The Ear and How It Works

Lastly, the cerebral cortex receives input and produces the sensation and perception from the brain. Energy in the auditory system contains information about the world. This energy has a stimulus which comes from sound waves like ripples on a pond. The type of energy that this is, is mechanical energy. The vibrations cause changes in pressure of the medium and speed is able to change as the function of medium, while it can also stimulate mechanoreceptors on occasion.

The structure of the outer ear catching sound waves as they move into the external auditory canal. The sound waves then hit the eardrum and the pressure of the air causes the drum to vibrate back and forth. When the eardrum vibrates its neighbour the malleus then vibrates too. The vibrations are then transmitted from the malleus to the incus and then to the stapes. Together the three bones increase the pressure which in turn pushes the membrane of the oval window in and out.

Each stereocilium is linked to another through structures called "tip links" (1) , (3) As the stereocilia move towards the tallest ones, the tip links cause ion channels to open, depolarizing the cell and allowing free K+ to move into the cell (1). Importantly, the stereocilia move in direct response to the sound waves and are cumulative rather than spiking. Neurotransmitter release corresponds to the frequency and amplitude (pitch and volume) of a sound input. Sounds must be sufficiently loud and within a given range in order to cause action potentials. Different sounds will produce different outputs, allowing for discrimination of harmony on a neural level (1).

Displacements are given + or - signs depending on the direction of the displacement. Amplitude is the largest distance from the normal position that the medium is displaced. The wavelength l of a wave is the distance from one point to the next corresponding point. The period T of a wave is the time in seconds that it takes one wavelength to pass by. In this time the medium will complete one oscillation.

Sound is one of the most common and substantial forms of energy that envelops our everyday life. Sound is a product of mechanical waves that initiates the natural frequency of an object. This natural frequency sends out vibrating waves that we hear as sound. In order to better understand mechanical waves and electrical impulses you must first be able to understand the properties of waves, speakers and electrical signals. A key component that is crucial in understanding sound is waves.

In the inner ear (cochlea) the sound is converted into neural activity. Basilar membrane acts as a divider of two fluids (scala media and the scala tympani) and the hair cells pick up movement in order to send a signal to the brain to interpret the sound. ii. The organ of corti is an extremely sensitive area of the cochlea. It transforms pressure waves into action potentials iii.

These sound waves cause the eardrum to vibrate. The vibrations are caught by the middle ear, a set of small bones, which transfer the vibrations to the cochlea (inner ear). Here, the sound waves are converted to neural impulses. The neural network in the human brain decodes information from both ears. Within the cochlea resides a basilar membrane, a supporting structure for the cochlea nerve.

Here, three small bones, the ossicles, vibrate in succession to produce a unique pattern of movements that embodies the frequencies contained in every sound we are capable of hearing. The middle ear is also an important component in what music we actually keep out of our 'head'. The muscles grasping the ossicles can contract to prevent as much as two thirds of the sound from entering the inner ear. (1, 2) The mechanical motions of the ossicles directly vibrate a small membrane that connects to the fluid filled inner ear. From this point, vibration of the connective membrane (oval window) transforms mechanical motion into a pressure wave in fluid.

Our auditory system is one of our ‘gates’ to the outer world. It helps us pick up sound stimuli from our environment, transduce these stimuli into neural impulses and finally, carry these impulses to specific locations in the brain. In fact, its basic function, if we could summarize that, is the transduction of mechanical energy (that is, those sound vibrations in the air) into electrical energy (electrical pulses in the brain). Now… When we say ‘mechanical energy’ we mean a sound wave that reaches our head. This sound wave is nothing more than changes in air pressure, that is caused when a sound source transmits sound.

Sound waves are the progressive longitudinal vibrations, found in an elastic medium, by which sounds are transmitted. It basically is used to refer to changes in air pressure that produce sound. Now, lets breakdown this definition sounds are vibration that travel through different mediums such as solids, liquids, and gases. Sound waves are created by the vibrations that sound makes. sound waves have two different vibrations, longitudinal and transverse.