neurobiology exam 6 (final)

15 16 17

inner ear anatomy: equilibrium

vestibular complex

inner ear anatomy: vestibular complex

3 semicircular canals

vestibule

• utricle

• saccule

inner ear anatomy: hearing

cochlea

inner ear consists of ____ ____ surrounding a _____ ____

bony labyrinth; membranous labyrinth

between the bony labyrinth and membranous labyrinth is fluid called

Perilymph

Within the membranous labyrinth is fluid called

Endolymph

fluids are very high in what??

K+

If you open K+ channels in cells here (inner ear), where will the K+ go?

potassium goes into the cell (depolarize)

the equilibrium: vestibule provides information about _____ ____ and _____ _______

head tilt; linear acceleration

two chambers of vestibule

utricle

saccule

utricle is what movement

horizontal

saccule is what movement

vertical

Macula

specialized membrane that houses sensory hair cells (mechanoreceptors)

Top of hair cells are embedded in a gelatinous _____ ________ with calcium carbonate stones

Otolithic membrane (otoliths)

oto = ear

lithic = stone

sensory hair cells

Modified epithelial cells with 20-50 extensions called Stereocilia and one Kinocilium

(excite) When stereocilia bend ______ the kinocilium, K+ channels are opened and K+ rushes into cell (extracellular environment is K+ rich).

towards

depolarization of sensory hair cells =

more action potentials

Hair cells release excitatory neurotransmitter, depolarizing sensory dendrites of the ______ ______

vestibulocochlear nerve

(inhibit) Bending ____ from kinocilium hyperpolarizes sensory dendrites (K+ channels close)

away

Helps code for detection of movement direction

______ add weight to help bend stereocilia

Otoliths

Equilibrium: Semicircular Canals

Project along 3 planes to detect rotation

Each canal contains a _____ ______ filled with endolymph

semicircular duct

At the base of each duct is an enlarged area called the _______

Ampulla

Hair cells are embedded in the _____ _____ with stereocilia stuck into a gelatinous ______

Crista ampullaris; Cupula

semicircular canal rotation steps

Rotation causes endolymph to push on cupula bending stereocilia → K+ channels open → depolarization

Branches of the __________ ______ synapse in the vestibular nuclei of medulla oblongata, the cerebellum & the thalamus

vestibulocochlear nerve

The vestibular nuclei send neurons to the _________ _____ of the brain stem to control eye movements & down the spinal cord to adjust body movements for balance

oculomotor area

balance pathway

nystagmus

jerky eye movement produced

can also be a symptom of neurological problems

If someone is spinning, eyes move towards the _______ direction of the spin to maintain a fixation point

opposite

vertigo

Nystagmus, anything that alters vestibular function, or a conflict between the eyes & vestibular system can cause a loss of equilibrium

• Can be accompanied by dizziness, pallor, sweating, nausea and vomiting

sound waves are characterized by

frequency

intensity

what is frequency

Measured in hertz (Hz). Higher frequencies = higher pitches

• Human range is 20-20,000Hz

intensity

loudness.

measured in decibels

3 regions of ear

outer ear

middle ear

inner ear

outer ear sound waves are funneled by the _____ into the external auditory canal which channels them to the _______ _____ (ear drum) which vibrates

Pinna (or Auricle); Tympanic membrane

tympanic cavity

Cavity between the tympanic membrane and inner ear

middle ear contains three bones called

ossicles

middle ear ossicles

malleus

incus

stapes

malleus

transmits and amplifies soundwaves by hitting the incus

incus

transmits and amplifies soundwaves by hitting the stapes

stapes is attached to the _____ ______ which transfers the vibrations into the inner ear

oval window

Very loud sounds makes the _____ and _____ _____ muscles contract dampening movement of the ossicles

Stapedius; Tensor tympani

Stapedius and Tensor tympani

Protects from nerve damage in cochlea

• Not quick enough to protect from sudden noise (shot)

inner ear cochlea

hearing part with 3 spiraling chambers

upper chamber is a portion of the bony labyrinth

scala vestibuli

lower chamber is a portion of the bony labyrinth called the

Scala Tympani

both the scala vestibuli and tympani are filled with

perilymph

The middle chamber is a portion of the membranous labyrinth called the

Scala media

Scala media is filled with

endolymph

three parts of the Scala media

Vestibular Membrane: Celling

Tectorial Membrane: Gel core

Basilar Membrane: Floor

sound transmission through the inner ear step 1

Vibrations from the oval window of the middle ear travel through the perilymph of the Scala Vestibuli

sound transmission through the inner ear step 2

Vibrations are passed into the endolymph of the Scala media, shaking the tectorial membrane

sound transmission through the inner ear step 3

Vibrations pass into the perilymph of the Scala tympani

sound transmission through the inner ear step 4

Vibrations leave the inner ear via the Round window

_____ ______ sounds travel further into the spiral of the cochlea

Low frequency

sound intensity

A louder sound will vibrate a larger portion of the tectorial membrane.

organ of corti

area of basilar membrane with hair cells

When sound waves enter the scala media the tectorial membrane vibrates bending the stereocilia on hair cells. This:

• Opens mechanically gated K+ channels

• K+ rushes in depolarizing the hair cell

• Releases glutamate onto sensory neurons

  • Information about frequency & intensity sent to brain

two types of hair cells

inner and outer

inner hair cells

Form one row that runs the length of the basilar membrane. Each is innervated by 10-20 sensory neurons

outer hair cells

arranged in 3-5 rows. Innervated by motor neurons that make them shorten when depolarized and elongate when hyperpolarized

auditory acuity and sensitivity

• Outer hair cells located closest to where vibrations occur in the scala media are depolarized more often & are shortened, enhancing depolarization of inner hair cells.

• Those farther away are hyperpolarized and elongate, dampening depolarization of more distant inner hair cells.

• This allows us to differentiate between very similar pitches and hear far softer sounds than would otherwise be possible

auditory cortex is said to be

tonotopic

what is tonotopic

specific areas represent different sound frequencies (sound map)

conduction deafness

Sound waves are not conducted from the outer to inner ear.

• Problem may be a foreign object, buildup of earwax, too much fluid in the middle ear, damage to the eardrum or overgrowth of bone in middle ear

• Impairs hearing of all sound frequencies

• Can be helped by hearing aids

sensorineural/perceptive deafness

Nerve impulses are not conducted from the cochlea to the auditory cortex

• May be due to damaged hair cells (from loud noises or aging), damage to cochlear nerve, brain tumors

• May only impair hearing of some sound frequencies and not others

• May be helped by cochlear implants