Sensory Innervation: Nerve Distribution and Sensory Modalities
Definition
Sensory innervation is the supply of sensory (afferent) nerve fibers to tissues, enabling perception of stimuli.
Sensory Neurons
Pseudounipolar neurons with cell bodies in dorsal root ganglia (spinal) or cranial nerve ganglia. Peripheral endings = receptors; central axons enter CNS.
Modalities & Receptors
| Modality | Receptors |
|---|---|
| Touch (light, pressure, vibration) | Meissner, Merkel, Ruffini, Pacinian corpuscles |
| Temperature | Thermoreceptors (TRP channels) |
| Pain (nociception) | Free nerve endings (Aδ, C fibers) |
| Proprioception | Muscle spindles, Golgi tendon organs, joint receptors |
| Taste, Smell | Specialized chemoreceptors (taste buds, olfactory epithelium) |
Organization
- Dermatomes: Segmental skin innervation (spinal nerve level).
- Peripheral nerves: Named nerves (median, ulnar, sciatic) carry mixed fibers.
- Density varies: Fingertips, lips, genitals have high receptor density → high acuity.
Clinical Relevance
Lesions cause sensory loss, paresthesia, neuropathic pain. Mapping deficits localizes pathology (nerve, root, cord, brain).
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