Chpt 17: Special Senses

The special senses include what 5 senses?

1. Taste

2. Smell

3. Sight

4. Hearing

5. Balance

*NOT TOUCH

Provide protection, lubrication, and support

Accessory Structures of the Eye

What are the 4 accessory structures of the eye?

1. Palpebrae (eyelids)

2. The superficial epithelium of eye

3. The lacrimal apparatus (tears)

4. Extra-occular muscles (movement of eye)

Gap that separates free margins of upper and lower eyelids

Palpebral fissure

Where two eyelids are connected

Medial canthus and lateral canthus

Hairs that prevent foreign matter from entering

Associated sebaceous glands (coats eyelids so they don’t stick)

• Inflammation=sty

Eyelashes

Secrete lipid-rich product that helps keep eyelids from sticking together

cyst=chalazion

Tarsal glands

On the superficial epithelium of the eye

Mass of soft tissue

Contains glands producing thick secretions

Contributes to gritty deposits that appear after good night’s sleep

Lacrimal caruncle

Epithelium covering inner surfaces of eyelids (palpebral conjunctiva)

Outer surface of eye (occular conjunctiva)

Conjunctiva

Protects the eye from outside objects

Eyebrows

Inflammation of mucous membrane —> pink eye

Conjunctivitis

Lacrimal Apparatus Order

1. Lacrimal gland: Produces tears (lacrimation)(Great)

2. Lacrimal puncta: Openings drain lacrimal secretions(Pandas)

3. Lacrimal canaliculi: Tubules that tears pass through(Came)

4. Lacrimal sac:Tears pass through(Souring)

5. Nasolacrimal duct: To reach inferior meatus in nasal cavity(Near)

Cranial nerve 6 (Abducens) associates with what eye muscle?

Lateral rectus

Cranial nerve 4 (trochlear) associates with what eye muscle?

Superior oblique

Cranial nerve 3 (oculomotor) associates with what eye muscle?

All remaining muscles (medial rectus, inferior rectus, superior rectus, inferior oblique)

How many tears do we produce per day?

1ml/day

What are tears composed of?

Water

Salt, Mucous, Lipids, Lysozyme, Antibodies

What are the functions of tears?

Protection

Cleanse the eye from debris in tears

Lubricate

What are the 3 layers of the eye?

1. Outer fibrous layer

2. Intermediate vascular layer

3. Deep inner layer

The white part of the eye, tendon like, provides support, attachment point for muscles

Sclera

What produces different colored eyes?

Melanin

This structure of the eye is avascular—no blood vessels, translucent, endothelial layer removes water to help keep this clear

Cornea

This structure is hollow and divided into two cavities:

1. Large posterior cavity

2. Smaller anterior cavity

• Ant. Chamber

• Post. Chamber

Eyeball

Border between cornea and sclera

Corneal limbus

Vascular layer that separates fibrous and inner layers posterior to ora serrata

The choroid

Contains ciliary processes, and ciliary muscle (when contracting, releases tension on lens) that attaches to suspensory ligaments (holds lens in place, aka zunule) of lens

Forms aqueous humor (fluid in eye)

Ciliary Body

Contains dilator (large) and constrictor (smaller) pupillary muscles

• Change diameter of pupil

Iris

Axons of ganglion—cells exit here

Optic disc

Controls the amount of light entering the eye

Pupil

Decreased light intensity

Increased sympathetic stimulation

Pupils become larger

Increased light intensity

Increased parasympathetic stimulation

Pupils become smaller

Why is the outer layer of the eye pigmented?

Cells have melanin

Inner layer of eye

Retina (neural part)

Membranous discs

See black + white

Blurry images

Sensitivity to light

Respond to almost any photon, regardless of energy content

Fovea centralis

Macula lutea

Rods

Folded membrane

Have characteristic ranges of sensitivity

Color (blue-shorter wavelength, red-larger wavelength, green)

Color blindness

Clear images

More active in day

Less sensitive to light

Cones

6 parts of inner layer of eye

1. Rods and cones (Red)

2. Outer synaptic layer (Octopuses)

3. Bipolar layer (2 processes, axon + dendrite)(Best)

4. Inner synaptic layer (In)

5. Ganglion layer (Green)

6. Axonal layer (axons of ganglion cells) (Algae)

Receptor colors of rods and cones layer, may lead to colorblindness

Red, blue, green

Fluid circulates within the eye

Diffuses through walls of anterior camber in pupil into scleral venous sinus (canal of Schlemm)

Re-enters circulation

Aqueous Humor

Fluid pressure in aqueous humor

Helps retain eye shape

Intraocular Pressure (12-22 mm of Hg)

Higher ocular pressure leads to what?

Glocoma (damage to retina + vision)

Gel-like body present in posterior cavity

Gelatinous mass

Helps stabilize eye shape and supports retina

Vitreous body

Biconvex, avascular, flexible, layered like onion

Contains fibers and cataract

The lens

Cells in interior of lens

No nuclei or organelles

Filled with crystallins, which provide clarity and focusing power to lens

Lens fibers

Condition in which lens has lost its transparency

Cataract

Bending of light by cornea and lens

Light Refraction

Specific point of intersection of light rays

Focal point

Distance between center of lens and focal point

Focal distance

The closer the light source, the _____the focal distance

Longer

The rounder the lens, the _______ the focal distance

Shorter

Shape of lens changes to focus image on retina

Accommodation

Condition where light passing through cornea and lens is not refracted properly

Visual image is distorted

Astigmatism

Clarity of vision

“Normal” rating is 20/20

Visual acuity

Eye is elongated

Can see close objects clearly, NOT distant objects

Corrected with a diverging, concave lens

Myopia (nearsightedness)

When object moves closer, image falls behind retina

Not enough retraction to focus image on retina

Hyperopia (farsightedness)

Older people become farsighted as their lens lose elasticity

Hyperopia due to age

Presbyopia

Normal vision

Emmetropia

Blindness (partial and complete)

Anopia

Narrow stalk connects outer segment to inner segment

Inner segment of rods and cones

Is where light absorption occurs

Visual pigment

Derivatives of rhodopsin molecule

Opsin + retinal

Retinal synthesized from what?

