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77 Cards in this Set
- Front
- Back
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What is the physical stimulus for hearing?
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Hearing spectrum for humans is 20 to 20,000 Hz
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Basics of Sound
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Hertz (Hz) – cycles per second of sound wave, perceived as pitch
Amplitude or intensity – perceived as loudness Pure tone – a tone with a single frequency – number of cycles – of vibration Music tone – modulated pure tones with repetition (rhythm) A fundamental is the basic frequency – harmonics are multiples of it. |
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Hertz (Hz)
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Hertz (Hz) – cycles per second of sound wave, perceived as pitch
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Amplitude
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Amplitude or intensity – perceived as loudness
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Pure tone
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Pure tone – a tone with a single frequency – number of cycles – of vibration
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Music tone –
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Music tone – modulated pure tones with repetition (rhythm)
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A fundamental
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A fundamental is the basic frequency – harmonics are multiples of it.
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Each Part of the Ear Performs a Specific Function in Hearing
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Sound, a mechanical force, is transduced into neural activity
The external ear and the ear canal collect sound waves The shape of the external ear transforms sounds Three ossicles – malleus, incus, and stapes – connect the tympanic membrane (eardrum) to the oval window |
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Sound
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Sound, a mechanical force, is transduced into neural activity
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The external ear
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The external ear and the ear canal collect sound waves
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Three ossicles of ear
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Three ossicles – malleus, incus, and stapes – connect the tympanic membrane (eardrum) to the oval window
The shape of the external ear transforms sounds |
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Each Part of the Ear Performs a Specific Function in Hearing
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Two muscles in middle ear vary linkage of ossicles:
Tensor tympani – attached to malleus and tympanic membrane Stapedius – attached to the stapes When activated muscles stiffen to dampen loud sounds |
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Two muscles in middle ear vary linkage of ossicles
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Tensor tympani – attached to malleus and tympanic membrane
Stapedius – attached to the stapes When activated muscles stiffen to dampen loud sounds |
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Inner ear
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Inner ear structures convert sound into neural activity
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cochlea
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Fluid-filled cochlea, a spiral structure with a base and an apex
The spiral increases sensitivity to low-frequency sound |
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ip links
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Thin fibers called tip links run across each hair cell’s stereocilia
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Sound Affects the Stereocilia on Cochlear Hair Cells
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Vibration makes stereocilia sway, causing ion channels to open
The hair cell depolarizes, and calcium influx at the base of the cell causes neurotransmitter release |
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Hair cells do not have axons and therefore do not generate action potentials
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Hair cells do not have axons and therefore do not generate action potentials
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Auditory Pathways of the Human Brain
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Cochlear nuclei targets the
Superior olivary nuclei – bilateral input Inferior colliculi – send on to the medial geniculate nuclei in thalamus, then to cortex |
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How Do We Discriminate Pitch (Frequency)?
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Frequency theory – firing rate of auditory neurons encodes pitch: 50 Hz sound causes auditory cell to fire 50 times a sec. Simple.
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volley principle:
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volley principle: frequency of the sound wave on top is too high for a single fiber to fire on every cycle. Each fiber only fires at a certain point in the cycle although it does not respond to each cycle.
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Place and Volley theories act together to code frequency
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1. Low frequencies are coded by frequency of nerve impulses (up to 50 Hz) – Frequency theory
2. High frequencies are coded in terms of the place along the basilar membrane which shows greatest activity (over 5000 Hz) – Place theory 3. For intermediate frequencies (from 50 to 5000 Hz) pitch is coded through combination of Volley & Place mechanisms |
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superior olive
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In mammals, superior olive is the main sound localization nucleus
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Where is that sound coming from?
