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Medicine YEAR 1 > Phase 1 - Week 11 (Ear, ear infection, temperature control, paracetamol), Phase 1 - Week 12 (Mock MILE - Eyes) > Flashcards

Phase 1 - Week 11 (Ear, ear infection, temperature control, paracetamol), Phase 1 - Week 12 (Mock MILE - Eyes) Flashcards

1
Q

List the cranial nerves

A
  1. Olfactory
  2. Optic
  3. Occulomotor
  4. Trochlear
  5. Trigeminal
  6. Abducens
  7. Facial
  8. Vestibulocochlear
  9. Glossopharyngeal
  10. Vagus
  11. Spinal accessory
  12. Hypoglossal
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2
Q

List the parts of the eye

A
  • Iris
  • Pupil
  • Sclera
  • Cornea
  • Anterior chamber
  • Lens
  • Posterior chamber
  • Vitreous chamber
  • Retina
  • Optic nerve (CN II)
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3
Q

Describe the path of visual information after it leaves the eyes

A

Optic nerves (CN II) -> Cross at optic chiasm -> Optic tracts -> Optic radiation -> Occipital lobes of brain

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4
Q

Where are tears produced?

A

Lacrimal gland - washed across eye from medial to lateral

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5
Q

What is the function of tears?

A
  • Lubricate eye movement

- Remove debris

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6
Q

Where do tears drain into?

A

The nasal cavity

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7
Q

List the bones of the orbit

A
  • Frontal
  • Sphenoid
  • Zygomatic
  • Palatine
  • Ethmoid
  • Lacrimal
  • Maxilla
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8
Q

Sinuses

A
  • Orbital, nasal and oral cavities
  • Paranasal sinuses = maxillary (under eyes), frontal (forehead), ethmoid and sphenoid (posterior to nose)
  • Reduce weight of skull, especially anteriorly
  • Allow circulation of mucus
  • Contribute to resonance of sounds
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9
Q

Which cranial nerves control extra-ocular muscles?

A

CN III (occulomotor), CN IV (trochlear) and CN VI (abducens)

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10
Q

List the extra-occular muscles and their innervations

A
  • Superior rectus muscle (CN III)
  • Lateral rectus muscle (CN VI)
  • Inferior rectus muscle (CN III)
  • Inferior oblique muscle (CN III)
  • Medial rectus muscle (CN III)
  • Superior oblique muscle (CN IV)
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11
Q

Describe the function of the nasal cavity

A
  • Warm air
  • Humidify air
  • Filter air - trap foreign particles
  • Olfaction
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12
Q

How is the structure of the nasal cavity suited to its function

A
  • Rich, superficial blood supply (warm air)
  • Mucous provides moisture
  • Mucous and hairs trap particles
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13
Q

Explain the process of olfaction

A
  • Olfactory nerve (CN I)
  • Converts chemical information to electrical
  • Superior surface of nasal cavity
  • Conchae (turbinates) - increase surface area, increase chance of olfactory exposure
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14
Q

List the parts of the tongue

A
  • Root of tongue
  • Foramen caecum
  • Terminal sulcus
  • Foliate papillae
  • Fungiform papillae
  • Filiform papillae
  • Vallate papillae
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15
Q

Which nerves are involved in innervation of the tongue?

A
  • Lingual nerve (CN V3 and VII)
  • Chorda tympani (from CN VII)
  • Glossopharyngeal nerve (CN IX)
  • Hypoglossal nerve (CN XII)
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16
Q

What is the role of the lingual nerve?

A
  • Carries axons from two cranial nerves (V3 and VII)

- Taste and general sensation from anterior 2/3

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17
Q

What is the function of the glossopharyngeal nerve in innervation of the tongue?

A

Taste and general sensation from posterior 1/3

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18
Q

What is the function of the hypoglossal nerve in innervation of the tongue?

