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Clinical Neuroscience > Somatosensory Pathways > Flashcards

Somatosensory Pathways Flashcards

1
Q

What are the classifications of sensation?

A
  • General sensation > somatic + visercal
  • Special sensation
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2
Q

What are the types of general sensation?

A

Visceral - unconscious
Somatic - conscious

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3
Q

What are the special senses?

A

Vision
Hearing
Balance
Taste
Smell

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4
Q

What are modalities?

A

Units of sensation relying on a distinct receptor type
Part of somatic sensation

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5
Q

What are the types of modalities?

A
  • Spinothalamic system:
    -temperature
    -pain
    -pressure/crude touch
    .
  • Dorsal column-medial lemniscus system:
    -vibrations
    -proprioception
    -fine touch
    -two point discrimination
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6
Q

What is two point discrimination?

A

The ability to distinguish between two nearby objects touching the skin as two distinct points, not one

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7
Q

What modalities are part of the spinothalamic system?
What are the associated receptors?

A

Temperature thermoreceptors
Pain nociceptors
Pressure/crude touch mechanoreceptors

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8
Q

What modalities are part of the dorsal column-medial lemniscus system?
What are the associated receptors?

A
  • Vibration mechanoreceptors
  • Proprioception muscle spindles + Golgi tendon organs
  • Fine touch mechanoreceptors
  • Two point discrimination mechanoreceptors
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9
Q

Location of the cell body of first order neurones

A

Dorsal root ganglion

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10
Q

Location of the cell body of second order neurones

A

Dorsal horn - spinothalamic pathway
Medulla - dorsal column

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11
Q

Location of the cell body of third order neurones

A

Thalamus

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12
Q

Difference in strong and weak receptor activation

A
  • Strong receptor activation > high frequency AP
  • Weak receptor activation > low frequency AP
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13
Q

Difference between rapidly + slowly adapting receptors
Examples

A
  • rapidly adapting receptors: frequency of firing diminishes rapidly e.g. mechanoreceptors
  • slowly adapting receptors: frequency of firing changes very little e.g. nociceptors
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14
Q

What difference between large and small receptive fields?
Examples of a location for each

A
  • large receptive field: low sensory acuity/poor 2 point discrimination e.g. skin on back
  • small receptive field: high sensory acuity/good 2 point discrimination e.g. skin on fingertips
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15
Q

What is the function of somatotropy representation?

A
  • This way of organisation minimises the amount of ‘wiring’ required to transmit sensory information
  • Dermatome modalities converge on the way to the homunculus
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16
Q

Describe the layout of the dorsal column-medial lemniscus system

A
  • 1st order neurones ascend ipsilaterally through dorsal columns of spinal cord:
    -lower body ascend through gracile fasciculus to gracile nucleus in medulla
    -upper body ascend through cuneate fasciculus to cuneate nucleus in medulla
    -lower body is more medial than upper body
  • 2nd order neurones decussate to thalamus in medial lemniscus
  • 3rd order neurones > primary sensory cortex:
    -lower body to medial portion
    -upper body to lateral portion
17
Q

Topographical organisation of the dorsal columns

A

Lower body - medial
Upper body - lateral

18
Q

What effect could a central lesion of the spinal cord do in relation to dorsal column medial lemniscus system?

A

Affects dorsal column modalities radiating up the body:
-fine touch
-two point discrimination
-proprioception
-vibration

19
Q

What is syringomelia?

A

Disorder characterised by development of syrinx in central canal > effects sphinothalamic modalities decussated in white ventral commissure

20
Q

What spinal levels correspond to the upper vs lower body?

A

upper - T6 + above
lower - T7 + below

21
Q

Describe the first order neurones ascent in the dorsal column

A

Ascend ipsilaterally to medulla
- lower body: up through gracile fasciculus to gracile nucleus
- upper body: up through cuneate fasciculus to cuneate nucleus

22
Q

Describe the connection of 3rd order neurones of the upper vs lower body to the primary sensory cortex

A

upper body to lateral portion
lower body to medial portion

23
Q

Describe the layout of the spinothalamic pathway

A
  • 1st order neurones project to ipsilateral side of cord
  • 2nd order cell bodies are in dorsal horn
  • 2nd order cells decussate at ventral white commissure > form spinothalamic tract > to thalamus
  • 3rd order neurones > primary sensory cortex:
    -lower body to lateral portion
    -upper body to medial portion
24
Q

Outline Brown-Sequard syndrome

A

Lesion to one half of the spinal cord > unilaterally completely destroying:
- dorsal + ventral horn
- dorsal + ventral roots
- all other cord grey matter
- all white matter pathways
.
This causes:
- ipsilateral complete anaesthesia affecting single dermatome (destruction of dorsal structure)
- ipsilateral loss of dorsal column modalities below
- contralateral loss of spinothalamic modalities below

25
Q

What does brown sequard syndrome cause?

A
  • ipsilateral complete anaesthesia affecting single dermatome (destruction of dorsal structure)
  • ipsilateral loss of dorsal column modalities below
  • contralateral loss of spinothalamic modalities below
26
Q

Outline Lissauer’s tract

A

1st order neurones can ascend a couple spinal cord levels in Lissauer’s trac before synapsing to 2nd order neurones in the dorsal horn

27
Q

Why does rubbing a sore area relieve pain?

A

Rubbing a sore area activates encephalinergic interneurones > encephalins release > inhibits Nociceptors > reduced pain

28
Q

What effect could a central lesion of the spinal cord do in relation to spinothalamic system?

A

Affects the spinothalamic modailites radiating down the body:
-pain
-pressure/crude touch
-temperature

29
Q

What is a syrinx?

A

Fusiform cyst

30
Q

What is the most common location affected by syringomelia?

A

Cervical region of central canal

31
Q

What are the initial symptoms of syringomelia?

A
  • damage to Spinothalamic pathway
  • loss of sensitivity to pain + thermal stimuli
  • preserved sensitivity to touch + proprioception

Clinical Neuroscience (20 decks)

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