Special Senses (Vision) Flashcards
Accessory structures of the eye (5):
- Eyebrows - shade eyes & block sweat
- Eyelids - protective
- Conjunctiva - transparent mucous mb that covers eye, produces lubricating mucous
- Lacrimal apparatus - tears & secretion ducts
- Extrinsic eye muscles
LEEEC
Lacrimal caruncle
Aka medial canthus. At medial commissure (innermost corner), produces white oily secretion
Eyelid muscles
- Orbicularis - sphincter that closes eye
- Levator palpebrae - raises eyelid
TEARS contain:
- Mucous
- Antibodies
- Lysozymes - antimicrobial enzymes
**Clean, lubricate & protect the eyes. Constantly released, spread by blinking, drain through nasolacrimal duct
6 muscles that MOVE the eye:
- Lateral rectus
- Medial rectus
- Superior rectus
- Inferior rectus
- Superior oblique (downward & lateral movement)
- Inferior oblique (upward & lateral movement)
“Badminton birdie” of muscles
Cranial nerves: (SO4 LR6)3
Layers/”Shells” of the eyeball:
- FIBROUS layer (most external) - sclera & cornea
- VASCULAR layer - choroid, ciliary body & iris
- INNER layer (retina, most internal) - pigmented layer & neural layer
Sclera
“White” of eye -Tough & tendon-like, protects and shapes eyeball (FIBROUS layer)
**Continuous w/ dura mater of brain
Cornea
Most anterior of FIBROUS layer
“Transparent dome” : allows in light while protecting eye
Avascular but w/ many nerve endings
Choroid
Dark brown layer between sclera and retina, VASCULAR - nourishes eye & helps absorb light so it doesn’t “scatter”
Ciliary body
**Holds lens in place via ligaments & controls its shape
Anterior aspect of choroid, made of interlacing bundles of smooth muscle
Iris
**Colored part of the eye that controls how much light enters.
Continuous w/ ciliary body + choroid: Contains PUPIL and sphincter pupillae/dilator pupillae* (under sympathetic control)
Retina
**Receptor for sight : Millions of photoreceptors + other neurons/glia
Cup shaped - does not go all the way around.
Layers of the RETINA (2):
- Pigmented layer : single cell thick, absorbs light and stores vitamin A*
- Neural layer
(superficial) Sclera | Choroid | Pigment epithelium | Neural layer (deep)
Neural layer of RETINA - main types of neurons (3):
- Photoreceptors (most posterior)
[ signal ↓ ] - Bipolar cells
[ signal ↓ ] - Ganglion cells (most anterior)
[ right angle bend + OUTPUT as optic nerve ]
Optic disc
Spot where the **optic nerve attaches to the eye
“Blind spot” (no photoreceptors ; brain fills in information to compensate)
Types of photoreceptors (2):
- RODS: more numerous, active in dim light & peripheral vision
- CONES: active in bright light, high-resolution color vision. C for Color & Clarity.
** Respond to light!
Macula lutea
Part of the retina responsible for sharp, detailed central vision
Lateral to optic disc, mostly cones
Density of cones declines moving away from the macula
Fovea centralis
Very center of macula - ONLY cones
Segments and chambers of eye (4):
Anterior SEGMENT: ant. to lens, aqueous humor**
- Anterior chamber: between cornea & iris
- Posterior chamber: between iris & lens
Posterior SEGMENT: post. to lens, vitreous humor**
“Bed chamber” = small space
Aqueous humor
Clear fluid similar to blood plasma.
Forms, drains & circulates continually
In ANTERIOR SEGMENT
Vitreous humor
Thick, clear gel: formed in embryo & lasts lifetime.
Support posterior lens & presses layers of retina together. “Intraocular pressure”
Lens
BICONVEX shape, transparent & flexible : Changes shape to focus light on retina
Visible light has a wavelength of ______.
400-700nm
We perceive an object to be the color of the wavelengths of light it ______.
Reflects
Lens ____ for far vision and _____ for close vision.
Flattens, bulges
Explain the visual pathway
The lens inverts images on the retina.
From retina, each optic nerve travels posteromedially.
They meet at the optic chiasm - medial nerve fibers cross over, lateral fibers do not → optic tracts travel to the thalamus → to primary visual cortex
Receptor TYPE for SMELL =
Chemoreceptors
Airborne chemicals dissolve in fluids coating nasal membranes
Receptor for smell =
Olfactory epithelium** in roof of nasal cavity w/ millions of olfactory sensory neurons + supporting cells / stem cells
Olfactory sensory neurons (characteristics):
Long cilia for increased receptor surface area
Gather in small fascicles and pass through “cribriform plate” of ethmoid bone → synapse in olfactory bulbs
Thin & non-myelinated
Live man of 30-60 days
Explain the olfactory pathway
- Olfactory nerves sense airborne chemicals (dendrite cilia in mucous mb)
- Transmit signal through “cribriform plate” of ethmoid bone.
- Synapse w/ mitral cells in olfactory bulbs at GLOMERULI (each glomerulus represents a single aspect of an odor** - each odor activates a unique set.
- Mitral cells refine, amplify & relay signals: olfactory bulbs → olfactory tracts → olfactory cortex (temporal lobe) + frontal lobe interpretation and **direct connection to LIMBIC SYSTEM
Receptor for TASTE =
Gustatory epithelial cells** (w/ gustatory hairs bathed in saliva)
Chemoreceptors (primary) + thermoreceptors, mechanoreceptors & nociceptors
BASAL epithelial cells act as stem cells*, replacing taste buds
Signal pathway for TASTE:
- Chemicals dissolved in saliva contact gustatory hairs
- Signal travels along CN VII (Facial) & CN IX (Glossopharyngeal) to thalamus → gustatory cortex
+ hypothalamus/limbic system** & triggering of gastric reflexes