A

Motor control of most tongue muscles

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19
Q

Describe the divisions of the ear

A
  1. External ear
  2. Middle ear
  3. Inner ear
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20
Q

Ear ossicles

A
  • Transmit vibrations through the middle ear
  • 3 bones:
    1. Malleus (attached to tympanic membrane)
    2. Incus (anvil)
    3. Stapes (stirrup)
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21
Q

Describe the features of the tympanic cavity

A
  • Lateral wall - tympanic membrane (ear drum)
  • Medial wall - vestibular window (oval window), opening into the vestibule or the inner ear, closed by base of stapes
  • Cochlear window (round window), opening into the cochlear portion of the inner ear
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22
Q

Describe the function of the cochlea

A
  • Sound amplification
  • Conversion from vibration to electrical signal
  • Signal transmitted via cochlear part of vestibulocochlear nerve (CN VIII)
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23
Q

Describe the function of the semicircular canals

A
  • Balance

- Innervated by vestibular part of vestibulocochlear nerve (CN VIII)

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24
Q

List the bony landmarks around the ear

A
  • Mastoid process

- Styloid process

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25
Q

List the parts of the external ear

A
  1. Auricle (or pinna)

2. External acoustic meatus (auditory canal)

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26
Q

Describe the structure and function of the auricle of the ear

A
  • Visible part
  • On side of head
  • Made of elastic cartilage covered by skin
  • Shape causes sound to be directed into external acoustic meatus

Parts:

  1. Helix - outer curved margin of auricle
  2. Tragus - flat triangular prominence, partially occludes entrance to external acoustic meatus
  3. Lobule - highly vascularised flap of skin, most inferior part of auricle, no cartilage
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27
Q

Describe the structure and function of the external auditory meatus

A
  • S-shaped passage
  • Begins as opening in the auricle -> tympanic portion of temporal bone -> terminate at tympanic membrane
  • Lined w/ mucous membrane containing sebaceous glands + modified sweat glands - ceruminous glands
  • Directs sound waves to tympanic membrane
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28
Q

Ceruminous glands

A

Secretory ducts can open independently into external auditory meatus

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29
Q

Describe the secretions of the sebaceous and ceruminous glands

A

= Cerumen (ear wax)

  • Prevents entrance of foreign particles
  • Reduces risk of bacterial + fungal infection
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30
Q

List the parts of the middle ear

A
  1. Tympanic membrane
  2. Tympanic cavity
  3. Tensor tympani
  4. Stapedius
  5. Ossicles
  6. Eustachian tube
  7. Oval window
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31
Q

Tympanic membrane

A
  • Ear drum
  • Separates external ear from middle ear
  • Thin, semi-transparent, concave sheet composed of epithelium and collagen fibres
  • Fixed within ring in temporal bone
  • Vibrates in response to sound, transmits vibrations to malleous
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32
Q

What connects the tympanic cavity to the nasopharynx?

A

Pharyngotympanic (Eustachian) tube

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33
Q

Tensor tympani

A
  • Small muscle of middle ear
  • Originates from pharyngotympanic tube + greater wing of sphenoid bone
  • Inserts into malleus, works w/ stapedius to tense tympanic membrane (response to abrupt noise - in anticipation of loud vocalisation)
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34
Q

Stapedius

A
  • Small muscle of middle ear
  • Attached to temporal bone + neck of the stapes
  • Dampens vibrations of ossicles - contracts in response to high intensity sounds
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35
Q

What is the function of the Eustachian tube?

A

Allows equalisation of pressure between tympanic cavity and the local barometric pressure

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36
Q

List the parts of the cochlea

A
  • Bony labyrinth
  • Scala vestibuli
  • Scala tympani
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37
Q

Bony labyrinth of the cochlea

A
  • Tube of bone coiled around a central pillar (modiolus)
  • Resembles a snail shell
  • Between bony + membranous labyrinth = 2 fluid filled spaces - scala vestibuli + scala tympani
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38
Q

