Ch 6 Neuro Exam

How does the human auditory system detect sound?

Amplitude and frequency

Amplitude

measured in decibels (dB) and perceived as loudness

Frequency

* measured in number of cycles per second, or hertz (Hz)
* a physical property of a sound
* perceived as pitch

Pitch

* our subjective perception of sound
* higher frequency = higher pitch

How does sound, a mechanical force, become neural activity?

Transduction

What is the external ear made of?

The pinna and ear canal

Pinna

* the visible part of the ear
* collects sound waves

Ear canal (auditory canal)

a tube running from the outer ear to the middle ear

What does the middle ear do?

Concentrates sound energies

What are the parts of the middle ear?

Three ossicles connect the tympanic membrane (ear drum) to the oval window

What are the three ossicles called?

Malleus, incus, and stapes

What is the tympanic membrane?

eardrum

What are the muscles in the middle ear that control volume?

Tensor tympani and stapedius

How do the muscles in the middle ear control volume?

When activated, the muscles stiffen and reduce sound's effect

What is the spiral shaped part of the inner ear?

Cochlea

What does the cochlea do?

Converts vibrations into neural activity

What are the three parallel canals of the cochlea?

* Scala vestibuli (vestibular canal)
* Scala media (middle canal)
* Scala tympani (tympanic canal)

Round window

a membrane that separates the tympanic canal from the middle ear; it can bulge outward a bit.

Organ of Corti

the part of the cochlea that converts sound into neural activity.

What are the structures of the organ of Corti?

* hair cells
* framework of supporting cells
* terminations of the auditory fibers

basilar membrane

the base of the organ of Corti

stereocilia

small hair-like projections on the tops of inner and outer hair cells

How do vibrations affect the basilar membrane?

Causes it to ripple

Where do high frequencies have the most effect?

have greatest effect at the base, where it is narrow and relatively stiff

Where do low frequencies have the greatest effect?

near the apex, where it is wider and more flexible

What parts of the cochlea convert sound into neural activity?

Hair cells in the basilar membrane

How are stereocilia connected to each other?

They are connected to each other by tip links

Tip links of stereocilia

tiny fibers that open ion channels when the stereocilia bend

How do hair cells depolarize?

The movement of the stereocilia causes opening of ion channels which allow K+ in to depolarize the hair cell, which causes a neurotransmitter to be released.

What are the two groups of hair cells un the cochlea?

* inner hair cells (IHCs)
* outer hair cells (OHCs)

How are inner hair cells (IHCs) organized in the cochlea?

a single row near the central axis

How are outer hair cells (OHCs) organized in the cochlea?

three rows

What nerve contacts the bases of the hair cells?

vestibulocochlear nerve (cranial nerve VIII)

How many kinds of neural connections to hair cells use different transmitters?

4

How do outer hair cell (OHC) afferents work?

OHC afferents convey information to the brain about the mechanical state of the basilar membrane, not sounds themselves.

What neurotransmitters do outer hair cell (OHC) afferents use?

GABA

How to outer hair cell (OHC) efferents work?

OHC efferents lead from the brain to OHCs, allowing the brain to modify the stiffness of the basilar membrane, thus sharpening and amplifying sounds.

What neurotransmitter do outer hair cells (OHCs) use?

ACh

How do inner hair cell (IHC) afferents work?

IHC afferents convey action potentials that provide sound perception to the brain.

What neurotransmitter do inner hair cell (IHC) afferents use?

ACh

How do inner hair cell (IHC) efferents work?

IHC efferents lead from the brain to the IHCs, allowing the brain to control responsiveness of IHCs.

What neurotransmitter do inner hair cell (IHC) efferents use?

Glutamate

How sensitive are inner hair cells (IHCs)?

Each IHC has a maximum sensitivity to a particular frequency, but will respond to others if they are loud enough.

What is the auditory neural pathway?

Cochlea -\> cochlear nucleus -\> superior olivary nucleus -\> inferior colliculus -\> medial genticulate nucleus -\> auditory cortex

Where do auditory fibers from the IHCs terminate?

the cochlear nuclei

Where does auditory information switch over?

* in the brainstem
* from the cochlear nucleus to the superior olivary nucleus

Where do cochlear nuclei send auditory information?

The superior olivary nuclei

Where do superior olivary nuclei send auditory information?

