Special Senses Flashcards
Accessory Structures of the Eyes
- Eyelids
- Eyelashes
- Eyebrows
- Lcrimal (tear-producing) apparatus
- Extrinsic Eye Muscles
Internal Structures of the Eye
- Ciliary Body
- Cornea
- Iris
- Pupil
- Anterior segment (Contains aqueous humor)
- Lens
- Posterior Segment (Contains vitreous humor)
The Fibrous Tunic
-Outermost layer of the eyeball wall (Protects and shapes eyeball)
Made of 2 distinct regions:
- THE SCLERA: Tough white layer of avascular connective tissue covering the posterior part of eyeball and provides anchoring points for extrinsic eye muscles.
- THE CORNEA: Transparent anterior part of the fibrous tunic which helps to focus image.
The Vascular Tunic (Uvea)
Middle layer of the eyeball wall consisting of:
- THE CHOROID: Contains blood vessels and pigment.
- THE CILIARY BODY: Anterior extension of choroid, muscles control the lens shape and produces aqueous humor which fills anterior cavity of eye and nourishes lens.
- THE IRIS: Contains a pigment (eye color). Ring of smooth muscle which controls aperture.
The Sensory Tunic (Retina)
The innermost layer of the eyeball which contains:
- Outer pigmented cells to prevent light scatter.
- Neural layer of photoreceptor cells, which respond to light, bipolar and ganglion cells.
- The fovea centralis in macula lutea where the sharpest image is obtained.
- The “blind spot” or optic disc where the optic nerve leaves the eye.
The Lens
Controlled by smooth muscle in ciliary body to change shape to focus image on retina.
Vitreous Humor
Jelly-like substance made up of collagen and hyaluronic acid that fills posterior cavity of eye to support it.
Optic Nerve
Attaches at the optic disc and carries information to the visual cortex of the brain.
Eyeball: Photoreceptor Cell Layer
- Pigmented Layer
- Rod
- Cone
Eyeball: Outer Synaptic Layer
Synaptic Terminals
Eyeball: Bipolar Cell Layer
- Horizontal Cell
- Bipolar Cell
- Amacrine Cell
Photoreceptors
Contain photopigments for absorption of light in a cyclical process that create a receptor potential.
- Rods
- Cons.
Cones
- Approx 6 million
- Need bright light to activate
- Produce color through RBG
- Most dense at the fovea (center of visual field)
Rods
- Approx 125 million
- Important for night-time vision
- Very sensitive in dim light
- Most dense at the periphery of the retina and absent at the fovea
- Have one type of visual pigment called rhodopsin
Macular Degeneration
Loss of central vision
3 Regions of the Ear
- External Ear
- Middle Ear
- Internal Ear
Auricle (Pinna)
The “ear” part of the ear, e.g. Reservoir Dogs
External Auditory Canal
Ear cannal
Tympanic Membrane
Ear Drum
Cerumen
Earwax, which is secreted by the ceruminous glands.
Auditory Ossicles
3 bones in the middle ear that transmit sound vibrations from the ear drum to the oval window:
MIS (Malleus, incus and stapes)
The auditory tube
Pharyngotympanic tube & eustachian tube which extends from the middle into the nasopharynx to regulate air pressure in the middle ear.
Rinne Test
Metal instrument that test air and bone conduction.
Weber Test
Tests equality of sound: L & R.
The Inner Ear
Contains a network of membranous tubes called the membranous labyrinth with a fluid, endolymph.
- Cochlea or cochlear duct (hearing)
- Utricle & saccule (balance)
- Semicircular canals (balance)
Process of Hearing
- Sound waves cause movement of the tympanic membrane
- The ossicles vibrate and transfer vibrations from the out ear to the inner ear (via oval window)
- These vibrations against the oval window cause pressure waves in the endolymph.
- Receptor hair cells in Organ of Corti move
- Neural impulse is generated in vestibulocochlear nerve.
- Information passes via the thalamus to the auditory cortex which perceives the sound.
Equilibrium (balance) exists in two forms:
- Static Equilibrium: maintenance of the body’s position relative to the force of gravity. Receptors located in utricle and saccule.
- Dynamic Equilibrium: maintenance of the body’s position in response to sudden movements. Receptors located at the base of the semicircular canals.
Vestibular Apparatus
The organs that maintain equilibrium. Includes SUOS: saccule, utricle, both otolithic organs and semicircular canals
Stand Upright Or Slip
Otoliths
Calcium carbonate crystals
Olfaction
“Smell”
Olfactory Epithelium
Covers the inferior surface of the cribriform plate and extends along the superior nasal concha
Gustation
Sense of taste:
- Sour
- Sweet
- Bitter
- Salty
- Umami (Meaty, savory)
Gustation Nerve Pathway
Tongue ➡️ Vagus/glosepharyngeal/facial nerve ➡️ Medulla Oblongata ➡️ Thalamus ➡️ Primary gustatory area of cerebral cortex