Scala vestibuli of the cochlea

A
  • Upper triangular canal
  • Bound by roof of bony cochlea above and vestibular membrane below
  • Passes through entire length of cochlea
  • Oval window at base of canal - connects to tympanic cavity
  • Helicotrema joins scala vestibuli to scala tympani
  • Contains perilymph - maintained by secretory epithelial cells lining the canal
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39
Q

Scala tympani of the cochlea

A
  • Lower triangular canal - space beneath basilar membrane
  • Passes entire length of cochlea
  • Round window at base - connects it to tympanic cavity
  • Helicotrema joins it to scala vestibuli
  • Contains perilymph
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40
Q

Membraneous labyrinth of inner ear

A
  • Coiled tube containing cochlear duct (or scala media)
  • Cochlear duct (scala media) - middle triangular canal, houses organ of corti
  • Roof = vestibular membrane
  • Floor = basilar membrane
  • Blind tube, ductus reuniens is only outlet, connects it to saccule
  • Contains endolymph
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41
Q

Vestibule of inner ear

A
  • Central part of bony labyrinth
  • Contains oval window in lateral wall
  • Connects inner ear w/ middle ear
  • Supports membraneous saccule + utricle within it - contain endolymph + some of the mechanoreceptors responsible from balance
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42
Q

Describe the microanatomy of the cochlear duct

A
  • Modiolus - cone-like central pillar of bone, forms centre of bony labyrinth which spiral canal of cochlea runs around, contains spiral ganglia of vestibulocochlear nerve (CN VIII) in Rosenthal’s cavitus
  • Vestibular membrane - thin transparent membrane which separates cochlear duct from scala vestibuli
  • Basilar membrane - supports organ of Corti, separates cochlear duct from scala tympani
  • Spiral ganglion - in modiolus, contains cell bodues of cochlear branch of vestibulocochlear nerve (VIII), supplies hair cells of organ of Corti
  • Cochlear nerve - branch of vestibulocochlear nerve (VIII), fibres pass from hair cells of organ of Corti, through the modiolus as spiral ganglia, continuous onto internal auditory meatus
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43
Q

Describe the structure of the organ of Corti

A
  • Sensory epithelium on top of the basilar membrane
  • Hair cells = sensory transducers of organ of Corti, rest on basilar membrane w/ their stereocillia (hairs) embedded in the underside of the tectorial membrane
  • Two layers - outer (3/4 rows) + inner (1 row), separated by rows of supporting cells
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44
Q

Inner hair cells

A
  • Pear-shaped
  • Curve slightly towards surface of organ of Corti
  • Not much movement in response to vibrations - due to position on basilar membrane
  • Each inner hair cell has 3/4 rows of stereocillia - make contact w/ tectorial membrane
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45
Q

Describe the function of inner hair cells

A
  • Sensory tranducers - mechanical energy -> neural energy

- Detect + send signals to brain - info about amplitude and frequency of sound waves

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46
Q

Outer hair cells

A
  • Long, cylindrical cells - twice as tall as inner hair cells
  • Arranged by size in a gradient - outermost and closest to apex = tallest
  • Each has flat apical surface - 3 rows of stereocillia protrude through
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47
Q

Describe the function of outer hair cells

A
  • Key to high sensitivity + sharp tuning ability of organ of Corti
  • When stereocillia are displaced, entire cell shortens and elongates causing displacement of stereocillia
  • Outer hair cells then push up against tectorial membrane amplifying the vibrations felt by the basilar membrane at specific points - enabling us to hear quieter sounds
48
Q

Stereocillia of hair cells

A
  • ‘Hairs’
  • Membrane-bound cellular projections of inner + outer hair cells
  • Arranged in unique patterns on apical surface of both types of hair cells
  • Vital role in sound transduction
  • Protrude through hair cell’s reticular membrane, point towards the tectorial membrane above - only tallest make contact w/ tectorial membrane
49
Q

Describe the function of stereocillia of hair cells

A
  • Bend forwards and backwards in response to shearing force created by movement of tectorial and basilar membranes - also created streaming movement in surrounding fluid
  • Movements cause stereocillia to depolarise - sending info to rest of hair cell - mechanical energy -> neural signal
50
Q

