Passive electrical spread is characteristic of ( select any/all a nswers that ap
ID: 3473912 • Letter: P
Question
Passive electrical spread is characteristic of (select any/all answers that apply):
the axonal membrane when injected currents are hyperpolarizing.
the axonal membrane when injected currents are depolarizing but sub-threshold.
the axonal membrane when injected currents are depolarizing and reach threshold.
synaptic potentials generated in dendrites.
synaptic potentials generated in the soma.
A.the axonal membrane when injected currents are hyperpolarizing.
B.the axonal membrane when injected currents are depolarizing but sub-threshold.
C.the axonal membrane when injected currents are depolarizing and reach threshold.
D.synaptic potentials generated in dendrites.
E.synaptic potentials generated in the soma.
Explanation / Answer
Option B, D and E are correct. There are two types of electrical potential generated in neurons and other excitable cells. Electrotonic potential (passive spread of charges, non propagated, local potential) and action potential (a propagated impulse). Electrotonus potential occurs due to local change in ionic conductance. It becomes exponentially smaller (intensity decreases) when it spreads through a stretch of membrane and attenuates rapidly. It does not lead to the generation of new current by action potential. neurons of smaller length like some neurons in the brain have only electrotoic potential. Longer neurons use this electrotonic potentials to trigger the action potential. Hence if an axonal membrane receives current which are depolarizing but below the level of threshold value then it will only generate electrotonic potential locally which will attenuate after traveling a very short distance. Electrotonic potential are generally used by the cell body (soma) of the neuron to increase the voltage beyond threshold level to trigger the action potential. Multiple channel in dendrites also uses electrotonic potential to spread local potential. All the synaptic or sensory neurons utilize electrotonic potential to generate local potential. Electrotonic potential may be depolarizing or hyperpolarizing but below the level of threshold value and if it reaches to threshold value then it will trigger the action potential.