Auditory And Visual The Special Senses Flashcards
What is soud? And what is the pressure of the softest and loudest sounds that we can hear?
- Sound is a tiny pressure wave. Waves of compression and expansion of the air.
- Threshold for the softest sound is 1/10^10 atm pressure
- The loudest sounds (bordering pain) is 1/1000 atm pressure
Describe pitch. What is pitch heard in?
- Our subjective perception of pitch is a logarithmic function of the physical variable (frequency)
- Pitch is perceived in octaves.
Multipe frequencies: complex sounds
- Natural sounds have multiple frequencies and are constantly changing.
- There is a hierarchial system to extract and encode higher frequencies.
Describe loudness. What is it measured in?
- Loudness is measured in decibels.
- Loudness perception is also a logarithm of the physical variable (intensity)
- Defined log scale (Bel)
- Threshold is 0 dB (1/1010 atm pressure)
- The maxiumu sound we can hear is 5,000,000 larger in amplitude and 1013 in power
- There is a HUGE range of loudness
- It also adapts to this huge range (just like light intensity)
ITD and timing
- Timing is used to locate sound sources
- It is not perceived directly, but it is critical for locating sources of sound in space
- ITD as source moves away from the midsaggital place
- In adult humans, the max ITD is 700 microseconds
- We can locate sources to an accuracy of a few degrees. This means we can measure ITD with an accuracy of about 10 microseconds
- This, the auditory system needs to keep track of time to the same accuracy
- This is unique to the auditory system
Ear anatomy:
The outer ear includes the pinna
-The pinna helps to collect and direct the sound into the ear. Certain aniamls have beautifully developed pinna. They can rotate them and that helps them to locate the sounds in space
The Middle ear includes the bones and the semicircular canals and the ear drum
- We have 3 semicircular canals that are responsible for rotational information
- The three bones of the ear are the malleus, incus and stapes. The eardrum impinges in the malleus that is connected to the incus that is connected to the stapes.
The inner ear includes the cochlea
-The cochlea mediates auditory stimuli
The Eustachian tube helps to funnel the airways toward the tympanic membrane/ear dru
Describe the path the sound takes as it enters the ear. How do we transduce this airwave into a mechanical signal?
When the sound enters the ear, the tympanic membrane vibrates. That vibration causes the malleus to move in this axis, which causes the incus to translate that movement to the stapes. The stapes has this stirrup-like ending that is inserted into the oval window. So, the movement of the stapes into and out of the oval window is what translates the mechanical airways into a fluid contained structure within the cochlea
What does the outer ear consist of?
The pinna and ear cannal
What does the middle ear consist of?
The 3 bones (ossicles)- malleus, incus and stapes
And the ear drum
What does the inner ear consist of?
Semicircular cannals and the cochlea
What connects the states to the cochlea, and what is it’s function?
The oval window-it displaces the perilymph
What is the job of the round window?
It is a flexible membrane that bulges out everytime the stapes presses into the oval window. It allows for the transduction of hat pressure wave everytime the stapes presses it. The pressuer wave goes through the cochlea and the round window bulges out, so that allows for the transduction of that mechanical wave from air fluid.
Where is the tectorial membrane located?
On the apical surface of the hair cells
frequency mapping
Most natural sounds are very complex in frequency composition, so each frequency component of the sound will cause vibration at unique points alone the basilar membrane
How do we encode intensity in the ear?
Intensity is going to have to do with the amplitude of the deflection of the basilar membrane. So, the louder the noise, the larger the deflection of the basilar membrane will be.
Where is perilymph present and what is it’s ionic composition?
Perilymph fills the scala vestibuli and the scala tympani. It has a high concentration of Na and Cl and a low K concentration.
Where is endolymph present and describe it’s ionic composition.
Endolymph filles the scala media. It has a very high K concentration and low Na and negligible Cl. It also has a very positiove potential of +80 mV compared to perilymth.
