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Physiology 300L > PHS 305 Sensory System & Vision > Flashcards

PHS 305 Sensory System & Vision Flashcards

1
Q

Examples of general senses on special senses

A

– General senses
• Touch, pressure, pain, heat, cold,

– Special senses
•Vision, hearing, equilibrium, olfaction, taste.

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2
Q

Comparison of general and special senses

A

General sensations
• Include somatic sensations (tactile, thermal, pain and proprioceptive) and visceral sensations.
• scattered throughout the body
• simple structures
• Receptors are free nerve endings

Special senses
• Include smell taste vision hearing and equilibrium
• concentrated in specific locations in the head
• anatomically distinct structures
• complex neural pathway
• receptors are specialized cells

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3
Q

Properties of Sensory Systems

A

• Stimulus - energy source – Internal
– External
• Receptors
– Sense organs - structures specialized to respond to stimuli
– Transducers - stimulus energy converted into action potentials
• Conduction
– Afferent pathway
– Nerve impulses to the CNS
• Translation
– CNS integration and information processing – Sensation and perception – your reality

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4
Q

What are sensory receptors?

A

• Are morphologically and functionally specialized protein molecules, cells, or cell processes that physically interact with a force (energy or chemical) basically monitoring conditions in/outside the body.
• Are optimally selective (specific) for a certain type of stimulus “Receptor protein specificity”.
• Are transducers (energy converters) changing incoming stimulus of pressure, vibration, light, e.t.c into electro-chemical neuron impulses.

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5
Q

Classification of sensory receptors based on function

A

• Mechanoreceptors – respond to touch, pressure,
vibration, stretch, and itch
• Thermoreceptors – sensitive to changes in temperature
• Photoreceptors – respond to light energy (e.g., retina)
• Chemoreceptors – respond to chemicals (e.g.,
smell, taste, changes in blood chemistry)
9

• Nociceptors – sensitive to pain-causing stimuli.
• Osmoreceptors – detect changes in concentration of
solutes, osmotic activity
• Baroreceptors – detect changes in fluid pressure

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6
Q

Classification of sensory receptors based on Location

A

Exteroceptors – sensitive to stimuli arising from outside
the body
– Located at or near body surfaces
–Include receptors for touch, pressure, pain, and temperature
• Interoceptors – (visceroceptors) receive stimuli from internal viscera
– Monitor a variety of stimuli
• Proprioceptors–monitor degree of stretch
– Located in musculoskeletal organs e.g. Muscle spindles, golgi tendon organs, Joint kinesthetic receptors.

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7
Q

What are the Extrinsic Eye Muscles

A

Muscles attach to the outer surface of the eye

Produce eye movements and maintain the shape of the eyeball

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8
Q

What are the extrinsic eye muscles that movements and nerves

A
  1. Superior oblique
  2. Lateral rectus
  3. Medial rectus
  4. Superior rectus
  5. Inferior rectus
  6. Inferior oblique
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9
Q
  1. Superior oblique
A

Depresses eye, turns it laterally
IV (Trochlear)

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10
Q
  1. Lateral rectus
A

Turns eye laterally
VI (Abducens)

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11
Q
  1. Medial rectus
A

Turns eye medially
III (Oculomotor)

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12
Q
  1. Superior rectus
A

Elevates eye
III (Oculomotor)

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13
Q
  1. Inferior rectus
A

Depresses eye
III (Oculomotor)

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14
Q
  1. Inferior oblique
A

Elevates eye, turns it laterally
III (Oculomotor)

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15
Q

Layers of the eye

A

Fibrous outer layer
Middle vascular tunic (uvea)
Inner layer 

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16
Q

Describe the fibrous outer layer of the eye

A

Cornea
• Anterior one-sixth of the fibrous tunic
• Composed of stratified Squamous externally, simple squamous internally
• Refracts (bends) light

Sclera
• Posterior five-sixths of the tunic
• White, opaque region composed
irregular connective tissue Provides shape and an anchor for eye muscles,

