Nervous Control: In Depth: Ms H

Question 1

Describe what is happening during RESTING POTENTIAL

Answer 1

• ELECTROCHEMICAL GRADIENT is MAINTAINED by Na,K PUMP
• More Na+ leaving the AXON and More K+ ENTERING AXON
• Some K+ DIFFUSES out of VG-K+ CHANNEL

Question 2

Describe what is happening during a WEAK STIMULUS

Answer 2

• Some VG-Na+ channels OPEN
  –> Some Na+ diffuses IN via Facilitated Diffusion
• However, THRESHOLD is NOT reached
• Na,K pump RESTORES RESTING POTENTIAL

Question 3

Describe what is happening during a STRONG STIMULUS

Answer 3

• GENERATOR POTENTIAL reaches THRESHOLD
• MANY VG-Na+ channels OPEN
  –> Na+ DIFFUSES into AXON
  —> POTENTIAL DIFFERENCE RAPIDLY Inc.
  —-> Resulting in MORE VG-Na+ channels opening, so MORE Na+ diffuses IN
• This is POSITIVE FEEDBACK

Question 4

Describe what is happening in REPOLARISATION

Answer 4

• VG-K+ channels OPEN & VG-Na+ channels CLOSE
• K+ diffuses OUT

Question 5

Describe what is happening during HYPERPOLARISATION

Answer 5

• MEMB. POTENTIAL is more (-)VE than RESTING POTENTIAL
• Caused by an ‘OVERSHOOT’ where the VG-K+ channels are to SLOW to CLOSE

Question 6

Why is the REFRACTORY PERIOD neccessary?

Answer 6

• To ensure ACTION POTENTIALS do NOT OVERLAP
• But instead pass as SEPARATE IMPULSES
• And so ACTION POTENTIALS only TRAVEL in 1 DIRECTION