UNIT 5- The special senses eye and vision Flashcards
Special senses
-Sight
- Smell
- Taste
- Hearing
- Equilibrium
Functions of especial senses
To provide us with information about our internal and external environment.
Sensation
an awarenes of a change in our internal and/ or external environment ( but might not be on a conscious level)
Perception
our conscious interpretation of those stimuli
conditions requiered for perception
stimulus
receptor
conduction
interpretation
Orbit
Bone socket around the eye protecting the porterior 80%
Eyebrows
-Help shade the eyes from sunlight
-Prevent sweat from trickling into the eyes
Eyelids= Palpebrae
▪ Protect the front of the eye.
▪ Eyelashes offer added protection by preventing entry of dust and other particles.
Levator palpebrae supeioris muscle
Muscle that raises the eyelid
Conjuctiva
▪ Mucous membrane that lines inside surface of the eyelid and portion of the anterior surface of the eye (it covers the sclera but not the cornea)
Function:
Produces a lubricating mucus that prevents the eye from drying out.
Lacrimal apparatus
▪ Consists of ductwork and the lacrimal gland which makes lacrimal fluid (tears).
▪ Lacrimal fluid contains mucus, antibodies, and lysozyme, an enzyme that destroys bacteria.
▪ Overall, lacrimal fluid cleanses and protects eye as well as lubricates and moistens the eye.
Pathway of lacrimal fluid flow
- Blinking spreads tears from lacrimal gland across to medial corner of eye.
- Tears flow through lacrimal puncta into lacrimal canaliculi.
- Tears next enter lacrimal sac.
- Then, the nasolacrimal duct.
- Finally, lacrimal fluid empties
into nasal cavity below
inferior nasal concha.
Extrinsic eye muscle
●Each eye has six associated extrinsic eye muscles that insert on the sclera and cause movement of the eyeball.
Innervation of the extrinsic eye muscles
▪ Lateral rectus is innervated by the abducens nerve (VI)
▪ Superior oblique is innervated by the trochlear nerve (IV)
▪ Other four are innervated by the oculomotor nerve (III)
Instrinsic eye muscles
▪ Ciliary muscles – control focusing of the lens.
▪ Iris – controls the diameter of the pupil; continuous with the ciliary body posteriorly.
Tunics of the eye - Fibrous tunic , vascular tunic , nervous tunic) - layers that form the outer part of the eye.
Fibrous tunic , vascular tunic , nervous tunic
Fibrous tunic - characteristics
▪ outermost
▪ tough fibrous connective tissue
▪ gives shape to eyeball
▪ protects inner structures
Firbous tunic - main parts
Sclera - white of the eye
Cornea - clear window over anterior portion of iris and pupil; permits entry of light
Vascular Tunic - characteristics
▪ middle layer
▪ has many blood vessels
Includes :
-Iris
-Ciliary body
- Choroid
Vascular tunic - includes
▪ Iris – anterior portion of vascular tunic that forms a ring of muscles around the pupil.
◦ Circular muscle fibers – when these contract, the pupil constricts
◦ Radial muscles fibers – when these contract, the pupil dilates.
- Pupil – opening that light passes through.*
Vascular tunic- includes 2
▪ Ciliary body – thickened portion of tunic located behind the iris; forms a muscular ring around the lens.
Function of ciliary body:
▪ Controls shape of lens, and thus the focus.
suspensory ligaments – c.t. fibers that connect ciliary body to lens.
Vascular Tunic - includes
▪ Choroid – darkly pigmented layer that surrounds most of the inside of the eye.
Function of choroid:
▪ Helps nourish eye.
▪ Absorbs light & prevents it from scattering/reflecting in eye.