40 Somatosensory System

Question 1

describe the cutaneous mechanoreceptors for touch

Answer 1

• Merkel’s disks and Meissner’s corpuscles = fine, discriminatory touch
• Pacinian corpuscles = deep pressure
• Ruffini’s endings = skin stretch

Question 2

describe cutaneous mechanoreceptors for vibration

Answer 2

• Meissner’s corpuscles = lower frequency vibration (50 Hz)
• Pacinian corpuscles = higher frequency vibration (200-300 Hz)

Question 3

name the main proprioceptors

Answer 3

• muscle spindle
• Golgi tendon organ

Question 4

describe the adaptations of sensory receptors (Meissners, Pacinian, Merkel, Ruffini)

Answer 4

Question 5

describe the primary afferent axons and which are myelinated vs unmyelinated

Answer 5

C axons are unmyelinated and perceive pain and temperature

Question 6

reactivation of varicella-zoster virus (shingles) usually affects neurons of one _____

Answer 6

reactivation of varicella-zoster virus (shingles) usually affects neurons of one dorsal root ganglion

Question 7

describe the touch pathway (dorsal column/medial lemniscus pathway)

Answer 7

major route by which discriminatory touch, vibration and proprioceptive information travels to the brain

• primary sensory touch axons enter at the ipsilateral dorsal root of the spinal cord

Question 8

explain the steps of the touch pathway (DCML)

Answer 8

• primary somatosenory neuron: connects receptor to ipsilateral medulla via fasiculi gracilis and cuneatus (dorsal column)
  
  • cuneatus = upper body
  • gracilis = lower body
• secondary somatosensory neuron: from medulla to thalamus via medial lemniscus; axon crossing midline in medulla
• tertiary somatosensory neuron: from ventral posterolateral nucleus of thalamus to postcentral gyrus (cortex) via internal capsule

Question 9

describe characteristics of the pain pathway (antero-lateral pathway aka spinothalamic pathway)

Answer 9

major route by which pain, temperature, crude touch info. travels to the brain

• thinly myelinated or unmyelinated
• primary sensory axons enter at ipsilateral dorsal root/dorsal horn of the spinal cord
• axons decussate to the contralateral side at the spinal entry segment

Question 10

describe the steps of the pain pathway

Answer 10

• primary pain neuron: connects receptor to dorsal horn in spinal cord
• secondary pain neuron: from dorsal horn to thalamus via spinothalamic tract; axon crossing midline at spinal segment level
• tertiary pain neuron: from thalamus to postcentral gyrus (cortex) via internal capsule

Question 11

describe the sensory loss during Brown-Sequard syndrome

Answer 11

Question 12

describe syringomyelia

Answer 12

• fluid-filled cavity (cyst aka syrinx) within the central canal of the spinal cord
• progressive expansion interrupts fibers that cross through the anterior white commissure

Question 13

describe the sensory loss in syringomyelia

Answer 13