Which of the following is the approximate threshold value for mammalian neurons?
A.
+35 mV
B.
-55 mV
C.
0 mV
D.
-80 mV
The Correct answer and Explanation is:
The approximate threshold value for mammalian neurons is B. -55 mV.
Explanation:
Neurons are specialized cells responsible for transmitting electrical signals throughout the nervous system. The generation and propagation of these electrical signals involve changes in the neuron’s membrane potential, which is the difference in electric potential between the inside and outside of the cell membrane.
The membrane potential of a neuron at rest is typically around -70 mV, which is termed the resting membrane potential. This negative value is due to the differential distribution of ions across the cell membrane, primarily maintained by the sodium-potassium pump and the selective permeability of the membrane to different ions.
To initiate an action potential, which is a rapid and transient change in membrane potential, the neuron must reach a specific critical level known as the threshold potential. This is the membrane potential at which voltage-gated sodium channels open, leading to a rapid influx of sodium ions into the cell and a consequent depolarization of the membrane.
In mammalian neurons, the threshold potential is typically around -55 mV. This value is slightly less negative than the resting membrane potential of -70 mV. When the membrane potential reaches this threshold, it triggers the opening of additional sodium channels in a positive feedback loop, causing a rapid depolarization that constitutes the action potential.
The other values listed in the options are not typically associated with the threshold potential for mammalian neurons:
- +35 mV represents the peak of the action potential, not the threshold.
- 0 mV is the point where the membrane potential is neither polarized nor depolarized and is not typically a threshold value.
- -80 mV is below the resting membrane potential and not related to the threshold for action potential initiation.
Thus, the correct answer is B. -55 mV, which aligns with the approximate threshold value needed to trigger an action potential in mammalian neurons.