Tectorial membrane

A
  • Semi-transparent, fibrogelatinous structure that overlies the hair cells of organ of Corti
  • Indented by stereocillia of outer hair cells in a W or V shaped pattern along Hensen’s striped
51
Q

Describe the function of the tectorial membrane

A
  • Purely mechanical role
  • Withstands mechanical stresses of cochlear fluid vibrations
  • As basilar membrane moves in response to sound waves from middle ear, shearing forces move stereocillia + depolarises them causing neural signals to be sent to the brain
52
Q

Describe the function of the supporting cells of the organ of corti

A

Series of specialised epithelial cells that provide mechanical support to sensory cells they surround

53
Q

Describe the steps involved in hearing

A
  1. Auditory transmission
  2. Auditory transduction
  3. Auditory pathway
54
Q

Define sound waves

A

Oscillations of pressure in a medium (air or liquid)

55
Q

Describe the path of sound waves during auditory transmission

A
  1. External sound waves
  2. Auricle
  3. External acoustic meatus
  4. Tympanic membrane (vibration)
  5. Malleus
  6. Incus
  7. Stapes
  8. Membrane covering oval window
  9. Cochlea
  10. Scala vestibuli (perilymph)

Cochlear duct (endolymph), separated by vestibular + basilar membrane

  1. Scala tympani (perilymph)
  2. Round window
56
Q

Describe the transmission of sound in the inner ear and how sound transduction is initiatied

A
  1. Vestibular membrane vibrates in response to pressure waves travelling up perilymph of the scala vestibuli
  2. Vibration transmitted through endolymph to the basilar membrane
  3. When basilar membrane vibrates stereocillia on organ of corti move against tectorial membrane
  4. Movement of hair cells initiates sound waves -> electrical impulses (sound transduction)
57
Q

What structures is responsible for the conversion of sound waves -> electrical impulses?

A

Inner hair cells of the organ of Corti

58
Q

How do hair cells cause sound transduction?

A
  1. At apex of each stereocillia is a mechanically-gated ion channel, connected to taller neighbouring stereocillium by a tip-link protein
  2. Displacement of stereocillia increases tension on the tip-link protein, opening the mechanically gated ion channels
  3. Cations flood into inner hair cells, depolarising them
  4. This causes voltage-gated calcium channels to open and calcium ions to enter the inner hair cells
  5. Increase in calcium ion levels cause the release of of a neurotransmitter from the base of the inner hair cells
  6. Neurotransmitter stimulates afferent neurons innervating the inner hair cells to fire action potentials, which are conveyed via the vestibulocochlear nerve to the brain
  7. Basilar membrane moves downwards, it displaces stereocillia in the opposite direction
  8. Reduces tension on the tip-link proteins, mechanically-gated ion channels close
  9. Cations can no longer enter the inner hair cell - become hyperpolarised
  10. Voltage-gated calcium channels close, calcium doesn’t enter the inner hair cell, stop releasing neurotransmitter
59
Q

How are different frequencies and amplitudes of sounds detected?

A

Different frequencies of sound make different regions of the basilar membrane vibrate and different amplitudes of sound make the basilar membrane vibrate at different intensities

60
Q

List the steps in the auditory pathway

A
  1. Hair cells
  2. Spiral ganglia
  3. Vestibulocochlear nerve: cochlear branch
  4. Cochlear nucleus
  5. Lateral lemniscus
  6. Superior olivary nucleus
  7. Inferior collicus
  8. Medial geniculate nucleus
  9. Primary auditory cortex
61
Q

Where does thermoregulation occur, and where are thermoreceptors located?

