Audition

Question 1

What are the dimensions and features of sound stimuli?

Answer 1

Amplitude: loudness
Frequency: pitch
Complexity: timbre

What is the range of sounds we can hear in our prime? 20-20,000 Hz

Sound stimuli is pressure in the air and pressure changes in the air that hit your inner ear

Question 2

What is the external ear for?

Answer 2

Captures and directs sound (pressure waves) down the auditory canal to the tympanic membrane
Differentiating where sounds are coming from on the vertical plane.

Question 3

What does the eardrum do?

Answer 3

Converts air sound waves to pressure waves in cochlea

Question 4

What does the fluid in the ear do? what are it’s properties?

Answer 4

Incompressible, the pressure waves travel down the cochlea and back bending the basilar membrane

The pressure waves are converted to changes in pressure in fluids which cause bending in certain parts causing receptors to change shape, when the pressure is changed, fluid travels around the middle portion of the basilar membrane and goes all the way around to the other side, when it hits the membrane on the other side, the membrane ‘gives’ and relieves pressure. Cells that care about different frequencies are all along the basilar membrane

Question 5

What is the basilar membrane?

Answer 5

Contains auditory receptors (hair cells)

Question 6

what is the tympanum?

Answer 6

membrane that amplifies pressure waves and focuses energy onto the oval window

Question 7

How does sensory transduction work in audition?

Answer 7

The basilar membrane bends in response to sounds

1. pressure hits tympanic membrane
2. fluid hits basilar membrane and pushes it down
3. pressure is released and the basilar membrane pops back up

Basilar membrane is thin/floppy at the end, but the base is rigid, so low frequencies cause bending at the far end and high frequencies cause bending close to the base

Question 8

What is the tonotopic map?

Answer 8

Structural properties of basilar membrane give rise to this

- preferential bending to low (floppy end) and high (rigid base) frequencies respectively

Question 9

What is the tectorial membrane?

Answer 9

Covers 16,000 receptor hair cells in basilar membrane and aids in bending/stimulating

because

Waves create shearing forces between membrane and the hair cells helping stimulate.

Question 10

What are the hair cells in basilar membrane made of?

Answer 10

Just cell body with silica arranged together, no axon!

At the base there are vesicles that will release onto a postynaptic cell and generate action potentials that way!

Question 11

How are physical forces of silica turned into electrical signals?

Answer 11

Depolarization due to POTASSIUM!

Bending towards Kinocilium opens the channels allowing POTASSIUM entry, depolarization and glutamate release

The receptor channels are just like AMPA.

The Silica are connected to each other through tip lengths

Question 12

What is the auditory pathway after the signal has been created?

Answer 12

From basilar membrane hair cells, those axons go to the
1. cochlear nerve to the
2. cochlear nucleus (where the tonotopic map is 1:1) which integrates info and somatosensory info about yourself to help you distinguish your sounds from the world
3. medial and lateral superior olives
medial: timing difference for localizing sounds
lateral: amplitude difference for localizing sounds
4. inferior coliculus: all ascendig pathways converge here for rapidly engaging fast automatic behaviors (projects to thalamus-A1 for more complex processing
5. superior coliculus: integrates everything (lso, mso cochlear nucleus) to get a rapid understanding of where something is happening in 3D space, also receives visual info for reflexively turning yourself
auditory and visual cues tell you where things are coming from
-subcortical rapid automatic behavhior

Question 13

How do we localize sounds in the horizontal plane?

Answer 13

We can detect a 1 degree difference in sound localization (only a 10us difference bewteen the two ears)

There is a circuit mechanism in the MSO: axons carrying info from both ears MEET and where the signals meet (coincident detectors) determines how far it is away from each ear (how far the signal could travel each direction (ITD > 0 left)

Location based receptive fields

Will only fire it if recieves info from both ears - neurons need the SUMMATION

Question 14

What is the maximal interaural timing difference?

Answer 14

600 us (mueseconds?)

Question 15

How is sound localized in the verticle plane?

