NATS 1860 Note 15
Mechanical Receptors and Hearing
- Exam information
- Review of visual cortical areas
- Sound and pressure
- The auditory system and frequency map
- Hair cells (auditory receptors)
- Artificial hearing: cochlear implants
- Sound localization
- Echolocation (bats and humans)
- It will be 60 minutes long.
- It is closed book: no notes, no computers, no calculators, no cell phones, etc.
- There are 30 multiple choice questions and about 6 from each week – 3 from
each lecture including the two from today
- There will be 5 options on each answer
- The only valid excuse for missing the exam is the valid medical notes
o Missing the exam or cheating results in a zero on the exam.
- Use the lecture and the previous lecture reviews to know exactly is necessary
o Use what is reviewed as to what is most important
Orientation Selective V1 Neuron
- LOOK AT FIGURE 6.8
- LOOK AT HOW RECEPTIVE FIELDS COMBINE TO PROCUDE THE VISUAL
FIELD IN THE PRIMARY VISUAL CORTEX
o This is usually three P cells that provide this
Motion Selective V1 Neurons
- There is excitation and inhibition from Retinal M Cells
- Excitation before inhibition: respond to motion
- Inhibition before excitation – no response
o If there is motion that hits the excitatory first, then there is a
response. If the opposite direction hits the inhibitory first, there is no
Dorsal and Ventral Visual Streams
- The Dorsal is on the front and the ventral at the bottom
o Remember that there are two hemispheres
o The Dorsal pathway receives its information from motion cells and is
involved in vision fraction
People with damage to this can tell you what it is, but can’t
They can’t control their movements
o The Ventral pathway gets its orientation from vision pathways, and it
involves in object recognition of tools, faces, houses, trees, etc. Damage to this area is when people can’t recognize them, but
can grab them.
- It starts with V1 then moves to higher form vision areas
o In V1 you have line an curve recognition
o Then you have those lines join together to make angles
o Those angles then form shapes
o And those shapes make faces and objects.
Hearing and Mechanical receptors
- They’re specialized neurons that are specialized for detecting changes in
- They’re present in skin (somatosensory receptors)
o All nerve cells have this characteristic (they’re sensitive to pressure)
- Hearing is a pressure sense – there are specialized cells that respond to
changes in pressure
- Key Point: deformation of the receptor membrane in a cell that is sensitive to
pressure opens ion channels, which depolarizes the neuron and causes it to
send spikes to the brain
o This occurs with all cells in our bodies
o Even though the cells in our retina are specialized for picking up
photoreceptors and ganglion cells for generating spikes, when
deforming those cells end up opening ion channels, depolarizing, and
then sending spikes to the brain
This is why when people get hit in the head they see stars
because it triggers action potentials to the brain.
- Auditory hair cells: specialized to respond to pressure waves in fluid.
o They’re receptors specifically to fluid.
Physics of Pure Tones
- The simplest way to produce a pure tone is to take a tuning fork or any
vibrating objects, and if you hit a tuning fork against a hard edge, the prongs
will vibrate back and forth, thus compressing the air in front of them in one
direction, and then rarify it in one of them
o What we hear is the alternate vibrations of higher density air, and
lower density vibrations
o This produces a smooth wavy curve.
- The speed of sound at sea level is about 340m/s
- Compress and expand air by vibrations.
- Vibrations cause alternate impressions and expansions (rarifications) of air
as something vibrates
- There is no sound in a vacuum (outer space)
o The sound of our brains end up as waves in water as well. - Figure 7.3 of our books shows how over a period of time the air pressure
relative to the average over time
o When listening to a pure tone, it has two characteristics:
The smaller the amplitude the softer, the larger the
Time: the amount before the sound repeats itself
This is called the period, which is just equal to the time
Frequency is equal to 1/period.
o Usually we talk about the frequency of sound.
o They are measured in Hertz (Hz) and it is equal
to cycles per second.
o Example; healthy auditory humans can hear
from about 20 Hz up to 20,000 Hz
o When bats use echolocation, they can hear up to
Therefore, humans do not have the widest
range of hearing in the animal kingdom
- Study Figure 7.5
o It shows the outer part of the ear, outer ear canal (cue tip)
o If you puncture the eardrum you will have hearing loss.
The eardrum vibrates if a sound is coming into our ear (it’s all
filled with ear) those sound waves hit the eardrum and cause it
o Behind the ear drums are small bones ossicles
They transmit the vibrations from the ear drum to the fluid
filled chamber that involves stimulating nerve cells when we
hear to the cochlea
The cochlea is all curled up in order to prevent sound
coming back to the other ear.
- Consider Figure 7.6
o Conceptually, you can unroll the cochlea – it’s not unrolled in our
brain, but it functions as a long tube.
The small bones are before the basilar membrane that runs
down the middle of the cochlea (it’s the medium blue
membrane of the cochlea)
This is where all of our auditory receptors sit.
Cochlea and Frequency
- How does the physical and mechanical properties of the basilar membrane
allow for the frequency of sound be analyzed o Figure on Page 176 shows the outer ear canal’s little bones
transmitting vibrations to the fluid filled cochlea
Cochlea is filled with fluid, causing the basilar membrane to go
up and down.
o Parenthetically, your ears pop when you go flying because your bones
go to the back of your mouth that equalize air pressures (important