Hearing Flashcards
Define ‘hearing’
Distinguishing different sounds and localisation of the sounds (capture/avoidance)
What is the function of the outer ear?
Detects air vibration and is involved in protection, localisation and amplification
What is the function of the middle ear?
Impedence matching and sound amplification
What is the function of the inner ear?
Splits complex sounds into simple components, outer hair cells amplify sound signals, transduction of mechanical signals by opening (depolarisation) or closing (hyperpolarisation) potassium channels
What is the function of the central auditory nervous system?
Receives electrochemical signals and is involved in information processing
What is impedence matching?
Involves the Eustachian tube due to a difference in area between the eardrum and the oval window, it works to compensate for the impedance mismatch between the air and cochlear fluid
Describe the flow of vibration in the inner ear
Stapes –> oval window –> periplymph in cochlear –> round window
How does the endolymph of the ear differ from the perilymph?
Endolymph is high in potassium and perilymph is high in sodium
What are the three canals within the cochlea?
Scala vestibule, scala tympani and scala media
Describe the scala vestibule and scala tympani of the cochlea
Both canals within the cochlea of the air that contain perlymph (has higher sodium levels than endolymph)
Describe the scala media of the cochlea
Contains the organ of Conti and endolymph (has higher potassium levels than perilymph)
What forms 95% of the cochlear nerve?
Inner hair cells from the organ of Conti
Describe the structure of the organ of Conti
Hair cells are present between the (upper) tectorial membrane and (lower) basilar membrane and these play a large role in the transmission of sound
Describe the inner hair cells of the organ of Conti
The inner hair cells (inner one layer of cells) form 95% of cochlear nerve and are involved in auditoy discrimination
Describe the outer hair cells of the organ of Conti
Outer hair cells (arranged in 3 outer rows), have cilia embedded in the tectorial membrane, and are involved in frequency tuning (they amplify the basilar membrane vibrations, enhancing sensitivity and frequency selection)
How do we differentiate sounds at different frequencies?
Vibration of perilymph –> reaches organ of Conti –> movement of basilar and tectorial membranes –> stimulates and depolarises certain hair cells –> stimulates cochlear aspect of CN VIII and specific hair cell stimulated allows the brain to relay that a different pitch is being received
How do we localise sound direction?
The superior olivary nucleus use interaural time differences (ITF - difference in time of sound reaching the two ears) and interaural level differences (ILD, using pressure) to localise sound cues.
Define pitch/frequency
Number of oscillations per second
Define intensity/loudness
Height of soundwave in dB
In the auditory pathway, what occurs at the ventral cochlear nucleus in the medulla?
Involved in the location and intensity of the sound
In the auditory pathway, what occurs at the dorsal cochlear nucleus in the medulla?
Involved in the pitch and quality of the sound
In the auditory pathway, what occurs at the superior olivary nucleus in the pons?
Involved in spatial localisation of sound
Describe the passage of the cochlear nerve in the auditory pathay
Primary cochlear nerve afferent –> internal auditory meatus –> synapses at cochlear nucleus in medulla –> second order neurone –> superior olivary nucleus in pons OR to inferior colliculus in midbrain –> then synapse at inferior colliculus –> medial geniculate nucleus in midbrain –> primary auditory cortex in cerebrum
What is conduction deafness?
Air conduction is impeded such as damage to the ear itself
