Olfactory, Eye, Ear`nOTES

7/26/2019 Olfactory, Eye, Ear`nOTES

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B. Olfactory Epithelium

1. located in the roof of the nasal cavity, contains olfactory receptor cells

2. to smell an odor it must be volatile and be dissolved in the fluid coating

the olfactory epithelium

3. the olfactory epithelium covers the superior nasal conchae on each side

of the nasal septum, and contains millions of bowling pin shaped

olfactory receptor cells

4. olfactory receptor cells are surrounded and cushioned by columnar

supporting cells

5. at the base of the olfactory epithelium lie the short basal cells.

6. olfactory receptor cells bipolar neurons, has thin apical dendrite with

olfactory cilia increase receptive surface area! covered by mucus

produced by supporting cells and olfactory glands!

". mucus acts as solvent dissolves airborne odorants!

#. unmyelinated a$ons of the olfactory receptor cells are gathered to the

filaments of the olfactory nerve cranial nerve %!

&. olfactory nerve pro'ect through the openings in the cribriform plate of

the ethmoid bone, where they synapse in the overlying olfactory bulbs.

Specificity of the olfactory receptors

human can distinguish 1(,((( or so odors, but research

suggests that our olfactory receptors are stimulated by different

combinations of olfactory )ualities.

Activation of the olfactory receptors

odorant must be volatile

must dissolved in the fluid coating the olfactory epithelium

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will stimulate the olfactory receptor by binding to protein

receptors in the olfactory cilium membranes and opening ion

sodium channels

this leads to a receptor action potential

Mechanism of smell transduction

odorant chemical binding to the * protein+associated receptor

sets the c- 2ndmessenger system into motion,

which causes /a0 and a20 channels to open.

%nflu$ of /a0 causes depolariation and impulses transmission

The Olfactory Pathway

ction potentials of the olfactory nerve filaments are transmitted

to the olfactory bulb where the filaments synapse with mitral cells

in glomeruli!.

he mitral cells send impulses via the olfactory tract to the

olfactory corte$ smells will be interpret and identified!

ibers carrying impulses from the olfactory receptors also pro'ect

to the limbic system elicits emotional responses to odors!.

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Eye

A. Accessory structure of the eye

1. yebrows shade the eyes from sunlight, eep sweat out

2. yelids protect the eye from physical damage and from drying out

3. on'unctiva a transparent mucous membrane that lines the eyelids

and anterior portion of sclera the visible white part of the eye!,

produces a lubricating mucous that prevent the eyes fro drying out

4. 7acrimal apparatus consists of lacrimal gland and ducts, the

secretion tear! cleanses the eye, and drains into nasolacrimal duct

5. 8i$ e$trinsic eye muscles innervated by / %%% 9culomotor!, %:

rochlear! ; :% bducens!, for moving the eyeball

B. Structure of the eyeball

1. hree tunics form the wall of the eyeball

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a! ibrous tunic the outmost layer, avascular, dense connective tissue,

includes 2 regions< cornea anterior portion! sclera posterior

portion!

sclera protects the eyes and gives it shape

cornea allows light to enter the eye

b! :ascular tunic uvea! middle layer, vascular, includes 3 regionsringB and this causes

them to pull on the suspensory ligaments, maing them tight.

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- he ligaments in turn pull on the lens, stretching it and maing it flatter.

his less rounded less conve$! lens causes less refraction.

- ccommodation to long distance is aided by the internal pressure of the

eye caused by the vitreous humour. his helps to widen the ciliary

muscles and tighten the ligaments.

'iewin) a near obect

- %f we now change to looing at a near ob'ect, the light rays entering the

eye from the ob'ect are spreading out diverging! and re)uire more

refraction to bring them to a focus

- he circular ciliary muscles contract, forming a narrower >ringB.

- he suspensory ligaments become loose as they are not being pulled by

the muscles.

- he lens is not stretched and because it is elastic it reverts to its naturalrounded shape.

- his fatter more conve$! lens causes more refraction, allowing a sharp

focus to be achieved.

M*OP!A %S+O#T,S!-+TE/ESS& 0rabun auh

-yopia is commonly nown as short+sightedness.

%t means that the eye is unable to focus on distant ob'ects, maing them

seem blurred.

:ision can usually be corrected with concave glasses or contact lenses,

or, in some cases, with laser eye surgery.

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Aow the eye focuses

7ight coming into the eye is focused onto the retina + an area on the rear

wall of the eyeball.

8eventy per cent of light entering the eye is focused by the cornea a cleardome which forms the outer covering of the pupil!. he rest is focused by

the lens, which sits behind the cornea.

%f the light is focused properly on the retina, we see a clear image.

%f the light focuses in front of the retina, the image is fuy. 8ee the

illustration above.

Cith myopia, the cornea is too curved or the eyeball too long. his means

that images are focused in front of the retina rather than directly on it.

+*PE#OP!A %$A#S!-+TE/ESS& 0rabun de1at

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+yperopiais a defect of vision caused by an imperfection in the eye

often when the eyeball is too short or when the lens cannot become

round enough!, causing inability to focus on near ob'ects, and in e$treme

cases causing a sufferer to be unable to focus on ob'ects at any distance.

s an ob'ect moves towards the eye, the eye must increase its power to

eep the image on the retina.

%f the power of the cornea and lens is insufficient, as in hyperopia, the

image will appear blurred.

-inor amounts of hyperopia are sometimes left uncorrected, however,

larger amounts may be corrected with conve$ lenses in eyeglasses or

contact lenses. Ayperopia is sometimes correctable with various refractive

surgery procedures.

P+OT#ECEPT!O/

hotoreception is the process by which the eye detects light energy.

o approach this sub'ect several areas need to be discussed

he functional anatomy of photoreceptor cells.

he location and pacaging of the visual pigments that absorb the light

stimulus.

he chemistry of the visual pigments and their response to light.

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ctivation of the photoreceptors and their response to varying levels of

light intensity

P+OTO#ECEPTO#

- he photoreceptor cells are found in the retina at the bac of the eye.

- here are 2 types of photoreceptor cells

1! rods

2! cones

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- here are present in large very large numbers, with appro$imately 12(

million rods and 6 millions cones per eye.

- @ods and cones have three main regions. he outer segment is the light

sensitive region containing photosensitive pigments. Aere light energy is

converted into a generator potential.

- %n rods this region contains up to 1((( membrane+lined vesicles. he

photosensitive pigment rhodopsin is embedded in the membranes of the

vesicles.

- :esicles are also present in cones but they consist of infoldings of the

outer membrane. he cones have a different photosensitive pigment,

iodopsin, embedded in the membranes.

- he inner segment of both rods and cones contains many mitochondria to

provide the energy to resynthesise the visual pigments after they have

been broen down by light.

- %t also contains the nucleus and many ribosomes to synthesis proteins

such as those needed to mae the vesicles.

- he synaptic one is the e)uivalent of the synaptic bulb in neurons and

allows the information of synapses with bipolar cells which in turn lin tothe optic nerve and then to the brain.

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'isual Transduction

'isual transductionis the process by which light initiates a nerve

impulse. he structure of a rod cell is

Olfactory, Eye, Ear`nOTES

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