Auditory and Vestibular Receptors

Hearing is the analysis of very small pressure changes which are converted into neural signals by the auditory system

By rapid movement against the air

Frequency is the number of sound wave cycles per unit of time.  It is measured in Hz.

Pure tone

amplitude

The loudness of a sound wave - the greater the energy the louder the sound

higher

This is when you break down the sum of a sound into its component sound waves.

Sound travels down the external ear canal and strikes the tympanic membrane.  This moves the auditory ossicles which hit the cochlea where the pressure wave is detected.

Fluid

Pressure waves strike the oval/vestibular window, move along the upper chamber, are reflected around to the lower chamber and move out of the round window.

Hair cells are connected to the basilar membrane of the organ of Corti through support cells.  The cilia project up ingot he tectorial membrane.  Each hair cell is associated with a sensory neurone pas siting it to the auditory nerve.  Sound waves cause both the tectorial and basilar membrane to reflect relative to each other.  This causes bending of the cilia and depolarisation of the hair cells, setting up an AP that is fired along the auditory nerve.

Pressure waves enter at the oval window.  When a high frequency sound enters it causes the basilar membrane near the oval window to deflect.  Whereas a low frequency sound causes the basilar membrane away from the oval window to deflect.  Deflection of the basilar membrane leads to APs in associated afferents and so the position of the deflection is frequency dependent.

At low intensity auditory fibres respond only to one frequency (the best frequency).  At higher intensity it responds to a range of frequencies.

Information from the cochlea is carried by the auditory nerve up dorsal and ventral pathways. From the cochlear nuclei most of the fibres pass over the olivary nucleus on the contralateral side of the medulla.  From there information projects up into the thalamus and auditory cortex.

The olivary nucleus - as this is the first place where fibres from left and right are brought together

• Semicircular canals
• Otolith organs - utricle and sacculus
• Ampullae
• Cupulae

Cochlea

Provides proprioceptive information about the head including forces of acceleration acting on the hear, direction of gravity, movement of head

The sensory cells are polarised cells.  They have a single kinocilium with increasing sizes of stereocilia as you move towards the kinocilium.  Bending of the stereocilia is what depolarises or hyperpolarises the cell

• Linear acceleration
• Ciliated cells sit on the macula and project up into the gelatinous layer with otoliths, which give the gelatinous layer some mass.  When you tilt the head/get linear acceleration the macula move relative to the otoliths.  This bends the cilia and causes hyperpolarisation or depolarisation of the cells.

They are orientated at right angles to each other

They sense rotational acceleration of the head.  Cilia of sensory cells are embedded in gelatinous cupula.  Rotation of the head causes fluid to move in the opposite direction, moving the cupula, bending the stereo cilia and leading to sensory input.