Lab #6- Eye dissection, Special senses

What are the five major special senses?

Vision, audition, gustation, tactile, and olfaction

What are sensations?

The result of stimuli that begin afferent impulses which eventually reach a conscious level in the cerebral cortex of the brain

What do sensations include?

Somatic senses (pain, cold , heat, touch, pressure) and special senses

What are sensory receptors?

End organs of afferent nerves

Two types of sensory receptors?

Exteroceptors and interoceptors

What do sensory receptors do?

Convert different types of stimuli into action potentials

Are sensory receptors generally specific?

Yes, responding readily to one form of energy over the other

What do exteroceptors do?

Detect stimuli beginning externally to the body

Where do exteroceptors detect stimuli?

Skin, Hearing, Vision

What do interoceptors do?

Detect stimuli originating within the body

What do interoceptors detect?

Stimuli for taste, smell, pH, distension, spasm, flow, equilibrium

What are proprioceptors?

Signal conditions deep within the body to the CNS

Where are proprioceptors located?

Skeletal muscles, tendons, ligaments, and joint capsules

What are proprioceptors responsible for?

Muscle position

Receptor organ for vision?

Eyes

Receptor stimuli for vision?

Light

Receptor cells for vision?

Photoreceptor cells

Structure of eye?

Eyeball (globe), optic nerve, accessory organs

Purpose of fat?

Protection and fixation

What happens to eyes when animals/humans are sick?

Eyes become sunken in, loss of fat

How many retractor muscles are innervated by cranial nerves?

Six

Muscles allow what types of eye movements?

Up/down, side/side, rotation, inward retraction

What is the optic nerve?

A bundle of sensory nerve fibers that transmits visual information from the retina of the eye to the brain

What are conjunctiva?

Membranes lining the eyelids, adhere to cornea

What does the conjunctiva form?

Conjunctival sac, accumulation of tears, where eye drops/ointments are applied

Pink color of conjunctiva

Normal

Pale color of conjunctiva

Lack of blood/anemia

Blue color of conjunctiva

Lack of oxygen

Yellow color of conjunctiva

Icterus

What are the three layers of the eye referred to as?

Tunics

Fibrous tunic:

Outermost , supporting layer of the eyeball

Anterior fibrous tunic

Cornea

Posterior fibrous tunic

Sclera

Vascular tunic (Uvea):

Middle layer of the eye

Choroid

Contains blood vessels, that nourish the retina

Ciliary body:

Adjusts the shape of the lens for focusing

Iris:

Colored part of the eye, regulates the amount of light entering the eye by controlling the "pupil" diameter

Nervous tunic:

The inner most layer of the eye

Retina

the layer where sensitive light receptor cells convert light into electrical signals that are transmitted through the optic nerve to the brain for visual perception

Sclera:

White of the eye , tough

What is the sclera the site of?

Muscle attachment

What is the cornea?

Transparent anterior portion of the fibrous layer that covers the iris and the pupil

What is the cornea a forward continuation of?

Sclera

Cornea is a:

Curved surface

What happens if the surface area ratio of the cornea to the sclera is increased?

Greater light transmission

Nocturnal animals have:

Larger cornea than diurnal animals

What makes up 90% of the thickness of cornea?

Collagen fibers (stroma)

The cornea is an:

Avascular structure

What does corneal neovascularization mean?

Body tries to heal, by growing new vessels

Corneal neovascularization is a sign of?

Healing, but can also impair/obstruct vision

What can help treat corneal neovascularization?

Different medications like steroids

What is keratoconus?

Condition where the cornea thins out and bulges like a cone

What does the abnormal shape of corneas cause?

Light rays to be out of focus

What is the aqueous humor?

The fluid that occupies all space anterior to the lens

Consistency of aqueous humor?

Watery

Anterior chamber of the eye:

Space behind the cornea, between the iris and the lens

Glaucoma

Buildup of aqueous humor results in increased intraocular pressure

What can glaucoma cause if left untreated?

headaches/blindness, painful

What is the iris?

A colored muscular diaphragm

The iris is a forward extension of what?

The choroid (vascular layer)

What does the iris control?

Diamter of the pupil

Two sets of smooth muscles in iris:

Circular and radial

Circular contraction in iris:

Decreases pupil size

Radial contraction in iris:

Increases pupil size

What is the pupil?

An allowed opening in the eye of varying sizes

The pupil is:

Larger in the dark, smaller in the light (to prevent burning)

Panoramic vision

Horizontal pupil constriction, domestic herbivores and pigs

Binocular vision

Elliptical (vertical) pupil constriction, cat

Is the lens of the eye transparent?

Yes

What is the term for the lens being curved on both sides?

Biconvex

What attaches the lens to the ciliary body?

Suspensory ligaments

What are sensory ligaments?

Fine fibers arising from the ciliary body

What is the ciliary body?

Anterior thickening of the choroid layer

What is the eyes ability to undergo accommodation?

The ability of the eye's lens to change its shape to focus on objects at different distances

What is lenticular sclerosis?

Grayish tint to the lens that occurs as an animal ages

When is lenticular sclerosis especially common?

In geriatric dogs

What is a cataract?

Clouding of the lends of the eye, obstructs passage of light

What are main contributors to cataract development?

Age and diabetes mellitus

Vitreous chamber:

Large cavity behind the lens; most of the volume of the eyeball

What is a vitreous body?

Viscous body (or humor), body is better term due to consistency

What is the retina?

Thin, tan membrane (innermost tunic of the eye)

Examples of photoreceptor cells?

Rods and cones

Rods

- Black and white color

- Light-sensitive and used for night vision

Cones

Colored vision

What photoreceptor cell do domestic animals mostly have?

Rods

What photoreceptor cell do domestic birds mostly have?

Cones

What is the macula lutea?

Area of retina with the most acute vision (focus on images)

What does the macula lutea have?

Highest concentration of rods and cones

Fovea Centralis (pit):

High visual acuity - details and forms of objects can be perceived accurately

Primates and birds have only packed _____:

Cones

Domestic animals (especially herbivores) lack ______:

Fovea

What do domestic mammals have instead of fovea?

Visual streaks

Optic disk:

Located where the optic nerve leaves the retina and contains no photoreceptors

Optic disk is also known as?

Blind spot

The choroid is:

Pigmented and vascular

The choroid prevents:

Light scattering

Ridges where muscles and ligaments were attached that held the lens in place are what?

Choroid

Individuals with a darker iris also have a darker _______:

Choroid

The tapetum lucidum is the:

Light reflecting layer of cells of the inner choroid; iridescent

What does the tapetum lucidum do?

Reflects some light back to the retinas photoreceptors, improving vision in low light