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Binaural cues signal sound location
Intensity differences – different loudness at the two ears Latency differences – different arrival times for sounds at the ears Accurate sound localization requires processing both intensity and latency differences In mammals, superior olive is the main sound localization nucleus |
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Frequency theory
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Low frequencies are coded by frequency of nerve impulses (up to 50 Hz)
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Place theory
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High frequencies are coded in terms of the place along the basilar membrane which shows greatest activity (over 5000 Hz)
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Auditory cortex analyzes complex sounds in two streams
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Dorsal stream (red)– frontoparietal lobe, involved in spatial location
Ventral stream (green) – temporal lobe, analyzes components of sound |
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Deafness has three categories
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Conduction deafness – disorders of outer or middle ear that prevent sounds from reaching the cochlea
Sensorineural deafness – from cochlear or auditory nerve lesions Central deafness - caused by brain lesions, with complex results |
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Conduction deafness
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disorders of outer or middle ear that prevent sounds from reaching the cochlea
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Sensorineural deafness
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from cochlear or auditory nerve lesions
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Central deafness
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caused by brain lesions, with complex results
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Cortical deafness
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Pure word deafness - fluent verbal output, severe disturbance of spoken language comprehension. Noverbal sounds are correctly identified.
Auditory agnosia - relatively normal pure tone hearing but inability to recognize verbal or nonverbal sounds (such as ringing telephone |
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measles
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Viral infections such as measles and CMV kill auditory hair cells.
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Sensori-neural hearing loss (SNHL)
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Dysfunction of the inner ear or auditory nerve
Nerve endings in cochlea or nerve pathways are damaged. Middle ear structures are intact. Viral infections such as measles and CMV kill auditory hair cells. |
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Causes of Conductive Hearing Loss: Middle Ear
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Otitis Media
TM Perforation Ossicular fixation |
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Auditory hallucinations
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Illusion of a complex sound such as music or speech. Occur in schizophrenia; they can also result from brain injury.
Commonly from injury to secondary auditory cortex, or result of a temporal lobe seizure. Occasionally auditory hallucinations can occur in damage to brainstem structures such as the superior olive. |
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Characteristics of SNHL:
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Inappropriately loud voice
High frequency loss common Speech sounds distorted Background noise makes listening more difficult |
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Tinnitus
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For example:
Outer hair cells ‘turn up the volume’ via efferent connections in response to loss of hearing from death of inner hair cells Auditory cortex , inferior colliculus, cochlear nucleus all contribute |
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Cochlea
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The cochlea is a fluid filled spiral structure. The spiral saves space and increases sensitivity to sound.
A membrane in the cochlea houses inner hair cells and outer hair cells. The inner hair cells are attached to the basilar membrane and the hair cells are stuck into the techtorial membrane |
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Inner hair cells
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They are connected through tip links- this ensures that the hairs move synchronously.
They mechanically open up Ca and K ion channels which causes depolarization. These hairs CAN’T generate action potentials but they release NT that activates the vestibular cochlear nerve. Inner hair cells are tranductors. |
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Outer hair cells
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They are amplifiers.
They are structurally similar to inner hair cells . This is associated with tinnitus. When function is lost in inner hair cells these outer hair cells amplify sound even more created undesirable noise- static. |
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Auditory pathway
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Order of transmission
Cochlear nuclei targets the Superior olivary nuclei – bilateral input Inferior colliculi – send on to the medial geniculate nuclei in thalamus, then to cortex MGN is a relay station for all the senses Anatomy is bilateral so hearing loss in one ear is indicative of a problem in the cochlear nucli. |
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Organization of Cortex
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There is a topographic organization of cortex.
