Special Senses 1 Flashcards
5 special senses
- olfaction
- gustation
- equilibrium (balance)
- vision
- hearing
Lacrimal Apparatus
Lacrimal Glands: produce tears(reduce friction, contain lysozyme which helps prevent infection)
Lacrimal Caruncle: soft tissue, contains a number of sebaceous glands
Lacrimal Canal: drainage of tears, if this isn’t properly developed you can get a build up of tears, causing pus and infection in the corner of the eye, required surgery
Structure of the eye: overall, membrane
- hollow ball
- 3 layers of connective tissue (tunics)
- anterior cavity: thinner and contains more aqueous solution, anterior and posterior chambers
- posterior cavity: filled with citrous body, gelatinous, allows circular nature of eye
- mucus membrane: protection
Structure of the eye: Sclera, cornea and Iris
- sclera: white portion of the eye, formed of tough connective tissue
- cornea: transparent portion through which light enters, begins to focus light, aids in directing photons that eventually end up in the retina, doesn’t have good blood supply, gets O2 from tears, can have a corneal transplant
- iris: coloured portion, contraction of iris muscles increases or decreases the size of its opening (pupil), has a good blood supply, helps maintain health of the eye
Pupil
- pupillary constrictor (sohincter) and pupillary dilator (Radial)
- if decreased light quality: increased sympathetic stimulation, the pupillary dilator muscles extend radially away from the edge of the pupil. Contraction of these enlarges the pupil.
- if increased light quality: increased parasympathetic stimulation. The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases.
Structure of the eye: Lens
A transparent structure that completes focusing of light onto the retina
- cells in inferior of lens
- no nuclei or organelles
- filled with crystalline, which provide clarity and focusing power to lens
Cataract
-condition in which the lens has lost its transparency (too much crystallin)
Close vision vs distant vision
For close vision: -ciliary muscle contracted -lens rounded For distant vision: -ciliary muscle relaxed -lens flattened
Myopia
Nearsightedness
if the eyeball is too deep or the resting curvature of the lens is too great, the image of a distant object is projected in front of the retina. The person will see distant objects as blurry and out of focus. Vision at close range will be normal because the lens is able to round as needed to focus the image on the retina.
Corrected with a diverging concave lens
Hyperopia
Farsightedness
If the eyeball is too shallows or the lens is too flat, hyperopia results. The ciliary muscles must contract to focus even a distant object to the retina. And at close range the lens cannot provide enough refraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity (presbyopia)
Corrected with a converging convex lens.
Vision
- begins with the capture of light energy by Photoreceptors
- **rods and cones (names relate to the structure of the receptor; red, green and blue cones)
- propagation of action potential along optic nerve to visual cortex of the occipital lobe
- visual information is used to determine both the direction and distance of an object
Three cell layers in the retina
-rods and cones (photoreceptors, activate other cells and then message travels through optic nerve)
-bipolar cells
-ganglion cells
(rods are more sensitive than cones, don’t need as much light to function why is why you can slightly see in the dark)
Transmit impulses to the brain via optic nerve
Rods and Cones
Rods -black and white -do not discriminate white colours -highly sensitive to light Cones -provide colour vision -densely clustered in fovea (part of macula lutea) -sharpest image formed at centre of macula lute
Sensory Transduction in the Eye
Know diagram and notes
Few qns in the exam
Photopigments
- unstable pigments that undergo a chemical change when they absorb light (this chemical change is what allows us to see)
- rods: rhodopsin
- cones: photopsins
- humans have three kinds of cones
The visual pathway
- begin at photoreceptors
- end at visual cortex of cerebral hemispheres
- message crosses two synapses before it heads towards the brain
- photoreceptor to bipolar cell
- bipolar cell to ganglion cell
