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PNB 2XB3 (Neuroanatomy) > Lecture 7 + Assignment 6 > Flashcards

Lecture 7 + Assignment 6 Flashcards

1
Q

Sound waves

Longi vs transverse

A

Wave of compression (particles close) and rarefaction (particles far)

Longitudinal: Pulse and vibration the same direction

Transverse: Pulse left/right, vibration up/down

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2
Q

Sound wave measurements

A

Speed = distance/time = wavelength/period

Frequency (Hz or s^-1) = 1/period

Speed = wavelength x frequency

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3
Q

Human voice frequency and wavelength

A

Men
- 100 Hz
- 3.44 m

Women
- 200 Hz
- 1.72 m

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4
Q

2 things that allow for sound localization

A
  1. Interaural intensity difference
  2. Interaural time difference
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5
Q

Interaural intensity difference

A
  • sounds louder in the ear that it’s near

bc head muffles sound

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6
Q

Interaural time difference

A

difference in speed of sound entering one ear vs. the other

brain calculates

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7
Q

Ascending auditory pathways

A

Destination: primary auditory complex in temporal lobe

Nucleus 1: in medulla cochlear nuclei

Nucleus 2: pons nuclei (ITD and IID) sup. olive

axons from the ear to the 8th cranial nerve (auditory nerve)
- spiral ganglion

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8
Q

Cranial nerves

General

A

Most rostral = 1
Most caudal = 12

don’t enter the spinal cord

enter through fossa holes in the cranium bone surrounding brain stem

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9
Q

Auditory cortex

A

tonotopic representation based on frequencies

closer to front corresponds with apex of cochlea

closer to back corresponds to base of cochlea (20 000 Hz)

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10
Q

Humans can hear what frequencies

A

20 Hz - 20 000 Hz

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11
Q

The superior olivary complex

Where is it

A

contains 2 nuclei for sound localization:

  1. LSO (lateral superior olive)
    - interaural loudness/level difference
  2. MSO (medial superior olive)
    - interaural time difference

in mid-pons

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12
Q

Lateral superior olive

A

interaural intensity difference

for high frequency sounds > 2000 Hz

smaller wavelengths than the diameter of the head (20cm)

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13
Q

LSO sound localization

A

each cochlear nucleus

excites:
- the ipsilateral LSO (same side)
- the contralateral MNTB

MNTB inhibits the ipsilateral (to itself) LSO

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14
Q

Medial superior olive

A

monitors interaural time difference for low-frequency sounds

under 2000 Hz
where there is NO head shadow

so do time instead of intensity

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15
Q

MSO sound localization

A

Jeffress Model

  • MSO gets input from both sides
  • different axon lengths to same nucleus in MSO
  • one will get EPSPs from both sides at the same time

coincidence detection = tells you location from each ear

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16
Q

Parts of the human ear

A

pinna
concha (shell/bowl)
external auditory meatus
tympanic membrane

Middle ear:
malleus
incus
stapes

Eustachian tube

Inner ear:
oval window (membrane)
vestibule
cochlea
round window
semicircular canals
hair cells

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17
Q

What does the eustachian tube do

A
  • equalizes pressure in the middle and outer ear
  • opens into throat
  • for tympanic membrane
  • allows it to not bulge and burst
  • so it can vibrate
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18
Q

Attenuation reflex muscles (2)

A

Tensor tympani muscle
- between cochlea bone and malleus

Stapedius muscle
- between bone and stapes

reduce ossicle vibration as to not damage hair cells in loud environment (constrict)

19
Q

Pressure amplification in the middle ear (2 mechanisms)

A
  1. The oval window is much smaller than the tympanic membrane
    - force funneled into a smaller area = increased pressure
  2. Stapes displaces the oval window much less than the tympanic membrane, but with more force
    - decrease distance, increase force (lever system)
20
Q

