Pacinian corpuscles are examples of receptors found in the skin. They belong to the family of mechanoreceptors. Pacinian corpuscles respond to the sensation of touch by transducing mechanical pressure into a generator potential, a type of nervous impulse.
Mechanoreceptors: a type of sensory receptors which transduce stimuli into signals through mechanically gated ligand ion channels.
Mechanoreceptors only respond to mechanical pressure caused by physical force. An example of this would be the pressure of your shoe against the sole of your foot when walking.
Generator potential is caused by depolarisation across the membrane that is typically produced in response to a stimulated sensory receptor. It is a graded potential, meaning that the changes in membrane potential can vary in size, rather than being all-or-none like action potentials are.
An overview of receptors
Before we dive into the details of Pacinian corpuscles, it is important to discuss what a receptor is.
A receptor is a cell or group that receives information from stimuli.
The stimulus may be external change, such as a decrease in the temperature outside, or an internal change such as a lack of food. The identification of these changes by receptors is called sensory reception. The brain then receives this information and processes it. This is called sensory perception.
Receptors are, therefore, essential in the body as they facilitate communication between the brain and different parts of the body, helping us adjust to external and internal environmental conditions. Receptors are a special class of proteins, so they are also referred to as receptor proteins.
When your fingers touch a piece of paper, the stimuli, in this case, would be the mechanical pressure caused by the paper pressing against your fingertip. The Pacinian corpuscles would transduce this pressure into a generator potential. This nervous impulse would then be sent to the central nervous system, allowing us to 'feel' the paper.
Where is the Pacinian corpuscle located?
Pacinian corpuscles are located all around the body. One key area is deep inside the skin, in the hypodermis layer. This layer is below the dermis and consists mainly of fat.
Pacinian corpuscles are encapsulated sensory nerve endings that act as pressure and vibration receptors.
In particular, Pacinian corpuscles in the skin are most abundant on the fingers, the soles of the feet, and the external genitalia, which is why these areas are so sensitive to touch. They are also commonly found in joints, ligaments, and tendons. These tissues are essential for movement - joints are where bones meet, ligaments connect bones, and tendons connect bones to muscles. Therefore, having Pacinian corpuscles is useful as they allow the organism to know which joints are changing direction.
Fig. 1 - The different types of skin sensory receptors
The only one you need to remember is the Pacinian Corpuscle (Figure 2), but the rest are good to be aware of to understand all the different changes our skin is sensitive to.
What is the structure of a Pacinian corpuscle?
The structure of Pacinian Corpuscles is quite complex - it consists of layers of connective tissue separated by a gel. These layers are called lamellae. This layered structure resembles that of an onion when sliced vertically.
At the centre of these layers of tissue is the ending of a single sensory neurone's axon. The sensory neurone ending has a particular sodium channel called a stretch-mediated sodium channel. These channels are called 'stretch-mediated' because their permeability to sodium changes when they are deformed, for example, by stretching. This is explained in more detail below.
Fig. 2 - Structure of the Pacinian Corpuscle
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