Nervous Coordinatiom

Question 1

Structure of a myelinated motor neurone

Answer 1

Axon terminal

Axon:
-contains myelin sheaths made out of Schwann cells
-node of ranvier between the sheaths

Cell body

Dendrite

Question 2

What is resting potential

Answer 2

Axon has a negative charge relative to the outside

Question 3

How can resting potential be established

Answer 3

Na+/K+ pump - active transport:
-3na+ out and 2K* into acon

Creates an electrochemical gradient
-higher K conc inside and higher Na conc outside

Differential membrane permeability:
More permanent to K (moves out via facilitated diffusion)
Less permeable to Na as channels are closed

Question 4

What are the 5 steps to a action potential

Answer 4

Stimulus

Depolarisation

Repolarisation

Hyperpolarsation

Resting potential

Question 5

Describe how an action potential is generated

Answer 5

Stimulus:
-Na+ channels open
-Na+ diffuse into axon down electrochemical gradient(causing depolarisation)

Depolarisation:
-is threshold potential is reached, action potential is generated
-more voltage Na gates open
-Na diffuses in more rapidly

Re-polarisation:
-voltage Na gates close
-voltage K gates open
- K diffuses out of axon

Hyperpolarsiation:
-K channels are slow to close so they slightly release to many K

Resting potential:
-restored via a Na/K pump

Question 6

Non-myelinated vs myelinated in generating nerve impulse

Answer 6

Non:
-action potential passes as a wave of depolarisation
-lost of Na in a region increases permeability by causing voltage gates Na channels open, adjoining regions also depolarise

My:
-myelination proved electrical insulation
-depolarisation of axon at nodes of ranvier
-resulting in salatory conduction
-no depolarisation along the whole length of axon

Question 7

What would damage to the myelin sheath do

Answer 7

Less saltatory conduction so depolarisation occurs for the length of the whole of the axon
-nerve impulse takes longer

Ions/depolarisation may leak to other neurones
-causing wrong muscle contraction

Question 8

What is the refractory period

Answer 8

Time taken to restore axon to resting potential when no further action potential can be generated

As na channels are closed

Question 9

Importance of refractory period

Answer 9

Ensure that action potentials don’t overlap
-limits freq of impulse transmission do there isn’t over reaction to a stimulus

Ensure that action potentials travel in 1 direction (can’t be propagated in a refractory period)

Question 10

Factors that affect speed of conduction

Answer 10

Myelination:
-depolarisation at nodes of ranvier only, saltatory conduction, dosent have to travel the whole length of axon

Axon diameter:
-bigger diameter means less resistance to flow of ions

Temp:
-increases rate of diffusion
-but proteins/enzymes could denature at a point