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Organs of special senses & endocrine systems > Physiology of vision > Flashcards

Physiology of vision Flashcards

1
Q

Perception of light

A
  • photons of shorter wavelengths have more energy
  • visible light occupies small portion of EM spectrum
  • light travels in straight lines
  • sunlight contains all wavelengths
  • objects absorb some wavelengths and reflect others, they present as the colour reflected
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2
Q

Lens system

A
  • in vertebrates
  • focuses light from objects in environment onto the retina at rear of eye
  • retina is where sensory cells are located
  • transmits information to the brain
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3
Q

Ciliary bodies

A

thickened anterior parts of choroid (between sclera and retina)
- produce aqueous humour

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4
Q

Lens

A

adjustable focus mediated by ciliary bodies

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5
Q

Optics of the eye

A
  • cornea refracts light entering the eye
  • parallel light rays hit biconcave lens, refracted to a point beyond the lens called PRINCIPLE FOCUS
  • principle focus distance is the distance between the lens and the principle focus
  • dioptres are unit of refractive measurement
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6
Q

Lens; focusing images

A
  • Further the object is, the smaller the distance between the lens and the focal point because light rays are parallel
  • Closer object’s refracted light rays are not parallel so distance increases
  • Increases curvature of lens (convexity) decreases distance
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7
Q

Accommodation to focus images

A

Process by which the curvature of the lens is increased to focus on a near object
- ciliary bodies contract
- distance between ciliary bodies decrease
- lens ligaments relax
- active process

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8
Q

Ciliary bodies role in accomodation

A
  • Lens is attached to ciliary body via zonulas
  • Zonulas are made of inelastic fibres
  • Ciliary bodies contract, tension released on zonulas
  • more convex shape formed
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9
Q

Iris

A
  • pigmented and opaque
  • contains constrictors of the pupil
  • and dilators of the pupil
  • controls amount of light let into the eye
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10
Q

Quantity of light control

A
  • Iris; smooth muscle in mammals, striated in birds and reptiles
  • autonomic innervation
  • radial muscle fibres dilate pupil
  • circular muscle fibres constrict pupil
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11
Q

Types of pupil shapes

A
  • Vertical slit; in some carnivores. Allows greater light control. Enhances distance judgement
  • Rectangle; in herbivores. Sheilds eye from sunlight, greater span of vision for predators
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12
Q

Vitreous humour

A

a gelatinous substance between the lens and the retina
- not continually replaced
- retains globe shape

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13
Q

Aqueous humour

A

a clear liquid that nourishes the cornea and the lens
* Bathes lens and cornea providing nutrients
* Drains into venous plexus at the filtration angle
* Production and drainage must remain balanced

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14
Q

Schlemm’s canal

A

at the junction between the iris and the cornea
- drains the aqueous humour

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15
Q

Sclera

A

outer layer of eye
- tough connective tissue
- merges with cornea

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16
Q

Cornea

A

transparent layer at front, for physical protection, refraction of light and highly sensitive

17
Q

Choroid

A

vascularised middle layer of the eye

18
Q

Retina

A
  • innermost layer containing sensory cells and
    neurons
19
Q

Cell types in retina

A
  • 2x sensory cell types; rods and cones
  • rods; sensitive for vision in low light
  • cones; colour vision
  • bipolar cells; connect sensory cells and ganglion cells
  • horizontal cells; connect groups of sensory cells
  • amacrine cells; forms connections between ganglion cells
20
Q

Layers of retina

A

3x layers
- Outermost layer; closest to choroid. Rods and cones
- Middle layer; conatins the interneuron cell types (bipolar, horizontal and amacrine)
- Innermost layer; ganglion cells that are connected to the optic nerve

21
Q

The Optic Disc

A

Axons of the ganglion cells converge to form the optic nerve
- Optic disc is the point where the optic nerve leaves the eye & blood vessels enter
- Blind spot

22
Q

Macula Lutea & Fovea Centralis

A
  • Macula lutea; yellow area near posterior pole marks location of fovea centralis
  • Fovea centralis; rod-free cone-packed area
  • NO blood vessels
  • Maximum visual accuity
23
Q

Retinal vessels

A
  • supply the bipolar and ganglion cells
24
Q

Choroid plexus

A
  • supplies the rods and cones
25
Q

Segments of rods and cones

A
  • Outer segment; modified cilia that form saccules and discs containing photosensitive compounds
  • Inner segments; contains a nuclear region rich in mitochondria
  • Synaptic zone; synapses with bipolar or horizontal cells
26
Q

Rods vs. cones

A
  • Cones have narrower tip compared to base
  • Rods have long outer segments of even thickness
  • Rods are more numerous usually and more sensitive
  • Cones are more abundant near fovea
  • Both have photopigments
27
Q

Photopigments

A
  • Photoreceptor cells hyperpolarise in response to light
  • Light removes cGMP so cyclic nucleotide-gated ion channels are closed
  • Rods and cones contain; Retinal and Opsins
  • cis-retinal is converted to all-trans-retinal in light
  • this activates transducin to convert cGMP to GMP
28
Q

Retinal

A
  • aldehyde of vitamin A
  • 11-cis-retinal is converted to all-trans-retinal in light
29
Q

Opsins

A
  • modifies retinals sensitivity to differing wavelengths of light
30
Q

Eye movements

A

-Saccadic eye movements (rapid) – take lots of snapshots which the brain interprets as a stable image
- Vestibulo-ocular reflex enables maintenance of an image despite rapid head movement

31
Q

Physiological nystagmus

A

When image extends past range of ocular motion a correcting saccade brings the eye back

32
Q

Pathological nystagmus

A

When the eye moves and saccades when the head is still indicating a problem with the vestibular system

33
Q

Colour perception

A
  • Depends on the different types of opsins and different cone types
  • Can be di, tri… chromats, refering to number of types of cones
34
Q

Visual Pathways

A
  • the right side of each retina collects light from the left visual field and vice versa
  • medial ganglia cross over at optic chiasm
  • lateral ganglia do NOT cross over
  • ## contralateral processing; both sides of the brain process info from both eyes
35
Q

Retinal Convergence

A
  • many rods can converge to just a single ganglion cells
  • individual cones can synapse with individual ganglion cells
36
Q

Vision processing and Ganglion cells

A
  • ganglion cells only detect a difference in light intensity between the centre and periphery of their receptive fields

Organs of special senses & endocrine systems (14 decks)

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