What is the specific role of the Pacinian corpuscle in the human body?

It acts as a mechanoreceptor that detects deep pressure and vibrations in the skin. It functions as a transducer, converting mechanical energy into electrical nerve impulses.

How does the structure of the Pacinian corpuscle contribute to its function?

It consists of concentric layers of connective tissue (lamellae) separated by gel. This structure allows mechanical pressure to be transmitted to the central sensory neurone ending, stretching its membrane.

What is the difference between a generator potential and an action potential in a Pacinian corpuscle?

A generator potential is a graded depolarization at the receptor site caused by $Na^+$ influx through stretch-mediated channels. An action potential is an all-or-nothing impulse triggered only if the generator potential reaches a threshold.

What specific type of ion channel is found in the membrane of the sensory neurone ending?

Stretch-mediated sodium channels. These channels are unique because they open physically in response to the stretching of the neurone's cell surface membrane.

Why does the influx of sodium ions cause a generator potential?

Sodium ions ($Na^+$) are positively charged. When they flood into the neurone via facilitated diffusion, they make the inside of the axon less negative (depolarization), creating the potential difference.

What is a common error when describing the movement of sodium ions into the neurone?

Students often incorrectly state that sodium ions move by active transport. In reality, they move down their electrochemical gradient via facilitated diffusion through opened stretch-mediated channels.

How does the intensity of pressure affect the nervous system's response?

Greater pressure causes more stretching of the membrane, opening more sodium channels and creating a larger generator potential. This results in a higher frequency of action potentials being sent to the brain.

What happens to the sodium channels when no pressure is applied to the skin?

The stretch-mediated sodium channels remain in their resting state, which is too narrow for $Na^+$ ions to pass through. Consequently, the resting potential of the neurone is maintained.

Why is it incorrect to say that the Pacinian corpuscle 'feels' pain?

Receptors are specific to one stimulus. Pacinian corpuscles only detect pressure and vibration; pain is detected by different, specific receptors called nociceptors.

What is the relationship between the 'lamellae' and the 'gel' in the corpuscle?

The lamellae are the structural layers of connective tissue, while the gel fills the gaps between them. Together, they transmit the mechanical energy from the skin's surface to the central axon.

The Pacinian Corpuscle | AQA A-Level Biology

Organisms Respond to Changes in their Environments (A Level only)

The Pacinian Corpuscle

Summary

The Pacinian corpuscle is a specialized mechanoreceptor found deep within the skin that functions as a biological transducer, converting mechanical pressure into electrical nerve impulses. Its unique lamellar structure allows it to respond specifically to changes in pressure and vibrations, initiating a generator potential through the opening of stretch-mediated sodium channels.

1. Definition & Core Concepts

Mechanoreceptors are specialized sensory cells designed to detect mechanical stimuli such as touch, pressure, and vibration.
The Pacinian corpuscle is a specific type of mechanoreceptor located deep in the dermis of the skin, as well as in joints and tendons.
These receptors exhibit specificity, meaning they are evolved to respond only to one particular type of stimulus—in this case, mechanical pressure changes.
As a transducer, the Pacinian corpuscle converts one form of energy (mechanical) into another (electrical energy in the form of a nerve impulse).

Diagram of a Pacinian corpuscle showing concentric lamellae surrounding a central sensory neurone ending.

2. Anatomical Structure

The corpuscle consists of a single sensory neurone ending (axon) located at the very center of the structure.
This nerve ending is surrounded by many concentric layers of connective tissue known as lamellae.
Between each layer of lamellae is a viscous gel, which helps transmit and modulate the mechanical pressure applied to the outer surface.
The entire structure is encapsulated, ensuring that the internal nerve ending is protected and only stimulated by significant mechanical deformation.

3. Mechanism: The Generator Potential

4. Initiation of Action Potentials

The magnitude of the generator potential is directly proportional to the intensity of the stimulus (the amount of pressure applied).
If the generator potential reaches a specific threshold level, it triggers the opening of voltage-gated sodium channels further along the axon.
Once this threshold is surpassed, an action potential (nerve impulse) is initiated and propagated along the sensory neurone to the Central Nervous System (CNS).

5. Key Distinctions

6. Exam Strategy & Tips