Archimedes

A
  • could move earth with a big enough lever

287-212 BCE

  • Greek guy

mechanical advantage principles

21
Q

The cochlea - basilar membrane

A

bm
- like a series of tuning forks
smallest near oval window
= base
= stiffer
= responds to the highest frequency

although the cochlea is bigger there, bm smaller

tonotopic map

150 microns at base
500 microns at apex

22
Q

Resonant frequency

A

some things only resonate at one frequency

ex. tuning forks or locations on the basilar membrane

23
Q

Tonotopy of the basilar membrane

A
  • different axons respond to different frequencies along the bm best
24
Q

The cochlea

A

3 chambers

  1. scala vestibuli
    - touches the oval window
    - connected to the scala tympani
    - makes the round window bulge out
  2. scala media
    - does acoustic transmission
    - not connected to others
    - different type of fluid = endolymph
    - contains hair cells with their tips touching the tectorial membrane
  3. scala tympani
    - connected to the vestibuli and round window
25
Endolymph vs perilymph
Endolymph - in scala media - high K concentration Perilymph - in other scalas - low K concentration
26
Arrangement of inner and outer hair cells
- stereocilia on top of hair cells touch tectorial membrane - basilar membrane houses supporting cells - when bm bounces, so do they - causes hairs to bend - opens mech gated ion channels in stereocilia = acoustic transduction
27
Organ of corti
15 000 hair cells 3500 are inner 1:5 ratio 95% of afferent axons innervate inner hair cells outer do motor function
28
Basilar membrane movement and hair cells
bm moving up - shearing force of tectorial membrane up moves stereocilia towards long one bm moving down - shearing force moves stereocilia towards short one
29
Threshold hair bundle deflection
displacement of 0.3 nm
30
Mechano-acoustical transduction
- have tip links = gating springs - connected to Ca/K ion channels - pull them open and depolarize - causes voltage gated Ca channels to open and transmit to afferent axon that goes to the auditory nerve - glutamate transmits OPEN WHEN DEFLECTED TO LONG END = increases tension causes outer hair cell to contract
31
Outer hair cell contraction motors
Prestin: the motor protein in the outer hair cell membrane depolarization causes OHC to contract hyperpolarization causes OHC to lengthen
32
Conductive hearing loss
- vibration impeded from reaching inner ear pre-oval window ex. - wax - otitis media (middle ear infection in kids) - otosclerosis (stapes fused to oval window bone)
33
Sensorineural hearing loss
- neural processing compromised post-oval window ex. - occupational deafness (loud sounds) - presbycusis (with age, high frequency BM not bendy) - antibiotic neuroma (damage hair cells) - acoustic neuroma tumor (aka vestibular schwannoma)
34
Thomas Edison
- bilateral conductive hearing loss - inventor of records - read a lot
35
Hearing loss today
- hair cells don't regenerate - cumulative damage more decibels = more danger protect your hearing!
36
Immunofluorescence - direct method
- Using antibodies visualise certain proteins and see where they are in neurons - Antigens (foreign) are recognized by antibodies in the immune system - Requires that the primary antibody be fluorescently tagged - More difficult bc you need to get the primary antibodies from the animal and tag them
37
Immunofluorescence - INdirect method
- More efficient - Different primary antibodies have the same tail region - Tagged secondary antibody can serve as an all-purpose labeller (Other animal makes antibodies) - Several tagged antibodies can bond to the same primary antibody tail = more light
38
Immunofluorescence - detecting noise damage
- Label synaptic ribbon that occurs between the inner hair cells and the afferent auditory nerves AND in the IHC nuclei → red - Label neurofilament protein (axons) → green After sound exposure: synapse loss + disordered cell body appearance + axon problems
39
Max firing rate of a typical neuron
500 AP / s 1 AP / 2ms due to refractory period
40
Why do rats hear much higher frequencies than humans
- their BM is much narrower at both ends = higher resonance frequencies
41
Cochlear implants vs. normal hearing aids
Cochlear implants - activate the auditory nerve axons by electrically stimulating them with electrodes threaded through the cochlea - profound sensorineural hearing loss mic on head -> speech processor -> transmitter -> receiver-stimulator -> electrode stimulation Conventional hearing aids - amplify sound
42
Tinnitus + most common cause
ringing or buzzing in the ears though no sound present - phantom sound/hallucination most common cause - hearing loss caused by exposure to loud noise - ringing heard at the frequency where hearing was lost - also age, congenital hearing loss, ear infections, etc. - maybe like phantom limb = spontaneous activity
43
Barn owl audition
- asymmetrical ears right = points up left = points down allows for vertical localization (elevation) as opposed to just horizontal (azimuthal)

PNB 2XB3 (Neuroanatomy) (10 decks)

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