Ch. 4 (eye)

Question 1

Nociceptors

Answer 1

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

Question 2

Fast and Slow Pain

Answer 2

• 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

Question 3

Neurotransmitters

Answer 3

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

Question 4

Innate Opiate System

Answer 4

• suppress transmission of pain; block substance P
• opiate receptors; endorphins and dynorphin
• “runner’s high”
  VS
• pain killers; morphine and codeine

Question 5

Eye Anatomy: Anterior and Posterior Chamber

Answer 5

• 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)

Question 6

Choroid

Answer 6

• 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

Question 7

Iris and Pupil

Answer 7

• pigment specific, smooth muscle

- opening

Question 8

Conjectiva

Answer 8

• mucous membrane, vulnerable to viruses
• conjunctivitis; leads to cornea and blindness
• Trachoma (non-trauma blindness)

Question 9

Retina

Answer 9

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

Question 10

Rods and Cones

Answer 10

• 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

Question 11

Night and Color Blindness

Answer 11

• genetic malfunction; “rod” deficiency of vitamin A

- genetic; more common in males, red and green most common

Question 12

Accommodation

Answer 12

shape and strength
- sympathetic: keeps eye flat; far vision
- para-sympathetic: rounds lens; near vision
Emmetropia is 20/20 vision

Question 13

Hyperopia, Myopia and Prebsypia

Answer 13

• far-sighted; need convex lens
• near-sighted; need concave lens
• bifocal lens; usually 48+ yrs

Question 14

Retina Photoreceptor Signal

Answer 14

rods and cones- bipolar cells (graded potential)- ganglion cells (action potential)- optic nerve (visual cortex)
** horizontal and amacrine cells

Question 15

Rod/Cone Anatomy

Answer 15

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

Question 16

Phototransduction: Rods/dark

Answer 16

• 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)

Question 17

Phototransduction: Cones/light

Answer 17

• 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

Question 18

Associated Pathway

Answer 18

optic nerve- optic chiasm- optic tracts- lateral geniculate body (thalamus)- optic radiations

Question 19

Sensitivity

Answer 19

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

Question 20

Glaucoma

Answer 20

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

Question 21

Macular Degeneration

Answer 21

• 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