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A and P semester 2 > Special senses > Flashcards

Special senses Flashcards

1
Q

What percentage of our sensory receptors does the eye contain?

A

70%

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2
Q

How much of the cerebral cortex is involved in processing visual information?

A

1/2

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3
Q

What is the function of the eyebrows, eyelids, and eyelashes?

A

to protect the eyes

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4
Q

What do the eyebrows do to protect the eyes?

A
  • SHADE eyes from bright light

- prevent sweat from trickling in to eyes

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5
Q

How do the eyelashes act to protect the eyes?

A

they are innervated with many sensory nerve endings that trigger reflex response to stimuli

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6
Q

How do the eyelids act to protect the eyes?

A
  • muscles are activated by reflex to cause blinking
  • spread fluids across the eye surface to prevent from drying out
  • lubricants are produced by glands on the edge of the eyelid and between the eyelash folicles
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7
Q

What muscle closes the eyelids?

A

contraction of orbicularis oculi

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8
Q

What muscle opens the eyelids?

A

contraction of levator palpebrae superioris

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9
Q

What is the conjunctiva of the eye?

A

the transparent mucous membrane that covers the eye

  • produces lubricating mucous to prevent drying of the eyes
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10
Q

What are the two parts of the conjunctiva?

A

PALPEBRAL conjunctiva: lines the eyelids and folds back over the anterior of eyeball

BULBAR conjunctiva covers the white of the eye (but not the cornea)

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11
Q

Where do contact lenses sit in the eye?

A

in the conjunctival sac

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12
Q

What makes up the lacrimal apparatus? What do each of these do?

A

Lacrimal GLANDS: continuously produce lacrimal fluid (tears)

Lacrimal FLUID: cleans, protects, disinfects the eye

Lacrimal DUCTS: drain tears into the nasal cavity (under normal flow rates)

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13
Q

What are some substances that the lacrimal fluid contains?

A

mucus
antibodies
lysozymes

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14
Q

How many extrinsic eye muscles are there?

A

6

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15
Q

What cranial nerves control the external eye muscles?

A

VI abducens
III Oculomotor
IV trochlear

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16
Q

What are the two types of movement of the eye balls that the extrinsic eye muscles allow?

A

SACCADES: quick jerky movements that allow eye to quickly see whole visual field

SCANNING MOVEMENTS: tracking or following of an object

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17
Q

What is diplopia?

A

homeostatic imbalance of extrinsic eye muscles:
it is double vision

Results when the extrinsic eye muscles are not properly coordinated

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18
Q

What are the two types of strabismus.

A 
homeostatic imbalance of extrinsic eye muscles:
Internal strabismus (cross-eyed)

external strabismus (wall eyes): eyes turn away from nose

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19
Q

What causes internal strabismus?

A

damage to the lateral rectus muscle or the abducens nerve

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20
Q

What causes external strabismus?

A

damage to the medial rectus muscle or oculomotor nerve

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21
Q

What are the three layers (or tunics) of the eyeball?

A

Fibrous (outer)
Vascular
Sensory

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22
Q

What are the two components of the fibrous tunic of the eye?

A

Schlera (white)

Cornea (transparent)

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23
Q

Describe the structure of the schlera of the eye

A

1) made up of opague, dense, tough CT

2) attaches to the dura mater posteriorly around the optic nerve

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24
Q

What is the function of the schlera of the eye?

A

protects and shapes the eyeball, provides strong anchoring site for the extrinsic eye muscles

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25
Q

Describe the structure of the cornea.

A

Forms the anterior portion of the fibrous tunic

  • composed of transparent, closely packed collagen fibers
  • many nerve endings; trigger blinking and tear reflexes
  • NO blood supply
  • vulnerable to damage but regenerates quickly
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26
Q

What is an important aspect of the cornea regarding implants?

A

makes it easy to find suitable donors because it has no blood supply (won’t be rejected)

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27
Q

What are the four components of the vascular tunic of the eye?

A

Choroid
Ciliary body
Iris
Lens

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28
Q

Describe the structure and function of the choroid of the vascular tunic of the eye.

A
  • pigmented layer at back off eyeball
  • MELANIN absorbs scattered light to prevent interference with vision
  • VESSELS supply nutrients to all the tunics
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29
Q

What is the ciliary body of the vascular tunic of the eye?

A

ring of tissue surrounding the lens.

consists of three parts

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30
Q

What are the three parts of the ciliary body? What do they do?

