Unit 2C (bone/air conduction to auditory nerve) Flashcards
Bone Conduction
Mechanisms for sound getting into our Ear (moving cochlear fluids).
Bone conducted sound vibrates the cochlea which causes the sensation of hearing (bypasses systems like outer and middle ear that may not be working as we would like them to).
we can leverage this to measure someone’s cochlea a bit more specifically instead of seeing the influence of the outer and middle ear
- impacts both ears equally
- can “bypass” the outer and middle ear.
- It is perceived exactly the same way as air conducted sound, but is more susceptible to environmental masking.
Air Conduction (traditionally used in typically functioning systems)
Mechanisms for sound getting into our Ear (moving cochlear fluids).
Air conduction moves the tympanic membrane, which moves the ossicles, which move the oval window to vibrate the cochlear fluids.
How does bone conduction relate to the major downside of clinical bone conduction testing?
You can hear the environmental sounds around you with bone conduction testing. If you have a healthy working conductive auditory system, then anything you send into the ear via bone conduction will fight with air conduction for intensity.
You can’t get ear specific information because it is going to vibrate both ears at the same time.
Carhart’s Notch
What auditory pathology causes it?
Bone conduction symbols dip down to meet up with the air conduction symbols to mirror them (meet up at 2,000 Hz because of properties of those two systems interacting – fixation of the stapes). This is because bone conduction doesn’t really bypass our middle ear, it will still vibrate the Ossicles in the middle ear.
Otosclerosis fixes the stapes in place (bony growth on stapes causes it to attach to the place where it meets the oval window – no rocking). When the vibration of ossicles is interrupted by something like Otosclerosis, it can cause a distinct pattern called Carhart’s notch. (bone and air meet up at 2,000 Hz because of a fixation of the stapes that is causing an interruption of air and bone conducted sound)
Auditory Nerve
Vestibulocochlear nerve. This is the eighth cranial nerve that connects the inner ear to the brainstem, responsible for transmitting sound information and contributing to balance by carrying signals from the cochlea to the brain, allowing us to hear.
A bundle of a bunch of individual neurons that travel together through the cochlea and up into the brain stem.
Nerve
a nerve is a bundle of neurons.
2 Types:
-cranial
-spinal
2 Types:
Afferent Nerve - Ascending up to the brain. Going from the cochlea up to the brain. They relay sensory information.
Efferent Nerve - Exiting the brain and traveling down to the cochlea in order to do something in that region of the body.
Neurons
individual fibers that will connect from a hair cell to the brain (or to another neuron that will then connect to the brain).
Neurons are activated by neurotransmitters that are released from sensory cells around them. (In the cochlea, the primary neurotransmitter is glutamate)
-have a resting potential of -70. When neurotransmitter is received, it starts to move that neuron to a more positive charge. As it gets closer and closer to to, when it reaches a point of -55 millavolts that is when an action potential will trigger.
Ganglion
a cluster of neuronal cell bodies OUTSIDE the brain.
Spiral ganglion - the cluster of auditory nerves/cells inside the cochlea is called the spiral ganglion because it wraps around the snail shaped cochlea.
Nucleus
a cluster of neuronal cell bodies INSIDE the brain.
Cochlear Nucleus - cluster of cell bodies inside the brainstem.
Vestibulocochlear Nerve (8th cranial nerve) VIII
Two branches:
Vestibular Nerve-innervated by the semicircular canals in the vestibular system.
Cochlear Nerve- filters into modialus and is innervated and ennervates the cochlea. is tonotopically organized in the way that our lowest frequency information is at the core, and as we move out in the bundle of nerves, we get higher and higher in frequency.
Phase Locking
This means that the firing pattern of the nerve is synchronized with the phase of the incoming auditory signal; thus, the nerve will only fire at certain phases of the periodic signal, or at integer multiples of the period of stimulation
Dynamic Range of a Neuron
The range of levels over which its firing rate increases linearly with the stimulus level.
Dynamic Range of Human hearing is covered by?
a combination of three different types of Type 1 neural fibers, with different spontaneous firing rates and dynamic ranges.
Ion
atom that has lost one or more
electrons and has a net charge
Neurotransmitter
a chemical that can
bind to the dendrites of a neuron and cause it to depolarize (fire)
Saltatory Conduction
rapid neural
conduction due to an insulating layer
(myelin) with gaps (Nodes of Ranvier)
Refractory Period
time required for
the neuron to recover before firing
again – about 1 msec
what is the mechanism that allows OHC electromotility?
One of a group of proteins called “anion transport-related proteins.” Most proteins of this type transport ions across membranes. Prestin is the only one that changes cell length. It is found only in the outer hair cells.
what does the Inner ear reflex do to the Outer hair cells?
When the inner ear reflex is activated, the
“dancing” of the OHCs is suppressed. This
facilitates binaural hearing in noise.
Downsides of Bone conduction?
Difficult to get ear-specific information. IN ORDER TO GET EAR SPECIFIC INFORMATION, you would have to cover up the hearing of the other side otherwise the sound will always go through at the same intensity in both ears.
Action potential
The activation of a neuron is called an action potential. Action potentials will travel down the axon of a neuron to conduct a signal and this is how all sensation and muscle activation works (through either afferent or efferent pathways).
-neurons typically have a resting potential of -70. When neurotransmitter is received by neurons, it starts to move that neuron to a more positive charge. As it gets closer and closer to, when it reaches a point of -55 millavolts that is when an action potential will trigger.
What makes a neuron fire?
Neurotransmitters are released by telodendria and then absorbed by the dendrites of another neuron which will make a postsynaptic cell.
(the release of neurotransmitter can make a cell either more or less likely to fire)
