FUNCTIONAL ANATOMY - Hearing, Olfaction and Taste Flashcards
What are the two properties of sound?
Frequency
Amplitude
Describe how sound is transmitted down the external and middle ear and into the inner ear
Sound waves enter the auricle and are transmitted down the external acoustic meatus to the tympanic membrane. The tympanic membrane vibrates and transmits these vibrations through the ossicles which vibrate the vestibular (oval) window into the inner ear
What is the function of the organ of corti?
The organ of corti which converts sound vibrations into neural impulses which can be transmitted to the brain
Describe the structure of the organ of corti
The organ of corti consists of hair cells innervated by the cochlear branch of cranial nerve VIII and fixed to the basilar membrane
Describe how sound waves are converted to neural impulses by the organ of corti
Vibration of the stapes against the vestibular (oval) window creates pressure waves which move through the fluid within the scala vestibuli, cochlear duct and the scala tympani to the cochlear (round) window where the pressure will be dissipated into the middle ear. As the pressure waves travel through the cochlear duct, the basilar membrane is displaced leading to displacement of the sterocilia of the hair cells and transmission of action potentials down the cochlear branch of cranial nerve VIII
What is the difference between inner and outer hair cells?
Inner hair cells convert sound waves into neural impulses whereas outer hair cells amplify and fine-tune sounds through altering the tension of the basilar membrane
How does the basilar membrane exhibit topographical organisation?
Different regions of the basilar membrane are sensitive to different frequencies of sound. The base of the basilar membrane is sensitive to high frequency so higher frequency sounds are going to deflect the basilar membrane closer to the vestibular (oval) window whereas the apex of the basilar membrane is sensitive to low frequency so lower frequencies are going to deflect the basilar membrane further from the vestibular (oval) window
How do the cochlear neurones of cranial nerve VIII exhibit tuning curves?
Each cochlear neurone of cranial nerve VIII exhibits a tuning curve which shows the range of frequency that specific neurone can detect and respond to, with each neurone having an optimal frequency
How does an increase in amplitude (dB) influence frequency?
An increase in amplitude (dB)/sound intensity results in a wider range of frequencies in which cochlear neurones can respond to
Describe the auditory pathway
Neural impulses are transmitted along the cochlear neurones of cranial nerve VIII to the cochlear nucleus in the brain stem. Information is then transmitted to the superior olivary nucleus in the brainstem, followed by the caudal colliculus in the midbrain, to the medial geniculate nucleus in the thalamus and finally to the auditory cortex
What is the key function of the superior olivary nucleus in the auditory pathway?
Processing and integration of sound arrival time and intensity in both ears to localise the direction of a sound source
What are the two divisions of the superior olivary nucleus?
Lateral superior olive
Medial superior olive
What is the function of the lateral superior olive?
Processing and integration of sound intensity
What is the function of the medial superior olive?
Processing and integration of sound arrival time
What is conduction deafness?
Disorders of the external and middle ear causing hearing impairment/loss
