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CNM BIOMEDICINE II > 18. SENSE ORGANS > Flashcards

18. SENSE ORGANS Flashcards

- Senses of hearing, sight, smell and taste - structure and function. - Pathologies of these organs.

1
Q

Name the structures of the outer ear

A
  1. Pinna (auricle)
  2. External auditory canal
  3. Tympanic membrane
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2
Q

Name the three auditory ossicles of the middle ear

A

Malleus
Incus
Stapes

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3
Q

How is the middle ear connected to the nasopharynx?

A

Via the eustachian tube (pharyngotympanic tube)

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4
Q

What is the main role of the tympanic membrane?

A

This thin, semi-transparent membrane transmits sounds from the outer ear to the auditory ossicles in the middle ear by converting sound waves into mechanical vibration.

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5
Q

Explain the role of the ‘stapedius’

A

Stapedius is a small muscle connected to Stapes which functions to dampen large vibrations

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6
Q

Describe the structure of the inner ear

A

The inner ear (labyrinth) consists of a complicated series of canals.
There is an outer bony labyrinth that encloses an inner membranous labyrinth. The bony labyrinth can be divided into:
- three semicircular canals and vestibule which are receptors for balance
- the cochlea, which is the receptor for hearing.
The vestibule is the central oval portion connecting the cochlea to the canals.

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7
Q

Which two bones of the inner ear send nerve impulses for balance?

A

Vestibule

Semicircular canals

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8
Q

Explain how very loud noises can affect the inner ear

A

Very loud noises create strong movement in the endolymph within the labyrinth, which could kill the the stereocilia (receptors for hearing) and cause hearing loss.

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9
Q

List two main functions of the inner ear

A

It provides hearing and balance

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10
Q

What structure does the stapes connect to?

A

It rocks against the oval window of the cochlea

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11
Q

How do stereocilia trigger an electrical impulse?

A

The fluid movement (of the endolymph) in the labyrinth causes the stereocilia to move, creating a receptor and then electrical impulse.

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12
Q

Name the cranial nerve that provides sensory information for hearing and balance.

A

Vestibulocochlear nerve (CN VIII)

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13
Q

What is the unit through which volume of sound is measured?

A

Decibels (dB)

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14
Q

Describe in specific detail how external sound waves are perceived as ‘sound’ in the cerebrum of the brain.

A
  1. The auricle concentrates sound waves and directs them along the auditory canal.
  2. Vibrations are transmitted through the middle ear by movement of the three auditory ossicles
  3. Footplate of the stapes rocks at the oval window, setting in motion fluid waves in the cochlear perilymph.
  4. Pressure waves are transmitted into the cochlea, which causes the round window to bulge in the middle ear.
  5. Pressure wave is transmitted into the endolymph
  6. which results in vibration of the basilar membrane and hair cells (stereocilia).
  7. Bending of stereocilia creates a receptor potential - generating an action potential.
  8. This nerve impulse pass to the brain via the vestibulocochlear nerve
  9. which transmits the impulses to the hearing area in the cerebrum where sound is perceived.
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15
Q

Describe the difference between ‘pitch’ and ‘volume’ of sound waves.

A

Pitch is the frequency of sound waves - the higher the frequency of vibration, the higher the pitch.
Volume is the amplitude of sound waves - the bigger the amplitude, the louder the sound.

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16
Q

Above which decibel rating can hearing loss occur?

A

Prolonged sounds of over 90dB

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17
Q

Explain the main function of white noise

A

As a constant noise that contains all the different frequencies, it is a background noise that the brain ignores and can be used to mask other sounds, making it a sleep aid and provides relief from tinnitus

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18
Q

List two functions of the eustachian tube

A

The eustachian tube is to equalise pressure in the middle ear and functions to drain mucus from the pharynx.

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19
Q

Explain why children are more prone to middle ear infection

A

The eustchian tube in children is more horisontal, shorter and narrower, creating a common route for infection due to mucus draining from the pharynx.

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20
Q

Describe the structure of the otholitic membrane

A

The stereocilia within the vestibule and semicircular canals is covered with a gelatinous matrix upon which rests a dense layer of calcium carbonate crystals. This is called the otolithic membrane

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21
Q

List three forms of input the cerebellum can use to make postural adjustments to maintain balance.

