Ch.8: Special Senses Flashcards
Special senses include:
- Smell
- Taste
- Sight
- Hearing
- Equilibrium
What are special sense receptors?
- Large, complex sensory organs
* Localized clusters of receptors
Concept Link
Recall the three basic functions of the nervous system (Figure 7.1, p. 226). Each of the special senses gathers unique sensory information that, once integrated, will influence motor output. For example, if you saw a ball moving toward your head, this sensory input might result in a motor output that would move your body out of the path of the ball. Additionally, each type of sensory information is processed in a specialized area of the cerebrum. (Figure 7.13c, p. 242).
70 percent of all sensory receptors are in the:
Eyes
Each eye has over _____ nerve fibers carrying information to the brain
1 million
Accessory structures of the eye include:
- Extrinsic eye muscles
- Eyelids
- Conjunctiva
- Lacrimal apparatus
Where do eyelids meet?
At the medial and lateral commissure (canthus)
What are the properties of eyelashes?
- Tarsal glands produce an oily secretion that lubricates the eye
- Ciliary glands are located between the eyelashes
What is conjunctiva?
- Membrane that lines the eyelids and eyeball
- Connects with the transparent cornea
- Secretes mucus to lubricate the eye and keep it moist
Lacrimal gland + ducts=
- Lacrimal apparatus
- Lacrimal gland—produces lacrimal fluid (tears); situated on lateral end of each eye
- Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity
Tears contain:
- Dilute salt solution
- Mucus
- Antibodies
- Lysozyme (enzyme that destroys bacteria)
What are the function of tears?
Cleanse, protect, moisten, lubricate the eye
What is the function of extrinsic eye muscles?
- Six muscles attach to the outer surface of the eye
* Produce gross eye movements
What are the three layers, or tunics, which form the wall of the eyeball?
- Fibrous layer: outside layer
- Vascular layer: middle layer
- Sensory layer: inside layer
_____ are fluids that fill the interior of the eyeball.
Humors
_____ divides the eye into two chambers.
Lens
Sclera + cornea=
Fibrous layer
What is the sclera?
- White connective tissue layer
* Seen anteriorly as the “white of the eye”
What is the cornea?
- Transparent, central anterior portion
- Allows for light to pass through
- Repairs itself easily
- The only human tissue that can be transplanted without fear of rejection
What is the vascular layer of the eyeball?
• Choroid is a blood-rich nutritive layer that contains a pigment (prevents light from scattering)
• Choroid is modified anteriorly into two smooth muscle structures
*Ciliary body
*Iris
What is and what is the function of the iris?
- Pigmented layer that gives eye color
- Regulates amount of light entering eye
- Pupil—rounded opening in the iris
What is the sensory layer of the eyeball?
Retina contains two layers
1. Outer pigmented layer absorbs light and prevents it from scattering
2. Inner neural layer contains receptor cells (photoreceptors)
• Rods
• Cones
Electrical signals pass from photoreceptors via what two-neuron chain in the sensory layer?
- Bipolar neurons
* Ganglion cells
Signals leave the _____ toward the brain through the _____ in the sensory layer.
- Retina
* Optic nerve
_____ is where the optic nerve leaves the eyeball.
- Optic disc (blind spot)
* Cannot see images focused on the optic disc
What is the function of rods in the sensory layer?
- Most are found toward the edges of the retina
- Allow vision in dim light and peripheral vision
- All perception is in gray tones
What is the function of cones in the sensory layer?
• Allow for detailed color vision • Densest in the center of the retina • Fovea centralis–lateral to blind spot *Area of the retina with only cones *Visual acuity (sharpest vision) is here
No photoreceptor cells are at the:
Optic disc, or blind spot
What is cone sensitivity?
- Three types of cones
* Each cone type is sensitive to different wavelengths of visible light
What is a lens?
- Flexible, biconvex crystal-like structure
* Held in place by a suspensory ligament attached to the ciliary body
The lens divides the eye into what two chambers?
- Anterior (aqueous) segment
* Posterior (vitreous) segment
What is the anterior (aqueous) segment of the lens?
- Anterior to the lens
* Contains aqueous humor, a clear, watery fluid
What is the posterior (vitreous) segment of the lens?
- Posterior to the lens
* Contains vitreous humor, a gel-like substance
What is aqueous humor?
- Watery fluid found between lens and cornea
- Similar to blood plasma
- Helps maintain intraocular pressure
- Provides nutrients for the lens and cornea
- Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm
What is vitreous humor?
- Gel-like substance posterior to the lens
- Prevents the eye from collapsing
- Helps maintain intraocular pressure
What is an opthalmoscope?
- Instrument used to illuminate the interior of the eyeball and fundus (posterior wall)
- Can detect diabetes, arteriosclerosis, and degeneration of the optic nerve and retina
What is the pathway of light through the eye and light refraction?
- Light must be focused to a point on the retina for optimal vision
- Light is bent, or refracted, by the cornea, aqueous humor, lens, and vitreous humor
- The eye is set for distant vision (over 20 feet away)
- Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away)
Image formed on the retina is a:
• Real image
What are real images?
- Reversed from left to right
- Upside down
- Smaller than the object
What is the optic nerve?
Bundle of axons that exit the back of the eye carrying impulses from the retina
What is the optic chiasma?
- Location where the optic nerves cross
* Fibers from the medial side of each eye cross over to the opposite side of the brain
What are optic tracts?
- Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye
- Synapse with neurons in the thalamus