The Pacinian Corpuscle: a Pressure Receptor Pacinian corpuscles Most are found in the dermis of the skin Are the largest skin receptors Consist of a single neurone ending surrounded by a bulb of lamellae and a capsule, made of connective tissue Are also found in joints, tendons and in the tissue lining blood vessels and organs Provide information about how and when we move Are sensitive to changes in pressure They are transducers, converting pressure energy into electrochemical energy of a generator potential Give a graded response, the greater the pressure the greater the frequency of nerve impulses along the neurone

Photomicrograph showing a Pacinian Corpuscle capsule Subject to copyright clearance a suitable imqge showing a Pacinian Corpuscle could be inserted here. e.g. one similar to that found at: http://www.montgomerycollege.edu/faculty/~wolexik/public_html/Pacinian%20Corpuscle-100x.jpg

The Pacinian Corpuscle Capsule of connective tissue Lamellae separated by gel X Y Single neurone ending (naked) Direction of impulse Transverse section X-Y Myelin sheath Axon of sensory neurone

The Pacinian corpuscle is a pressure receptor External pressure causes the corpuscle to deform The greater the pressure the more deformation The sodium channels in the neurone membrane are pressure sensitive An increase in pressure causes sodium channels to open pressure

Pressure on the skin is transmitted to to the corpuscle in the dermis The shape of the corpuscle is changed Causing sodium ion channels in the neurone membrane to open Sodium ions diffuse into the neurone down the concentration gradient Depolarising the membrane Called a generator potential The greater the pressure the more sodium channels open causing a bigger generator potential If the threshold of that neurone is reached An action potential develops and is transmitted along the sensory neurone pressure

Pressure causes sodium channels in the neurone membrane to open Na+ Pressure causes sodium channels to open Na+ pressure Sodium ions diffuse into the neurone Na+ Na+ Down the concentration gradient Na+ Na+ Creating a generator potential Na+ Na+ Na+ Na+ Na+ Neurone ending in corpuscle

The greater the pressure the more sodium channels open More sodium ions diffuse in down the concentration gradient Na+ pressure Na+ A larger generator potential is created Na+ If the threshold is reached an action potential develops Na+ Na+ Action potentials will continue to be developed while the generator potential is at or above the threshold Na+ Na+ Na+ The greater the pressure the greater the frequency of nerve impulses along the neurone Na+ Na+ The maximum frequency is limited by Na+ the refractory period Neurone ending in corpuscle

Pacinian Corpuscles Show A Graded Response Potential difference across membrane Action potentials at low frequency threshold Generator potential resting potential time pressure

Greater pressure results in a higher frequency of impulses along the neurone Potential difference across membrane Action potentials at high frequency and for a longer time threshold Generator potential resting potential time Greater pressure

Adaptation When pressure is first applied impulses are transmitted along the neurone With continuous pressure the frequency of the action potentials decreases, and then stop This is known as adaptation (it occurs in most sensory receptors) It prevents the nervous system being overloaded with insignificant information e.g. the pressure from clothing

Click on the marks to check Questions Where are Pacinian corpuscles found in the body? (1mark) Explain how pressure on the skin is perceived. (5marks) Explain why slight pressure on part of the skin may go unnoticed. (2marks) Explain how differences in pressure applied to the same part of the skin are detected. (2marks) What is meant by adaptation and why is it useful? (2marks) Click on the marks to check your answers Click here to finish

In the dermis of the skin, tendons and joints Answer Q1 In the dermis of the skin, tendons and joints Back to question

Pressure deforms the Pacinian corpuscle Answer Q2 Pressure deforms the Pacinian corpuscle Causing sodium channels to open in the neurone membrane Sodium ions diffuse into the neurone Down a concentration gradient Creating a generator potential/depolarising the membrane If the generator potential is above the threshold Impulses /action potentials are conducted along the sensory neurone to the brain Any 5 from the above Back to question

Slight pressure will cause fewer sodium ion channels to open Answer Q3 Slight pressure will cause fewer sodium ion channels to open Fewer sodium ions diffuse in creating a lower generator potential If this is lower than the threshold there will be no action potentials/no impulses to the brain Any 2 from the above Back to question

The greater the generator potential created Answer Q4 The greater the pressure applied the greater the number of sodium ion channels opened The greater the generator potential created Larger generator potentials cause an increase in the frequency of impulses sent along the neurone Back to question

Answer Q5 Continuous stimulation of a sensory neurone can result in a decreased frequency of impulses and even stop them, this is known as adaptation. It is useful as it prevents overloading the nervous system with insignificant information e.g. the pressure from clothing Back to question

What synoptic links can you think of? Relationship between structure, shape and function of protein Facilitated diffusion and active transport Respiration – energy required from respiration to restore receptors after transduction / presence of mitochondria