Lamellar corpuscles, or Pacinian corpuscles, are one of the four major
types of mechanoreceptor. They are nerve endings in the skin responsible for
sensitivity to vibration and pressure. They respond only to sudden disturbances
and are especially sensitive to vibration. The vibrational role may be
used to detect surface texture, e.g., rough vs. smooth. Lamellar corpuscles
are also found in the pancreas, where they detect vibration and possibly very
low frequency sounds. Lamellar corpuscles act as very rapidly adapting
mechanoreceptors. Groups of corpuscles respond to pressure changes, e.g. on
grasping or releasing an object. Structure
Lamellar corpuscles are larger and fewer in number than Meissner's corpuscle,
Merkel cells and Ruffini's corpuscles. The Lamellar corpuscle is approximately
oval-cylindrical-shaped and 1 mm in length. The entire corpuscle is wrapped
by a layer of connective tissue. Its capsule consists of 20 to 60 concentric
lamellae including fibroblasts and fibrous connective tissue, separated by
gelatinous material, more than 92% of which is water. The lamellae are
actually very thin, flat, epithelial Cells inside the capsule and modified
Schwann cells inside the inner core of the corpuscle. The center of the
corpuscle is a neurite of single afferent with oval cross-section and
unmyelinated at the receptive region. Function
Lamellar corpuscles are rapidly adapting receptors that detect gross pressure
changes and vibrations in the skin. Any deformation in the corpuscle causes
action potentials to be generated by opening pressure-sensitive sodium ion
channels in the axon membrane. This allows sodium ions to influx, creating a
receptor potential. These corpuscles are especially
susceptible to vibrations, which they can sense even centimeters away. Their
optimal sensitivity is 250 Hz, and this is the frequency range generated upon
fingertips by textures made of features smaller than 1 µm. Lamellar corpuscles
cause action potentials when the skin is rapidly indented but not when the
pressure is steady, due to the layers of connective tissue that cover the nerve
ending. It is thought that they respond to high-velocity changes in joint
position. Lamellar corpuscles have a large
receptive field on the skin's surface with an especially sensitive center.
Mechanism Lamellar corpuscles sense stimuli due to
the deformation of their lamellae, which press on the membrane of the sensory
neuron and causes it to bend or stretch. When the lamellae are deformed, due to
either pressure or release of pressure, a generator potential is created as it
physically deforms the plasma membrane of the receptive area of the neuron,
making it "leak" Na+ ions. If this potential reaches a certain threshold,
nerve impulses or action potentials are formed by pressure-sensitive sodium
channels at the first node of Ranvier, the first node of the myelinated section
of the neurite inside the capsule. This impulse is now transferred along the
axon with the use of sodium channels and sodium/potassium pumps in the axon
membrane. Once the receptive area of the neurite
is depolarized, it will depolarize the first node of Ranvier; however, as it is
a rapidly adapting fibre, this does not carry on indefinitely, and the signal
propagation ceases. This is a graded response, meaning that the greater the
deformation, the greater the generator potential. This information is encoded
in the frequency of impulses, since a bigger or faster deformation induces a
higher impulse frequency. Action potentials are formed when the skin is
rapidly distorted but not when pressure is continuous because of the mechanical
filtering of the stimulus in the lamellar structure. The frequencies of
the impulses decrease quickly and soon stop due to the relaxation of the inner
layers of connective tissue that cover the nerve ending. This adaptation is
useful, as it stops the nervous system from being overloaded with unnecessary
information such as the pressure exerted by clothing.
Nomenclature The Pacinian corpuscle was named after
its discoverer, Italian anatomist Filippo Pacini.
The term Golgi-Mazzoni corpuscle is used to describe a similar structure found
only in the fingertips. Additional images
See also List of human anatomical parts named
after people Pacinian neuroma – a very rare benign
tumor of Pacinian corpuscles References
External links Virginia Commonwealth University
Anatomy Atlases - Microscopic Anatomy, plate 06.124
Medical Illustration