LECTURE 17 - SPECIAL SENSES: THE EYE

what are the 2 classes of functional receptors? what type of stimuli does each detect?

-general senses

• temperature, pain, touch, stretch, and pressure

• distributed throughout the skin and organs

-special senses

• taste, smell, sound, equilibrium, and vision

• housed within specialty organs of the head

where are exteroceptors found? interoceptors? proprioceptors?

exteroceptors: detect stimuli from the external environment

interoceptors: detect stimuli in the viscera

• stretch receptors found within the smooth muscle of different organs (stomach, small and large intestines)

proprioceptors: detect stimuli within the muscles, tendons, and joints

what are 5 types of exteroceptors? what type of stimuli does each detect?

-mechanoreceptors: detect touch and pressure

-thermoreceptors: detect temperature

-nociceptors: detect pain

-photoreceptors: detect light

-chemoreceptors: detect taste and smell

what is the function and composition of lacrimal fluid? what structure produces the lacrimal fluid? where does it flow to?

lacrimal gland produces lacrimal fluid

-excretes lacrimal fluid (tears)

• composition: water, salts, and bacterial fighting enzymes

• function: moistens, cleans, and lubricates the eye

• exits via the lacrimal duct

where is the conjunctiva found?  what is its funciton? histology?

-composition: stratified squamous epithelium and stratified columnar epithelium

-covers the inner surface of the eyelids and the anterior of the eye

• forms conjunctival sac

function: lubricates and moistens the eye; detection of foreign objects

what are the 3 tunics of the eye? what structures comprise each tunic?

• fibrous layer (outer)

• vascular layer (middle)

• nervous layer (inner)

fibrous layer (outer)

• sclera

  • white layer of dense irregular connective tissue

  • supports, protects, and shapes the eye

• cornea

  • transparent, convex collagen fibers

  • serves for preliminary focus—→bends entering light (refraction)

what are the 3 tunics of the eye? what structures comprise each tunic?

• fibrous layer (outer)

• vascular layer (middle)

• nervous layer (inner)

vascular layer (middle)

• choroid

  • vascular, darkly pigmented layer with melanin

  • contains ciliary vessels supplying O2

  • absorbs light, preventing scatter and reflection

• ciliary body

  • anterior portion is continuous with choroid

  • serrated ring of ciliary muscles covered by ciliary processes

  • focuses the lens via suspensory ligaments

• lens

  • avascular, thick, transparent, biconvex, “disc” of compact epithelial cells

  • changes shape via constriction/relaxation of the ciliary muscles

    • allows light to be refracted onto the retina

• iris

  • anterior most portion of middle layer

  • attaches to the ciliary muscles: found between the cornea and lens

  • forms the opening called the pupil that allows for the passage of light

  • contains circular and radial smooth muscles

    • allows for constriction and dilation of pupil

  • may be pigmented with melanin

what are the 3 tunics of the eye? what structures comprise each tunic?

• fibrous layer (outer)

• vascular layer (middle)

• nervous layer (inner)

nervous layer (inner)

• retina

  • photoreceptive layer

  • contains rods and cones

  • maintained by branches of the central artery

  • includes: macula lutea, central fovea, and optic disc

• rods

  • detect low levels of light

  • “black/white” vision

• cones

  • detect “higher” wavelengths of light

  • color vision

• optic nerve

  • protected by the meninges

  • exits the eye carrying sensory information toward the brain

know the location, function, and histology (when relevant) of each eye structure listed in class.

• sclera

• cornea

• ciliary body

• lens

• iris

• choroid

• retina

• optic nerve

• sclera

  • location: outer white layer of eyeball

  • function: supports, protects, and shapes the eye

  • histology: white layer of dense irregular connective tissue

• cornea

  • location: clear curved front part of eye

  • function: serves for preliminary focus —→bends entering light (refraction)

  • histology: convex collagen fibers

• ciliary body

  • location: ring shaped structure behind the iris, around the lens

  • function: focuses the lens via suspensory ligaments

• lens

  • location: behind iris and pupil

  • function: focuses light onto retina by changing shape

• iris

  • location: colored part of the eye in front of lens

  • function: controls size of the pupil to regulate how much light enters

  • histology: smooth muscle tissue, avascular, thick, transparent, biconvex “disc” of compact epithelial cells

• choroid

  • location: layer between sclera and retina

  • function: absorbs light, preventing scatter and reflection

• retina

  • location: inner layer lining the back of the eye

  • function: contains photoreceptors (rods and cones) that detect light and send signals to the brain.

• optic nerve

  • location: back of the eye, connecting retina to brain

  • function: exits the eye carrying sensory information toward the brain

what is the optic disc?

blind spot that occurs at the optic nerve (area lacks rods and cones)

what is the macula lutea? where is the central fovea found?

-macula lutea is the center of the retina

-central fovea is found inside the macula; highest cone cell density

what do rods detect? cones?

rods: detect low levels of light

• “black/white” vision

cones: detect “higher” wavelengths of light

• color vision

what are the 2 cavities/segments of the eye? what fluid fills each?

the internal space within the eye is subdivided by the lens into two cavities/segments:

• anterior segments

  • filled with aqueous humor

• posterior segments

  • filled with vitreous humor

what are the two chambers of the eye? where is each found?

in the anterior segment it is subdivided into two chambers via the iris:

• anterior chamber: between the cornea and iris

• posterior chamber: between the iris and the lens

what is the flow of aqueous humor through the anterior segment?

FLOW OF AQUEOUS HUMOR

• secreted by the ciliary body into the posterior chambers —→

• flows through the posterior chamber across the anterior surface of the lens —→

• through the pupil —→

• into the anterior chamber —→

• exits via the scleral venous sinus (canal of schlemm) —→

• blood stream

be able to identify the following structures on a diagram of the eye:

• sclera

• cornea

• conjunctiva

• iris

• ciliary body

• suspensory ligaments

• choroid

• retina

• optic disc

• macula lutea

• optic nerve

• anterior segment

• posterior segment

• anterior chamber

• posterior chamber