The inferior colliculi

inferior colliculi

the primary auditory centers of the midbrain

Where do inferior colliculi send auditory information?

The medial genticulate nuclei

Where is the medial genticulate nuclei?

the thalamus

Where do medial genticulate nuclei send auditory information?

The auditory cortex

What part of the brain does sound activate?

* the primary auditory cortex (A1)
* Speech sounds also activate other, more specialized auditory areas

Which signals from the cochlea inform the brail about pitch?

place coding and temporal coding

Place coding

pitch is determined by the location of the activated hair cells

temporal coding

encodes the frequency of auditory stimuli in the firing rate of auditory neurons

ultrasound frequencies

very high frequencies

infrasound frequencies

very low frequencies

What kind of sounds is the auditory cortex specialized for?

biologically relevant sound, such as footsteps, animal vocalizations, and speech.

Heschl's gyrus is much larger in what kind of people?

professional musicians

conduction deafness

disorders of the outer or middle ear prevent sounds from reaching the cochlea

sensorineural deafness

hair cells fail to respond to movement of the basilar membrane; no action potentials fired

Is conduction deafness or sensorineural deafness more common?

sensorineural deafness

What causes sensorineural deafness?

genetic mutations, infections, ototoxic effects of drugs, loud sounds

tinnitus

a persistent ringing in the ears, which can be caused by damage to hair cells

What causes central deafness?

damage to auditory brain areas, such as by stroke, tumors, or traumatic brain injury

Word deafness

selective difficulty recognizing normal speech sounds; normal speech and hearing of nonverbal sounds

cortical deafness

difficulty recognizing all complex sounds, verbal or nonverbal; rare

What tastes do taste receptors detect?

saltiness, sourness, sweetness, bitterness, and umami

What tastes do taste receptors possibly detect?

Possibly fat, starch, carbonation, calcium, water

What kind of sugars are detected as sweet?

fructose, sucrose, artificial sweeteners (saccharin and aspartame)

What flavors and ions are detected as bitter?

ions like K+ and Mg2+, quinine, and caffeine

What kind of substances are detected as bitter that help survival?

poison

What part of the tongue is sensitive to sweetness?

Tip of the tongue

What part of the tongue is sensitive to bitterness?

Back of the tongue

What part of the tongue is sensitive to saltiness and sourness?

Sides of the tongue

T or F: All areas of the tongue detect all five tastes?

True

papillae

small structures found on the upper surface of the tongue

What are the types of papillae?

* Foliate papillae
* Vallate papillae
* Fungiform papillae

taste buds

The taste buds are taste receptors containing cells (gustatory cells) found in the oral cavity lining the sides of each papillae

How many taste buds are found on the tongue?

Over 10,000

Where are taste buds found?

Sides of papillae on the tongue, soft palate, and inner surface of the cheek

tastants

Chemicals that stimulate gustatory receptor cells

What do tastants do?

* Pass directly through ion channels
* Bind to and block ion channels
* Bind to G-protein-coupled receptors and activate second messenger to open ion channel

How are salty and sour taste sensations detected?

Through ion channels

How are sweet, bitter, and umami tastes detected?

GPCR

How do salty tastes make cells depolarize?

Sodium (Na+ ) ions enter taste cells via sodium channels, causing depolarization.

What salt sensor increases sensitivity to Na+ and also detects cations of other salts in food?

TRPV1 (transient receptor potential vanilloid type 1)

What ion tastes sour?

Acids release hydrogen ions (H+ ) and taste sour

The same receptor of which taste also detects carbonation?

Sour

How do sour tastes depolarize the cell?

Sour taste cells all seem to contain the same type of ion channel that allows an influx of protons, which depolarizes the cell.

How are sweet tastes detected?

a heterodimer of T1R2 and T1R3

How are bitter tastes detected?

T2R receptors

How are umami tastes detected?

* metabotropic glutamate receptor
* receptor that is a combination of T1R1 and T1R3

What do metabotropic glutamate receptors respond to?

Glutamate

What stimulates metabotropic glutamate receptors?

monosodium glutamate (MSG), a flavor enhancer

T1R1 and T1R3 receptors respond to what?

most dietary amino acids

gustatory system pathway

Tongue -\> brainstem nuclei -\> thalamus -\> somatosensory cortex

Where does the tongue send gustatory information?

brainstem nuclei

Where do brainstem nuclei send gustatory information?

thalamus