Special Senses

• Vision
• Taste
• Smell
• Hearing
• Equilibrium

___% of body's sensory receptors in eye

70%

Accessory Structures of the Eye

– Eyebrows
– Eyelids (palpebrae)
– Conjunctiva
– Lacrimal apparatus
– Extrinsic eye muscles

Eyebrows

• Overlie supraorbital margins

the eyes are protected by the mobile _______ or _______

eyelids or palpebrae

Eyelids separated at

palpebral fissure

Eyelids meet at

medial and lateral commissures

At medial commissure there is a fleshy elevation called the

Lacrimal caruncle

The Lacrimal Caruncle contains

sebaceous (oil) and sweat glands

During sleep the caruncle can produce a whitish oily secretion called

sandmans eye sand

In most Asian peoples a vertical fold of skin called ________ commonly appears on both sides of the nose and sometimes covers the medial commissure.

epicanthic fold

They eyelids are thin skin cover folds supported internally by connective tissue sheets called

tarsal plates

The tarsal plates also anchor the ________ and the ___________ muscles that run within the eyelid

obicularis oculi
levator palpebrae superioris

An infected tarsal gland results in an unsightly cyst called a _________. Inflammation of any of the smaller glands is called a ________

-chalazion
-sty

Which eyelid is more mobile and why

The upper
because of the levator palpebrae superioris

Which glands are associated with the eyelids

–Tarsal (Meibomian) glands
Modified sebaceous glands
Oily secretion lubricates lid and eye
–Ciliary glands between hair follicles
Modified sweat glands

Conjunctiva

Transparent mucous membrane that produces a lubricating mucous secretion

Palpebral conjunctiva

lines eyelids

Bulbar conjunctiva

covers white of eyes

Conjunctival sac

between palpebral and bulbar conjunctiva

– Where contact lens rests

Inflammation of the conjunctiva called

conjunctivitis

a conjuctival infection caused by bacteria or viruses is highly contagious

Pinkeye

The Lacrimal Apparatus consists of

the lacrimal gland and the ducts that drain into the nasal cavity

the lacrimal gland lies

in the orbit above the lateral end of the eye

What are Lacrimal secretion and what does it contain.

Dilute saline solution containing mucus, antibodies, and lysozyme

Blinking spreads tears toward the __________

medial commissure

Once tears reach the medial commissure, they then enter the paired_________ _________ via two tiny opening called _________ ________

Lacrimal canaliculi
lacrimal puncta

From the lacrimal canaliculi, the tears drain into the_______ ______ and then into the _____________ _____

lacrimal sac
nasolacrimal duct

finally tears empties into the nasal cavity at the

inferior nasal meatus

How many extrinsic eye muscles
how many rectus
how many oblique

6
4
2

Name the rectus muscles and the oblique muscles

Rectus:
Superior, inferior, lateral, medial

Oblique:
Superior and inferior

Lateral rectus

action:
Controlling CN:

Action: Moves eye Laterally
Controlling CN: VI (abducens)

Medial rectus

action:
Controlling CN:

action: Moves eye medially
Controlling CN: III (oculomotor)

Superior rectus

action:
Controlling CN:

action: Elevates eye and turns it medially
Controlling CN: III (Oculomotor)

Inferior Rectus

action:
Controlling CN:

action: Depresses eye and turn medially
Controlling CN: III (Oculomotor)

Superior Oblique

action:
Controlling CN:

action: Depresses eye and turns it laterally
Controlling CN: IV (Trochlear)

Inferior Oblique

action:
Controlling CN:

action: Elevates eye and turns it laterally
Controlling CN: III (oculomotor)

What are the three layers of the eyeball

– Fibrous
– Vascular
– Inner

The eyeball's internal cavity filled with fluids called________.

humors

What separates internal cavity into anterior and posterior segments (cavities)?