A

ciliary PROCESSES: produce the aqueous humour

ciliary ZONULE (suspensory ligaments):
- extends from ciliary process to lens, hold lens upright

ciliary MUSCLES: bundles of smooth muscle which control lens shape by changing tension in the ciliary zonule

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31
Q

Describe how the lens flattens and bulges to accommodate for near and close objects

A

When objects are far away, light is more direct therefore require less refraction in the lens to absorb the light so lens flattens. When the object is close, need more refraction to absorb so lens bulges

Ciliary muscles are circular 0 and lens is in the middle attached by ciliary zonule

ciliary muscles contract to dec tension -> bulging
ciliary muscles relax to inc tension -> flattening

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32
Q

Describe the Iris of the eye

A

it is the coloured portion of the frontal eye
- anterior portion of the choroid

located between the cornea and the lens

contains two layers of smooth intrinsic muscles to control pupil size

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33
Q

How are the intrinsic muscles of the iris of the smooth muscle of the eye innervated? what do each of these cause

A

dual innervation by the ANS

Parasympathetic triggers constriction
Sympathetic triggers dilation

34
Q

What are the two layers of smooth muscle in the iris of the eye? How do these two layers interact to control constriction/dilation of the pupil?

A 
CONSTRICTION of pupil:
circular layer (sphincter) contracts, longitudinal (dilator) layer relaxes
DILATION of pupil
circular layer (sphincter relaxes, longitudinal layer (dilator) constricts
35
Q

Describe the structure of the Lens.

A

Biconvex disc composed of transparent fibrous PROTEIN

  • changes shape to focus image on the retina
  • held in place behind iris by ciliary zonule
  • has NO blood supply
36
Q

Describe what happens to the lens of the eyes as we age.

A

new fibers are added over time so it becomes thicker and less flexible.

37
Q

Describe what cataracts are.

A

homeostatic imbalance of the lens:
inadequate nutrient supply to inner lens -> change in chemical structure of protein fibers -> lens becomes opaque

  • most cases associated with age
    risk factors: genetics, UV light exposure, chemicals, smoking, and diabetes
38
Q

Describe what presbyopia is.

A

homeostatic imbalance of the lens:
also age related

lens becomes thicker and less flexible with age -> cannot accommodate for CLOSE vision

  • close objects are blurred. ex reading
39
Q

Describe the sensory tunic

A

Also called the retina.

Outer pigmented layer: absorbs stray light and prevents scattering

inner neural layer: contains photo receptors and conducting cells

3 layers of neurons in the neural layer

40
Q

What are the three layers of neurons in the inner neural layer of the sensory tunic (or retina) of the eye?

A

deepest -> superficial with superficial being the closest to the surface of the inner eye

PHOTORECEPTORS: absorb and transduce light

BIPOLAR cells: process and conduct signals

GANGLION cells: process and conduct signals. Axons run along the inner surface of the retina and join to form the optic nerve

41
Q

What are the two kinds of photoreceptors? explain the function and location of each.

A

RODS: low light and peripheral vision

  • densest in periphery and none in fovea
  • pathways converge resulting in fuzzy and indistinct images

CONES: high light and high acuity colour vision

  • concentrated in fovea, none at periphery
  • pathways do not converge resulting in detailed, high resolution images
42
Q

Explain what causes the blind spot in our eye.

A

It is the site where the axons of the ganglion join to form the optic nerve

there are no photoreceptors present here

43
Q

Describe what the macula lutea is.

A

a oval spot at the posterior pole of the eye.

It is an area concentrated with mainly cones

light is focused onto this spot, passes directly to cones and there are no overlying neurons

44
Q

Describe what the fovea centralis is.

A

a depression in the macula lutea that contains ONLY cones

  • area of greatest visual acuity
45
Q

What are the two segments of the eye? What structures divide the eye into these two segments?

A

Posterior segment
Anterior segment

seperated by the lens and suspensory ligaments

46
Q

What is the function of the posterior segment?

A
  • transmit light
  • reinforce the eyeball, support lens
  • holds the retina in place against the pigmented layer
  • contributes to intraocular pressure
47
Q

What type of fluid does the posterior segment contain and when is this fluid formed?

A 
Vitreous humor (gel-like)
- formed prior to birth, lasts for lifetime
48
Q

what type of fluid is in the anterior chamber? what is its function

A 
Aqueous humor (watery):
- provides O2 and nutrients to lens and cornea
49
Q

Describe how the aqueous humor is formed and how it drains.

A

Continuously formed by ciliary processes from the capillary blood

DRAINS through the scleral venous sinus (canal of Schlemm) into the blood

50
Q

What are the two chambers of the anterior segment and what divides it.

A

Anterior chamber: between iris and cornea

Posterior chamber: between iris and lens

IRIS

51
Q

What wavelengths of light can the eye detect?

A

400 - 700 nm

52
Q

What is the purpose of the lens in the eye?

A

to control the degree to which the light is refracted in order to focus it on a focal point of the retina

focal point is the macula lutea

53
Q

Describe how the image is formed on the retina

A

Upside down and reversed right to left

54
Q

Describe the pathway of light as it enters the eye.

A

cornea, aqueous fluid, pupil, lens, vitreous humor, neural layer of the retina, photoreceptors

55
Q

What is the normal preset of the eyes regarding focus.

