Action/Resting Potential, Refractory Period, Myelination And Saltatory Conduction

Question 1

Myelinated motor neurone?

Answer 1

• the cell body of the neuron contains the organelles found in a typical animal cell
• proteins and neurotransmitters are made here

Question 2

Dendrites?

Answer 2

• carry action potentials to surrounding cells

Question 3

Axon?

Answer 3

• conductive, long fibre
• carries nerve impulses along motor neurone

Question 4

Schwann cells?

Answer 4

• wrap around axon to form myelin sheath - lipid so doesn’t allow charged ions to pass through it
• gaps between myelin sheath called nodes of Ranvier

Question 5

Resting potential?

Answer 5

• neuron not conducting an impulse - difference between electrical charge inside and outside of neuron
• more positive ions (Na+ and K+) outside compared to inside - inside of neuron more negative

Question 6

Establishing a resting potential?

Answer 6

• maintained by sodium-potassium pump, involving active transport and ATP
• pump moves 2 K+ ions and 3 Na+ ions out
• creates electrochemical gradient - causes K+ to diffuse out and Na+ to diffuse in

Question 7

Action potential?

Answer 7

• neutron’s voltage increases beyond a set point from the resting potential - generates nervous impulse
• increase in voltage, or depolarisation, is due to neuron membrane becoming more permeable to Na+

Question 8

All-or-nothing principle?

Answer 8

• if depolarisation doesn’t exceed -55mV no action potential or impulse is produced (Nothing)
• any stimulus that does exceed depolarisation of -55mV will always peak at the same max voltage (All)
• Bigger stimuli increase frequency of action potentials
• Makes sure animals only respond to large enough stimuli

Question 9

Refractory period?

Answer 9

• after action potential is generated, membrane enters refractory period when it can’t be stimulated because sodium ion channels are recovering and can’t be opened

Question 10

Importance of refractory period?

Answer 10

• ensures that discrete impulses are produced - action potentials can’t be generated one after another so this makes sure that each is separate
• ensures that action potentials travel in one direction - stops action potential from spreading out in two directions which would prevent a response
• limits number of impulse transmission - prevent over reaction to stimulus

Question 11

Factors affecting speed of conductance?

Answer 11

• myelination and saltatory conduction
• axon diameter
• temperature

Question 12

Myelination and saltatory conduction?

Answer 12

• action potential jumps from node to node (saltatory conduction), which means action potential travel along the axon faster

Question 13

Axon diameter?

Answer 13

• wider diameter increases speed of conductance - less leakage of ions and therefore action potentials travel faster

Question 14

Temperature?

Answer 14

Higher temperatures increases speed of conductance because:
- ions diffuse faster
- enzymes involved in respiration work faster - more ATP for active transport in the sodium-potassium pump