Auditory System Flashcards
Sound wave
A sound stimuli that causes the air to vibrate to compress and decompress air molecules as a sound wave
Amplitude
The greater the wave height, the louder the sound
Frequency
The shorter the wavelength, the higher the pitch
Pure tone
A sound consisting of only a single frequency
Complex tone
A sound consisting of multiple frequencies with multiple underlying patterns (ex: human speech)
What is the human hearing frequency sensitivity?
Between 1000 and 4000 Hz is the optimal sensitivity, which aligns with the greatest range for human speech
Structures of the outer ear
Pinna, ear canal, tympanic membrane
Pinna
External cartilage that collects sound
Ear canal
The tube that funnels and concentrates energy and mildly amplifies sound
Tympanic membrane
The membrane that vibrates in response to sound and transfers this energy to the inner ear
Structures of the middle ear
Ossicles, tensor tympani, stapedius
Ossicles
Hammer, anvil stirrup; bones that vibrate in response to energy to transfer and amplify energy
Tensor tympani and stapedius
Muscles that stiffen the ossicles and pull the stirrup back to protect against loud sounds
Structures of the inner ear
Cochlea, oval window
Oval window
The location on the cochlea where energy is transferred from the ossicles to inside the cochlea
Cochlea
Fluid-filled cavity that produces nerve impulses in response to sound energy
Structures of the cochlea
Organ of Corti, hair cells, basilar membrane, tectorial membrane
Organ of Corti
A structure containing hair cells on the basilar membrane that converts sound vibrations to neural signals
Hair cells
Hearing receptor cells where transduction occurs in the cochlea
Basilar membrane
The membrane containing hair cells
Tectorial membrane
A gel-like membrane that stimulates hair cells
Sound transference and amplification process
- Compressed and decompressed air moves to the pinna and funnels through the ear canal
- Tympanic membrane vibrates, which passes the vibrations through the ossicles
- The vibration reaches the cochlea to make the fluid inside move in waves
- The basilar membrane vibrates which activates hair cells to transduce movements of the basilar membrane
- Hair cells connect to the vestibulocochlear nerve which sends the electrical signal to the brain
How is volume registered?
By the number of hair cells activated
Place coding
Each frequency activates a certain area of hair cells so that the CNS responds based on which neurons respond
Frequency/ temporal coding
Auditory nerve axons produce action potentials at the same frequency of the basilar membrane vibrations
Volley principle
Gets all cells to work together to extend their firing rate to be able to hear high frequencies
Tonotopic organization
The center (apex) signals low frequency while the end (base) signals high frequency
Where does tonotopic organization occur?
The basilar membrane, auditory neuron, cochlear neurons
Auditory neural pathway
- Bipolar spiral ganglion cell generates an action potential
- The action potential travels from the basilar membrane to the first synapse on the cochlear nucleus
- The action potential travels to second synapse on the superior olivary nucleus
4: Input from the left and right ears are shared to the same and opposite olivary nuclei - The action potential third synapses on the inferior colliculus
- The action potential fourth synapses on the medial geniculate nucleus of the thalamus
- The thalamus sends information to the auditory cortex
Sound localization
The ability to determine where a sound is coming from
Interaural time difference
A difference in the time a sound reaches both ears
Interaural intensity difference
A difference in the volume that each ear detects
What directions of sound do we have trouble locating?
Front, back, directly above
How do we fix disparity in sound localization?
Our vision can be used to help clarify the sound source by seeing the source itself
How does the auditory cortex organize sound?
By frequency and tonotopically
Anterior auditory pathway
The path from the medial geniculate nucleus to the prefrontal and auditory cortex to understand WHAT a sound is
Posterior auditory pathway
The path from the medial geniculate nucleus to the posterior temporal lobe and parietal cortex to understand WHERE a sound comes from
Conduction deafness
A problem with the transference of vibration in the ossicles, preventing sound to reach the cochlea
Sensorineural deafness
Damage to hair cells or to the auditory nerve so that hair cells fail to fire an action potential or the action potential cannot reach the cortex
Central deafness
Damage to the auditory cortex affect hearing in many ways
What does loud noise do?
Hair cells in the cochlea become crushed and flattened to result in deafness from corresponding frequencies
