Complex senses; The eye. Chapter 15 Part I
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Describe the function of "Tarsal Glands"
lubricates the eye and the eyelid
Describe the function of the "Conjunctiva"
produces a lubricating mucous secretion that prevents the eye from drying out
Describe the function of the "lacrimal gland"
- Secretes lacrimal fluid which contains:
- Saline solution
Describe the three layers of the eyeball
- fibrous layer
- vascular layer
- retinal layer
Describe the fibrous layer of the eyeball
- dense, avascular
- two regions: sclera and the cornea
describe the function of the "cornea"
bends light as it enters the eye
Describe the function of the "sclera"
- protects the eye
- shapes the eye
- anchors extrinsic eye muscles
Name the 3 regions of the vascular layer of the eye
Describe the function of the "choroid"
- supplies blood to all layers of the eye
- it is pigmented, thus absorbs light to prevent light scattering
Describe the function of the Ciliary Body
- a ring of muscle that surrounds the lens to manage the shape of the lens
- ciliary zonule = keeps lens in position
- ciliary process = secretes aqueous humour
Describe the function of the "Iris"
contains the pupil which regulates the amount of light entering the eye
parasympathetic stimulation to the iris causes _______, while sympathetic stimulation to the eye causes ___________.
Describe the 2 layers of the retina
- Outer pigmented layer (absorbs light)
- Inner neuronal layer
Name 3 types on neurons from the inner neuronal layer in the retina
- ganglion cells
- bipolar cells
- photoreceptor cells
Describe what a 'cone' is
- responsible for visual acuity in bright light
- provides colour vision
- less numerous than rods
- concentrated in the central part of the retina
- exclusive to the fovea centralis
- adapt quicker to light than rods to dark
Describe the pathway of light entering the eye
- 1)light hits the Cornea
- 2)aqeous humour
- 4)vitreous humor
- 5)entire neuronal layer of retina
Describe the role of the 'ciliary body' and the 'ciliary muscle'
these structure are responsible for producing aqueous humour and managing the lens in terms of position and shape
Describe how the eye focuses for near vision (<6m)
- 1)Accommodation of the lens (shape of lens changes to increase light refraction)
- 2) Constriction of the pupil (prevents divergent light rays from entering the eye)
- 3) Convergence of eyeballs
Describe the cause, consequence and possible treatment for "astigmatism"
- Cause: uneven curvature of the eyeball or irregular cornea
- Consequence: refractive error
- Corrected by: eyeglasses (required additional cylinder lens), contact lens, refractive surgery
Describe the cause, consequence and possible treatment for "hyperopia"
- Cause: short eyeball, focal point behind the retina.
- Symptoms: far-sighteness (can't read close objects)
- Corrected by: convex lens
Describe the cause, consequence and possible treatment for "myopia"
- Cause: long eye ball, focal point is in front of the retina
- Symptoms: near-sightenness, blurred vision
- Correction: concave lenses
Describe the sequence of "phototransduction"
- 1) Retinal absorbs light and changes shape. VISUAL PIGMENT activates.
- 2) Visual pigment activates transducin
3) transducin activates phosphodiesterase
4) Phosphodiesterase converts cGMP to GMP. cGMP levels drop.
- 5) As cGMP levels, cGMP-gated cation channels close resulting in hyperpolarization.
describe similarities between rods and cones
- absorb light
- neuron receptors
- found in inner neuronal layer
- form synapses with bipolar cells
- embedded in pigmented layer of retina
describe differences between rods and cones
- rods more numerous than cones
- cones provide colour vision, rods shades of gray
- rods concentrated in peripheral part of the retina, cones are concentrated in the centre
- Rods provide vision in the dark, cones require light
- cones provide visual acuity
- cones are found exclusively in the fovea centralis, no rods found here
Describe adaptation to light
- pupils constrict
- visual acuity improves 5-10 mins
- rod system turns off
- retinal sensitivity decreases
- cones and neurons adapt quickly
Describe dark adaptation
- pupils dilate
- cones stop functioning
- rod system turned off, rhodopsin accumulates in the dark
- retinal sensitivity increases in 20-30 min
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