Receptors - Pacinian Corpuscles (AQA A-Level Biology): Revision Notes
Receptors - Pacinian Corpuscles
Introduction to sensory reception
The central nervous system receives information from both internal and external environments through various receptors. Each receptor type responds to a specific stimulus. Sensory reception refers to the detection of stimuli by these receptors, whilst sensory perception involves the brain processing and interpreting this information.
The key distinction here is that sensory reception is simply the detection of stimuli, while sensory perception involves the brain's interpretation of that detected information into meaningful sensations we can understand.
Pacinian corpuscles provide an excellent example of how sensory receptors function, demonstrating key principles that apply to all sensory reception.
Key features of sensory reception
Pacinian corpuscles illustrate two fundamental characteristics of sensory receptors:
Stimulus specificity
Pacinian corpuscles only respond to mechanical pressure. They will not respond to other stimuli such as heat, light, or sound. This specificity ensures that each receptor type provides precise information about particular environmental changes.
Transduction function
All receptors act as transducers - they convert one form of energy into another. Pacinian corpuscles convert mechanical energy (pressure) into electrical energy (nerve impulses). This conversion process creates a generator potential, which can trigger action potentials that travel to the central nervous system.
Energy Transduction Principle
The stimulus always involves an energy change, and receptors convert this energy into the electrical energy of nerve impulses that the nervous system can process. This is the fundamental principle underlying ALL sensory reception.
Structure and function of Pacinian corpuscles
Location and distribution
Pacinian corpuscles are found deep within the skin and are particularly abundant in:
- Fingertips
- Soles of feet
- External genitalia
- Joints, ligaments and tendons
This distribution allows the body to detect pressure changes and monitor joint movement effectively.
Structural organisation
The Pacinian corpuscle has a distinctive layered structure resembling an onion when cut in cross-section. Key structural features include:
Anatomical Components
- Concentric layers of connective tissue separated by viscous gel
- Sensory neurone ending at the centre
- Capsule surrounding the entire structure
- Blood capillary supplying the receptor
This layered arrangement is essential for the corpuscle's function as a pressure detector.
Mechanism of action
Resting state
In the absence of pressure, stretch-mediated sodium channels in the sensory neurone membrane remain closed. The channels are too narrow to allow sodium ions through, maintaining the neurone's resting potential.
Response to pressure
Worked Example: Mechanotransduction Process
When mechanical pressure is applied to a Pacinian corpuscle:
Step 1: Physical deformation
The corpuscle and surrounding membrane become stretched
Step 2: Channel activation
Stretch-mediated sodium channels in the membrane widen
Step 3: Ion movement
Sodium ions diffuse into the neurone down their concentration gradient
Step 4: Electrical change
The membrane potential becomes less negative, creating a generator potential
Step 5: Signal transmission
If the generator potential exceeds the threshold, an action potential (nerve impulse) travels along the neurone to the central nervous system
This sequence demonstrates how mechanical energy converts into electrical energy through the process of mechanotransduction.
Key Points to Remember:
- Pacinian corpuscles detect mechanical pressure only - they show stimulus specificity
- They act as transducers, converting mechanical energy into electrical energy (generator potentials)
- The layered structure with viscous gel between layers enables pressure detection
- Stretch-mediated sodium channels open when pressure deforms the membrane, causing depolarisation
- All sensory receptors work on the same principle of transduction - converting stimulus energy into nerve impulses