Answer 15

The shape of your ear governs this
- your brain learns the frequencies of certain sounds when they are in different vertical planes around you. If you change the shape of your ear this is messed up.

High frequency sounds, affected much more by this:
Low frequency sounds aren’t really different if coming from above/below

Question 16

How is the auditory cortex organized?

Answer 16

Primary distinguisher is frequency (tonotopic maps)

Tonotopic organization in A1: discrete layout of sounds. relevant sounds occupy a greater area
(musicians have a larger area devoted to frequencies here, shows plasticity)

Columnar organization: columns respond to specific frequencies (some show ear dominance -like ocular dominance!)

Higher order auditory regions: respond to complex combination of sounds (rather than pure tones)
-heirarchical processing is less understood here

Question 17

What are the four types of mechanoreceptors?

Answer 17

Mechanoreceptors: respond to force and change shape to cause depolarization
Rapidly Adapting: when you apply stim, cell will fire, but then adapt quickly and stop. sensitive to CHANGES in pressure
Slowly Adapting: will fire as long as stimulus is there
Type 1: small receptive fields, near the surface, more sensitive, high spatial acuity
Type 2: larger receptive fields, deeper in skin, less resolution

Question 18

What are examples of the 4 mechanoreceptors?

Answer 18

Rapid Type 1: Meissner corpuscle (most common, lateral motion/slippage/initial contact)
Rapid Type 2: Pacinian corpuscles (responds to vibrations (0.01um-1000hz, reduce with age -2400 to 300)

Slow Type 1: Merkel cells (edges, points, fine details)
Slow Type 2: Ruffini endings (aligned at folds of hand to detect motion and stretch of skin, detect large object shape and hand position)

Question 19

Which type of receptors do you need for if something is slipping in your hand?

Answer 19

Fast adapting

Type 1, meissner corpuscles

Question 20

What does acutiy depend on?

Answer 20

Receptive field size and receptor density

-threshold of detection of 2 stimuli is lowest for fingers, then feet, then face then back etc.

Question 21

How are somatosensory infos represented in the cortex?

Answer 21

Thalamic inputs project to layer 4 of the S1 (postcentral gyrus of parietal lobe)

Somatotopic map: Adjacent parts of the body are NEAR each other, not always exactly beside
Not every stimulus gets equally important representation (some parts are bigger than others relatively)

Columnar organization: neurons in the same column respond to similar stimuli types, have similar receptive fields.

Larger receptive fields are in the cortex than in your actual skin: BUT you have inhibition that increases contrast (think LATERAL INHIBITION, on/off exitatory/inhibitory fields in S1)
Sharpen and refine receptive fields to help percieve edges of an object **

Question 22

What are higher order somatosensory representations involved with?

Answer 22

not just presence/location of a stim, they concern size, orientation, shape, movement, grip force, hand posture
Cares about different experiences (bike riding vs. holding a hammer)
- higher order you go, cells care about multiple things from both hands/areas

S2 and posterior parietal cortex RFs can be bilateral!

Question 23

Describe the olfactory system

Answer 23

Hundreds of different odorant receptors
Different receptor types are scattered across epithelium
All receptor neurons of the same class project to the same few glomeruli. 
A single odor activates multiple receptors/glomeruli, and each receptor binds multiple odorants. This pattern of activity or POPULATION CODE is unique for each odor.

Question 24

What is a chemotopic map?

Answer 24

Anatomical organization of receptors and glomuli: it exists but is apparently random

Question 25

How do odorants bind receptors?

Answer 25

Ligant gated cause of depolarization
Nerve endings are exposed to air in nasal passage
Some smells bind more strongly to receptors than others do, helping create the population code

Question 26

What are some different Odorant receptors that can be expressed in mRNA to show overlapping distribution?

Answer 26

K20, K21 L45, A16, and OMP (all odorant receptors)

Shows wide distribution

Question 27

What is an advantage to having population coding in the olfactory system?

Answer 27

THere are thousands of different odors, trying to have receptors for all would be too much, this way we can infer the smell from the PATTERN and there can be multiple of those
-spatially favourable