2.2 anatomy

External ear

auricle, external acoustic meatus

elastic cartilage

Middle ear

Auditory ossicles, stapes, incus, mallus, tympanic cavity, tympanic membrane, oval window, round window, auditory tube

inner ear

semicircular canals, vestibulocochlear nerve (NC VIII), cochlea, oval window, round window, vestibule, auditory tube

What is equilibrium in the context of the vestibule system?

Awareness and monitoring of head position

Where does equilibrium occur in the body?

In the vestibular apparatus

What do semicircular ducts detect?

Angular acceleration

What do the utricle and saccule detect?

Static equilibrium and linear acceleration

Ampulla

region at the Base of each semiciruclar canal

- each ampulla contains crista ampullaris

Crista ampullaris

Region of mechanoreceptors for dynamic equilibrium

Crista Ampullaris mechanisms

- when head roatates, enolymph pushes against cupula

- cupula bends stereocilia and changes hair cell voltage

- if stereocilia bent towards kinocilium, the hair cell depolarizes

- if the stereocilia bent away from kinocilum, the hair cell hyperpolarizes

vestibule

Macula- receptor for static equilibrium and linear acceleration located in utricle and saccule of vestibule

- composed of hair cells with a single kinocilium and stereocilia which are embedded in a gelatinous otolithic membrane (gel like matrix containing otoliths (calcium carbonate crystals))

Macula: head tilted upward

Stereocilia bent toward kinocilium

-hair cells depolarize, increasing neurotransmitter release

-increased nerve singal frequency along vestibular branch of CN VII

-excitation

Macula: head upright

Stereocilia parallel to kinocilium

- neutransmitter released at regular interval

- steady rate of nerve signals are transmitted along vestibular branch of CN VII

- standard nerve signal frequency

Macula: head tilted down

- sterreocilia bent away from kinocilium

- hair cells hyperpolarize, inhibitng neutrotransmitter release

-decreased nerve signal frequency along vestibular branch of CN VIII

- inhibition

Cochlea

Bony labyrinth:(cochlea) outer layer of the snail shell looking thing

Membranous labyrinth(cochlear duct): second most outer layer

Apex of cochlea: Contains helicotrema --> Middle part of snail looking shell

Cochlea

Spiral organ

Fluid pressure waves in scala vestibuli push vestibular membrane causing pressure waves in endolymph of cochlear duct

- specific region of basilar membrane move (depending on sound wave frequency) distorting hair cells

cochlear hair cell stimulation step 1

-inner hair cells contain ion channels at their tips and tip link proteins connect them

Cochlear hair cell stimulation step 2

- hair cells are bathed in K+ rich endolymph that is far more positive than the fluid inside the cell

Cochlear hair cell stimulation step 3

-when basilar membrane moves up, hair cells are pushed into tectorial membrane and their tips are tilted, causing the tip links to pull open ion channel causing K+ to diffuse into hair cell depolarization

Cochlear hair cell stimulation step 4

hair cells releases neurotransmitters from its base, exciting the sensory neuron and initiating an action potential

Cochlear hair cell stimulation step 5

- when basilar membrane moves down, the process quickly reverses

step 1

1. Sound waves are directed by the auricle into the external acoustic meatus, causing the tympanic membrane to vibrate

2.

tympanic membrane vibration moves auditory ossicles (malleus, incus, and stapes); amplifying the sound waves and transmit the waves to oval window

3.

the stapes at the oval window generates pressure waves in the perilymph within the scala vestibule

4.

Fluid pressure waves in scala vestibuli push vestibular membrane causing pressure waves in endolympth of cochlear duct. specific regions of basilar membrane move (depending on sound wave frequency). hair cells in the spiral organ are distorted, initiating nerve signals in the cochlear branch of the vestibulocochlear nerve (CN VIII)

5.

Remaining pressure waves are transferred to the perilymph within the scala tympani and are absorbed as the round window bulges slightly

pitch

depends on the frequency (meausred in Hertz) of the vibrating object

- humans can hear 20-20,000 Hz

- high frequency sounds excite cells in narrower, stiff basilar membrane near oval window

- low frequency sounds excited cells in the wider, flexible basilar membrane near the apex

Eye anatomy

-Fibrous tunic

-sclera

-cornea

- vascular tunic

-iris

-ciliary body

-choroid

-retina

Fibrous tunic

-sclera

-cornea

sclera

tough outer vascularized "white" of the eye

Cornea

Clear convex avascular layer that refracts light

Vascular tunic

iris

ciliary body

choroid

Iris

"colored" muscular portion of eye that forms pupil

Ciliary body

Muscles that support and change the shape of the lens (attached to suspensory ligaments) and processes tha secrete aqueos humor of the eye

Choroid

blood vessels supply retina and melanin absorbs light preventing it form scattering

Retina

Pignmented layer

nueral layer

Pigmented layer

Absorbs extraneous light and provides Vitamin A for photoreceptors

Neural layer

where phototransduction occurs (light energy converted into an electrical signal)

Vision summary 1.