Lens

What is the outermost coat of the eyeball

The fibrous layer

What are the two different regions of the fibrous layer

-Sclera
-Cornea

Which is called the "white of the eye"
A. sclera
B. cornea

A. Sclera

Answer correctly :
Sclera forms the______
A. Opaque anterior region
B. Opaque posterior region

B. Opaque posterior region

What are some functions of the Sclera

anchors extrinsic eye muscles
shapes eyeball
protect

What helps to maintain clarity of cornea

Sodium pumps of corneal endothelium on inner face

How much of the fibrous layer does the cornea take up?

1/6

Name a function of the cornea

Bends light as it enters eye

Name of the layer that forms the middle coat of the eyeball

Vascular layer

T or F
The Vascular Layer is Pigmented

True

What are the Three regions of the Vascular layer

choroid,
ciliary body,
and iris

Choroid region

• Posterior portion of uvea
• Supplies blood to all layers of eyeball
• Brown pigment absorbs light to prevent light scattering and visual confusion

Anteriorly the choroid becomes the ____________

ciliary body

Ciliary body is a

thickened ring of tissue that encircles the lens

ciliary muscles

interlacing smooth muscle bundles that chiefly make up the ciliary body and control the lens shape.

ciliary processes

secrete the fluid that fills the cavity of the anterior segment of the eyeball

The ciliary zonule

extends from the ciliary process to the lens. helps hold the lens in its upright position

Iris

Visible colored part of the eye
most anterior portion of the vascular layer

Pupil

central opening that regulates amount of light entering eye

what muscle contracts for Close vision and bright light

sphincter pupillae

What muscle contracts for Distant vision and dim light

dilator pupillae

The innermost layer of the eyeball is the

Retina

The Retina originates as an

outpocketing of the brain

What are the two layers the Retina consists of

-Outer Pigmented Layer
-Inner neural Layer

Only the ____________ of the retina plays a direct role in vision

Inner neural layer

The outer pigmented layer act as phagocytes participating in___________ Cell renewal.

And store vitamin _____

photoreceptor

A

The neural layer is composed of three main types of neurons

photoreceptors
bipolar cells
ganglion cells

T or F
The Neural Layer is transparent

T

Optic Disc

where the optic nerve exits the eye

The optic disc is also called the blind spot because it lacks _____

photoreceptors

Rods

Dim light and peripheral vision
no sharp no color vision

cones

bright light
high resolution color vision

Macula lutea

• Mostly cones
• Fovea centralis
– Tiny pit in center of macula with all cones; best vision

What are the two sources of blood supply to the retina

– Choroid supplies outer third (photoreceptors)
– Central artery and vein of retina supply inner two-thirds
• Enter/exit eye in center of optic nerve
• Vessels visible in living person

Internal Chamber Posterior segment contains ________ humor

vitreous

Internal Chamber Anterior segment contains ________ humor

aqueous

Glaucoma

blocked aqueous humor

cataract

clouding of lens

Visible light spectrum range

400-700nm

light can be small particles or packets of energy called

photons or quanta

How does light move sequentially into the eye

1. cornea
2. aqueous humor
3. lens
4. vitreous humor
5. neural layer of retina
6. photoreceptors

During its passage into the eye, what three times is light bent

1. entering the cornea
2. entering the lens
3. leaving the lens

The Majority of refractory power is in the ________

cornea

Light passing through convex lens (as in eye) is bent so that rays converge at

focal point

Image formed at focal point is ________ and reversed _________

upside-down
right to left

transduction

The neural layer of the retina is directly involved in changing light energy to nerve impulses that the brain can interpret

Are our eyes best adapted for distant or close vision

distant

The Far point of vision

that distance beyond which no change in lens shape is needed for focusing

For the normal or emmetropic eye, the far point is

6m (20 feet)

Close vision requires eye to make active adjustments using three processes:

• Accommodation of lenses
• Constriction of pupils
• Convergence of eyeballs

Accommodation of lenses

– Changing lens shape to increase refraction

Presbyopia

loss of accommodation over age 50

Constriction of pupils

pupillary reflex constricts pupils to prevent most divergent light rays from entering eye

Convergence of eyeballs

Medial rotation of eyeballs toward object being viewed

Myopia

nearsightedness
– Focal point in front of retina, e.g., eyeball too long
– Corrected with a concave lens