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17
Q

Scleral venous sinus

A

allows aqueous humor to drain

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18
Q

Middle Vascular Tunic (Uvea)
Has three regions:

A

choroid, ciliary body, and iris

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19
Q

Choroid region

A

• A dark brown membrane that forms the posterior portion of the uvea
• A blood-rich nutritive tunic that supplies blood to all eye tunics
• Pigment prevents light from scattering (prevents reflection of light rays within the eye, has melanin) by absorbing extra light.
• Modified interiorly into two structures; cilliary
body and iris.

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20
Q

Iris and Pupil

A

– Composed of smooth muscle, melanocytes, and blood vessels that forms the colored portion of the eye.
– Function: It regulates the amount of light entering the eye through the pupil.
– It is attached to the ciliary body.
– Pupil is the opening in center of iris through which light enters the eye

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21
Q

Ciliary body

A

– A thickened ring of tissue surrounding the lens
– Composed of smooth muscle bundles (ciliary muscles)
– Located on each side of the lens
– Anchors the suspensory ligament
–Made up of three parts; Ciliary Muscle, Ciliary process and zonules

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22
Q

Suspensory ligaments / Zonule

A

– Radiate from ciliary body and attach to lens
– Hold lens in place
–Assist in adjusting shape of lens for proper focusing of eye

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23
Q

Ciliary Muscles

A

control lens shape
Responsible for adjusting lens to view near objects

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24
Q

Ciliary Processes

A

Secrete aqueous humor

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25
Q

The inner layer of the eye is formed by

A

The retina

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26
Q

The retina contains 2 layers:

A

– Pigmented layer made of a single layer of melanocytes, absorbs light after it passes through the neural layer

– Neural layer – sheet of nervous tissue, contains three main types of neurons
• Photoreceptor cells • Bipolar cells
• Ganglion cells

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27
Q

Types of photoreceptors

A

Rod cells

• Extremely sensitive to light hence, can be triggered by a very small number of photons
• Allow vision in dim light
• In periphery
• They do not give colour sensation because only one type of photoreceptor cell is active

– Cone cells
• Operate best in bright light
• High-acuity (highly sensitive)
• Color vision – blue, green, red cones
• Concentrated in fovea, also found in the macula lutea

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28
Q

THE LENS

A

• A thick, transparent, biconvex disc
• Held in place by its ciliary zonule
• Lies behind the iris
• Refracts light greatly
• The greater the curvature of the lens surface the greater is its refractive power and the closer is the focused image to the lens.
• Curvature of the lens is adjustable
• The image formed by eye’s lens system is smaller than the object viewed, inverted (upside-down) and reversed (right-left)

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29
Q

Aqueous Humor

A

• Watery fluid found in the anterior chamber, between
the lens and cornea. Lies in front of the lens.
• Afreeflowingfluid
• Similartobloodplasma
– Formed by ciliary processes by diffusion, ultrafiltration and active transport through the epithelial cells lining the ciliary processes.

30
Q

Describe the formation and reabsorption of aqueous humor

A

•Continually being formed and reabsorbed
• The balance between formation and reabsorption of aqueous humor regulates the total volume and pressure of the intraocular fluid.
– Reabsorbed into venous blood through the canal of Schlemm

31
Q

FUNCTIONS OF AQUEOUS HUMOR

A

• Helps maintain the intraocular pressure
• Maintains the shape of eyeball
• Provides nutrients, oxygen and electrolytes to the avascular structures of the eye (the lens and cornea).
• Removes the metabolic end products from lens and cornea.