A

Thermoregulatory centre in the hypothalamus -

  1. Thermoreceptors in hypothalamus monitor temp. of blood through brain (core temp.)
  2. Thermoreceptors in the skin (esp. on trunk) monitor the external temp.
62
Q

Describe how homeostasis would be achieved following a drop in body temperature

A
  • Heat conservation centre in hypothalamus stimulated
  • Skeletal muscles activated - shivering
  • Blood vessels in skin constrict - divert blood from skin to core, reducing heat loss from skin surface
  • Body temp. increases
  • Heat conservation centre ‘shut off’
63
Q

Describe how homeostasis would be achieved following a rise in body temperature

A
  • Heat loss centre in hypothalamus activated
  • Blood vessels in skin dilate - heat lost from skin surface
  • Sweat glands activated - evaporative cooling
  • Body temp. decreases
  • Heat loss centre ‘shut off’
64
Q

List the effectors involved with thermoregulation

A
  • Smooth muscles in arterioles in skin
  • Sweat (eccrine) glands
  • Errector pilli muscles in skin (attached to hairs)
  • Skeletal muscles
  • Adrenal and thyroid glands
65
Q

Describe the stimulation of smooth muscles in arterioles in skin in response to

a) Low temp.
b) High temp.

A

a) Vasoconstriction. Less heat lost from surface of body, maintains core temp. Extremities turn blue and feel cold
b) Vasodilation. More heat carried from core -> surface of skin. Lost by convection and radiation. Skin turns red.

66
Q

Describe the stimulation of the sweat glands in response to

a) Low temp.
b) High temp.

A

a) No sweat produced

b) Glands secrete sweat onto surface of skin - evaporates, causing heat loss

67
Q

Describe the stimulation of erector pilli muscles in the skin in response to

a) Low temp.
b) High temp.

A

a) Muscles contract, raising hairs and trapping an insulating layer of warm air. Causes goosebumps.
b) Muscles relax, lowering hairs and allowing air to circulate over the skin, encouraging convection and evaporation

68
Q

Describe the stimulation of skeletal muscles in response to

a) Low temp.
b) High temp.

A

a) Shivering - muscles contract and relax repeatedly generating heat by friction + metabolic reactions
b) No shivering

69
Q

Describe the stimulation of the adrenal and thyroid glands in response to

a) Low temp.
b) High temp.

A

a) Glands secrete adrenaline + thyroxine - increase metabolic rate in different tissues, esp. liver
b) Glands stop secreting adrenaline + thyroxine

70
Q

Define fever

A

Body temperature >38 degrees

71
Q

List the pathological causes of fever

A
  1. Infection
  2. Neurological conditions
  3. Cancer
  4. Dehydration
  5. Pulmonary embolism
  6. After transfusion of incompatible blood
72
Q

Describe the cause of fever

A
  • Pyrogens
  • Phagocytes secrete cytokines:
    1. IL-1, IL-6, tumour necrosis factor alpha (TNF-alpha)
    2. Reach hypothalamus via circumventricular organs adjacent to 3rd ventricle where blood-brain barrier is relatively permeable to large molecules
    3. Increased production of prostaglandin E2 - acts on neurones in preoptic area to initiate febrile response
73
Q

Describe the febrile response

A
  • Heat conserved inappropriately through thermoregulatory responses of body
  • Increased temperature but feel cold + shiver + peripheral vasoconstriction
  • When PGE2 synthesis returns to normal, set point returns to normal, patient feels hot - peripheral vasodilation + sweating occur
  • Kills bacteria, inhibits viruses
74
Q

Define otitis media

A
  • Middle ear infection
  • Presence of inflammation in middle ear associated with an effusion, accompanied by rapid onset of symptoms of ear infection
  • Causes by viruses/bacteria
  • Very common in children
75
Q

List the risk factors associated with otitis media

A
  • Children
  • Especially those exposed to passive smoking, attend nursery etc., are formula fed, have craniofacial abnormalities (Down syndrome or cleft palate)
  • More common in males than females
76
Q

List the complications of otitis media

A
  • Recurrence of infection
  • Hearing loss
  • Tympanic membrane perforation
  • Mastoiditis
  • Meningitis
  • Intercranial abscess
  • Sinus thrombosis
  • Facial nerve paralysis
77
Q

