11 - Viscerosomatic Sensation

Question 1

4 Somatic Modalities

Answer 1

1. Discriminative/fine touch (mechanoreceptors)
2. Proprioception
3. Temperature
4. Nociception

Question 2

2 types of DRG neuron terminals in periphery

Answer 2

1. Encapsualted by a nonneural structure (Pacinian corpusles)
2. Bare nerve ending

Question 3

Group 1 Axons

Answer 3

• DRG Proprioceptors of skeletal muscle
• Large diameter
• Myelinated = faster conduction velocity

Question 4

Aß Axons

Answer 4

• DRG axons in skin
• Mechanoreceptors = fine touch
• Large-diameter
• Myelinated = fast conducting
• Include:
  
  • Meissner’s corpuscle
  • Merkel’s disk
  • Pacinian corpusle
  • Ruffini ending

Question 5

Axons for thermorecption or nocicepttion

Answer 5

• DRG A∂ or C axons
• A∂ = cool, sharp pain
• C = warm & cool, aching pain, itch

Question 6

A∂ Axons

Answer 6

• DRG skin/viscera axon
• Myelinated
• Cool temp
• Sharp pain

Question 7

C fibers

Answer 7

• DRG axons
• Unmeylinated
• Warm, cool temp
• Aching pain
• Itch

Question 8

1st Order Neuron

Answer 8

• Primary afferent nerve cell (DRG or CN sensory ganglion)
• Enters dorsal root or cranial nerve

Question 9

2nd Order Neuron

Answer 9

• Located in spinal cord gray matter or brainstem
• Cross midline (decussates)
  
  • Enters a tract that ascends to thalamus

Question 10

3rd Order Neurons

Answer 10

• Located in thalamus
• Project to higher-order neurons in cerebral cortex for conscious perception

Question 11

Meissner’s Corpuscles

Answer 11

• Aß axon (myelianted mechanoreceptor)
• Fast-adapting
• Superficial layer of skin
  
  • Smaller receptive field, more precise
• Stoking, fluttering: Low vibrations (30-50Hz)

Question 12

Merkel’s Disck

Answer 12

• Aß axon (myelinated mechanoreceptor)
• Slow-adapting
• Superficial skin
• Pressure (indentation) sense

Question 13

Pacinian Corpuscle

Answer 13

• Aß axon (myelinated mechanoreceptor)
• Fast-adapting
• Deep subcutaneous tissue
• High vibration (250-300 Hz)

Question 14

Ruffini Endings

Answer 14

• Aß axon (myelinated mechanoreceptor)
• Slow-adapting
• Deep subcutaneous tissue
• Skin stretch

Question 15

3 Types of Proprioceptors and their functions

Answer 15

1. Muscle Spindles
   
   • Signal muscle length
     
     • 1a: fast-adapting to changes
     • 2: slow-adapting to steady state
2. Golgi Tendon Organ
   
   • 1b: signal tendon tension, prevent strain
3. Joint receptors
   
   • Encode changes in joint angle at extremes

Question 16

Thermoreceptor Temp Range

Answer 16

5-45 degrees celcius

Question 17

Ascending Somatosensory System Pathways

Answer 17

1. Spinothalamic system
   
   • Pain, temp, crude touch
2. Trigeminothalamic system
   
   • Pain, temp, crude touch, fine touch, conscious proprioeption
3. Dorsal column-medial lemniscus system (DCML)
   
   • Fine touch, conscious proprioeption

Question 18

Descending Motor Pathways

Answer 18

1. Corticospinal
2. Corticobulbar

Question 19

Spinothalamic Tract Purpose, Pathway, Lesion

Answer 19

• Sensory pathway for pain, temp, itch, tickle
• Pathway:
  
  • Neuron 1: DRG
  • Neuron 2: Spinal cord (dorsal horn)
    
    • Decussates right away,
  • Ascends in contralateral spinothalamic tract
  • Neuron 3: Thalamus (VPL)
• Lesion: loss/decrease of pain/temp sensation on one side of body, depending on rostrocaudal location

Question 20

Dorsal Column-Medial Lemniscus System (DCML) Function, Pathway, Lesion

Answer 20

• Sensory pathway for discrim touch, conscious proprioception
• Pathway:
  
  • Neuron 1: DRG
    
    • Ascends in dorsal column (GT, CT) to medulla
  • Neuron 2: medulla
    
    • Decussates in medulla
    • Ascends via medial lemniscus tract
  • Neuron 3: thalamus
• Lesion: loss of 2-point discrim, vibration sense, limb position sense, kinesthesia

Question 21

Thalamus (VPL) Function

Answer 21

• All sensory pathways relay in the thalamus EXCEPT for olfaction
• “Links” cortical activity

VPL: major relay for somatosensory signals originating in the body