Ch. 4 (eye) Flashcards
Nociceptors
somatic: exercise
visceral: reffered eg. heart
neuropathic: chronic condition; millions suffer- no pinpoint or cure
phantom: lmg eg. 50% of amputees; nerves form neuroma’s which become active
- do not adapt to repetitive or sustained stimulation
- thermal, mechanical and chemical
- histamine, potassium, serotonin and substance P affect inflammatory response
Fast and Slow Pain
- sharp, A-delta fibres, 30m/sec; ex. cold, warmth, mechanical stimuli
- duller, unmyleinated C-fibres, poorly localized that persists for a longer time and is more unpleasant, 1-2 m/sec; ex. slow pain, heat, cold and mechanical stimuli
Neurotransmitters
Substance P: secreted by afferent neutron at terminal
- goes into spinal cord to higher levels, brain stem and RAS to thalamus to higher cortex
- hypothalamus (fight/flight)
Glutamate: secreted by afferent neutron; most primary
- excitatory
- 2 receptors: NMDA- release Ca+, hypersensitivity, activated second messenger
AMPA: Na+ channels open goes to cortex
ex. histamine and prostaglandins
Innate Opiate System
- suppress transmission of pain; block substance P
- opiate receptors; endorphins and dynorphin
- “runner’s high”
VS - pain killers; morphine and codeine
Eye Anatomy: Anterior and Posterior Chamber
- aqueous humor; fills anterior cavity and supplies nutrients
- lens divide: transparent for light to pass
- vitreous humor/ gelatinous
- gives eye shape (sclera becomes cornea at anterior)
Choroid
- middle layer underneath sclera
- ciliary body secretes aqueous humour; used then drained
- canal of Schlemm drains blood
- blocked= Glaucoma; pressure build up
- can surgically drain but eventually lead to blindness by irritating optic nerve 2
Iris and Pupil
- pigment specific, smooth muscle
- opening
Conjectiva
- mucous membrane, vulnerable to viruses
- conjunctivitis; leads to cornea and blindness
- Trachoma (non-trauma blindness)
Retina
photoreceptors - leaves eye through optic nerve CN2 - optic disc: blind spot; nerve and blood vessels go through - fovea: acuity and macula Macula: small ring of connective tissue - Macular degeneration
Rods and Cones
- more abundant, night vision, black and white, highly sensitive and periphery region
- color vision, red is highest wave length, blue is lowest, green is middle, fovea
Night and Color Blindness
- genetic malfunction; “rod” deficiency of vitamin A
- genetic; more common in males, red and green most common
Accommodation
shape and strength
- sympathetic: keeps eye flat; far vision
- para-sympathetic: rounds lens; near vision
Emmetropia is 20/20 vision
Hyperopia, Myopia and Prebsypia
- far-sighted; need convex lens
- near-sighted; need concave lens
- bifocal lens; usually 48+ yrs
Retina Photoreceptor Signal
rods and cones- bipolar cells (graded potential)- ganglion cells (action potential)- optic nerve (visual cortex)
** horizontal and amacrine cells
Rod/Cone Anatomy
Outer: rhodopsin- opsin and retinal (light absorbing); closest to eye’s exterior, facing the choroid
Inner: organelles; metabolic machinery of the cell
Terminal: attach to bipolar cell; ; transmits the signal to next cells in visual pathway
Phototransduction: Rods/dark
- cGMP (second messenger) is high concentration
- retinal or renitence (vit A) is in cis-form (inactivated)
- Na+ channels open in absence of stimuli by cGMP and depolarization occurs
- synaptic terminal, Ca+ channels remain open
- signals neurotransmitter to release (not sharp image)
- no action potential, excited in absence of stimulation (depolarized by darkness)
Phototransduction: Cones/light
- cGMP breaks down; low concentration
- retinal is in trans form; change by jumping out of opsin
- G-protein, transducin is activated which activates enzyme phosphodiesterase and decreases cGMP
- Na+ channels close
- decrease neurotransmitter which causes stops depolarization and causes hyperpolarization and closes Ca+ channels, inhibitory transmitter released, exciting bipolar cells, creating action potential
- photoreceptors are inhibited by their adequate stimulus (hyperpolarized by light)
- brighter the light, greater the hyperpollarizing and greater the reduction of neurotransmitter release
Associated Pathway
optic nerve- optic chiasm- optic tracts- lateral geniculate body (thalamus)- optic radiations
Sensitivity
dark adaptation: regeneration of rod photopigment; opsin regeneration (recovery phase) to bring back to cis-form
light adaptation: rapid breakdown of cone photopigment; recovery phase; occurs when entering area with more light
Glaucoma
improper drainage of aqueous humour, not as rapidly as formed, excess will accumulate in anterior cavity causing pressure to rise
- lead to blindness if not treated
- blockage in the canal of Schlemm
Macular Degeneration
- leading cause of blindness
- loss of photoreceptors in macula lute in association with age
- “doughnut” vision
- lose middle of their visual field and left with less distinct peripheral vision
