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EYE (Optic Tract + radiation (Optic tract Runs posteriorly from optic…
EYE
Optic Tract + radiation
Optic tract
Runs posteriorly from optic chiasma towards lateral geniculate nucleus in thalamus
Most fibres synapse LGN
Fibres that don't pass to superior colliculus (tectum of midbrain)
visual reflexes
LGN, fibres pass posteriorly through optic radiation to primary visual cortex (calcarine sulcus occipital bone)
Optic nerve in optic canal carries visual info from retina to visual cortex brain
Superior branch oculomotor
: Superior rectus
Inferior branch oculomotor
: Inferior rectus, medial rectus + inferior oblique
Gives off branch caries PS fibres to sphincter pupillae and ciliary muscle
Lateral Geniculate Nucleus
6 layers
Relay centre thalamus visual pathway
Parvocellular layer
Outer layer 3 to 6
Cones perception of colour and detail
Magnoceullar
Inner layers 1 + 2
Rods: perception of movement and depth
Correlation signals achieve 3d representation of object
Changing position
Adducted Position
Superior rectus primarily intorts
Inferior rectus primarily extorts
Superior oblique depresses
Inferior oblique elevates
Abducted Position
Superior rectus elevates only
Inferior rectus depresses only
Superior oblique intorts
Inferior oblique extorts
Structure
Embedded in orbital fat
Separated from it by fascial sheath
3 coats
Vascular
Ciliary body
Continuous with choroid and anteriorly lies behind peripheral margin iris
Chroid
Outer pigmented layer (absrobs light) + inner highly vascular layer
Nervous
Retina
Anterior edge wavy ring,
ora serrata
+ nervous tissue ends
Anterior part retina non receptive : pigment cells only
Posterior part retina site of macula lutea: most distinct vision
Macula lutea: central depression
Fovea centralis
Optic nerve leaves retina 3mm to medial side macula lutea optic disc
Lack of receptor cells (blind spot)
Outer pigmented layer + inner nervous layer
Outer surface contact with choroid and inner surface in contact with vireous body
Posterior three quarters of retina receptor organ
Fibrous
Sclera
Posterior opaque part
Dense fibrous tissue
Pierced by optic nerve
Fused with dural sheath of nerve
Cornea
Anterior transparent part
Responsible refraction light entering eye
Avascular
Photoreceptor cells
Specialised neurons capable of phototransduction
Absorbs photons triggering membrane potentials converting light into biological messages
Cones
Higher light levels
Colour vision
Short, middle and long wavelenght sensitive
High spatial acuity
Central fovea just cones
Rods
Vision at low light levels
No colour
Low spatial acuity
Iris
Thin, contractile, pigmented with central aperture (pupil)
Suspended in aqueous humour between cornea and lens
Periphery attached anterior surface ciliary body
Divides space between lens + cornea into anterior + posterior chamber
Muscles
Involuntary
Circular + radiating fibres
Cicular fibres from sphincter pupillae + arrnaged around margin of pupil
Constricts pupil in pressence of birght light
Radial fibres from dilator pupillae
Dilates pupil in presence of dim light
Eyeball
Distant focus: Contracted muscle
Close focus: relaxed muscle
Contents
Aqueous humor
Supports wall of eyeball: exerts internal pressure, maintaining optical shape
Nourishes cornea + lens (avascular) + removes products of metabolism
Vitreous body
Transparent gel
Fills eyeball behind lens + supports posterior surface lens
Hold neural part of retina against pigmented part
Lens
Transparent, biconvex structure, enclosed transparent capsule
Elastic lens capsule under tension, form globular rather than disc shape
Circumference of lens attached to cillary body by suspensory ligaments
Pull of radiating fibres on suspensory ligaments keep elastic lens flattened: eye can be focused on distant objects
Aqueous humor
Clear fluid fills anterior + posterior chambers of eyeball
Fluid enters posterior chamber before flowing into anterior chamber through pupil where it drains away
Movements
Elevation
Adduction
Abduction
Depression
Lateral rotation (extorsion)
Medial rotation (intorsion)
Muscles
6
From tendinous ring in post wall of orbit (annulus of Zinn) to eyeball
Medial rectus
Adduction
Lateral rectus
Abduction
Inferior rectus
Depression
Adduction
Extorsion
Superior Oblique
Depression
Abduction
Intorsion
Inferior oblique
Elevation
Abduction
Extorsion
Superior rectus
Elevation
Adduction
Intorsion
Looking up
Superior Rectus & Inferior Oblique
Visual association areas
Parietal, temporal, occipital association areas
Provide meaning perceptive experience of world
Integrate sensory info and facilitate with memory
Blood Supply
Opthalmic Artery: gives off branches which accompany nerve
Optic chiasm