Electrical tuning is a mechanism by which

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s such as

frog A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...

s and

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s, which lack a long

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus (cochlea), modiolus. A core component of the cochlea is the organ of Cort ...

, discriminate

sound In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the br ...

Mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s have long cochleae, and are able to distinguish different sounds by mechanisms such as mechanical tuning, in which the stiffness and length of

hair cell Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. ...

s’

stereocilia Stereocilia (or stereovilli or villi) are non-motile apical cell modifications. They are distinct from cilia and microvilli, but are closely related to microvilli. They form single "finger-like" projections that may be branched, with normal cel ...

makes a given cell best suited to respond to a certain type of stimulus. The

basilar membrane The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down ...

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 channel Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (''e.g.'' muscle, glial cells, neurons) with a permeability to ...

s and calcium sensitive K⁺ channels, the cells set up an

oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

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 Ca²⁺ entry always occurs within about 1 ms. Thus, by varying the length of delay for K⁺ to leave, cells' ion

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...

s can oscillate at specific

frequencies Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

. 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 The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

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