Question 40

The approximate threshold value for mammalian neurons is -55 mV.

Mammalian neurons typically have a threshold value of around -55 mV, which is the membrane potential level that must be reached for an action potential to be initiated.

A) -80 mV

This option is incorrect as -80 mV is generally considered the resting membrane potential of many neurons, rather than the threshold for action potentials. The threshold is higher than the resting potential, allowing depolarization to occur.

B) -55 mV

This option is correct because -55 mV is widely recognized as the threshold potential for triggering action potentials in mammalian neurons. When the membrane potential reaches this level, voltage-gated sodium channels open, leading to depolarization.

C) 0 mV

This option is incorrect because 0 mV is not the threshold for action potentials; rather, it is the point at which the neuron would be fully depolarized. The threshold is required to initiate this depolarization phase, which occurs at a more negative value.

D) +35 mV

This option is incorrect as +35 mV represents a peak action potential rather than a threshold. The threshold must be reached before the neuron can depolarize to this level, making it an unsuitable choice for this question.

Conclusion

In summary, the threshold for mammalian neurons is definitively -55 mV, as it is the critical point for initiating action potentials. All other options fail to represent the actual threshold value, either being too negative or representing other phases of neuronal activity.