Auditory and Vestibular Receptors
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What is hearing?
Hearing is the analysis of very small pressure changes which are converted into neural signals by the auditory system
How is sound generated?
By rapid movement against the air
What is frequency? And what is it measured in?
Frequency is the number of sound wave cycles per unit of time. It is measured in Hz.
What kind of tone does a sine wave have?
The energy associated with sound is proportional to the ... of the sound wave?
What do we perceive the energy of a sound wave as?
The loudness of a sound wave - the greater the energy the louder the sound
The greater the frequency the higher/lower the pitch?
What is a Fourier analysis?
This is when you break down the sum of a sound into its component sound waves.
Describe how sound travels through the ear
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.
The cochlea is filled with air/fluid?
Describe how sound moves through the cochlea
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.
Describe the structure of the organ of Corti and how it turns sound into APs
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.
How does the cochlea detect different frequencies of sound?
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.
How does the intensity of sound affect the ability of the cochlea to carry out a natural fourier analysis?
At low intensity auditory fibres respond only to one frequency (the best frequency). At higher intensity it responds to a range of frequencies.
Describe the path taken by information from the cochlea up into central projections (the brain)
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.
What structures is involved in sound localisation?
The olivary nucleus - as this is the first place where fibres from left and right are brought together
List the structures that make up the vestibular apparatus
- Semicircular canals
- Otolith organs - utricle and sacculus
What structure is not part of the vestibular apparatus but attached to it?
What is the function of the vestibular apparatus?
Provides proprioceptive information about the head including forces of acceleration acting on the hear, direction of gravity, movement of head
Describe the structure of sensory cells within the vesicular apparatus.
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
What do the otolith organs measure? How do they do this?
- 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.
How are the utricle and saccule orientated with regards to each other?
They are orientated at right angles to each other
What do the semicircular canals sense? And how do they do this?
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.
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