A
  1. Vestibular feedback
  2. Visual feedback
  3. Proprioceptors in the skeletal muscles
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22
Q

Compare the following pathologies by way of definition:

a) Otitis externa
b) Otitis media
c) Otitis interna

A

a) Inflammation of the outer ear (90% bacterial infection). Also called ‘swimmer’s ear’ as is common in swimmers.
b) Infection of the middle ear, commonly caused by bacterial spread from eustachian tube.
c) A balance disorder associated with inflammation of the membranous labyrinth, also called ‘Labyrinthitis’.

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23
Q

Explain why insufficient earwax can predispose to ear infections

A

Earwax contains lysozymes and oil that create an acidic, lubricating coat which inhibits bacterial growth. Insufficiency thus predisposes to infection.

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24
Q

Name two pathologies that increase the risk of Otitis Externa.

A
  • Diabetes mellitus
  • HIV
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25
Q

List two signs and/or symptoms of Otitis Externa

A
  • Pain (especially upon movement of pinna)
  • Discharge
  • Swollen, itchy and red auditory canal
  • Hearing deficit
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26
Q

List two causes of Otitis Media

A
  • Infectious organisms spread from nasopharynx

- Allergies

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27
Q

Describe how ‘secretory otitis media’ can result in hearing impairment

A

The gluey fluid that builds up in the middle ear dampens the tympanic membrane and ossicle vibrations

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28
Q

How does a tympanostomy tube (grommet) relieve secretory otitis media?

A

A tiny pipe is inserted into the tympanic membrane through which fluid can drain and air can circulate in the middle ear in order to resolve the inflammation.

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29
Q

Describe two characteristic signs/symptoms of otitis interna

A

The onset of sudden, severe vertigo that is not triggered by movement, as well as nausea, vomiting and tinnitus.

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30
Q

Using definitions, compare Ménière’s Disease to Tinnitus.

A

Ménière’s disease is a disorder of the inner ear, caused by excess fluid in the labyrinth, associated with progressive distention of the membranous labyrinth, of which episodes of tinnitus is a symptom.
Tinnitus is the perception of ringing, buzzing, roaring, hissing or whistling sound originating from within the head rather than outside.

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31
Q

List one autoimmune cause of Ménière’s disease

A

Rheumatoid Arthritis

Systemic Lupus Erythematosus

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32
Q

Explain why a low salt diet is recommended in Ménière’s disease

A

It reduces the fluid build-up in the inner ear

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33
Q

List two causes of the following:

a) Objective tinnitus
b) Subjective tinnitus

A

a) Pulsatile: carotid stenosis, valve disease. Muscular: spasm of tympanic membrane.
b) Ménière’s, ear infection, wax, head injury, MS, tumour, meningitis, excessive NSAID use, loop diuretics, TMJ dysfunction, hyperthyroidism, anaemia

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34
Q

Describe the key difference between ‘conductive’ and ‘sensory’ hearing impairment.

A

Conductive hearing impairment is due to structural factors such as ear canal obstructions, ossicle abnormalities and ruptured tympanic membrane. Sensory hearing impairment is due to poor hair cell function, infection or noise truama.

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35
Q

List two viral causes of hearing impairment

A

Measles
Meningitis
Mumps
Rubella

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36
Q

Name the three layers of the eyeball

A

Outer layer: Sclera and the cornea anteriorly
Middle layer: Uvea (consists of the iris, ciliary body and choroid)
Inner layer: Retina

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37
Q

Describe the main role of the iris

A

The iris controls the amount of light reaching the retina by adjusting the pupil size.

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38
Q

Describe how the following accessory organs protect the eye:

a) Eyebrows
b) Eyelids/lashes
c) Lacrimal apparatus
d) Conjunctiva

A

a) Eyebrows: prevent sweat and other substances from entering the eye
b) Eyelids/lashes: spread secretions over the eye
c) Lacrimal apparatus: Produces tears
d) Conjunctiva: Thin, transparent mucous membrane lines the internal eyelids and anterior eyball. Secretes oily material to delay tear evaporation.

39
Q

What is the immunological function of tears?

A

Tears contain IgA and lysozymes and serve as a first line of defense.

40
Q

Name the cranial nerve that controls tear secretion

A

The trigeminal nerve (CN V)

41
Q

To achieve clear vision, light must be focused on the retina. Name three ways in which this is achieved.

