Midterm 1 - Audition & Olfaction

Question 1

Sound Pathway

(Process Overview)

Answer 1

1. Sound
2. Ear canal
3. Tympanic membrane (eardrum) vibrates
4. Ossicles (stapes) press against membrane behind oval window (opening to inner ear)
5. Air transferred to liquid medium in cochlea
6. Organ of Corti
7. Shearing of basilar and tectorial membrane (where hairs are anchored)
8. Mechanoreceptors open
9. K+ enters
10. Membrane depolarizes
11. Release of NTs
12. 8th CN (auditory nerve)

Question 2

Ear Anatomy

(Overview)

Answer 2

Question 3

Organ of Corti Unrolled & Place Code

Answer 3

Question 4

Organ of Corti

Answer 4

• Within cochlea and contains tectorial membrane (where hair cells are anchored), basilar membrane (what vibrates), hair cells, mechanoreceptors, CN#8

Question 5

Shearing Effect

(Visual)

Answer 5

Question 6

Shearing Effect

Answer 6

When the tympanic membrane vibrates, there is a “shearing effect” between the basilar and tectorila membranes. This results in hair cells getting pulled. If they get pulled far enough, their mechanoreceptor will open and K+ will rush in, causing depolarization.

Question 7

Cranial Nerve # 8

Answer 7

Acoustic/Vestibulocochlear

The axons leaving the hair cells form a bundle of axons that go to the brain. Even though we have a greater number of outer hair cells, the majority of the axons are from inner hair cells (which are closer to CN#8).

Question 8

Mechanoreceptor

Answer 8

The ion channels in the tectorial membrane open as a result of the shearing effect (as opposed to a ligand binding).

When the mechanoreceptors open, K+ rushes in and causes depolarization.

Question 9

2 Different Ways of Conveying Sound Messages to the Brain

Answer 9

1. Frequency
2. Place Code

Question 10

Frequency

(conveying of sound message to the brain)

Answer 10

AKA “Rate Coding”

If there’s a low frequency (pitch measured in Hz), the hair cells will fire in synchrony with the low tone.

Question 11

Place Code

Answer 11

As the cochlea is laid out, it goes from high tones to low tones. The brain can tell the tone of the sound based on where it comes from in the organ of corti.

Question 12

Tonotopy Based on Place Code

Answer 12

The auditory cortex maintains the frequency specificity of the cochlea. Organized as a tonotopic map in MGN and A1.

Question 13

Auditory Pathway

(Starting with CN # 8)

(Visual)

Answer 13

Question 14

Auditory Pathway

(Verbal)

Answer 14

1. The auditory nerve makes a synapse in the cochlear nucleus in the brain stem.
2. The projections from the cochlear nucleus mostly cross and synapse in the superior olive.
3. Axon collaterals then go to the inferior colliculus of the midbrain. Main information however goes directly to the thalamus.
4. The inferior colliculus projects to the thalamus (medial geniculate nucleus).
5. The medial geniculate projects to primary auditory cortex in the superior temporal lobe.

Question 15

Inferior Colliculus

Answer 15

• Midbrain
• Directly below superior colliculus
• Allows you to start orienting head in a particular direction if we hear an alarming sound (you turn your head towards sound).

Question 16

Primary Auditory Cortex

(A1)

Answer 16

On the upper bank of the temporal lobe, just below the lateral fissure.

Question 17

Pleasure of Sound & Recruitment

Answer 17

Because we have a tonal map, neurons in cochlea, MGN and A1 can all fire at the same frequency. Then they will “recruit” other neurons around them which will start firing at the same frequency.

When huge populations of neurons in the brain fire together, it’s very pleasurable.

Question 18

If sound enters left ear, where does it go?

Answer 18

Ends up in A1 of the right side.

We know that sound information crosses by performing dichotic listening tasks.

Question 19

Vestibular System

Answer 19

• Balance
• You can tell which way your head is going by the way fluid moves in the semi-circular canals.
• Part of the auditory system.

Question 20

Olfactory Pathway

Answer 20

1. Raw olfactory molecules attach to mitral cells (in olfactory bulb) that are sitting in the cribriform plate.
2. Most of the axons of the mitral cells go straight into cortex (pyriform cortex, entorhinal cortex) via CN # 1. NOT TO THALAMUS.

• Raw olfactory information goes straight to the pyriform and entorhinal cortices (have something to do with emotion and memory; could be primary olfactory cortex?). There is no filtering of raw olfactory information b/c it doesn’t go to the thalamus.