V1 dermatome: the ophthalmic division of the trigeminal nerve
Ophthalmic division of the trigeminal nerve
Where is the V1 dermatome?
V1, the ophthalmic division of the trigeminal nerve, supplies the forehead and scalp to the crown, the upper eyelid and the bridge and tip of the nose. The spinal standard gives the face no key sensory point; the forehead is the usual test point. No disc compresses V1: it is a cranial nerve, not a spinal root.
| Type | Ophthalmic division of the trigeminal nerve |
|---|---|
| Key sensory point | Not part of the spinal standard: the forehead is the usual test point |
| Key movement | None: the face is tested by touch |
| Tendon reflex | None tests it on its own |
| Usual disc | None: a cranial nerve, not a spinal root |
V1 and the tendon reflexes
No tendon reflex tests V1 on its own.
Why no disc compresses V1
The face is supplied by the trigeminal nerve, a cranial nerve whose three divisions leave the skull through separate openings, so a lesion of one division numbs its own area of the face. It is not a spinal root, so no disc presses on it.
What a lesion of V1 does
- Sensation. Numbness over the V1 area of the face.
- Strength. None: V1 carries no motor fibers, which in the trigeminal nerve run only in V3.
- Reflexes. No tendon reflex depends on V1.
A teaching map. Root territories overlap and vary between people, and a root lesion is diagnosed by examination and imaging, not by a map. Numbness between the legs or around the anus, new bladder or bowel problems, or quickly spreading weakness need emergency care.
Neighboring dermatomes
- V2: the lower eyelid, the cheek, the side of the nose and the upper lip
- V3: the lower lip, the chin, the jaw except its angle, the temple and the front of the ear
See also
- Dermatome and Myotome Map Explorer, with V1 lit on a front and back body map
- Every dermatome, with the disc levels and key movements side by side
- Head and Neck Explorer, the head and neck in 3D
- Skull Bones Explorer, the bones of the skull in 3D
Sources. Key sensory points and key movements: International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), American Spinal Injury Association, 2019 revision. Muscles: Aids to the Examination of the Peripheral Nervous System, Medical Research Council and the Guarantors of Brain, 5th ed. (2010), cross-checked with Kendall et al. (2005). Reflex roots: Walker (1990), Clinical Methods, 3rd ed., Table 72.1, and StatPearls, “Physiology, Deep Tendon Reflexes”; the main root as the MSD Manual’s “How to Assess Reflexes” names it. Overlap: Sherrington (1893), Phil Trans R Soc Lond B 184:641-763.
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