April 21, 2014 – Hearing and equilibrium

1. What is sound and how is it perceived?2. Functional anatomy of the mammalian (human) ear.3. Distinguishing volume and pitch4. Other modes of animal hearing5. Ears and equilibrium in mammals6. Equilibrium in other critters

What is sound?

Captures and funnels sound to tympanic membrane

Townsend's big-eared bat (Corynorhinus townsendii)

Harbor seal(Phoca vitulina)

Amplifies sound and transfers energy the oval window

• Pathway:1. Sound waves in air

travel through outer ear until they reach tympanic membrane

2. Sound waves vibrate membrane, which in turn vibrates 3 bones of middle ear:

Malleus

Incus

Stapes

(outin: “MIS”)

Hearing- Mammals (con’t)

• Pathway:

3. Stapes transmits sound to the oval window

-membrane on the surface of cochlea

Hearing- Mammals (con’t)

Detects sound frequency transmits signal to the auditory nerve

• Pathway:

3. Stapes transmits sound to the oval window

-membrane on the surface of cochlea

4. Vibration on oval window causes vibration of perilymph (fluid) in the cochlea

Hearing- Mammals (con’t)

Side view of uncurled Cochlea

Vestibular canal

Tympaniccanal

Cochlear duct

Tectorialmembrane

Hair cells

Axons of sensoryneurons

Hair cells

• Two Components of Sound Wave:There are two main components of the sound

wave that are detected and used by the auditory system:

1. Volume- Amplitude (height of wave)

Hearing- Mammals (con’t)

2. Pitch or Frequency (no. of waves per unit time)

1. Amplitude

larger amplitude= louder sound

-larger amplitude results in stronger pressure on the hair cells, more rapid firing of action potentials

Hearing- Mammals (con’t)

1. Amplitude

larger amplitude= louder sound

-larger amplitude results in stronger pressure on the hair cells, more rapid firing of action potentials

2. Pitch

- basilar membrane varies in thickness and flexibility

-base= narrow and stiff; stimulated by higher frequencies

-tip (apex)= wider and more flexible; stimulated by lower frequenices

Hearing- Mammals (con’t)

Cochlear animation

• http://www.hhmi.org/biointeractive/cochlea

Age-related hearing loss is often associated with a reduced ability to hear high-pitched sounds. Propose a mechanism to explain this.

Blackburnian Warbler(Setophaga fusca)

Cochlear implants

http://www.ted.com/talks/charles_limb_building_the_musical_muscle.htmlCharles Limb TED talk:

1. Fish- have inner ear, but no tympanic membrane and no opening to outside

-pathway: sound waves skull inner ear brain

-inner ear has small calcium carbonate particles called otoliths

-stimulating otolith stimulates connected hair cells

2. Amphibians

-have tympanic membrane on outside surface of body

-pathway: sound waves tympanic membrane middle ear bone inner ear brain -single middle ear bone

Hearing in other vertebrates

Evolution of the vertebrate ear

• Inner fish– http://www.pbs.org/your-inner-fish/

interactives/explore-your-inner-animals/

Hearing- Invertebrates

• Two main ways to detect sounds:

1. Hairs on body

-vibrate in response to sound waves

-vary in stiffness and length

2. Tympanic Membrane

-thin sheet stretched across an internal air space

-localized on different parts of the body

-pathway: sound waves tympanic membrane connected nerves brain

Equilibrium- Mammals

Semicircular Canals

1. Organs to detect body position and maintain balance located in inner ear

a. Utricle and Saccule (2 parts of same organ)

-located next to oval window

-detect which direction is up and detect body position and accleration

b. Semicircular Canals (3 canals in total)

-next to utricle

-detect angular movements

2. Pathway:

a. Utricle and saccule contain clusters of hair cells embedded in a gel called a cupula

b. Cupula contains otoliths

c. Cupula (with otoliths) is heavier than the endolymph (fluid) in the utricle and saccule, so gravity is pulling the cupula down on to the hairs of the hair cells

2. Pathway (con’t):

d. Changes in angle of body (i.e. changes in position of head) change the force on the hair cells

-causes stimulation of some cells that weren’t stimulated before

-causes some to increase/decrease their signals

3. Semicircular Canals

a. 3 canals (“loops”)

-1 for each plane:

side-to-side

front and back

up and down

b. same mechanism of stimulation as for utricle and saccule (cupula with otoliths, hair cells, etc.)

Equilibrium- Mammals

Semicircular Canals

Equilibrium- Aquatic OrganismsLateral Line System 1. Fish: lateral line on both sides of body

a. series of mechanoreceptors called neuromasts on body just under the epidermis

b. Small openings (pores) in epidermis allow for water to enter into lateral line canals

Lateral Line Systemc. Water stimulates clusters of hair cells in the neuromasts by

bending the cupula (gelatinous cap over the hair cells)

d. Stimulation causes release of neurotransmitters, sending signals through sensory nerves to brain

Equilibrium- Lateral Line (con’t)

1. Most invertebrates have sensory “organ” called statocysts

a. Parts of statocyst:

-layer of ciliated receptor cells surrounding an open chamber

-inside chamber are 1+ grains of dense material called statoliths

Equilibrium- Invertebrates

2. Pathway: a. Gravity causes statoliths to settle downwardb. Once reach bottom of chamber, stimulating cilia of

receptor cellsc. Stimulated cells release neurotransmitters, stimulating

connecting sensory nerve fibers