Factors increasing excitability
Warming
Alkalosis
Increase Na+ permeability
Increase K+ extracellular
Factors decreasing excitability (nerve block)
- Cooling
- Acidosis
- Decrease Na+ permeability
- Decrease K+ extracellular
Types of action potential
- Biphasic action potential
- Monophasic action potential
- Compound action potential
- Graded potential
Biphasic action potential changes between 2 areas of outer surface (A and B)
- A & B are positive …… No potential differences
- A depolarizes (-ve) and B (+ve) …… deflection
- A repolarizes (+ve) …… No potential differences
- B depolarize (-ve) …… deflection in opposite direction
- B repolarizes, A and B (+ve) …… isoelectric line
Monophasic action potential
- Recording of potential differences between inside and outside of nerve fiber membrane
What is Demarcation potential?
Two electrodes are on the outer surfaceof membrane but one point is damaged by acid or alkali
Compound action potential
Action potential with multiple peaks that occur in mixed nerve
What is the cause of multiple peaks in compound action potential?
Variation in threshold of stimulus in distance from electrode and speed of conduction (according to its thickness)
Graded potential (receptor potential)
Local, non - propagated, and can be summated (doesn’t obey all or none law)
Subthreshold stimulus has a response?
No apparent response (no AP)
Threshold stimulus has a response?
Apparent potential changes
Effect of subthreshold stimulus (2 answers)
Local response
Electerotonus
Definition of electrotonus?
It’s the localized potential change that occur in nerve during its stimulation by subthreshold constant stimulus
The stimulus of electrotonus is obtained from …………… and either the ………….. (-ve) or …………… (+ve) electrode can be used to stimulate nerve
Battery
Cathode
Anode
The potential change that occur at cathodal end is called ……………. and at the anodal end called ………………
Catelectrotonus
Anelectrotonus
Catelectotonus:
- definition
- cause
- excitability
- chronaxie
- effect of more stimulation
- Localized partial depolarization
- passive addition of negative charges at outer surface membrane
- increased
- Short
- local response
Anelectrotonus:
- definition
- cause
- excitability
- chronaxie
- effect of more stimulation
- Localized hyperpolarization
- Passive addition of positive charges to outermembrane surface
- decreased
- long
- anodal block
A depolarization at cathode is
Local response
The opened gates are not enough to produce action potential ………………. prevent the threshold of action potential to occur with ………………..
K+ efflux
Rapid repolarization
Local response:
- stimulus
- type
- can or can’t be graded?
- does or doesn’t obey all or none law?
- can or can’t be summated
- has or hasn’t absolute refractory period?
- excitability?
- subthreshold
- localized
- can be graded
- doesn’t obey all or none law
- can be summated
- no absolute refractory period
- excitability increased
Action potential:
- stimulus
- type
- can or can’t be graded?
- does or doesn’t obey all or none law?
- can or can’t be summated
- has or hasn’t absolute refractory period?
- excitability?
- threshold or suprathreshold
- propagated
- can’t be graded
- obeys all or none law
- can’t be summated
- has absolute refractory period
- excitability is variable
Catelectrotonus:
- stimulus
- depolarization
- mechanism
- forces affect the membrane
- subthreshold
- less than 7 mV
- passive
- repolarization mask this effect
Local response:
- stimulus
- depolarization
- mechanism
- forces affect the membrane
- subthreshold
- from 7 to 25 mV
- passive and partial active
- repolarization mask this effect
Firing level:
- stimulus
- depolarization
- mechanism
- forces affect the membrane
- threshold or more
- 25 or more
- active
- depolarization
