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Flashcards in Fitz Deck (20):
1

Eyelid movements are mediated by what three muscles?

How are they innervated?

Three muscles

orbicularis oculi and levator palpebrae superioris (ACh acts on nicotinic receptros to cause contraction)

superior tarsal muscle (sympathetic innervation via a1 receptors)

 

2

dopaminergic

 

 

3

emmetropic

4

focusing power =

1/focal length

5

accomodation 

focusing power

fatter lens = more accomodation

 

6

Distance vision

sympathetic activation!

relaxation of ciliary muscle 

via activation of ß2 receptors

7

Near vision

parasympathetic activation

contraction of ciliary muslces 

muscarinic receptors

8

hyperopia 

farsightedness

Axial length < focal length

caused by lens that is too short or lens that is too weak

correct with convex lens to increase refractive power

9

Myopia

nearsightedness

correct with concave lens

axial length > focal length

10

presbyopia

less flexible lens

decrease in accomodation 

middle age...

11

astigmatism 

uneveness in lens

part of visual field will be out of focus

 

12

cataracts

opaquness in lens 

physical damage, radiation, high [glucose]

remove lens, replace

13

pupillary light reflex

causes miosis (parasympathetic stimulation of sphincter pupillae via muscarinic receptors)

and

mydriasis (sympathetic stimulation (a1 receptors) that activates the dilator pupillae muscles)

light in one eye --> constriction in another... used to test brain injury. 

 

14

increased intraocular pressure can cause permanent vision loss

closed angle glaucoma (medical emergency) -- caused by blockage of fluid outflow

open angle glaucoma (slowly developes) -- caused by increase in aqueous humour production or a blockage of outflow

----------------- 

increased interocular pressure!!

1. cornea -- halos, blurring; 2. photoreceptor pressure; 3. optic nerve pressure; 4. arterial supply

15

aqueous humor volumn and intraocular pressure

inflow -- sympathetics --> ß2 (increases flow) and alpha1 (decreases flow) of H2O via carbonic anhydrase

outflow -- parasympathetics --> canal of Schlemm contract sphincter pupillae

intraocular pressure = 20 mmHg (>30 glaucoma)

(Pressure = flow x resistance (V = IR))

16

Cells and circritry of the retina

 

1. Generate receptor potential-- transduction

2. Bipolar cells -- graded potential

3. Ganglion cells -- action potential generated (axons form optic nerve)

17

Rods and Cones

Rods are responsible for scotopic vision (black and white; monochromatic vision)--high sensitivity! less precise!

Cones; 3 types-- blue, green, and red; or short, medium, and long (respectively). 

Cones have better spatial and temporal resolution than rods; photopic vision

18

visual acuity

spacial acuity: where is something in space (snellen eye chart to determine). Cones: Best in fovea. 

Temporal acuity: ability to distinguish 2 events as separate. 

Spectral acuity: ability to distinguish differences in wavelength (color) -- how well cone system is functioning

19

phototransduction

1. activation of rhodopsin

2. rhodopsin joins with transducin

3. GTP --> GDP; activated phosphodiesterase, which breaks down cGMP

4. cGMP holds open Na+ channel, which then releases. 

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