A
  • Refraction of light rays
  • Accommodation of the eyes
  • Changing the size of the pupils
42
Q

Describe in detail the difference between:

  1. Greater refraction
  2. Less refraction
A
  1. When objects appear closer than 6m, the light rays need to be refracted more in order to be focused on the back of the retina. This is achieved by the ciliary muscle contracting and reducing the tension of the suspensory ligament, causing the lens to become more convex, resulting in greater refraction.
  2. When an object is distant, the ciliary muscle relaxes, increasing the tension of the suspensory ligament and flattening the lens, which leads to less refraction.
43
Q

How is the pupil size affected by:

a. Sympathetic nervous system
b. Parasympathetic nervous system

A

a. Sympathetic stimulation contracts the radial muscle fibres of the iris to dilate the pupils.
b. Parasympathetic stimulation contracts the circular muscle fibres to constrict the pupils.

44
Q

Explain why an individual may experience ‘double vision’

A

If the extra-ocular muscles do not enable complete medial movement of the eyeballs so that both are directed towards the object, two images are sent to the brain, leading to diplopia (double vision).

45
Q

Describe what is meant by binocular vision

A

In binocular vision, both eyes focus on one object, which allows for the perception of depth and three dimensionality.

46
Q

Name the location where the optic nerve crosses over in the brain.

A

The optic nerve crosses over in the brain at a location known as the optic chiasma.

47
Q

Explain why a pituitary tumour can cause ‘tunnel vision’

A

The optic chiasma is located next to the pituitary gland, which is why a pituitary tumour can press on this area and cause tunnel vision.

48
Q

Name one investigative tool that can be used to view the retina

A

An opthalmoscope

49
Q

Name the location where the optic nerve exits the eyeball

A

The optic disc (‘blind spot’)

50
Q

List two layers of the retina

A
  • A pigmented layer of melanin-containing epithelial cells

- A layer of ‘photoreceptors’ which are specialised visual cells called rod and cone cells.

51
Q

Describe three differences between ‘rod cells’ and ‘cone cells’

A
  1. Rod cells are much more numerous: 120 million, compared to only 6 million cone cells
  2. Cone cells produce colour vision while rod cells and provide black, white and greyscale vision and allow us to see in dim light
  3. Cone cells are shorter and have a cone appearance while rod cells are long and thin.
52
Q

Describe two features of the ‘fovea centralis’

A

The fovea centralis is a small depression in the centre of the macula lutea (exact centre of the retina) and contains only cone cells. It is also the area of highest visual acuity.

53
Q

Where in the retina would you expect to find rod cells?

A

At the periphery of the retina

54
Q

How does light affect photo-pigments?

A

When light hits the photo-pigments (transmembrane proteins within the discs of the rod & cone cells), it changes shape, initiating an action potential which is then relayed to the brain.

55
Q

Where is vitamin A stored in the eye?

A

The pigmented layer of the retina stores large quantities of vitamin A in the form of retinal.

56
Q

Name the protein that binds to retinal in the eye

A

Opsin

57
Q

List two food sources of

a. Pre-formed vitamin A
b. Carotenoids

A

a. Liver, egg yolk

b. Sweet potato, carrot, leafy greens, mango

58
Q

Explain why carotenoids are not considered toxic

A

Carotenoids are precursors of vitamin A and are metabolised to retinol in the intestines as and when needed, which regulates the absorption thereof.

59
Q

Describe how the eyes adjust in the following situations:

  1. Moving from a dark to light sensitivity
  2. Moving from light to dark sensitivity
A
  1. The eyes adjust within seconds by decreasing its sensitivity
  2. Sensitivity increases slowly over some minutes
60
Q

How long do rod and cone cells take to regenerate respectively?

A

Cone cells can regenerate their photo-pigments within the first eight minutes, while rod cells take much longer.

61
Q

By way of definition, compare ‘blepharitis’ with a ‘stye’

A

Blepharitis is the inflammation of the eyelid margin due to staphylococcus aureus or dermatitis while a stye is inflammation of the sebaceous glands of the eyelid, usually also due to a bacterial infection.

62
Q

How do the signs and symptoms of blepharitis differ from that of a stye?

A

In blepharitis there can be red eyelid margins with sore, gritty eyes and scales and flakes.
A stye presents as a red, swollen and painful infection of the sebaceous glands of the eyelid and usually affects the upper eyelid.

63
Q

Name one endocrine pathology that increases the risk of styes.

A

Diabetes Mellitus

64
Q

With regards to conjunctivitis, describe the key difference in discharge from the eye due to a:

a. Virus / Allergy
b. Bacteria

A

a. Watery discharge

b. Purulent discharge

65
Q

State two parts of the uvea affected in uveitis.

