Nerve Impulse and action potential Flashcards
Characteristics of nerve impulse (action potential) in a nerve fiber
- Nerve impulse propagates.
- Nerve impulse propagates along a fiber with a constant amplitude.
- Nerve impulse is created when the intensity of stimulation is equal or greater to threshold.
- Nerve impulse propagates along a fiber with the same speed.
- The nerve fiber obeys the law of all or none.
- At threshold there is a response with a maximum amplitude that remains the same with
increasing intensity of stimulation.
Specify the factors that affect the speed of the nervous message in a nerve
Nerve is a group of fibers of different nature and different diameter, the speed of the nervous message
is faster in a myelinated fiber than in a non –myelinated fiber(since the nervous message in a myelinated
fiber jumps from one node of ranvier to the second=saltatory conduction.
Also , the nervous message is affected by the diameter of the fiber: as diameter increases , the speed of
the nerve impulse increases.
There is an external factor that also affects the speed which is temperature. As temperature increases ,
the speed of the nerve message increases.
Characteristics of nerve impulse in a nerve
The characteristics are:
1. At threshold, there is an action potential with a minimum amplitude.
2. As intensity of stimulation, after threshold, increases the amplitude increases till maximum
where all fibers are stimulated then it remains constant.
3. The nerve impulse is coded by modulation in amplitude.
4. The nerve obeys the law of summation
What is the direction of the nervous message
the nervous message is unidirectional because of the refractory period
define refractory period
It is the interval of time , during which a given zone(across the nerve fiber) that depolarizes its
neighboring zone is in a state of repolarization (gradual closure of Na + ion channels), which means that it
is unexcitable. This explains the fact that the action potential cannot propagate backwards.
