The sensory system

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The sensory system

• Vth year 2002/2003

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The sensory system

• Spinothalamic system (tractus spinothalamicus)
  exteroceptive sensation) pain
• temperature
• light touch
• Dorsal column pathway ( lemniscus medialis)
  conscious proprioception joint position
• vibration
• deep pressure
• two point discrimination
• graphaesthesia, stereoaesthesia
  
• Dorsal and ventral spinocerebellar pathway
  unconscious proprioception

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Spinothalamic system

• Pain perception
• C fibers thin, unmyelinated
• A delta thinly myelinated
• Temperature
• A delta thinly myelinated

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Dorsal column pathway/lemniscus medialis
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Spinal cord pathways - somatotopia
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Segmental innervation (dermatomes)Peripheral
innervation
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Sensory disturbances

• Positive symptoms
• Pain
• Hyperalgesia when threshold to pain appears
  lowered
• Hyperpathia pain threshold elevated, but once
  reached, the painful stimulus is
  excessively felt
• Hyperaesthesia
• Paraesthesiapins and needles sensation,burning
  feeling
• Dysaesthesia/allodynia when touching is painful
• Neuralgia
• Causalgia spontaneous burning sensation in the
  distribution of the injured nerve with
  increased sensitivity to painful stimuli
  (efferent sympathetic fibers link up to
  afferent somatic fibers ?)
• Phantom limb pain

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Sensory disturbances

• negative symptoms
• Hypaesthesia decreased sensation
• Anaesthesia loss of feeling

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Examination of the sensory system 1.

• Special standpoints
• Subjective examination
• Requires good cooperation on the patients side.
• Allows accurate localisation of the pathology.
• Preliminary diagnosis is needed. Examine
  according to the expected damage !
• Most often we compare different parts of the
  body.
• Do not tell the patient what should be felt !
• The patient should not see the examined part of
  the body !
• Subjective sensory disturbance ( pain,
  paraesthesia ) is not necessarily accompanied by
  objective sensory disturbance (hypaesthesia,
  anaesthesia )

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Examination of the sensory system 2.

• Pain pin prick, tooth picks
• Light touch use a wisp of cotton wool !
• Temperature use a cold (5-10 0C) or a hot (40-45
  0C object (test tubes) ! Depends on the
  duration of the stimulus, size of the
  surface of contact.
• Examine the patient with his/her eyes closed !
• Instruct the patient to reply
• Tell me if you feel the stimulus ! Name the
  area stimulated ! State the nature of the
  stimulus ! What do you feel?
• Is it equal on both sides? What is the
  difference ?
• Map out the extent of abnormality !
• Move from the abnormal to the normal area (Tell
  me if sensation changes!)
• Pin must be discarded after single use

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Examination of the sensory system 3.

• Joint position / motion
• - Hold the sides of the patients finger !
• - Move it up and down at random !
• - Ask to specify the direction of movement !
• - Normal individual is able to detect movement
  of 1 2 0 at the interphalangeal joints
• - If these senses are lost in the digits examine
  joints further up (wrist, elbow) !
• - Note the promptness or the hesitation of the
  response !
• - Disturbance of deep sensation are accompanied
  by abnormal movements ( pseudoathetosis, ataxia )
  especially with closed eyes.

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Examination of the sensory system 4.

• Vibration
• - Place a vibrating tuning fork on a bony
  prominence ( ankle, knee, processus spinosus,
  processus styloideus radii et ulnae, elbow,
  clavicula)
• - lt 128 c/s
• - Ask the patient to indicate when the vibration
  ceases !
• - If impaired, move more proximally and repeat !
• - Vibration sense does not necessarily change
  parallel with joint position sense.
• - Patients may use different words for the
  description of the vibration (shaking,
  tingling, itching)

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Examination of the sensory system 5.

• Two point discrimination
• -The ability to discriminate two blunt points
  when applied simultaneously.
• -3-5 mm on the finger, 4-7 cm on the trunk
• Sensory inattention (perceptual rivalry)
• -The ability to detect sensory stimuli applied
  simultaneously on both limbs.
• -Subdominant parietal lobe, associative areas
• Stereoaesthesia
• - An object is placed in the patients hand.
• - Ask patient to describe its size, shape,
  surface, material !
• - Stereoanaesthesiadisturbance of the sensory
  afferent tracts.

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Examination of the sensory system 6.

• Astereognosis
• -Inability to identify an object by palpation
• -The primary sense data being intact
• -Lesion of the opposite hemisphere,
  postcentral gyrus
• Tactile agnosia
• -The patient is unable to recognize an object
  by touch in both
• hands
• -Disorder of perception of symbols.
• -Lesion of the dominant parietal lobe,
  associative areas
• Graphaesthesia
• - The ability to recognize numbers of letters
  traced out
• on the palm.

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Examination of the sensory system

• Nerve conduction studies
• sensory antidrom neurography
• median nerve, ulnar nerve
• Somatosensory evoked potentials (SEP)
• median nerve, tibial nerve

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Sensory syndromes 1.

• Peripheral nerve
• according to the distribution area of the
  affected nerve
• Polyneuropathy
• glove stocking distribution,
• more pronaunced distaly, more on the lower
  extremities
• Dorsal root ganglia or radicular laesions
• segmental, localised to dermatomes

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Sensory syndromes 2.

• Spinal cord
• -complete cord lesion
• -hemisection of spinal cord Brown Sequard
  syndrome
• -central cord lesion (Syringomyelia, dissociated
  sensory loss
• loss of pain and temperature, preservation
  of proprioception)
• -posterior tract lesion (funicular myelosis
  loss of
• proprioception, ataxia)
• -conus laesion (sensory loss of sacral area,
  saddle
• anaesthesia)
• Brain stem Wallenberg syndrome
• Thalamus Dejerine Roussy syndrome
  (contralateral hemihypaesthesia, ataxia, pain)
• Sensory cortex contralateral hemihypaesthesia

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Sensory syndromes spinal ganglion
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Sensory syndromes funicular myelosis
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Sensory syndromes
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Sensory syndromes
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Sensory syndromes
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Sensory syndromes
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Sensory syndromes visceral pain