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Pacinian Corpuscle

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Biology

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.

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.

Pacinian corpuscle Sensory receptors different types of receptors found in the skin StudySmarterFigure 2. The different types of skin sensory receptors. Source: macrovector, via Freepik.

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.

How does a Pacinian corpuscle perform its function?

As mentioned above, the Pacinian corpuscle responds to mechanical pressure, its stimulus. How does the Pacinian corpuscle transduce this mechanical energy into a nerve impulse that the brain can understand? This has to do with sodium ions.

Resting state

In the normal state of the Pacinian corpuscle, i.e. when no mechanical pressure is applied, we say that it is in its 'resting state'. During this state, the stretch-mediated sodium channels of the connective tissue membrane are too narrow, so sodium ions cannot pass through them. We refer to this as the resting membrane potential in the Pacinian corpuscle. See StudySmarter's other article on Action Potential for more information about what a resting membrane potential means.

Application of pressure

  1. When pressure is applied to the Pacinian corpuscle, the membrane becomes stretched as it is deformed.

  2. As the sodium channels in the membrane are stretch-mediated, the sodium channels will now widen. This will allow sodium ions to diffuse into the neurone.

  3. Due to their positive charge, this influx of sodium ions will depolarise the membrane (i.e. make it less negative).

  4. This depolarisation continues until a threshold is reached, triggering a generator potential to be produced.

  5. The generator potential will then create an action potential (nerve impulse). This action potential passes along the neurone and then to the central nervous system via other neurones.

  6. Directly after the activation, the sodium channels do not open in response to a new signal - they are inactivated. This is what causes the refractory period of the neurone. Remember that the refractory period is where the nerve cannot fire another action potential. This only lasts for a very brief time, normally around 1 millisecond.

Pacinian Corpuscle - Key takeaways

  • A receptor is a cell or group of cells that receive information from stimuli such as a change in temperature. Receptors are specific and work by acting as transducers.

  • A key example of a receptor is the Pacinian corpuscle, which is a mechanoreceptor (detects changes in mechanical pressure). Other examples include chemoreceptors and photoreceptors.

  • Pacinian corpuscles are located in the skin (particularly the fingers, soles of the feet, and external genitalia) and in joints, ligaments, and tendons.

  • The structure of a Pacinian corpuscle consists of a single sensory neurone ending surrounded by connective tissue, separated by a gel. Stretch-mediated sodium channels are embedded in this membrane.

  • In its resting state, a Pacinian corpuscle does not send out nerve impulses as the stretch-mediated sodium channels are too narrow, so sodium ions cannot enter to depolarise the membrane. When pressure is applied to the Pacinian corpuscle, the membrane is stretched, causing the sodium channels to open. The influx of sodium ions will depolarise the membrane, leading to a generator potential and an action potential, which passes to the central nervous system.

Pacinian Corpuscle

Pacinian corpuscles allow us to distinguish between different levels of pressure that we touch as they respond differently to different levels of pressure.

A transducer is simply something that converts energy from one form to another. So, because the Pacinian corpuscle converts mechanical energy into a nervous impulse, we can describe it as a transducer.

The hypodermis contains the Pacinian corpuscle. This is found deep below the skin below the dermis.

Pacinian corpuscles are mechanoreceptors in the body. They act as transducers by converting mechanical energy into nerve impulses which are sent to the brain.

They detect mechanical energy in the form of pressure and movement, so are very important for distinguishing touch.

Final Pacinian Corpuscle Quiz

Question

In what layer of the skin do we find Pacinian corpuscles? 


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Answer

In a layer called the hypodermis, which is situated deep in the skin below the dermis.

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Question

Where are Pacinian corpuscles most abundant in the skin?


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Answer

The fingers, soles of the feet, and the external genitalia

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Question

Aside from the skin, where else are Pacinian corpuscles usually found, and what is the function of them here?


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Answer

They are commonly found in joints, ligaments, and tendons. They are useful here as they allow the organism to know which joints are changing direction.

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Question

Why do we say that the structure of a Pacinian corpuscle resembles that of an onion?


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Answer

Similar to the layered structure of an onion, the Pacinian corpuscle consists of layers of connective tissue separated by a gel.

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Question

What type of neurone is in the centre of a Pacinian corpuscle?

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Answer

Sensory neurone

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Question

What is meant by the term ‘stretch-mediated sodium channel’?


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Answer

This means that the permeability of the channel to sodium changes when the channel is deformed, for example, by stretching.

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 What is meant by the term ‘resting state’?


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Answer

This is the normal state of the Pacinian corpuscle, where the membrane is not deformed as there is no mechanical pressure applied.

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Question

Why does the Pacinian corpuscle not generate an action potential when it is in its resting state?


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Answer

During this state, the stretch-mediated sodium channels of the connective tissue are too narrow, so sodium ions are unable to pass along them. This means that the membrane has its resting potential and is not depolarised. Therefore, the membrane cannot reach the generator potential in order to trigger an action potential (nerve impulse).

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Question

When pressure is applied to the Pacinian corpuscle, what causes the sodium ions to diffuse into the neurone?


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Answer

The membrane will become stretched as it is deformed. This causes the sodium channels to widen as they are stretch-mediated. So, sodium ions will be able to diffuse into the neurone.

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Question

How does the influx of sodium ions into the membrane lead to the production of an action potential? 


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Answer

The depolarisation continues until a threshold is reached, which triggers a generator potential to be produced. This generator potential will then create an action potential.

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Question

What is meant by mechanical pressure?

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Answer

The pressure caused by physical force. An example of this would be the pressure of your shoe against the sole of your foot when walking. 

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Question

In a Pacinian corpuscle, what are lamellae?

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Answer

Layers of connective tissue separated by a gel.

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Question

What properties of sodium ions allows them to depolarise membranes?

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Answer

 They are positively charged ions

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Question

What causes the refractory period in a Pacinian corpuscle?

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Answer

Directly after the creation of the action potential, the sodium channels do not open in response to a new signal - they are inactivated. This is what causes the refractory period.

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Question

What happens to the nerve during the refractory period?

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Answer

The nerve cannot fire another action potential for a temporary amount of time, normally around 1 millisecond

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Question

Select the answer that is NOT true about the structure of Pacinian corpuscles

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Answer

We can find stretch-mediated calcium channels in a Pacinian Corpuscle 

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