Lecture 16: Hearing 2 and Olfaction

Question 1

Inferior Colliculus

Answer 1

-Receives converging sound information from cochlear nucleus and superior olive.
- Sends information about sound location to the visual superior colliculus.
- Synchronizes auditory and visual maps.

Question 2

Auditory Cortex (AC)

Answer 2

• Splits into left and right auditory cortex
• Higher level auditory processing station

Question 3

Auditory Cortex Lesions

Answer 3

• Don’t become deaf
• Animals can still detect and respond to sounds
• AC Lesions impair recognition of complex sounds (such as speech) and impair hearing in noisy environments

Question 4

Neurons in the Auditory Cortex

Answer 4

• Neurons in the AC respond to both simple and complex sounds
• Their receptive field can be described in a frequency response area (FRA)

Question 5

Best/Characteristic Frequency

Answer 5

The sound frequency that makes a neuron respond the strongest

Question 6

The AC is organized ____________

Answer 6

Tonotopically; by in order by characteristic frequency

Question 7

The AC exhibits _________________

Answer 7

Experience-dependent plasticity

Question 8

Odor Guided Navigation Experiment

Answer 8

• Odor info coming through two nostrils can be used to identify odor location
• Blind Eastern American Moles trained to detect odor source
• Blocking of one nostril caused errors to the opposite side

Question 8

Odorants

Answer 8

A molecule that has a smell

Question 9

Odors

Answer 9

The sensation that a mix of odorants gives

Question 10

Olfactory Epithelium

Answer 10

• Found at the top of the nasal cavity
• Odorants enter either through the nose or back of the throat and dissolve in the mucus covering of the epithelium

Question 11

Olfactory Sensory Neuron

Answer 11

• Converts smells to neural signals
• Odorants bind to receptors on the cilia of olfactory sensory neurons
• Unlike most neurons, these neurons undergo constant turnover every 4-6 weeks (like the hippocampus)

Question 12

Olfactory Transduction

Answer 12

• Binding of an odorant causes the olfactory receptor to interact with a G-protein
• Causes a chain of reactions which leads to influx of calcium and sodium –> depolarization
• If the olfactory sensory neuron is sufficiently depolarized it will fire an action potential

Question 13

Olfactory Receptors

Answer 13

• Each olfactory sensory cell expresses only 1 type of receptor
• Each receptor can bind to a number of odorants (combinatorial coding)

Question 14

Glomeruli

Answer 14

• Olfactory receptor cells project to glomeruli in the olfactory bulb
• Each glomerulus receives input from just one type of odorant receptor

Question 15

Olfactory Bulb to Rest of Brain

Answer 15

• Output cells of the olfactory bulb send information directly to the olfactory cortex via the olfactory nerve
• Information also sent to entorhinal cortex (memory), hypothalamus (appetite), amygdala (fear and emotion), and the prefrontal cortex

Question 16

Anosmia/Hyposmia

Answer 16

Lost/reduced sense of smell
- Can occur following head injury, exposure to certain chemicals, medications, etc.
- Is a predictor of Alzheimer’s