transmission of nerve impulses + factors affecting conduction+ refractory period- Neuronal communication

Question 1

how can an AP only travel in one direction

Answer 1

-depolarisation causes sodium channels to open further up the axon= an influx of sodium ions in one direction
-previous part of axon is unresponsive as it is in repolarisation
-i.e a wave of depolarisation

Question 2

all or nothing principle

Answer 2

-an impulse is only transmitted if the initial stimulus goes above the threshold frequency

Question 3

receptor potential

Answer 3

-increases as strength of stimulus increases
-frequency not amplitude of waves increase

Question 4

when does the refractory period occur

Answer 4

-After an AP, there is a period of time where both sodium and potassium ion channels are closed (during hyperpolarisation)
-axon membrane is in a period of recovery and is unresponsive

Question 5

significance of refractory period

Answer 5

-ensures action potentials are discrete i.e dont merge
-ensures one way transmission of impulse as region behind is recovering
-as a result, ensures ‘new’ APs are generated ahead
-means there is a minimum time inbetween each AP can be generated
-length of refractory period determines frequency of APs

Question 6

3 main factors affecting speed of conduction

Answer 6

-myelination, temp and diameter of axon

Question 7

myelination affecting speed of conduction

Answer 7

-unmyelinated v slow as depolarisation must happens along whole of axon
-myelinated increases speed as impulse jumps from node to node, shwann cells prevent depolarisation in myelin sheath

Question 8

saltatory conduction

Answer 8

-impulse jumps from node to node due to presence of schwann cells

Question 9

diameter of axon affecting speed of conduction

Answer 9

-axons with larger diameter = faster conduction as less resistance
(apparently have larger SA than smaller diameters=increases rate of diffusion

Question 10

temp affecting speed of conduction

Answer 10

-colder conditions = less kinetic energy for ions so facilitated diffusion is slower= slower speed of conduction