32
Q

VITREOUS HUMOR

A

• Also known as vitreous body
• A Gel-like substance present behind the lens; in the space between lens and retina.
• Highly viscous and gelatinous substance.
• Formed by a fine fibrillar network of proteoglycan molecules.
• Major components are the albumin and hyaluronic acid which enter the vitreous body from the blood by means of diffusion

33
Q

Functions of the vitreous humor

A

• Refractslightslightly.
• Transmitslight.
• Supports the posterior surface of the lens.
• Holds the neural retina firmly against the pigmented layer; Holds lens and retina in place.
• Contributes to intraocular pressure.
• Blindness can result if vitreous humor escapes from eye.

34
Q

Nerve cells involved in visual pathway

A

• The photoreceptors (the rods and cones)
• The horizontal cell
• The bipolar cells
• The amacrine cells
• The ganglion cells

35
Q

The photoreceptors (the rods and cones)

A

transmit signals to the outer plexiform layer, where they synapse with bipolar cells and horizontal cells.

36
Q

The horizontal cells

A

transmit signals horizontally in the outer plexiform layer from the rods and cones to bipolar cells.

37
Q

The bipolar cells

A

transmit signals vertically from the rods, cones, and horizontal cells to the inner plexiform layer, where they synapse with ganglion cells and amacrine cells.

38
Q

The amacrine cells

A

transmit signals in two directions, either directly from bipolar cells to ganglion cells or horizontally within the inner plexiform layer from axons of the bipolar cells to dendrites of the ganglion cells or to other amacrine cells.

39
Q

The ganglion cells

A

transmit output signals from the retina through the optic nerve into the brain

40
Q

Cone Pathway

A

– Cones bipolar cells ganglion cells
• Likewise, horizontal cells transmit inhibitory signals laterally in the outer plexiform layer, and amacrine cells transmit signals laterally in the inner plexiform layer.

41
Q

Rod Pathway

A

For pure rod vision, the pathway is
– Rods bipolar cells amacrine cells ganglion cells.
• Also, horizontal and amacrine cells provide lateral connectivity.

42
Q

The image forming mechanism

A

• Eyelids act as a shutter of the camera.
• Cornea and crystalline lens act as a focusing system of the camera.
• Iris acts as a diaphragm, which regulates the size of the aperture (pupil) and therefore the amount of light entering the eye.
• Choroid and pigment epithelium of retina help in forming the darkened interior of the camera.

• Neural retina acts as a light-sensitive plate or film on which images of the objects in the environment are focused. The light rays striking the retina generate potentials in the rods and cones. Therefore, the eye converts energy in the visible spectrum into action potentials in the optic nerve.
• Optic nerve and its connections convey the impulses generated in the retina to the occipital region of the cerebral cortex where they produce sensation of vision.

43
Q

The refractive index of the Cornea

A

1.37

44
Q

The refractive index of the Aqueous humour

A

1.33

45
Q

The refractive index of the Crystalline lens

A

1.42

46
Q

The refractive index of the Vitreous humour

A

1.33

47
Q

PROCESS OF VISION

A

• Structures in the eye bend light rays
• Light rays converge on the retina at a single focal point
• Light bending structures (refractory media)
– The lens, cornea, and humors • Accommodation
– This is the adjustment of eye to see near objects clearly.

48
Q

VISUAL PATHWAY TO THE CORTEX

A

• Pathway begins at the retina
– When light strikes the retina, the rods and cones
generate impulses.
– Light activates photoreceptors
– Photoreceptors signal bipolar cells
– Bipolar cells signal ganglion cells
– Axons of ganglion cells exit eye as the optic nerve through the optic disc or blind spot because it lacks photoreceptors.

49
Q

COMPONENTS OF THE VISUAL PATHWAY

A

• Optic nerve
• Optic chiasm
• Optic tract
• Thalamus
• Visual cortex
• Other pathways include the midbrain and diencephalon

50
Q

OPTIC NERVE

A

A bundle of more than one million nerve fibers that carries visual messages from the retina to the brain.

51
Q

OPTIC CHIASMA

A

At the optic chiasma, nasal fibers of each optic nerve cross the midline and join the uncrossed temporal fibers of opposite side, to form the optic tract.

