SPR L21 Pathophysiology of Sensory Systems Flashcards Preview

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Flashcards in SPR L21 Pathophysiology of Sensory Systems Deck (25):

Learning Outcomes

Pathophysiology of...

  • hearing
  • vision 
  • somatosensory systems


Physiology of hearing

Outline the anatomy of the ear


Physiology of hearing

Outline the physiology of hearing

Central auditory pathways

  • cochlear nuclei
    • brainstem
  • inferior colliculus
    • midbrain
  • med. geniculate nuclei
    • thalamus
  • auditory cortex
    • temporal lobe


Pathophysiology of deafness

  1. How can conductive deafness occur?
  2. How can Sensorineural deafness occur?

  1. auditory canal (wax), tympanic membrane/middle ear (ruptured tympanic membrane, otitis media, otosclerosis)

  2. cochlea (ageing (presbycusis), acoustic trauma, Ménière’s disease) cochlear nerve (part of VIIIth nerve - acoustic neuroma), central auditory pathways (rare)


Pathophysiology of deafness

What can be the causes of deafness?

  • Conductive deafness
    • auditory canal
      • wax
    • tympanic membrane/middle ear
      • ruptured tympanic membrane
      • otitis media
      • otosclerosis
  • Sensorineural deafness
    • cochlea
      • ageing (presbycusis)
      • acoustic trauma
      • Ménière’s disease
    • cochlear nerve (part of VIIIth nerve)
      • acoustic neuroma
    • central auditory pathways (rare)


Pathophysiology of deafness

Describe what the following tests can show

  1. Rinne's
  2. Weber's test
  3. Audiometry

1. positive (normal) = air conduction > bone conduction

negative (conductive d.) = bone conduction > air conduction

2.  ‘lateralises’ to side of conductive deafness


  • generalised hearing loss at all frequencies in conductive d.
  • high tone hearing loss eg with aging


Physiology of vision (1)


  1. Outline the optics of vision
  2. Outline the photoreceptors involved

  1. cornea, lens (accommodation = parasympathetic), inverted retinal image, transparent light path

  2. rods = higher sensitivity, low resolution, monochromatic

    cones = lower sensitivity, high resolution, colour vision

Bipolar cells, Ganglion cells and optic nerve


Physiology of vision (2)


Outline the central visual pathways

  • optic nerves (II)
  • optic chiasm
  • optic tract
  • lat. geniculate nuclei
    • thalamus
  • optic radiation
  • visual cortex
    • occipital lobe


Assessing visual function

  1. What is a normal visual acuity?
  2. What is reduced?
  3. What is the normal level for driving?

  1. 6/6
  2. 6/>6
  3. 6/9


Assessing visual function

  1. What should Intraocular pressure be?
  2. What is this maintained by?

  1. 10-20mmHg
  2. Ciliary body and Trabecular meshwork/canal of Schlemm


Assessing the retina

Give examples of pathological changes to the retina

  • papilloedema
  • hypertensive retinopathy
  • diabetic retinopathy


Pathophysiology of vision: refractive defects

What are the following

  1. presbyopia
  2. myoptic eye
  3. hypermetrophic eye

  1. loss of elasticity, receding ‘near point’, reading glasses (convergent, convex)

  2. minimum focussing power too great for eye length, distant vision poor, divergent (concave) lenses

  3. maximum focussing power inadequate for eye length, near vision poor, convergent (convex) lenses 


Pathophysiology of vision: central visual defects

Outline defects 1-8 seen in the picture


  1. Retina: paracentral scotoma
  2. Optic nerve: monocular field loss
  3. Optic chiasm: bitemporal hemianopia
  4. Optic tract: homonymous hemianopia
  5. Optic radiation; temporal lesion: homonymous quadrantanopia (upper)
  6. Optic radiation; parietal lesion: homonymous quadrantanopia (lower)
  7. Occipital cortex or optic radiation: homonymous hemianopia with macular sparing
  8. Occipital pole: homonymous hemiscotoma


Physiology of pupillary reflexes

Pupil Responses

What are the mechanisms involved in the following?