List the symptoms associated with otitis media

A
  • Earache
  • Younger children - pull/rub ear, irritability, crying, poor feeding, restlessness at night
  • Rhinorrhoea (runny nose)
  • Fever
  • Tympanic membrane - red/yellow + cloudy + bulging
  • Air/fluid level behind tympanic membrane
  • Perforation of tympanic membrane and/or discharge in external auditory meatus
78
Q

Describe the the treatment of otitis media

A

Admit for immediate paediatric/specialist assessment:

  • Children <3 months, >38 degree temp.
  • Adults/children w/ suspected acute complications e.g. meningitis, mastoiditis or facial nerve paralysis

Other treatment:

  • Treat pain + fever w/ paracetamol or NSAIDs e.g. ibuprofen
  • No antibiotic or delayed antibiotic prescribing (majority viral)
  • Antibiotics - systemically unwell, high risk of serious complications, immunocompromised, symptoms last more than 4 days
  • Long-term - hearing aids, grommets, adenoidectomy
79
Q

How are grommets used in the treatment of otitis media?

A

Tubes inserted to drain fluid + keep eardrum open

80
Q

Describe the use of paracetamol

A
  • Commonly used for its analgesic and antipyretic effects
  • Lacks anti-inflammatory, anti-platelet + gastric ulcerative effects
  • Used for the relief of fever, headaches and other minor aches + pains
81
Q

Paracetamol

A
  • Acetaminophen
  • Extremely safe in standard doses, deliberate or accidental overdoses not uncommon
  • No problems w/ addiction, dependence, tolerance or withdrawal
82
Q

Describe the mechanism of action of paracetamol

A
  • Primarily in CNS
  • Increases pain threshold by inhibiting both isoforms of cyclooxygenase, COX-1, COX-2 and COX-3 enzymes involved in prostaglandin synthesis
  • Doesn’t inhibit cyclooxygenase in peripheral tissue so has no peripheral anti-inflammatory effects
  • Reduces fever by affecting hypothalamic heat-regulating centre
83
Q

Define pyrogens

A
  • Substance which induces fever

- Can be either internal (endogenous) or external (exogenous) to the body

84
Q

Endogenous pyrogens

A
  • Cytokines produced by activated immune cells
  • Cause increase in the thermoregulatory set point in the hypothalamus
  • Main endogenous pyrogens = interleukin 1 (alpha and beta) and interleukin 6
  • Also - IL-8, tumour necrosis factor-beta/alpha, macrophage inflammatory protein-alpha/beta and interferon alpha/beta/gamma
  • Secreted into the circulation, migrate to the circumventricular organs of the brain due to easier absorption caused by blood-brain barrier’s reduced filtration action there
  • Cytokines then bind with endothelial receptors on vessel walls or interact with local microglial cells
  • When they bind, the arachidonic acid pathway is activated
85
Q

Exogenous pyrogens

A
  • Cause the release of endogenous cytokine pyrogens, which activate the arachidonic acid pathway
  • Immunological protein called lipopolysaccharide-binding protein (LBP) binds to LPS (lipopoysaccharide) which is a cell wall component of gram-negative bacteria
  • LBP-LPS complex binds to CD14 receptor of machrophage, results in synthesis and release of various endogenous cytokine factors e.g. IL-1, IL-6 and TNF-alpha
86
Q

Describe the arachidonic acid pathway involved in the febrile response

A

The enzymes cyclooxygenase-1 and 2, phospholipase A2 and prostaglandin E2 synthase metabolise arachidonic acid to prostaglandin G2 and H2 which may be converted to various prostaglandins - e.g. PGE2

87
Q

Describe the role of PGE2 in the febrile response

A
  • Ultimate mediator of the febrile response
  • Set point temperature of the body will remain elevated until PEG2 is no longer present
  • Acts on neurones in the preoptic area through the prostaglandin E receptor 3
  • EP3-expressing neurones in the POA innervate the dorsomedial hypothalamus, the rostral raphe pallidus nucleus in the medulla oblongata and the paraventricular nucleus of the hypothalamis
  • Fever signals sent to these areas lead to stimulation of the sympathetic output system - causes thermogenesis
88
Q

