-Each subunit consists of six transmembrane segments (S1 to S6).
-S1 to S4 form the voltage-sensing domain, and S5 and S6 form the pore-forming domain

Question 23

comparison of K+ channels and Na+ channels

Answer 23

• Na+ channels alpha subunits are linked whereas in K+ they are four separate units

Question 24

how does the action potential propagate along the axon

Answer 24

• can only travel in one direction from the cell body down the axon
  -travels without a loss in amplitude

Question 25

local current

Answer 25

-A local current =the flow of ions across the cell membrane in a localized region of a neuron -

Question 26

length constant

Answer 26

- the distance it takes for the potential to fall to thity7% of its original value - influences how efficiently the action potential is propagated down the axon. -Neurons with longer length constants can propagate action potentials more effectively over longer distances without significant loss of the depolarizing signal

Question 27

saltatory conduction

Answer 27

-The membrane is only depolarised at the nodes of Ranvier -creates a longer localised circuit; -increases the rate of impulse transmission; -occurs in myelinated neurones

Question 28

neuromuscular junction

Answer 28

- the synapse between a nerve and a skeletal muscle fibre -called a chemical synapse

Question 29

actions at the neuromuscular junction

Answer 29

-An action potential travels down the axon of a motor neuron -When the action potential reaches the axon terminals at the neuromuscular junction, it triggers the opening of voltage-gated calcium channels in the presynaptic neurone -there is an influx of calcium ions -calcium ions bind to synaptotagmin -the snare complex makes vesicles containing ACh to fuse with the presynaptic membrane -Acetylcholine is released into the synaptic cleft ( -Acetylcholine diffuses across the synaptic cleft and binds to acetylcholine receptors on the postsynaptic membrane (motor end plate) of the muscle fibre. The binding of acetylcholine to its receptors causes the opening of these ion channels, allowing an influx of sodium ions into the muscle fibre. -This influx results in a local depolarization which causes an action potential triggering muscle contraction

Question 30

nicotinic receptor

Answer 30

- ACh binding site ACh binds to each alpha subunit causing a conformational change leading to the opening of the pore

Question 31

competitive blockof ACh by d-tubocurarine

Answer 31

- competes with ACh for the binding site on the nicotinic receptor -prevents a conformational change from occurring therefore inactivation of the receptor

Question 32

block of ACh by succinylcholine

Answer 32

-succinylcholine functions as a depolarizing neuromuscular blocker, leading to a prolonged activation of the nicotinic receptors -Succinylcholine initially acts as an agonist at the nicotinic receptors. It binds to the receptor sites on the postsynaptic membrane at the neuromuscular junction. -Unlike acetylcholine, which is rapidly broken down by acetylcholinesterase after binding to the receptor, succinylcholine is more resistant to enzymatic degradation. As a result, succinylcholine induces a persistent depolarization of the postsynaptic membrane. -Succinylcholine keeps the nicotinic receptors activated for a more extended period compared to acetylcholine. -This prolonged depolarization prevents the muscle fibre from responding to subsequent nerve impulses and leads to temporary paralysis.

Question 33

clinical use of neuromuscular blockers

Answer 33

= They are added in combination with general anaesthetic to cause temporary paralysis during surgery

Question 34

difference between ACh binding to nicotinic and muscarinic receptors

Answer 34

-nicotinic receptors produce a fast depolarisation because it is a ligand-gated ion channel -muscarinic receptor produces a slower response because they are G =-protein =s which trigger a cascade of events in the cell