Podcast
Questions and Answers
Which structure receives auditory information as it ascends from the cochlear nuclei?
Which structure receives auditory information as it ascends from the cochlear nuclei?
What anatomical feature is primarily responsible for improving sound localization in humans?
What anatomical feature is primarily responsible for improving sound localization in humans?
Where does the auditory information first get processed after leaving the cochlea?
Where does the auditory information first get processed after leaving the cochlea?
How do cochlear implants assist individuals with hearing loss?
How do cochlear implants assist individuals with hearing loss?
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Which statement about the auditory pathways is true?
Which statement about the auditory pathways is true?
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What is the primary role of the pinna in the auditory system?
What is the primary role of the pinna in the auditory system?
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How do sound waves cause the eardrum to vibrate?
How do sound waves cause the eardrum to vibrate?
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What happens to mechanical vibrations when they reach the cochlea?
What happens to mechanical vibrations when they reach the cochlea?
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What type of sensations does tinnitus encompass?
What type of sensations does tinnitus encompass?
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What is the function of hair cells in the inner ear?
What is the function of hair cells in the inner ear?
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Which structure in the auditory system forms the vestibulocochlear nerve?
Which structure in the auditory system forms the vestibulocochlear nerve?
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What characterizes chronic tinnitus?
What characterizes chronic tinnitus?
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Which part of the ear is responsible for amplifying sound waves before they reach the inner ear?
Which part of the ear is responsible for amplifying sound waves before they reach the inner ear?
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Study Notes
Hearing
- Hearing commences with the capture of sound waves by the ear
- Sound waves - small areas of high and low pressure propagating outward from the source
- Sound waves are converted into neural signals which are then processed by the brain.
- Sound waves are captured by the outer ear and ultimately converted into an electrical signal by hair cells in the cochlea.
The Ear
- Composed of outer ear, middle ear and inner ear.
Outer Ear
- Pinna - supported by cartilage (captures sound and focuses it into the auditory canal)
- Auditory canal - ends at the eardrum
Middle Ear
- Eardrum = tympanic membrane
- The middle ear contains three bones – Malleus, Incus and Stapes.
- Sound vibrations cause the eardrum to vibrate
- The vibrating eardrum causes the bones of the middle ear to vibrate
- Vibrations are transmitted to fluid in the inner ear via vibration of the membrane at the oval window
Inner Ear
- Cochlea - spiral, fluid filled (contains hair cells that serves as receptors for audition)
- Vibrations in the cochlea fluid cause hair cells to move
- Hair cells convert mechanical signal > electrical signal
- Hair cells synapse on spiral ganglion cells
Tuning Curve
- Spiral ganglion cells are tuned to specific frequencies
- Firing rates dropping of rapidly for lower and higher frequency sounds
Tinnitus
- Hearing noise in the absence of any sound stimulus
- Subjective sensation (buzzing, humming, whistling)
- Can be caused by a variety of factors, including exposure to loud noise, ear infections, and certain medications.
- Temporary tinnitus after loud music
- Caused by a disease processes affecting the cochlea or auditory nerve (can be cause by spontaneous activity)
- Transient - short lived, spontaneous, related to exposure and environment
- Chronic - highly disrupted, everyday, disease processes
Inner Ear to CNS
- Axons of spiral ganglion cell exit the cochlea and converge with the axons of vestibular neurons to form the vestibulocochlear nerve
- Auditory information - travels via vestibulocochlear nerve > brain stem
Vestibulocochlear Nerve
- Carries signal from the cochlea > brain stem
- Spiral ganglion cells synapse on neurons in the cochlear nuclei (located at the lower pons-upper medulla)
Thalamus
- Top of brain stem
- Many nuclei on thalamus
- Medial geniculate nucleus - receives information from the inferior colliculi (the midbrain)
- Sends auditory information to the primary auditory cortex.
Auditory Pathways
- Cochlear nuclei (auditory information ascends bilaterally) > inferior colliculi (in the midbrain)
- Neurons in the inferior colliculi > synapse onto medial geniculate nucleus (thalamus)
- Medial geniculate nucleus > synapse onto primary auditory cortex
Auditory Cortex
- First region to process sound
- In the superior temporal lobe in the lateral sulcus
- A1 (Heschl Gyri)
- Frequency tuning properties of the cells define a tonotopic map
Sound Localization
- Sounds can be localised based on slight asymmetrics in the arrival time of two stimuli (two cars arriving)
- Interaural time - difference inn arrival time of a sound at each ear
- Sound localisation along the vertical plane isn't as good
- To determine elevation of sound sources, humans depend on bumps and ridges of the outer ear (produce reflections of the entering sound)
- Elevation of a sound sensory is very impaired if the pinnae are covered
- Not all information crosses the midline, each of our ears can project information to both hemispheres of the brain
- Information may be transferred unilaterally or bilaterally. If information is transferred unilaterally, it helps to determine damage to the sensory system.
- This is why both ears can project information to both hemisphere of the brain.
- Damage to one of the sensory pathways could be identified in this manner.
Cochlear Implants
- Severely reduced cochlear function
- Internal
- Electrode stimulates remaining spiral ganglion cells
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Description
Explore the fascinating process of hearing, from the capture of sound waves by the outer ear to the conversion of those waves into neural signals. This quiz delves into the anatomy of the ear, including the outer, middle, and inner ear structures, and their functions in the auditory process.