Light rays enter the eye as they pass through the cornea, aqueous humor (anterior chamber) and go through the pupil

Vision summary 2.

the lens focuses the light on the retina through the vitreous humor (posterior chamber)

Vision Summary 3.

Photoreceptors respond to the light by creating an electrical signal which gets carried through the optic nerve to the brain

Iris

Pigmented, vascularized and contains muscles which control the pupil (opening) diameter therefore controlling the amount of light entering the eye (pupillary reflex)

- iris separates the anterior from the posterior chambers

pupil constriction: Bright light, sphincter pupillae contracts (parasympathetic innervation)

Pupillary dilation: low light, dilator pupillae (sympathetic innervation)

FOUND IN VASCULAR TUNIC

Ciliary body

FOUND IN VASCULAR TUNIC

- aqueous humor is secreted by the ciliary processes, travels through the pupil into the anterior chamber and is eventually resorbed into the scleral venous sinus

Lens shape for distant vision:

ciliary muscles relaxed, lens flattened, suspensory ligaments taut

lens shape for near vision (accommodation)

Ciliary muscles contract, moving ciliary body closer to the lens

- lens thickened, more spherical, suspensory ligaments relaxed

Retina

Pigmented layer: attached to choroid (internal to it)

- provides vitamin A for photoreceptors

- absorbs stray light to prevent light scatter

Neural layer: houses photoreceptors and associated neurons

- receives light and converts it to nerve signals

Neural layer of retina

Photoreceptors cells

rods

cones

bipolar cells

ganglion cells

Photoreceptor cells

FOUND IN NEURAL LAYER OF RETINA

contains photopigments that react to light which triggers a change in the membrane potential

Rods

NUERAL LAYER OF RETINA

- more numerous than cones

- specialized for DIM light, night vision

- cannot distinguish color; poor at sharpness of vision

Cones

NEURAL LAYYER OF RETINA

- less numerous than cones

- responds to stimulation by bright light

- specialized for color recognition and sharpness of vision

subdiided into blue green and red cones

- absence or deficit in one type of cone cell

Bipolar cells:

NEURAL LAYER OF RETINA

- reciev input from photoreceptor cells and send infromation to ganglion cells

Ganglion cells

NEURAL LAYER OF RETINA

- responds to bipolar cells, send of action potential when stimulated, axon gather at optic disc and form optic nerve (Axon of ganglion cells become optic nerve)

Photoreceptors

The outer region of photoreceptors contain photopigment containing discs

-photopigments are embedded in the membrane and are composed of the opsin protein and the light absorbing retinal (formed from vitamin A)

-type of opsin protein determines the wavelength range of the light transduced (each photoreceptor contains one type)

- rods contain rhodopsin which is most sensitive to 500 nm wavelength

Cones contain photopsin in which there are three types (Blue, green, and red cones)

bleaching reaction and regeneration of rhodopsin step 1

Rhodopsin (opsin +cis retinal) absorbs light rays

bright light

bleaching reaction and regeneration of rhodopsin step 2

cis-retinal is transformed to trans-retinal

bleaching reaction and regeneration of rhodopsin step 3

trans-retinal dissociates from opsin, as opsin becomes activated (bleaching reaction)

bleaching reaction and regeneration of rhodopsin step 4

Trans-retinal is reconverted to cis-retinal within the pigmented layer of the retina using ATP

bleaching reaction and regeneration of rhodopsin step 5

cis-retinal associates with opsin to re-form rhodopsin

dark or low light

In the dark (photoreceptors)

Photoreceptors depolaried due to the opne cation channel causing it to continually release the neurotransmitter gluatmate

- gllutamate casues hyperpolarization of teh bipolar cells (inhibits signal)

In the light (photoreceptors)

Stimulation by light causes the photoreceptor cells to hyperpolarize due to the closing of the cation channels

- lack of glutamate means that the bipolar cell is no longer inhibited and therefore becomes depolarized and releases glutamates stimulating the ganglion cells to fire sending a nerve signal to the brain

retinal regions

Optic disc

macula lutea

peripheral retina

Optic disc:

Contains no photoreceptors- blind spot

where ganglion axons exit towards the brain

Macula Lutea

Rounded, yellowish region lateral to optic disc

macular degeneration (leading cause of blindness) is the physical deterioration of the macula lutea

contains fovea centralis (central pit)

-highest proportion of cones (hardly any rods) area of sharpest vision

Peripheral retina

Contains primarily rods

functions most effectively in low light