Describe the ways in which fever can be useful

A
  • Some important immunological reactions sped up by temperature
  • Pathogens w/ strict temperature preferences could be hindered
  • Increased mobility of leukocytes
  • Enhanced leukocyte phagocytosis
  • Endotoxin effects decreased
  • Increased proliferation of T cells
89
Q

Define NEWS

A

National early warning score:

  • Bedside score and tirck and trigger system which staff calculate from routinely collected physiological observations
  • Aims to detect early signs of patients’ deterioration and prompts more timely medical review and treatment of patients duet to the inbuilt escalation protocol
  • Does not replace clinical concern for the patients
  • Does not apply to patients in the paediatric or obstetric departments
90
Q

List the physiological parameters included in the NEWS

A
  1. Respiratory rate
  2. Oxygen saturations
  3. Temperature
  4. Systolic blood pressure
  5. Pulse rate
  6. Level of consciousness
91
Q

Define vital signs

A

A vital sign is a sign that pertains to life, without which life would not exist - respiratory rate, pulse, blood pressure and temperature. Changes in these reflect an increased risk of death, hence the importance of detecting, observing and recording these vital signs early, thereby allowing staff to deliver timely treatment and normalise these vital signs.

92
Q

Describe how consciousness level is measured

A

2 Types :

  • AVPU
  • Glasgow coma scale
93
Q

Describe the AVPU scale

A 
A = the patient is awake 
V = the patient responds to verbal stimulation
P = the patient responds to painful stimulation U = the patient is completely unresponsive
94
Q

Describe the Glasgow coma scale

A
  • Eyes:
    1. Does not open eyes
    2. Opens eyes to painful stimuli
    3. Opens eyes in response to voice
    4. Opens eyes spontaneously
  • Verbal:
    1. Makes no sounds
    2. Incomprehensible sounds
    3. Utters incoherent words
    4. Confused, disoriented
    5. Oriented, converses normally
  • Motor:
    1. Makes no movements
    2. Extension to painful stimuli
    3. Abnormal flexion to painful stimuli
    4. Flexion/withdrawal to painful stimuli
    5. Localises to painful stimuli
    6. Obeys commands
95
Q

Describe the structure and function of the sclera

A
  • White of eye
  • Avascular
  • Limits light entering eye, supports shape of eyeball
96
Q

Describe the structure and function of the cornea

A
  • Transparent dome over anterior of eye

- Refracts light towards pupil

97
Q

Describe the structure and function of the choroid

A
  • Layer of blood and and lymphatic vessels
  • Blood vessels supply nutrients to eye
  • Lymphatic vessels drain fluid from posterior cavity
98
Q

Describe the structure and function of the ciliary body

A
  • Anterior part of choroid, posterior to iris
  • Smooth muscle forming ring around lens
  • Has suspensory ligaments attached which change shape of lens
99
Q

Describe the structure and function of the iris

A
  • Two pigmented rings of smooth muscle (pupillary constrictor and pupillary dilator)
  • Forms the pupil at its centre, changes diameter of pupil
100
Q

Describe the structure and function of the retina

A
  • 10 layers of neural, epithelial and supporting cells
  • Contains rod and cone cells
  • Light is detected by rod and cone cells and converted into a neural signal
101
Q

Describe the structure and function of the optic nerve

A
  • Cranial nerve II
  • Passes from back of eyeball and enters the middle cranial fossa of the skull via the optic canal in the sphenoid bone
  • The optic nerves from each eye cross at the optic chiasma and pass posteriorly to visual structures in the brain
  • Relays the neural signal from the eye to the brain where it is processed
102
Q

Describe the structure and function of the aqueous humour

A
  • Clear, watery fluid

- Maintains the intraocular pressure and provides nutrients to the cornea and sclera

103
Q

Describe the structure and function of the lens

A
  • Transparent, avascular elliptical structure

- Refracts light onto the focal point on the retina

104
Q

Describe the structure and function of the vitreous body

A
  • Gelatinous mass of collagen and proteoglycans

- Supports the shape of the eye

105
Q

Describe the path of light through the eye

A

Light hits the eye and passes through the cornea, which refracts it towards the pupil. The lens refracts light so that it is focussed onto the retina. Suspensory ligaments of the ciliary body can change the curvature of the lens so that light reaches a focal point on the retina.

