Visual System Flashcards
Percentage of body’s sensory receptors in eye?
70%
How much of the brain processes visual information
About half
What protects the eye?
- Cushion of fat
- Bone
Accessory structures of the eye
- Eyebrows
- Eyelids (palpebrae)
- Conjunctiva
- Lacrimal apparatus
- Extrinsic eye muscles
Eyebrows and eyelid
- Overlie supraorbital margins
- Shades eye from sunlight
- Prevents sweat from reaching eye
Levator palpebrae superioris
Upper eyelid mobility
How often do people blink?
Every 3-7 seconds
Why do we blink?
Protect the eye and spread secretions to moisten eye
Conjunctiva
- Transparent mucous membrane
- Produces a lubricating mucous secretion
Palpebral conjunctiva
Lines eyelids
Bulbar conjunctiva
Covers white of eyes
Conjunctival sac
- Between palpebral and bulbar conjunctiva
- Where contact lens rest
Conjunctivitis
- Pinkeye
- Can be caused by adenovirus, viral infections
Lateral rectus
- Action: Moves eye laterally
- Cranial nerve: VI (abducens)
Medial rectus
- Action: Moves eye medially
- Cranial nerve: III (oculomotor)
Superior rectus
- Action: Elevates eye and turns it medially
- Cranial nerve: III (oculomotor)
Inferior rectus
- Action: Depresses eye and turns it medially
- Cranial nerve: III (oculomotor)
Inferior oblique
- Action: Elevates eye and turns it laterally
- Cranial nerve: III (ovulomotor)
Superior oblique
- Action: Depresses eye and turn it latterally
- Cranial nerve: IV (trochlear)
Layers of eyeball wall
- Fibrous
- Vascular
- Inner
Fluid filling eye’s internal cavity
Humor
Iris muscles
- Sphincter pupillae
- Dilator pupillae
Response to parasympathetic stimuli
- Sphincter pupillae muscle contracts
- Pupil size decreases
Response to sympathetic stimuli
- Dilator pupillae muscle contracts
- Pupil size increases
Optic disc
- Blind spot
- Site where optic nerve leaves eye
- Lacks photoreceptors
Types of photoreceptors
- Rods
- Cones
Characteristics of rods
- Noncolor vision (one visual pigment)
- High sensitivity; functions in dim light
- Low acuity (many rods converge onto one ganglion cell)
- More numerous (20 rods /er cone)
- Mostly in peripheral retina
Characteristics of cones
- Color vision (three visual pigments)
- Low sensitivity; functions in bright light
- High acuity (one cone per ganglion cell in fovea)
- Less numerous
- Mostly in central retina
Myopic eye
- Nearsighted: can see near but not far
- Uncorrected: focal point is in front of retina
- Corrected: concave lens moves focal point further back
Hyperopic eye
- Farsighted: can see far but not near
- Uncorrected: focal point is behind retina
- Corrected: convex lens moves focal point forward
What happens if there is an injury to the optic chiasma?
- Damage to this area will cause possible damage to the temporal field in both Rt and Lt eye
- Will not see from the sides peripheral
What happens if there is an injury to the optic tract?
- Damage to this area will cause possible damage to the temporal filed of the Rt eye and possible damage to the nasal field of the Lt eye.
- Will not see from the side (peripheral vision) in Rt eye.
- Will not see what is in front from the Lt eye
What happens if there is an injury to the primary visual cortex?
- Damage to this area will cause possible damage to the temporal filed of the Lt eye and possible damage the nasal field of the Rt eye
- Will not see from the side (peripheral vision) in Lt eye.
- Will not see what is in front from the Rt eye.
