nervous communication

Question 1

what type of cell makes up the membrane of the myelin sheath?

Answer 1

Schwann cell

Question 2

neurones are well adapted to their function because:

Answer 2

-Dentrites provide large SA for multiple connections to other cells
-Long axon allows impulses to travel longer distances continuously (fewer synapses)
-Myelin sheath provides insulation and increases impulse speed (ions can only be transported at the node of ranvier)
-They contain many mitochondria to provide ATP for active transport of ions

Question 3

The refractory period

Answer 3

This takes place when the membrane is repolarising and the voltage gated Na+ channels are closed. It is the period of time when the membrane can’t transmit another impulse.
-it ensures that discrete impulses are produced
-it ensures that action potentials travel in one direction
-limits the number of impulse transmissions

Question 4

Basic principles of action potential

Answer 4

The influx of Na+ ions causes more voltage gated Na+ channels to open in the next part of the membrane causing depolarisation. Behind the depolarised region, the voltage gated Na+ channels close and the K+ ones open, allowing this part of the membrane to repolarise until it reaches resting potential.This impulse passes along the whole membrane like this until it reaches the end of the neurone. this is a wave of depolarisation.

Question 5

where does depolarisation occur in a myelinated neurone?

Answer 5

nodes of Ranvier

Question 6

Advantages to the cell of having saltatory conduction

Answer 6

faster speed of transmission
less ATP is used because fewer Na/K pumps are required to return the membrane to the resting potential

Question 7

All or nothing principle

Answer 7

Each neurone has a threshold- this is the level of stimulus which triggers an action potential. if the depolarisation doesn’t reach threshold, there will be no action potential because the voltage gated sodium ion channels stay closed.

if the threshold is reached, the voltage gated Na+ channels open by a process of positive feedback- the more depolarisation occurs, the more channels open.

Question 8

If action potentials are always the same size, how can we discriminate between different sizes of stimulus?

Answer 8

stronger the stimulus, the more frequent the action potential.

Question 9

Factors affecting speed of conduction

Answer 9

-Myelinated neurones transmit impulses fasted than any unmyelinated neurones.
-Axon diameter affects speed of transmission too- wider neurones transmit impulses faster

Question 10

why do wider neurones transmit impulses faster? (axon diameter)

Answer 10

(more ions leak at thinner diameter)
wider diameter increases speed of conductor . less resistance to flow of ions from cytoplasm than in narrower axons. also axons with wider diameter have smaller SA to VR than axons with smaller diameter. causes fewer ions to leak out of axon. easier for action potential to propagate.

Question 11

temperature increases will increase speed of transmission. explain why.

Answer 11

-ions diffuse faster due to more kinetic energy
-enzymes involved in respiration work faster. therefore there is more ATP for active transport in the Na+/K+ pump