A

normal preset is for distance vision

  • ciliary muscles are relaxed, ciliary zonule is tense, lens is flat

dec refraction

56
Q

Describe the three ways that the eyes accommodate for close vision.

A

1) ACCOMODATION of lens:
Parasympathetic stimulation -> ciliary muscles contract -> dec tension in ciliary zonule -> lens bulges -> inc refraction

2) CONSTRICTION of pupil:
Parasympathetic stimulation -> circular muscles contract
- eliminates divergent light rays

3) CONVERGENCE of the eyeballs:
- extrinsic muscles cooperate to rotate eyes medially
- image focused on fovea in both eyes

57
Q

Describe what myopia is.

A

Short sightedness

focus in front of retina because eyeball is too long

TREATMENT: concave lenses (or laser surgery)

58
Q

Describe what hyperopia is.

A

Far sightedness

focuses behind the retina, eyeball is too short

Treatment: convex lenses

59
Q

Describe what astigmatism is.

A

Unequal curvature in lens or cornea

corrected with lenses, corneal implants, or laser procedures

60
Q

Describe how the photo receptors function.

A

Outer segments contain pigments that change shape as they absorb light.
Inner segments attached to cell body

change in shape of the pigments -> change in permeability of the membrane -> receptors become hyperpolarized and stop release of neurotransmitter

info is transmitted by shutting off of stimulus, rather than turning it on.

61
Q

How do rods perceive light?

A

as grey tones only

62
Q

What is the pigment for rods?

A

Rhodopsin

63
Q

Describe how rhodopsin functions for rod vision.

A

Rhodopsin accumulates in the dark by regeneration from bleached retinal and formed from Vit A

light is absorbed -> rhodopsin bleaches -> retinal and opsin separate -> membrane potential becomes hyperpolarized

64
Q

Describe how colour is determined

A

Different types of cones have one of these cone pigments:
Red, green, or blue

colour is perceived by combining these stimuli

pigment absorbs light -> bleaches -> retinal and opsin separate -> membrane becomes hyperpolarized

65
Q

What causes colour blindness?

A

a deficiency in one of the cone pigments (red, blue, green)

66
Q

Describe regeneration of photoreceptors

A

terminal segments of both rods and cones are damaged by absorbing light

  • rod terminal discs replaced at end of night
  • cone terminal segments are replaced at the end of the day
67
Q

Describe how the signal is transmitted in the retina of the eye

A

photo receptors and bipolar cells generate graded potentials

light hyperpolarizes rods and cones -> stop releasing inhibitory neurotransmitter glutamate -> bipolar cells then release their neurotransmitter onto ganglion cells -> ganglion cells generate action potentials and transmit along optic nerve

68
Q

Describe how the eye adapts to light

A
  • temporary blind because rod pigments are rapidly bleached
  • pupils constrict -> directs light to macula lutea
  • sensitivity decreases as it switches from rods to cones
69
Q

Describe how the eye adapts to dark.

A

cones stop functioning because light intensity is too low

pupils dilate -> rhodopsin accumulates in the rods and they take over

takes 20-30 minutes to reach peak sensitivity

70
Q

Describe the visual pathway of transmission from photoreceptors to the brain.

A

photoreceptors -> bipolar cells -> ganglion cells -> axons of ganglions form optic nerves -> medial fibers cross at optic chiasma, later fibers do not cross -> most fibers continue through the lateral geniculate body of the thalamus -> to visual areas of cortex

71
Q

Where are the three places that optic fibers can go to?

A

visual cortex

hypothalamus: to coordinate circadian rhythms
midbrain: visual reflex centers

72
Q

Where does visual processing occur?

A

RETINA: activation of photoreceptors (sensation)

THALAMUS: preliminary sorting and organizing before sending to cortex

CEREBRAL CORTEX: primary and association cortex. Conscious perception

73
Q

What do olfactory neurons respond to

A

chemicals in aqueous solutions

74
Q

Where is the olfactory epithelium located?

A

below the cribriform plate of the ethmoid bone

75
Q

Describe the structure of olfactory neurons

A

bipolar with a long apical dendrite that terminates in a knob with cilia that extend into the mucous

76
Q

What type of cells embed the olfactory neurons? what is there function?

A

columnar epithelial cells

- cushion and support

77
Q

What is the life span of the olfactory receptors?

A

60 days

78
Q

How many chemicals can be detected by olfactory neurons, how many receptor types are there, and what does this suggest about smell?

A

10000 smells and 1000 receptor types

suggests there is an interaction between them

79
Q

how many type of receptors does each olfactory neuron have?

A

just one type

80
Q

describe the process of smell

A

substance dissolves in fluid, binds to receptor protein on olfactory cilia -> g protein mech is activated -> produces cAMP as secondary messenger -> opens cation channels -> depolarization -> receptor potential

A and P semester 2 (10 decks)

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