Table I

Classification of Joint Receptors in a Cat Knee^*

Type	Morphology	Dimensions, μm	Location	Axon diameter, μm	Functional characteristics
I	Globular or ovoid corpuscles. Fine capsule. Arborizing nerve terminal, linked in clusters of 3–6 corpuscles	100 × 40	Superficial joint capsule	5–8	Mechanoreceptor (low threshold, slowly adapting)
II	Cylindrical or conical corpuscles. Thick laminated capsule (up to 10–12 layers). Single nerve terminal: may be bifid or trifid. Linked in clusters of 2–3 corpuscles	280 × 120	Fibrous capsule (deep layers), fat pads	8–12	Mechanoreceptor (low threshold, rapidly adapting)
III	Fusiform corpuscles. Thin capsule (1–3 layers). Densely arborizing nerve terminal. Usually single, occasionally linked in clusters of up to 3 corpuscles	600 × 100	Ligament, tendon	13–17	Mechanoreceptor (high threshold, slowly adapting)
IV	(a) Unmyelinated plexuses	< l.5	Fibrous capsule, ligament, fat pad, blood vessel, subsynovial	2–5 (thinly myelinated)	Nociceptor (non-adapting)
	Unmyelinated free nerve endings	0.5–1.5	Ligments, tendons	< 2 (unmyelinated)	Nociceptor (non-adapting)
	(b) Unmyelinated nerve terminals	< 1.0	Walls of small arteries and arterioles	< 2	Vasomotor, efferent