52
Q

OPTIC TRACT

A

Optic tract is formed by uncrossed fibers of optic nerve on the same side and crossed fibers of optic nerve from the opposite side. Then, the fibers turn around the cerebral peduncle to reach the lateral geniculate nucleus in the thalamus.

53
Q

LATERAL GENICULATE NUCLEUS

A

The fibers of each optic tract then synapse in the dorsal lateral geniculate nucleus of the thalamus, and from there, geniculocalcarine fibers / tracts pass by way of the optic radiation to the primary visual cortex in the calcarine fissure area of the medial occipital lobe.

54
Q

Primary Visual Cortex

A

Primary cortical center for vision is called visual cortex, located . The primary visual cortex also called Area 17 is concerned with the perception of visual impulses.

55
Q

Other Areas of visual cortex and their functions

A

• Secondary visual area or visual association area (area 18): Concerned with the interpretation of visual impulses.
• Occipital eye field (area 19): Concerned with the movement of eyes.

56
Q

Discuss the visual pathway left and right hemifield

A

Information from the right visual hemifield is seen by the nasal right retina and the temporal left retina.
• Likewise, information from the left visual hemifield is carried by the nasal left retina and temporal right retina.
• Therefore, each eye sees a portion of each of the visual hemifield.
• Axons from the nasal retina crosses to the opposite
brain and axons from the temporal retina projects to
the ipsilateral side of the brain at the optic chiasm.

After the crossing of optic nerves at the optic chiasm, the right optic tract carries information solely about the left visual hemifield while the left optic tract carries information about the right visual field.
• Therefore, the left lateral geniculate nucleus receives visual information from the right visual field; nasal right retina and temporal left retina.
• Likewise, the right lateral geniculate nucleus receives visual information from the left visual field, nasal left retina and temporal right retina.

57
Q

Accommodation

A

• In an emmetropic eye, parallel rays of light coming from infinity are brought to focus on the retina with accommodation at rest.
• Our eyes have been provided with a unique mechanism that helps in focusing the diverging rays coming from a near object on the retina in a bid to see clearly.
• This mechanism is called accommodation. In it there occurs an increase in the power of the crystalline lens

58
Q

VISUAL ACQUITY

A

Acuity of vision/ Vision Acuity is the ability of eye to determine the precise shape and details of the object.
• Visual acuity is also defined as the ability to recognize the separateness of two objects placed together.
• Cones of retina are responsible for acuity of vision. Visual acuity is highly exhibited in fovea centralis, which contains only cones.
• It is greatly reduced during the refractory errors.

59
Q

REFRACTORY ERRORS

A

• If there is any difficulty in seeing the distant object or the near object, the defect is known as error of refraction.
• Occur when eyeball is abnormally shaped
• Occur when lens has lost ability to accommodate to near vision
• Vision will be blurred
• Can be adjusted with corrective lenses
Can be diagnosed with:
• Snellen chart which is used to test the acuity of vision for distant vision in the diagnosis of refractive errors of the eye.
• Jaeger chart which is used to test the visual acuity for near vision.

60
Q

HYPERMETROPIA/ HYPEROPIA/ FARSIGHTEDNESS

A

• Refractive error characterized by the inability to see near object i.e. distant vision is normal but, near vision is affected.
• Results in blurred vision due to light rays focused behind the retina because eyeball is shorter than normal or occasionally, the lens system is too weak.
• It also occurs as a result of decreased anteroposterior diameter of the eyeball.
• It is corrected by using biconvex lens which converge light rays before entering the eyes.

61
Q

Myopia (Nearsightedness)

A

• It is characterized by the inability to see the distant object
• In myopia, the near vision is normal but the far point is fixed at a definite distance, unlike in emmetropia which has an infinite far point.
• It is usually due to too long an eyeball, but it can result from too much refractive power in the lens system of the eye, resulting in blurred distant vision due to light rays focused in front of retina.
• It also occurs as a result of abnormally long anteroposterior diameter of the eyeball.
• Corrected by using a biconcave lens, which diverge light rays before entering the eye.

