Lymphatic Vessels

1. Overview

Lamellated corpuscles, also known as Pacinian corpuscles, are large, encapsulated mechanoreceptors specialized for detecting deep pressure, high-frequency vibration, and mechanical deformation. As part of the sensory apparatus of the integumentary system, they provide rapid feedback about stimuli that affect the deeper layers of the skin and subcutaneous tissue. Their unique onion-like structure allows them to rapidly adapt to mechanical changes, making them essential for detecting transient tactile signals.

2. Location

Pacinian corpuscles are located in the deeper layers of the skin and other tissues. Common sites include:

• Hypodermis (subcutaneous tissue): Particularly in the palms of the hands, soles of the feet, and fingers.

• Deep dermis: Found in thick skin and pressure-sensitive areas.

• Joints, periosteum, and mesentery: Detecting mechanical stress in non-cutaneous structures.

• External genitalia and nipples: Areas associated with sensory input and sexual response.

3. Structure

Pacinian corpuscles are large, oval, encapsulated structures measuring 0.5–2 mm in length. Their layered appearance resembles a sliced onion. Structural features include:

• Central axon terminal: The distal end of a myelinated sensory neuron loses its myelin sheath and becomes unmyelinated as it enters the corpuscle.

• Lamellae: Multiple concentric layers of flattened Schwann cells and collagen fibers surrounding the axon.

• Capsule: An outer connective tissue capsule encasing the corpuscle and separating it from surrounding tissue.

The layered structure deforms in response to mechanical pressure, allowing the central axon to initiate action potentials in response to rapid changes in pressure.

4. Function

Pacinian corpuscles serve as rapidly adapting mechanoreceptors. Their key functions include:

• Detection of deep pressure: Respond to initial compression or indentation of the skin.

• Sensation of vibration: Most sensitive to high-frequency vibrations (~250 Hz).

• Rapid adaptation: Respond quickly to changes in mechanical force, but stop firing with constant pressure.

They are especially important in tasks requiring precision touch or manipulation, such as tool use and texture discrimination.

5. Physiological role(s)

Pacinian corpuscles support several physiological sensory functions:

• Tactile feedback and coordination: Aid fine motor skills and manipulation of objects through vibratory feedback.

• Grip adjustment: Provide sensory information that helps modulate force during grasping or holding objects.

• Proprioceptive input: When located near joints, they contribute to awareness of limb position and movement.

• Protective reflexes: Help trigger withdrawal reflexes in response to sudden pressure or vibration.

6. Clinical Significance

Alterations in Pacinian corpuscle function or number can be associated with various clinical conditions:

• Peripheral neuropathy:

  • Conditions like diabetes mellitus can reduce Pacinian corpuscle density and impair vibration sensation.

• Occupational overuse:

  • Repeated exposure to vibration (e.g., in construction workers or machinists) may desensitize or damage corpuscles over time.

• Aging:

  • The number and sensitivity of Pacinian corpuscles decrease with age, contributing to reduced tactile acuity.

• Diagnostic testing:

  • Vibration perception tests (e.g., tuning fork, biothesiometer) assess the integrity of Pacinian corpuscles in neurologic exams.

• Benign Pacinian neuroma:

  • Rare condition involving hypertrophy or clustering of Pacinian corpuscles, sometimes causing localized pain or hypersensitivity.