Vitamin A

Retinal with side chain bent

Can combine with opsin

No light, cis

Retinal with side chain straight

Cannot combine with opsin

Light, trans

Photon strikes retinal portion of rhodopsin molecule embedded in membrane of disc

Opsin is activated

Photoreception

Events of Phototransduction (5)

1. Light (photons) activate visual pigment

2. Visual pigment activates transducin (G protein)

3. Transducin activates phosphodiesterase (PDE)

4. PDE converts cGMP (controls sodium + calcium channels) into GMP, causing cGMP levels to fall

5. As cGMP levels fall, cGMP-gated cation channels close, resulting in hyperpolarization

Signal transmission in the retina in the dark

1. cGMP-gated channels open, allowing cation influx; the photoreceptor depolarizes (releasing neurotransmitters)

2. Voltage-gated Ca+ channels open in synaptic terminals

3. Neurotransmitter is released continuously

4. Neurotransmitter causes IPSPs in bipolar cell; hyperpolarization results

5. Hyperpolarization closes voltage-gated Ca+ channels, inhibiting neurotransmitter release

6. No EPSPs occur in ganglion cell

7. No action potentials occur along the optic nerve

Signal transmission in the retina in the light

1. cGMP-gated channels are closed, so cation influx stops; the photoreceptor hyperpolarizes

2. Voltage-gated Ca+ channels close in synaptic terminals

3. No neurotransmitter released

4. Lack of IPSPs in bipolar cell results in depolarization

5. Depolarization opens voltage-gated Ca+ channels; neurotransmitter is released

6. EPSPs occur in ganglion cell

7. Action potentials propagate along the optic nerve

Rhodopsin molecule breaks down into retinal and opsin

Bleaching

Most visual pigments are fully receptive to stimulation

Dark Adaptation

Pupil constricts

Bleaching of visual pigments occurs

Light Adaptation

Begin at photoreceptors

End at visual cortex of cerebral hemispheres

Message crosses two synapses before it heads toward brain

• Photoreceptor to bipolar cell

• Bipolar cell to ganglion cell

Visual Pathways

3-Step Neuron

Bipolar—> Ganglion—> Thalamic

Pituitary gland tumor affects what structure?

Optic chiasm

Enopia

Blindness

A lesion to the optic nerve of one eye will lead to loss of the complete visual field of that eye

Monocular vision loss

A lesion to optic chiasm that leads to loss of the temporal (lateral) visual field in both eyes

Bitemporal hemianopia

A lesion of the optic tract will lead to the loss of the contralateral visual field in both eyes (lateral on one side and medial on the other)

Contralateral homonymous hemianopia

Obtained by comparing relative positions of objects between left-eye and right-eye images

• Need input from both eyes

Depth perception

Integumentary glands along external acoustic meatus

• Secrete waxy material (cerumen)

Ceruminous glands in external ear

Also called tympanic cavity

Communicates with nasopharynx via auditory tube

• Equalization of pressures

• Communication with mastoid antrum via epitympanic recess

Otitis media (infection of middle ear) and Mastoiditis

The Middle Ear

What are the three auditory ossicles of the middle ear?

1. Malleus (hammer)

2. Incus (anvil)

3. Stapes (stirrup)

What are the two muscles of the middle ear?

Tensor tympani (attached to meatus)

Stapedius (attached to stapes)

What is the fluid of the membranous labyrinth of the internal ear?

Endolymph (rich in K+)

The bony labyrinth that surrounds and protects membranous labyrinth in the internal ear contains what?

Perilympth (rich in Na+)

The internal ear is subdivided into what three divisions of the bony labyrinth?

Vestibule: Cochlea connects here

Semicircular canals

Cochlea: snail-like portion

The membranous labyrinth of the internal ear contains what three structures?

Semicircular ducts

Utricle and saccule

Cochlear duct (scala media)

Semicircular canals + ducts’ function and receptor

Equilibrium; rotational (angular) acceleration

Crista ampullaris

Vestibule + utricle + saccule function and receptor

Equilibrium; head position relative to gravity, linear acceleration

Macula

Cochlea + cochlear duct (scala media) function and receptor

Hearing (auditory)

Spiral organ

Sensations provided by receptors of vestibular complex

Equilibrium

Basic receptors of inner ear

Provide information about direction and strength of mechanical stimuli

Hair cells

These ducts are continuous with utricle

Semicircular Ducts

Each semicircular duct contains this

Ampulla

Resemble long microvilli on surface of hair cell in semicircular duct

Stereocilia

Single large cilium in semicircular duct

Kinocilium

2 oval structures where hair cells cluster (saccule-vertical, utricle-horizontal), can detect change in movement

Maculae

Densely packed calcium carbonate crystals on surface of gelatinous mass

Statoconia

Ear stone

Gelatinous matrix and statoconia

Otolith

What do cochlear duct receptors (aka organ of corti) provide?

Sense of hearing

Spongy bone core of cochlea

Modiolus