106
Q

What is responsible for the conversion of optical images into a neural signal?

A

Photoreceptors in rod and cone cells in the retina

107
Q

Describe the structure and function of rod cells

A
  • Contain the photopigment rhodopsin

- Sensitive to low light and provide black and white vision

108
Q

Describe the structure and function of cone cells

A
  • 3 types - blue, green and red
  • Provide colour vision
  • Sensitive to high light levels
  • Contain the photopigment photopsin
109
Q

Describe the structure and function of photopigments

A
  • Composed of retinal and opsin
  • Opsins determine the wavelength of light that a photopigment can absorb
  • Rod cells only have one type of opsin, cones have three types
  • Retinal is the light-absorbing part of the photopigment derived from vitamin A
  • Two form of retinal - trans-retinal and cis-retinal
110
Q

Describe visual processing

A
  • Rod and cone cells absorb light, which changes the shape of their photopigments
  • Retinal changes rom cis-retinal to trans-retinal in a process called isomerisation
  • This leads to generation of a receptor potential
  • In darkness, sodium ions flow into the outer segments of the photoreceptors through channels gated by the ligand cyclic guanosine monophosphate (cGMP)
  • This inflow partially depolarises the photoreceptor, stimulating the release of glutamate, an inhibitory neurotransmitter
  • Glutamate hyperpolarises bipolar cells so they do not send neural signals to ganglion cells
  • When the retina absorbs light, enzymes which break down cGMP are activated, decreasing the inflow of sodium ions and glutamate released
  • This produces a neural signal in bipolar cells, which passes through ganglion cells and the optic nerve to the primary visual cortex in the brain where the information is processed
111
Q

Define tunnel vision

A

Condition which occurs when there is a deterioration of complete loss of peripheral vision. Caused by several diseases.

112
Q

List the causes of tunnel vision

A
  1. Damage to the optic nerve
  2. Damage to the brain
  3. Damage to the retina
  4. Temporary loss of peripheral vision
113
Q

Give an example of a condition which causes tunnel vision due to damage to the optic nerve

A

Glaucoma:

  • Common eye disease
  • Damage to optic nerve occurs through increased intraocular pressure
  • Normal IOP = 10-21mmHg, glaucoma can increase to 70mmHg
  • Two types - primary open angle glaucoma and acute angle-closure glaucoma
  • Primary open angle glaucoma causes gradual, painless loss of peripheral vision and is treated through reducing the IOP by reducing the aqueous production or increasing its drainage
  • Acute angle-closure glaucoma is an ophthalmic emergency in which the IOP suddenly increases to over 50mmHg
114
Q

Give an example of a condition which causes tunnel vision due to damage to the retina

A

Retinitis pigmentosa:

  • Common, inherited degenerative disease of the retina
  • Can lead to tunnel vision
  • No treatment - Vitamin A supplementation may slow the progression
115
Q

Give an example of a condition which causes tunnel vision due to damage to the brain

A

Stroke:
A stroke may damage parts of the brain where images are processed which causes scotomas (an area of alteration in field vision where vision is partially diminished or entirely degenerated)

116
Q

Describe the causes of temporary loss of peripheral vision

A

High levels of adrenaline (due to high stress, anxiety or anger) can cause temporary tunnel vision. Drugs and alcohol may also cause tunnel vision. Normal vision will usually return without treatment.

Medicine YEAR 1 (18 decks)

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