62
Q

Astigmatism

A

• Astigmatism results when the cornea surface does not resemble the surface of a sphere (e.g. is more oblong) i.e. abnormally shaped.
• Hence, the image of distant and near objects cannot be focused regularly on the retina.
• Astigmatism is corrected with a cylindrical lens having a curvature that corrects for the corneal astigmatism.

63
Q

PRESBYOPIA

A

• Accommodation is defined as the ability of the lens to increase its refractive power for viewing near objects. It is like 14 diopters in children and it decreases with age.
• As a person grows older, the lens grows larger and thicker and becomes far less elastic, partly because of progressive denaturation of the lens proteins.
• Therefore, the ability of the lens to change shape decreases with age hence, the power of accommodation decreases to less than 2 diopters by the time a person reaches 45 to 50 years.

• It then decreases to essentially 0 diopters at age 70 years. Thereafter, the lens remains almost totally non-accommodating i.e. each eye remains focused permanently at an almost constant distance.
• This condition is known as “presbyopia” which is a condition that occurs in old age
• Also called farsightedness due to better clarity of distant objects
• To see clearly both in the distance and nearby, an older person must wear bifocal glasses with the upper segment focused for far-seeing and the lower segment focused for near-seeing (e.g., for reading).

64
Q

GLAUCOMA

A

• This is an ocular disorder that occurs as a result of increase in intraocular pressure.

65
Q

Chronic open-angle glaucoma

A

– Primary disorder
– Breakdown in drainage system of the circulation of aqueous humor
• Gradual elevation of internal pressure leads to decreased blood supply to optic nerve and retina
•Peripheral vision is gradually lost when untreated

66
Q

Acute closed-angle glaucoma

A

– Mouth of drainage system is narrow and closes
completely
– Allowing no flow of aqueous humor
• Rapid occurrence characterized by severe pain, blurred vision, photophobia, redness, and seeing “halos” around light
• If untreated, person can lose his or her
sight within several days

67
Q

NIGHT BLINDNESS

A

• Night blindness, the inability to see well in dim light or at night, is usually caused by a deficiency of vitamin A, although some night blindness may occur with aging. Vitamin A is necessary for the synthesis of rhodopsin in the rods.
• Without sufficient vitamin A, there is not enough rhodopsin present to respond to low levels of light.
• Also called nyctalopia or defective dim light (scotopic) vision.

68
Q

COLOUR BLINDNESS

A

• Color blindness is a genetic disorder in which one of the three sets of cones is lacking or non- functional. It is characterized by an inability to sharply perceive visual colours.
•Daltonism: Inability to distinguish greens from reds
• Achromatic Vision: Inability to distinguish any color; perceives only white, gray, and black. Total color blindness, the inability to see any colours at all, is very rare.

• The most common form is red-green colour blindness, which is the inability to distinguish between these colours.
• If either the red cones or green cones are non-functional, the person will still see most colors, but will not have the contrast that the non-working set of cones would provide.

69
Q

STRABISMUS

A

– Failure of eyes to gaze in same direction due to weakness in muscles controlling position of eye
• Most common type is non-paralytic strabismus
• Inherited defect in which the eye position of the two
eyes has no relationship.

70
Q

Convergent Strabismus

A

•Caused by the paralysis of the lateral rectus.
•Usually develops in infancy or early childhood

71
Q

Divergent Strabismus

A

– Also known as “Walleye”
– Also known as “Exotropia”
– Affected eye turns outward
– Caused by the paralysis of the medial rectus.

72
Q

Nystagmus

A

– Vertical, horizontal, rotary, or mixed rhythmic
involuntary movements of the eye(s)
•Caused by use of alcohol or certain drugs, lesions on the brain or inner ear, congenital abnormalities, nerve injury at birth, or abnormal retinal development

Physiology 300L (7 decks)

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