  1. sympathetic dilatation
  2. parasympathetic constriction

  1. pre-ganglionic T1

    superior cervical ganglion

    internal carotid

    dilator pupillae (radial)

  2. pre-ganglionic IIIrd cranial n.

    ciliary ganglion

    ciliary nerves

    sphincter pupillae (circular)


Physiology of pupillary reflexes

Pupil Responses

What are the mechanisms involved in the following?

  1. light reflex: direct and consensual

  2. accommodation reflex


  1. 1. optic nerve

    2. LGB

    3. pre-tectal n.

    4. Edinger-Westphal n. (IIIrd n.)

    5. IIIrd n, ciliary g. ciliary n. to sphincter pupillae

  2. 1. & 2. as above +

    spindle afferents from extraocular muscles

    convergence centre

    4. & 5. as above


Pathophysiology of pupillary reflexes

What are the signs of Sympathetic lesion (Horner’s syndrome)

  • ipsilateral defects
  • pupillary constriction (miosis)
  • ptosis
  • enophthalmous
  • sweating loss


Pathophysiology of pupillary reflexes

What do the following indicate?

  1. Dilatation of 1 pupil: fixed to light
  2. Bilateral pupillary dilatation: fixed to light

  3. Bilateral pupillary constriction: fixed to light

  1. IIIrd nerve compression (parasympathetic loss)

    may indicate neurosurgical emergency

  2. deep coma/brain death

  3. pontine lesions





Pathophysiology of peripheral sensation 

What are the somatosensory modalities?


Give examples of sensory symptoms/signs

  • touch
  • vibration
  • joint position sense (proprioception)
  • pain
  • temperature


  • loss of sensation
    • numbness
    • clumsiness/stamping gait
    • areas of sensory loss on clinical testing (signs)
  • abnormal sensations
    • tingling/ ‘pins & needles’ (paraesthesia)
    • pain (neuralgia)


Dermatomes and somatosensory pathways

  1. What does the lateral spinothalamic tract transmit?
  2. What does the posterior column transmit?

  1. pain and temperature
  2. vibration, position, touch


Pathophysiology of peripheral sensation 

  1. In somatosensory loss, what reflectsthe site of lesion?
  2. What is involved with peripheral nerve damage?
  3. What is involved in nerve root damage?

  1. distribution and nature of defect
  2. distribution of the nerve, loss of all sensation, loss of motor activity (LMN)
  3. dermatome, loss of all sensation, ± loss of motor activity (LMN)


Pathophysiology of sensory pathways 

Outline pathology assciated with 

  1. posterior columns
  2. spinothalamic tract damage

1. ipsilateral sensory defects below site of damage

  • position sense
  • vibration sense
  • light touch

2. contralateral sensory defects below site of damage

  • pain
  • temperature
  • coarse touch


Pathophysiology of sensory pathways 

What will bilateral damage to the spinal cord give rise to? (eg transverse section)


  • total sensory loss below level of damage
  • bilateral UMN weakness below level


Pathophysiology of sensory pathways 

What will unilateral cord damage (Brown-Séquard syndrome) give rise to?


  • ipsilateral loss of proprioception, vibration, light touch
  • contralateral loss of pain, temperature, coarse touch
  • ipsilateral UMN weakness below lesion
  • LMN defect at level of lesion


Pathophysiology of sensory pathways 

  1. What will a lesion in the brainstem (eg stroke) give rise to?
  2. What wil a lesion above brainstem (eg stroke)



  • contralateral sensory defects below site of damage
  • ipsilateral loss of facial sensation
  • all sensory modalities


  • contralateral sensory defects: face and body

  • all sensory modalities


Pathophysiology of sensory pathways 


What is polyneuropathy/peripheral neuropathy?


  • symmetrical peripheral loss of sensation (glove and stocking)
  • affecting excitability/conduction in many/all nerves in region
  • may be sensory, motor and autonomic features

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