Which fluid is the basolateral portion of the hair cells bathed in?
Perilymph
What is the potential inside the hair cells?
-60 mV
What does the hair bundle consist of?
stereocilia (modified microvilli) connected by tip links
Where does the transduction of sound waves take place?
At the stereocilia
Describe the path of K and Ca through the air cell
The apical surface of the hair cell is bathed in endolymph which has a very high potential of +80 mV. Inside the cell is -60 mV so the electrochemical force of K will flow into the apical surface . K will flow down to the basolateral portion of the hair cell and then flow out through K cannels there into the perilymph. The flow of K is purely PASSIVE. The membrane potential will be more negative as K leaves. And Ca will open and Ca will flow in from the perilymph to the basolateral portion
What sits on the apical surface of the hair cells?
the tectorial membrane
An excitatory stimulus is when the hair bundle is deflected toward or away from the kinocelium?
towards
What kind of structure can we classify the tip link as?
A protein structure
What is the function of the tip link?
When the bundle is deflected, the tip link acts as a spring and pulls on the gate of this mechanically gated ion channel and K can flow in and depolarize the cell. And that’s how we transduce the mechanical signal into an electrical signal.
Why is the adaptation of hair cells important?
Because very few sounds are over quickly, they usually have some endurant quality to them. And we always want to be able to respond to new incoming stimuli. Every sensory system has a mechanism of adaptation that allows the sensory system to remain sensitive to novel stimuli in the face of ongoing stimuli. So, adaptation will allow the hair cells to remain sensitive to new stimuli at the same frequency, even though there’s an ongoing stimulus in the background.
How many rows of inner/outer hair cells do we have?
3 rows of outer hair cells, and 1 row of inner hair cells.
What happens to the hair cell/ tip link in the case of ongoing stimuli?
The little myosin molecules walk down the actin . They relax the tip link, becuase normally there is tension in the tip link when the stereocilia are deflected due to a stimulus. So when they relax the tip link, some of those mechanically gated channel start to close, even though the stimulus is still going on. That is the mechanism for adaptation. It is literally the tip link relaxing as the myosin walks down the actin and the taller stereocilia are releasing the tension of the mechanically gated chanels and allowing some of them to close.
Describe ribbon synapses
They have this halo of vesicles that are arranged around the ribbon in a very close relationship to it. (readily releasible pool is responsible for very fast NT release).
The vesicles are small clear vesicles (about 100) that are tethered to the surface. Each ribbon has about 100 voltage gated calcium channels.
Why do we see light at these wavelengths?
Because that’s where the sun radiates electromagnetic energy. The peak of the suns energy as it’s striking the earth is in the visible range. Therefore, we have evolved to detect the radiation that was most abundant and therefore useful
Describe the pathway of light in terms of the left/right visual field to the primary visual cortex.
The retina on each eye has 2 portions: the nasal portion closest to the nose and the temporal portion closest to the ear. The temporal side of the retina always detects light from the opposite side of the visual field than the eye it’s located on. So the temporal portion of the retina in the left eye detects light right the right visual field, and the right temporal portion detects light from the left visual field. The nasal portion of the retina on each eye detects light from the same visual field as the eye it’s located on. So the nasal portion on the left eye detects the left visal field and the nasal portion on the right eye detects the right visual field. The nasal portion of both eyes cross at the optic chiasm and therefore, are processed on the opposite side primary visual cortex than the visual field where it originated. So, the nasal portion of the right eye will detect the right visual field and cross through the optic chiasm and synapse on the left lateral geniculate nucleus in the thalamus and then procees to the left primary visual cortex.
Describe what happens to the layers of the retina as they approach the fovea
The bipolar cells and ganglion cells are pushed to the side, there are still conections, but they are pushed to the side, so that instead of light passing through the ganglion cells and the bipolar cells, to get to the outer segments of the receptors, the only think present at the fovea are the photoreceptors themselves. In facet, the receptors that are present in the fovea are uniquely the cones.
