L15

Question 1

explain graded potentials

Answer 1

• Greater the stimuli, greater magnitude of membrane potential change
  
  • Can make the RMP more neg. (away from threshold), called hyperpolarising
  • Can make RMP more pos. (towards threshold), called depolarising
    Occurs in resposne of opening of ion channels- triggering event

Question 2

explain stimulus strength of graded potentials

Answer 2

○ Amplitude depends on stimulus strength
○ Add together to create larger amplitude
If threshold reached, action potential result

Question 3

explain action potential

Answer 3

• Sequence of rapidly occuring events, decrease the membrane potential during
  which
  ○ Critical voltage (threshold voltage) is reached IF graded potentials summate
  ○ Rapid reversal of membrane potential (depolarisation, then restoration to resting by repolarisation and some hyperpolarisation
  
  • Action potentials are ‘all or nothing’ to propagate
    Caused by permeability change in the plasma membrane

Question 4

explain the stimulus strength of action potential

Answer 4

○ Only occur if reach threshold
So have subthreshold, threshold, and suprathreshold

Question 5

explain the steps of action potential

Answer 5

• Steps
  1. Resting state
  § All voltage gated Na+ + K+ channels closed

    2. Depolarisation
        § Threshold reached
        § Na+ channel opens
        § Influx depolarises, opening more Na+ channels
  		
    3. Repolarisation
        § Na+ channels inactivates + closes
        § K+ channels open
        § Outflux repolarises, restoring resting membrane potential
        § Na+ channels open, returning to resting when K+ gates close
  		
    4. Hyperpolarisation
        § Membrane repolarises BELOW resting membrane potential
        § Means TOO MUCH K+ out
        § Restored quickly

Question 6

explain refractory periods and the 2 types

Answer 6

§ For about 1msec, a second AP cannot be triggered (ABSOLUTE refractory period)
§ Acts to limit the rate at which signals can be transmitted down an axon without backflow
§ During RELATIVE refractory period, a action potential activate CAN occur with a STRONG graded potential- bad for excitable tissues like the heart

			□ Absolute refractory period- during depolarisation + repolarisation Relative refractory period- during hyperpolarisation

Question 7

label action potential curve

Answer 7

REFER TO ONENOTE

Question 8

compared graded and action potentials

Answer 8

• Graded
  ○ In dendrites + cell body
  ○ Ligand/mechanically gated ion channels
  ○ NOT propagated
  ○ Short distance communication
  ○ Amplitude depends on strength of stimulus
  ○ Longer duration
  ○ May be hyperpolarising or depolarising
  ○ No refractory period
  ○ Summation can occur
  
  • Potential
    ○ Trigger zone, then propagates along axon
    ○ Voltage gated channels for Na+/K+
    ○ Long distance
    ○ ‘all or nothing’ in regard to amplitude
    ○ Shorter
    ○ Always depolarising, followed by repolarising, then return to resting
    ○ Propagates
    ○ NO summation

Question 9

explain electrical signals in neurons

Answer 9

• Excitable cells communicate with each other via action or graded potentials
  
  • AP allows for short + long distance communication
    GP= allows for short distance communication