Auditory Senses Pt. 2

What are the sensory receptors of the auditory system in all vertebrates?

Hair cells

In mammals, where are the auditory hair cells located?

Within the organ of corti on a thin basilar membrane

Do hair cells regenerate after damage?

They do not; they only regenerate in birds

When hair cells are activated, what do they look like? At rest?

Bent when activated, erect when at rest

Where are the vesicles (Neurotransmitters) for hearing located?

The hair cells

What causes the stereocilia to bend towards the tallest one?

The basilar membrane moving up

What causes the stereocilia to bend away from the tallest one?

The basilar membrane moving down

What happens when the stereocilia are bent towards the tallest one?

The bending opens ion channels, causing depolarization, which causes the release of neurotransmitters and increases the firing rate so action potential moves to the brain

order these in the way that they are affected when stereocilia are bent: mechanical, sound, electrical energy

Sound —> Mechanical —> Electrical

How do loud noises lead to hearing loss?

Damaged basilar membrane near the base/beginning of the cochlea

Where in the cochlea are high frequency soundwaves picked up?

at the base/beginning of the basilar membrane

Where in the cochlea are low frequency soundwaves picked up?

At the apex/end of the basilar membrane

What is the type of sound pitch typically lost first with age or noise damage?

High pitched sound

Where is the organ of corti located?

The scala media/cochlear duct

What are the parts of the organ of corti?

1. basilar membrane

2. tectorial membrane

3. afferent axons (sensory)

What causes the movement in the oval window?

Incoming soundwaves move the ossicles of the middle ear

What enters the cochlea via the oval window?

Fluid waves

What type of movement is described by the oscillation in the basilar membrane?

Back and forth (up and down) movement

What is the result of the back and forth movement of the basilar membrane?

Bending of the stereocilia, which initiates the neural signal for hearing

What is the role of the stapes?

Vibrates against the oval window, pushing fluid (endolymph) in the cochlea

What is the role of the vestibuli?

Carries sound waves from the oval window

What is the role of the round window?

A flexible membrane that allows fluid waves to dissipate to avoid pressure build

What is the helicotrema?

The tip of the cochlea where the fluid wave passes from scala vestibuli to scala tympani

What happens to the hair cells, stereocilia, and basilar membrane when exposed to loud noises?

Loud noises could physically damage the hair cells and their stereocilia. Once damaged, they don’t regenerate which can lead to permanent hearing loss. Over time, damage also makes the basilar membrane weaker/stiffer, reducing hearing sensitivity.

What does the vestibular system deal with?

Balance and equilibrium

T/F The vestibular system deals with hearing

FALSE, it has nothing to do with hearing

What system deals with hearing ONLY

Cochlea

What is the vestibular apparatus?

The neurological equipment responsible for perceiving your body’s orientation relative to the earth

Give some examples on how the vestibular apparatus affects you

• Determines if you’re upside down, standing up, falling, etc.

• Informs your eyes and extremities how they should react accordingly

• Allows us to walk or run on uneven ground without falling, when to right ourselves, follow objects without getting dizzy

How many parts does the vestibular system have?

Two; Otolith and Semi-circular canals

What are the two organs of the otolith?

Utricle and Saccule

What do the utricle and saccule deal with?

Balance

What does the otolith do?

Detects head’s linear acceleration and gravity

How do the otolith organs work?

It contains hair cells with tiny crystals called otoliths. When you tilt or accelerate the crystals shift, bending the hair cells which signal which direction is down

What are the three semi-circular canals?

1. Anterior

2. Posterior

3. Horizontal

How many semi-circular canals are there total?

6 total, 3 on each side

What do the semi-circular canals detect?

The head’s rotation (Angular accelaration)

What are the semi-circular canals filled with?

Endolymph fluid

What is present at the end of each canal?

An ampulla that contains hair cells

What is an ampulla?

Expanded region of semi-circular duct that contains receptors called hair cells

How do the semi-circular canals detect head rotations?

When you rotate your head, the fluid inside lags behind (due to inertia), bending the hair cells inside the ampulla. This tells your brain the direction and speed of rotation

What is the kinocilium?

The tallest hair on an ampullas hair cell

Another name for posterior canal?

Inferior canal

Another name for anterior canal

Superior canal

What is a cupula?

A gelatinous structure that contains hair cells, and it moves when endolymph moves in response to head rotation in the plane of the semi-circular canal

What happens when the cupula shifts?

The kinocilia and stereocilia of the hair cells are distorted, resulting in the hair cells depolarizing and firing off action potentials

T/F The hair cells are in the ampulla, but their stereocilia are imbedded into the cupula

True

What happens when the whole cupula moves?

Kinocilium moves left or right

What happens when the stereocilia bend towards the kinocilium?

Depolarization (Stimulation), resulting in a high rate of action potentials

What happens when the stereocilia bend away from the kinocilium?

Hyperpolarization (Inhibition), resulting in a low rate of action potentials

What happens when the kinocilium bends towards the stereocilium?

Hyperpolarization

What happens when the kinocilium bends away from the stereocilium?

Depolarization

T/F If you are completely still, action potentials are still being sent

True, bcs never truly still

What are the signs of a disorder of the vestibular system?

• Ataxia

• Dizziness

• Head tilt (Can straighten the ehad but it will move back)

• Circling

• Motion sickness

What is ataxia?

When an animal is coming out of anesthesia and they’re stumbling

What are some vestibular system diseases?

• Ear infection

• Tumors

• Unknown causes (Idiopathic vestibular syndrome)

How does the brain know ypu are turning left vs right?

If you turn your head to the right:

The right ear will depolarize because the fluid pushes the stereocilia towards the kinocilia

The left ear will hyperpolarize because the fluid pulls the stereocilia away from the kinocilia