Hyperopia

(farsightedness)
– Focal point behind retina, e.g., eyeball too short
– Corrected with a convex lens

Astigmatism

– Unequal curvatures in different parts of cornea or lens
– Corrected with cylindrically ground lenses or laser procedures

Light Adaptation

• Rod system turns off
• Retinal sensitivity decreases
• Cones and neurons rapidly adapt

Dark Adaptation

– Cones stop functioning in low-intensity light
– Rod pigments bleached; system turned off
– Rhodopsin accumulates in dark
– Transducin returns to outer segments
– Retinal sensitivity increases within 20–30 minutes
– Pupils dilate

The axons of the retinal ganglion cells exit the eye in the

optic nerves

Medial fibers of optic nerve cross at the _________

optic chiasma

Most fibers of optic tracts continue to __________

lateral geniculate body of thalamus

Fibers from thalamic neurons form optic radiation and project to ________________________________

primary visual cortex in occipital lobes

Other optic tract fibers send branches to midbrain, ending in ________________________________________

superior colliculi (initiating visual reflexes)

The receptors for smell and taste are

chemoreceptors

The organ of smell is called the

olfactory epithelium

The olfactory epithelium is located in the

roof of the nasal cavity

the olfactory epithelium covers the

superior nasal conchae

Some of what we smell is really

pain

the nasal cavities contain _______ and _______ receptors that respond to irritants.

pain and temperature

Taste buds are _________ organs

receptor

Most 10,0000 taste buds are on

tongue papillae

Taste buds are also found on tops of

fungiform papillae

Taste buds are found on side walls of _____ and _______

foliate and circumvallate (vallate) papillae

There are even a few taste buds on

-Soft palate
-cheeks
pharynx
epiglottis

Each flask shaped taste bud consists of 50–100 flask-shaped epithelial cells of 2 types

gustatory epithelial cells
basal epithelial cells

Which is the taste cell
gustatory epithelial cells
basal epithelial cells

gustatory epithelial cells

What are the three major areas of the ear

1. External (outer) ear – hearing only
2. Middle ear (tympanic cavity) – hearing only
3. Internal (inner) ear – hearing and equilibrium

External Ear

• Auricle (pinna
• External acoustic meatus (auditory canal
• Tympanic membrane (eardrum

Auricle (pinna)Composed of

– Helix (rim); Lobule (earlobe)
– Funnels sound waves into auditory canal

External acoustic meatus (auditory canal)

– Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands
– Transmits sound waves to eardrum

Tympanic membrane (eardrum

– Boundary between external and middle ears
– Connective tissue membrane that vibrates in response to sound
– Transfers sound energy to bones of middle ear

Middle Ear

• Epitympanic recess
• Mastoid antrum
• Pharyngotympanic (auditory) tube

Epitympanic recess

superior portion of middle ear

Mastoid antrum

Canal for communication with mastoid air cells

Pharyngotympanic (auditory) tube

connects middle ear to nasopharynx
– Equalizes pressure in middle ear cavity with external air pressure

Two Major Divisions of Internal Ear

• Bony labyrinth
• Membranous labyrinth

Bony labyrinth has three regions

vestibule, semicircular canals, and cochlea

Semicircular canal function

-Equilibrium
-rational angular acceleration

Vestibule function

-Equilibrium
-head position relative to gravity
-linear acceleration

cochlea function

hearing

What are the two fluids that conduct the sound vibrations involved in hearing and that respond to the mechanical forces occuring during changes in body position and acceleration

perilymph
endolymph

Sound Pressure waves move through perilymph of

scala vestibuli

Equilibrium information goes to reflex centers in _________

brain stem

Impulses travel to vestibular nuclei in __________ or ________, both of which receive other input

vestibular nuclei
cerebellum

What are the three modes of input for balance and orientation:

- Vestibular receptors
– Visual receptors
– Somatic receptors

Meniere’s Syndrome

is a disorder of the inner ear that can affect hearing and balance to a varying degree. It is characterized by episodes of vertigo, low-pitched tinnitus, and hearing loss. The hearing loss is fluctuating rather than permanent,