Neurosurgery notes/Anatomy/Peripheral nerves anatomy/Sensory nerve

Sensory nerve

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Peripheral nerves anatomy

Sensory receptors

Classification of Sensory Receptors

Functional classification:

  • Exteroceptors
      • Free nerve endings: Pain
      • Tactile corpuscles of Meissner: Touch
      • Lamellated corpuscles of Pacini: Pressure
      • Bulbous corpuscles of Krause: Cold
      • Merkel cell receptors: Touch
      • Ruffini endings: Warmth
       
      Merkel's disk Rufini's ending Free nerve endings Lamellated corpuscle Meissner's corpuscle Bulb corpuscle
  • Proprioceptors
    • Golgi tendon organs
    • Muscle spindles
      • Annulospiral endings (nuclear bag, nuclear chain)
      • Flower spray endings
  • Interoceptors

Mode of stimulation:

  • Mechanoreceptors
  • Chemoreceptors
  • Photoreceptors
  • Thermoreceptors
  • Osmoreceptors

Structural classification:

  • Neuronal receptors (most exteroceptors)
  • Epithelial receptors (rods and cones)
  • Neuroepithelial receptors (olfactory mucosa)

Classification of sensory axons

Fibre type
Function
Sensory classification
Diameter (μm)
Velocity (m/s)
Myelination
A α
Muscle spindle, annulo-spiral ending
Ia
13–20
70–120
Myelinated
ㅤ
Golgi tendon organ
Ib
13–20
70–120
Myelinated
ㅤ
Somatic motor
–
13–20
70–120
Myelinated
A β
Muscle spindle, flower-spray ending
II
6–12
30–70
Myelinated
ㅤ
Touch, pressure
II
6–12
30–70
Myelinated
A γ
Motor to muscle spindles
–
3–6
15–30
Myelinated
A δ
Pricking pain, cold, touch
III
2–5
12–30
Myelinated
B
Preganglionic autonomic
–
1–5
3–15
Myelinated
C
Burning pain, temperature, itch, tickle
IV
0.2–1.5
0.5–2
Unmyelinated
ㅤ
Postganglionic autonomic
–
0.2–1.5
0.5–2
Unmyelinated

Group I (Aα)

  • Largest fibers
  • Fastest conducting (70–120 m/s)
  • Two functional subgroups:
    • Ia fibers—the afferents of muscle spindles,
    • Ib fibers—the afferents from Golgi tendon organs.
  • Myelinated

Group II (Aβ, Aγ)

  • (30–70 m/s
  • Afferents from
    • Muscle spindles
    • Cutaneous touch and pressure.
  • Myelinated

Group III (Aδ)

  • Smaller
  • 5–30 m/s
  • Afferents from
    • Sensations of
      • Temperature
      • Light touch
      • Sharp pain.
  • Myelinated

Group IV (C) fibers

  • 0.5–2 m/s
  • Afferents from
    • Temperature
    • Burning pain
  • Unmyelinated