Electrical tuning is a mechanism by which
vertebrates such as
frogs and
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s, which lack a long
cochlea, discriminate
sound.
Mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s have long cochleae, and are able to distinguish different sounds by mechanisms such as
mechanical tuning
Mechanical may refer to:
Machine
* Machine (mechanical), a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement
* Mechanical calculator, a device used to perform the basic operations ...
, in which the stiffness and length of
hair cells’
stereocilia makes a given cell best suited to respond to a certain type of stimulus. The
basilar membrane of animals with long cochleae also vibrates at different locations along the membrane in response to different frequency sounds. Since the reptilian ear lacks a long cochlea, electrical tuning provides an alternative mechanism for perceiving differences in sound.
With a combination of
voltage-gated calcium channels and calcium sensitive
K+ channels, the
cells set up an
oscillation in
voltage and oscillate in response to a
depolarizing stimulus.
Ca++ enters the cell and depolarizes it, opening
K+ channels which allow K
+ to leave and hyperpolarize the cell. Since the exit of K
+ from the cell is delayed, the voltage increases, but then with the exit of the K
+ the cell overshoots the membrane potential and hyperpolarizes. Different cells have different delays for K
+ leaving and thus the voltage oscillates at different frequencies. The delays can be as short as 0.7
ms or as long as 150 ms, whereas the Ca
2+ entry always occurs within about 1 ms.
Thus, by varying the length of delay for K
+ to leave, cells' ion
concentrations can oscillate at specific
frequencies
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
. Cells with higher oscillating frequencies respond best to higher-frequency sounds, while those with lower frequencies respond best to lower frequency ones. Which cells resonate best with a given sound tells the
brain what the frequency of the sound is. Hair cells that respond to high frequency stimuli send information to specific neurons, and the information remains segregated in the brain. Thus, information about sound frequency is preserved, rather than being lost as it would if all information from different hair cells converged on the same neuron or group of neurons.
References
*
{{Auditory system
Auditory system
Hearing
Sound