action potentials

Question 1

action potential

Answer 1

it i a transient depolarisation of a cell

Question 2

excitable cells

Answer 2

are cells that can generate action potentials
- for any particular cell an action potential is, within close limits, of fixed magnitude and duration.

Question 3

what do action potentials do?

Answer 3

they transfer information
it is then coded by the frequency of action potentials passing along a nerve.

Question 4

initiate cellular events

Answer 4

for example initiate muscular contraction (excitation-contraction coupling)

Question 5

all or nothing law

Answer 5

once an action potential has been initiated varying the stimulus strength does not alter the configuration of action potential

Question 6

threshold

Answer 6

to initiate an action potential it is necessary to depolarise the cell membrane to a critical (threshold) potential.

Question 7

ionic basis of action potential

Answer 7

experiments showed that the action potential depolarisation was due to transient increase of membrane Na+ permeability.

Question 8

membrane potential repolarises

Answer 8

back to resting potential and the action potential terminates.
repolarisation is aided by an even greater than normal increase of K+ permeability.

Question 9

process of an action potential

Answer 9

resting potential
depolarising stimulus
sodium and potassium channels open
sodium entry depolarizes cell
sodium cannels start to close
K channels stay open

Question 10

initiating a AP

Answer 10

cell must be depolarised from the resting membrane potential to a threshold potential

Question 11

At threshold voltage- activated ion channels

Answer 11

they open and callow cations( usually Na+) to enter the cell, generating an action potential.
to initiate action potential, energy must be added to the system in a form of stimulus.

Question 12

how to get to resting to threshold potential

Answer 12

1. artificial application of electrical current
2. at synapses between cells neurotransmitters bind to ligand-gated channels on target cell.
3. spontaneously in pacemaker cells
4. sensory cells- convert a stimulus to a change of membrane potential of the associated nerve, if stimulus is large enough it reaches threshold.

Question 13

how is an action potential conducted(1)

Answer 13

a local current precedes the action potential wavefront in the cytoplasm.

Question 14

trigger zone

Answer 14

the region of the cell that generates an action potential. it is represented by a reversal of the membrane potential polarity.

Question 15

how is an action potential conducted(2)

Answer 15

some current leaks across the membrane, depolarising it.
if the depolarisation is sufficient to reach threshold an action potential is initiated.

Question 16

factors affect AP conduction velocity

Answer 16

Cell diameter- CV increases as fibre diameter increases.
temperature- increases CV
myelination: vertebrate nerve fibres diameter>1um possess a myelin sheath which surrounded the axon with breaks about every millimetre.

Question 17

saltatory conduction

Answer 17

when the AP jumps from node to node.
if the actions are thick they will be quicker
temperature will increase speed of ions.

Question 18

coding information

Answer 18

As Stimulus increases number of action potentials generated increases.
the action potential frequency codes stimulus intensity.

Question 19

Active transport

Answer 19

movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by proteins and requiring energy.

Question 20

depolarisation

Answer 20

loss of the difference in charge between the inside and outside of the plasma membrane of muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior.

Question 21

myelinated fibres

Answer 21

an insulating layer(sheath) that forms around nerves which is made up of proteins and lipids. allows electrical impulses to transmit quickly and efficiently along nerve cells

Question 23

permeable

Answer 23

allows molecules to pass through it

Question 24

repolarisation

Answer 24

restoration of the difference in charge between the inside and outside of the cell membrane following depolarization.

Question 25

resting membrane potential

Answer 25

the electrical potential difference across the plasma membrane when the cells is in a non-excited stage.

Question 26

stimulus

Answer 26

change that occurs in the internal or external environment that disturbs homeostasis

Question 27

threshold potential

Answer 27

the membrane potential at the point where Na+ permeability caused by depolarization increases to make Na+ inward flow volume just to equal to the K+ outward flow volume.