Higher frequencies are inside/ in the back. Different types of neurons Want to know if there is sound so they respond to almost any range Want to know the specifics of sound so they respond to specific frequency ranges. |
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spatial location (where
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Dorsal stream – frontoparietal lobe, involved in spatial location (where
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Ventral stream
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– temporal lobe, analyzes components of sound (what)
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Conduction Hearing Loss
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Causes:
Otitis Media- middle ear infection (inflammation) TM Perforation- ruptured eardrum Ossicular fixation bones fixated to each other, or bones fixated to wall |
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Sensori-neural hearing loss (SNHL)
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Dysfunction of the inner ear or auditory nerve
Nerve endings in cochlea or nerve pathways are damaged. Middle ear structures are intact. Viral infections such as measles and CMVCytomegalovirus (CMV) infection kill auditory hair cells. Symptoms: Inappropriately loud voice High frequency loss common Speech sounds distorted Background noise makes listening more difficult |
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Presbycusis
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Presbycusis: Age related hearing loss
Age related hearing loss starts with higher frequencies first. |
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Noise Induced Hearing loss (NIHL)
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Loss can be sudden, as from an explosion
More often a gradual onset that goes unnoticed |
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adequate stimulus
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is the energy form for which the receptor is specialized.
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perception
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the interpretation of sensory information
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cochlea
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where the auditory stimulus is converted into neural impulses
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hearing
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we are able to hear frequencies ranging from about 20Hz up to 20,000Hz, we can detect a difference in frequencies of only 2 to 3 Hz
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the stimulus for hearing
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the adequate stimulus for audition is vibration in a conductive medium
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the range within which most conversation occurs
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2,000 Hz-4,000Hz
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pure tones
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have only one frequency
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complex sounds
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random combination of frequencies, noise
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pinna
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flap of ear, slightly amplifies sound by funneling it from the larger area of the pinna into the smaller area of the auditory canal. It also selects for souns in the front
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tympanic membrane
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the first part of the middle ear, the eardrum or tympanic membrane , is a very thin membrane stretched across the end of the auditory canal, its vibrations transmits the sound energy to the ossicles
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harmonics
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A fundamental is the basic frequency – harmonics are multiples of it.
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Music tone
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modulated pure tones with repetition (rhythm)
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Pure tone
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a tone with a single frequency – number of cycles – of vibration
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Amplitude
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or intensity – perceived as loudness
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tensor tympanic
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can stretch the ear drum tighter or loosen it to adjust the sensitivity to changing sound levels.
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ossicles
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tiny bones that operate in lever fashion to transfer vibrations from the tympanic membrane to the cochlea. Provide additional amplification by concentrating energy collected from the larger tympanic membrane onto the much smaller base of the stirrup/stapes, which rests at the end of the cochlea.The amplificication is enough to compensate for the loss of energy as the vibrations passes from air to the denser liquid inside the cochlea
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cochlea
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the ear's sound-analyzing structures are located
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oval window
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the stapes rests on a the oval window, a thin flexible membrane on the face of the vestibular canal
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vesitbular canal : scala vestibuli
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is the point of entry of sound energy into the cochlea, connects with the tympanic canal at the far end of the cochlea through an opening called the helicotrema. The helicotrema allows the pressures waves to travel through the cochlear fluid into the tympanic canal more easily
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cochlear canal
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where the auditory receptors are located, in vibration
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hair cells
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the hair cells are the receptors for auditory stimulation. Vibrations of the basilar membrane and the cochlear fluid bends the hair cells, opening potassium and calcium channels. This sets off impulses int he auditory neuron connects to the hair cell. When the hair cell moves back in the opposite direction, it relaxes and the potassium channels close.
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inner hair cells
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majority of information about auditory stimulation
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outer hair
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amplifying the signal produced by weak sounds, and provide adjustable frequency selectivity, embedded in the tectorial membrane
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Intensity difference –
Lateral SO |
Time difference –
Medial SO |
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The medial superor olive
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computes the location of low frequency sounds by interaural time differences
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Lateral superior olive
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encodes sound location of high frequency sound through interaural intesity differences
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kushlea
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had a viral infection such as meales and CMV kill auditory hair cells
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areas involved in identifying enviromental sounds
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recognized sounds active the ventral " what" / frontal pathway, unrecognized sound is activated by the right hemisphere
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