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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

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Photomicrograph showing a Pacinian Corpuscle

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

capsule

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The Pacinian Corpuscle

Direction of impulse

X Y

Transverse section X-Y

Capsule of connective tissue

Lamellae separated by gel

Single neurone ending (naked)

Myelin sheath

Axon of sensory neurone

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The Pacinian corpuscle is a pressure receptorpressure 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 An increase in pressure causes sodium channels to causes sodium channels to openopen

pressure

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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

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Pressure causes sodium channels in the neurone membrane to open

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Neurone ending in corpuscle

pressure

pressure

PressurePressure causes sodium channels to sodium channels to openopen

Sodium ions diffuseSodium ions diffuse into the neurone

Down the concentration gradientDown the concentration gradient

Creating a generator potentialgenerator potential

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The greater the pressure the more sodium channels open

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Neurone ending in corpuscle

pressure

pressure

pressure

More sodium ions diffuseMore sodium ions diffuse inin down the concentration gradient

A larger generator potentiallarger generator potential is created

If the threshold is reached an action potential develops

Action potentials will continue to be developed while the generator potential is at or above the threshold

The greater the pressure the greater thegreater the frequency of nerve impulsesfrequency of nerve impulses along the neuroneThe maximum frequency is limited bythe refractory period

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Pacinian Corpuscles Show A Graded Response

time

Potential difference across membrane

threshold

resting potential

Generator potential

Action potentials at low frequency

pressure

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Greater pressure results in a higher frequency of impulses along the neurone

time

Potential difference across membrane

threshold

resting potential

Generator potential

Action potentials at high frequency and for a longer time

Greater pressure

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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

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Questions

1. Where are Pacinian corpuscles found in the body?(1mark)

2. Explain how pressure on the skin is perceived.(5marks)

3. Explain why slight pressure on part of the skin may go unnoticed.

(2marks)4. Explain how differences in pressure applied to the same part

of the skin are detected.(2marks)

5. What is meant by adaptation and why is it useful?(2marks)

Click on the marks to check your answers

Click here to finish

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Answer Q1

• In the dermis of the skin, tendons and joints

Back to question

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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

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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

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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

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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

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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