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PHYS - NEURO > 11. SOMATOSENSATION I > Flashcards

11. SOMATOSENSATION I Flashcards

1
Q

What sensations does the somatosensory system detect?

A

Somatic sensations:

  1. Touch
  2. Proprioception (orientation, location etc.)
  3. Pain (Nociception), itch
  4. Temperature
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2
Q

What is the primary somatosensory cortex?

A
  • The primary somatosensory cortex is involved with processing somatic information from receptors
  • It consists of Brodman areas 1, 2, 3a & 3b
  • It is located in the post central gyrus & lateral to the central sulccus
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3
Q

What do the dorsal roots contain?

A
  • Sensory afferents
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4
Q

What do the ventral roots contain?

A
  • Motor afferents
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5
Q

What does the dorsal root ganglion contain?

A
  • Cell bodies of the sensory neurones of the somatosensory system
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6
Q

What do the dorsal ventral roots combine to form?

A
  • Mixed spinal nerve
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7
Q

What are the two main classes of fibres of the somatosensory system?

A
  1. LARGE FIBRES - TACTILE & PROPRIOCEPTIVE
    - large diameter, myelinated, fast conduction
  2. SMALL FIBRES - PAIN, ITCH, CRUDE TOUCH
    - small diameter, myelinated or unmyelinated, slow or medium conduction
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8
Q

Why is afferent fibre type important?

A
  • The quality & type of sensation depends on the afferent fibre type
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9
Q

What are the 4 sensory afferents?

A
  1. A alpha fibres
  2. A beta fibres
  3. A delta fibres
  4. C fibres
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10
Q

What are the characteristics of A alpha afferents?

A
  • Largest diameter
  • Myelinated
  • Fastest conduction velocity > 100m/s
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11
Q

What do A alpha afferents detect?

A
  • Proprioception
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12
Q

What do A beta afferents detect?

A
  • Tactile afferents/discrimination

- Discriminative touch

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13
Q

What are the characteristics of A beta afferents?

A
  • Large diameter
  • Myelinated
  • 2nd fastest conduction velocity (30 -70m/s)
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14
Q

What afferents are cutaneous receptors?

A
  • Cutaneous receptors are A beta afferents
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15
Q

What are the 4 types of cutaneous receptor?

A
  1. MERKEL’S DISCS
  2. MEISSNER’S DISCS
  3. RUFFINI CORPUSCLES
  4. PACINIAN ENDINGS
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16
Q

Which cutaneous receptors are superficial?

A
  • Merkel’s discs

- Meissner’s corpuscles

17
Q

Which cutaneous receptors are deep?

A
  • Ruffini corpuscles

- Pacinian endings

18
Q

What are the characteristics of the Merkel’s discs?

A
  • High spatial resolution
  • Fine tactile discrimination
  • Detect texture & shape
19
Q

What are the characteristics of Meissner’s corpuscles?

A
  • Lower spatial resolution than Merkel’s discs

- But can still detect discriminative touch

20
Q

What are the characteristics of Pacinian endings & Ruffini corpuscles?

A
  • Less spatial resolution
  • Can respond to stretch so are better for grip, texture, vibration
  • Pacinian = Vibration
  • Ruffini = Slipping or non-slipping
21
Q

What’s the importance of receptive fields in sensation?

A
  • Our ability to localise depends on sensory receptive fields
  • Small receptive fields are needed for fine discrimination
  • Many small receptive fields are better than few large receptive fields
  • Merkel’s discs & Meissner’s corpuscles have small receptive fields
  • Pacinian endings & Ruffini corpuscles have large receptive fields
22
Q

Which cutaneous receptor would be best adapted to fine tactile discrimination?

A
  • Merkel’s discs would be best for fine tactile discrimination
  • They have small receptive fields & a high spatial resolution
  • They are located at the finger tips
23
Q

What are the characteristics of A delta afferents?

A
  • Smallest diameter
  • Thinly myelinated
  • Moderate conduction velocity (<30m/s)
24
Q

What are the characteristics of C afferents?

A
  • Small diameter
  • Unmyelinated
  • Slow conduction (< 1m/s)
25
Q

Which two sensory afferents have free nerve endings?

A
  1. A delta fibres

2. C fibres

26
Q

What are the two central pathways of the somatosensory system?

A
  1. Dorsal columns- Medial Leminiscus (DCML)

2. Anterolateral system or Spinothalamic tract

27
Q

What fibres does the DCML receive input from & what does it detect?

A
  • The DCML receives input from A alpha & A beta afferents

- It detects proprioception, discriminative touch & vibration

28
Q

What fibres does the STT receive inputs from & what does it detect?

A
  • The STT receives inputs from A delta & C afferents

- It detects coarse touch (pressure), pain & temperature

29
Q

Describe the pathway for the DCML

A
  • A beta & alpha Sensory afferents enter the dorsal column of the spinal cord (dorsal roots)
  • The branches from the dorsal roots project into the dorsal column nuclei of the medulla: Cuneate & Gracile nucleus
  • The dorsal nuclei synapse in the mid-brain at the brainstem
  • It then dessicates into the VENTRAL POSTERIOR NUCLEAR cortex of the thalamus
  • Axons are then projected to the primary somatosensory cortex
    DORSAL ROOTS -> CUNEATE & GRACILE NUCLEUS (MIDBRAIN) -> BRAINSTEM (MIDBRAIN) -> VENTRAL POSTERIOR NUCLEAR COMPLEX (THALAMUS) -> PRIMARY SOMATOSENSORY CORTEX
30
Q

**Describe the pathway for the STT

A
  • A delta & C fibre afferents terminate in the dorsal horn of the spinal cord
  • The branches ascend into the medulla then into the midbrain. They then go into the VENTRAL POSTERIOR MEDIAL NUCLEUS of the thalamus
  • Dorsal horn -> Medulla -> Midbrain -> Ventral posterior medial nucleus
31
Q

What are the cortical connections of the primary somatosensory cortex?

A
  • Amygdala
  • Hippocampus
  • Motor & Pre-motor cortical areas

PHYS - NEURO (18 decks)

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