In physiology, sensory transduction is the conversion of a sensory stimulus from one form to another.
Auditory Transduction is the process of translating sound from when it enters the ear to when it reaches the neural impulses inside the ear. Because the human ear has three main parts: outer, middle, and inner pieces, the entire process of transduction has a lot of complicated and confusing components so here is a summary.
Transduction in the nervous system typically refers to stimulus alerting events wherein a physical stimulus is converted into an action potential, which is transmitted along axons towards the central nervous system where it is integrated.
A receptor cell converts the energy in a stimulus into a change in the electrical potential across its membrane. It causes the depolarization of the membrane to allow the action potential to be transduced to the brain for integration.
The outer part of the ear is called the pinna, and this is the visible part of the ear. When sound is created, there are changes in air pressure, and the pinna is able to collect those changes and carry them to the ear drum (tympanic membrane). To do this, the pinna funnels the changes in air pressure down the external auditory canal which is a tube goes from the outer ear to the middle ear. This part of the ear is made of cartilage and the inner ear is made up of more bones. Because this external auditory canal only travels to the middle ear, the changes in air pressure are then brought to the tympanic membrane, or more commonly called, the ear drum.
When the ear drum receives the changes in air pressure, it responds through vibrations that moves three tiny bones. These bones are the malleus, incus, and stapes. These three tiny bones together make up the ossicles and in latin, their names mean hammer, anvil, and stirrup because of their shapes. They work together to convert the vibrations from the ear drum into pressure waves that are amplified. These amplified waves are then sent to the fluid of the cochlea, which is in the inner ear. The waves have to be amplified because the fluid in the cochlea reduces sound.
Going from inner ear outwards, the stapes is first, the incus is second, and the mallets is on the outermost part of these three bones. At the end of the stapes is the cochlea that is filled with fluid , and the middle ear acts as a mechanical amplifier to make sure the sound waves will be able to reach and be interpreted by the organ of Corti. Here is a very brief description of how this all works:
At the end of the stapes, there is a footplate that is supposed to be translating vibrations into pressure waves. But the tympanic membrane (ear drum) is almost three times the size of this footplate. This is why it is important that all three bones in the ossicles work together. The incus acts as a lever and transmits force onto the stapes so that the vibrational energy is concentrated. This concentrated energy is what allows the middle ear to actually amplify the pressure waves so much (twenty-two times more than the air that initially entered the pinna).
At the base of the cochlea, there is an oval window, and this is what the footplate at the end of the stapes presses on. When the footplate presses on this oval window, it pressurizes the fluid in the vestibular canal which is the part of the cochlea that is filled with fluid and receives incoming acoustic vibrations. At the base of the cochlea, there is a round window that is a flexible membrane. It absorbs the pressure that is left after the stapes' footplate sends the pressurized waves into the cochlea and drains it from the system so that theres not limitless pressure going into the cochlea at all times without any release.
The basilar membrane is also an important part of the transduction process because it separates the scala media and the scala tympani: two tubes filled with liquid that run along the coil of the cochlea. When there is a transfer of pressure from one side to the other, the basilar membrane creates a traveling wave. The basilar membrane is important in the concept of tonotopy because the frequency distribution that the basilar membrane portrays through having a more flexible apex and a more stiff base. Depending on how far down the membrane you are from the base, a different frequency will result, so the different places in the membrane are sensitive to different frequencies which truly helps in the entire process of auditory transduction.
Auditory transduction is not the only marvelous type of transduction our body performs though. Here are some others:
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Video Transduction (physiology)
Transduction and the senses
The visual system
In the visual system, sensory cells called rod and cone cells in the retina convert the physical energy of light signals into electrical impulses that travel to the brain. The light causes a conformational change in a protein called rhodopsin. This conformational change sets in motion a series of molecular events that result in a reduction of the electrochemical gradient of the photoreceptor. The decrease in the electrochemical gradient causes a reduction in the electrical signals going to the brain. Thus, in this example, more light hitting the photoreceptor results in the transduction of a signal into fewer electrical impulses, effectively communicating that stimulus to the brain. A change in neurotransmitter release is mediated through a second messenger system. Note that the change in neurotransmitter release is by rods. Because of the change, a change in light intensity causes the response of the rods to be much slower than expected (for a process associated with the nervous system).
The auditory system
In the auditory system, sound vibrations (mechanical energy) are transduced into electrical energy by hair cells in the inner ear. Sound vibrations from an object cause vibrations in air molecules, which in turn, vibrate your ear drum. The movement of the eardrum causes the bones of your middle ear (the ossicles) to vibrate. These vibrations then pass in to the cochlea, the organ of hearing. Within the cochlea, the hair cells on the sensory epithelium of the organ of Corti bend and cause movement of the basilar membrane. The membrane undulates in different sized waves according to the frequency of the sound. Hair cells are then able to convert this movement (mechanical energy) into electrical signals (graded receptor potentials) which travel along auditory nerves to hearing centres in the brain.
The olfactory system
In the olfactory system, odorant molecules in the mucus bind to G-protein receptors on olfactory cells. The G-protein activates a downstream signalling cascade that causes increased level of cyclic-AMP (cAMP), which trigger neurotransmitter release.
The gustatory system
In the gustatory system, our perception of five primary taste qualities (sweet, salty, sour, bitter and umami [savoriness] ) depends on taste transduction pathways, through taste receptor cells, G proteins, ion channels, and effector enzymes.
The somatosensory system
In the somatosensory system the sensory transduction mainly involves the conversion of the mechanical signal such as pressure, skin compression, stretch, vibration to electro-ionic impulses through the process of mechanotransduction. It also includes the sensory transduction related to thermoception and nociception.
Maps Transduction (physiology)
References
Koike et al.: Modeling of the human middle ear J. Acoust. Soc. Am., Vol. 111, No. 3, March 2002
Faddis, B. T. (2008). "Structural and functional anatomy of the outer and middle ear". In W. Clark & K. Ohlemiller (Eds.), Anatomy and physiology of hearing for audiologists (pp. 93-108). Thomson Delmar Learning.
Source of article : Wikipedia
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