A

Iris, ciliary body, choroid

66
Q

List one viral cause of uveitis

A

Herpes

67
Q

Describe three characteristic signs / symptoms of uveitis

A
  • Progressive unilateral red eye with pain
  • Blurred vision
  • Photophobia
68
Q

Explain why a corneal ulcer is a medical emergency

A

A corneal ulcer can result in the loss of sight

69
Q

List one pathology that can cause strabismus

A

A stroke or a brain tumour (causing damage to nerves supplying extra-ocular muscles.

70
Q

Describe the difference between a healthy lens and a lens affected by cataracts.

A

A healthy lense is transparent due to the regular arrangement of lens fibres. In cataracts, new fibres are produced and become disorganised within the cytoplasm, leading to opaque lenses.

71
Q

List two cause of cataracts apart from age

A

Diabetes mellitus, smoking, steroids

72
Q

List two signs / symptoms of cataracts

A

Gradual painless loss of vision.

Diplopia.

73
Q

Define age-related macular degeneration (AMD)

A

AMD describes the ageing changes that occur in the macula (central areas of the retina).

74
Q

List two causes (not age) of AMD

A

Smoking, cardiovascular disease

75
Q

How is vision affected in AMD?

A

There is gradual and progressive loss of central vision and reduced visual acuity, particularly with near vision.

76
Q

List two diagnostic methods used to diagnose AMD

A
  • The Amsler grid.

- Opthalmoscopy.

77
Q

Describe how an individual experiences ‘floaters’

A

Small, dark, shadowy shapes floating in the field of vision (spots, thread-like strands, squiggly lines)

78
Q

Why do floaters develop in diabetic retinopathy?

A

Because of vitreous haemorrhaging

79
Q

Identify the following pathology: “Floaters in vision, flashing lights, curtains descending over vision.”

A

Retinal detachment

80
Q

How does retinal detachment develop?

A

Retinal detachment is the separation of the neurosensory layer of the retina from the pigmented epithelium that results in the accumulation of sub-retinal fluid in the potential space.

81
Q

How does glaucoma produce symptoms?

A

Increased intraocular pressure is caused by inadequate drainage, which causes compression of the retina and optic nerve.

82
Q

List one lifestyle factor that may cause glaucoma

A

Smoking

83
Q

List two signs / symptoms associated with:

a. mild acute glaucoma
b. severe acute glaucoma

A

a. Pain in the eyes and haloes around lights, relieved by sleep
b. Rapid deterioration of vision, intense eye pain, red and watery eyes, sensitivity to bright light, nausea and vomiting.

84
Q

List two signs / symptoms of late chronic glaucoma

A
  • Loss of peripheral vision

- Blurring of objects directly in front of person

85
Q

Describe the pathophysiology of diabetic retinopathy

A

Diabetic retinopathy occurs as a result of chronic hyperglycaemia which lead to retinal microvasculature changes and neovascularisation. This results in micro-aneurysms, oedema and haemorrhaging.

86
Q

Name the cranial nerve responsible for smell

A

The olfactory nerve (CN I)

87
Q

Describe how decreased sensitivity to odours occurs rapidly.

A

Through the process of adaptation, olfactory receptors adapt by decreasing sensitivity to smells by 50% in the first few seconds, and 80% within a few minutes.

88
Q

What is the main function of ‘olfactory adaptation’?

A

The aim of adaptation is to protect from danger. If a scent is not a danger, olfaction calibrates to be able to detect other smells which might indicate harm.

89
Q

Name the cranial nerve that innervates the tongue

A

The hypoglossal nerve (CN XII)

90
Q

Describe the role of the following in relation to taste buds:

a. Gustatory receptor cells
b. Basal cells

A

a. Gustatory receptor cells are for detecting taste and they only live for 10 days
b. Basal cells are the stem cells that produce new receptor cells

91
Q

Describe the difference between the following:

a. Circumvallate papillae
b. Fungiform papillae
c. Foliate papillae

A

a. Circumvallate papillae are the largest papillae. They are V-shaped and at the back of the tongue.
b. Fungiform papillae are mushroom shaped, present all over the tongue and contain about five taste buds each
c. Foliate papillae are located in small trenches at the lateral margins of the tongue and most degenerate during childhood

92
Q

Name five tastes

A 
Sweet
Sour
Salty
Bitter
Umami
93
Q

Name two cranial nerves involved in taste physiology

A 
Facial Nerve (CN VII)
Glossopharyngeal Nerve (IX)

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