c 12 mechano reception
TRANSCRIPT
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Laws of Sensory
Perception
Skin receptors-mechanical receptors
Pacinian receptors
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Receptors- Definition and Properties
- Sensory Receptors are special nerve endings,distributed throughout the body (in the skin,muscles, vessels, bones and joints, in lungs,heart, and another organs).
- They Convert Different Forms of Energy intoElectrical Signals. Thus they serve as
t ransducers, changing the particular form ofenergy ( e.g. mechanical, chemical, thermal, orelectromagnetic) into the electrical signal.
- Our body contains20 types of receptors that can
detect e.g.heat, pressure, stretch, acceleration,sound, light, smells, taste, partial pressure,concentration of salts, hormons...and other formsof stimuli (Only receptors for ionizing radiation aremissing)
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Receptors - Classification
I.According to locality: Externoreceptors- are placedwithin the skin, like receptors for touch, pressure, heat, cold or pain
Proprioreceptors-are placed in muscles, in bones and joints -theyinform about the lengt of muscles and ligaments
Internoreceptorsreceptors within the organs (heart, lungs,kidney) They detect plasma osmolarity, partial pressure of O2bloodpressure..
II.According to type of energy: Mechanoreceptors- theytransform mechanic energy into electric signal.E.g. exte-rorecep
tor, baroreceptors, pulmonary stretch receptors).
Fotoreceptors- receptors containing photopigments (rodsand cones at retina
Chemoreceptorstaste receptors in the tongue, smellreceptors within a nose, osmoreceptors in hypothalamus,..
Nociceptors- pain receptors - in skin, in organs ...
III.According to complexity: simple receptors (skin) andcomplex ones (eye, ear)
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Externoreceptors Sensitive to stimuli arising from outside
of the body
Typically located near the surface of the
body
Include receptors for Touch
Pressure
Pain
Temperature
Special sense receptors
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Internoreceptors or visceroceptors Respond to stimuli arising from within the
internal viscera and body organs,
Internoreceptors monitor a variety of internalstimuli Changes in chemical concentration
Taste stimuli
The stretching of tissues
Temperature
Their activation causes us to feel visceralpain, nausea, hunger, or fullness
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Proprioreceptors Located in the musculoskeletal
organs such as skeletal muscles,
tendons, joints and ligaments
Proprioreceptors monitor thedegree of stretch of these
locomotor organs and send input
to the CNS They are Encapsulated Dendritic
Endings
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Mechanoreceptors
general nerve impulses when they, or
adjacent tissues, are deformed by
mechanical forces
Touch
Pressure
Vibration
Stretch
Itch
Thermoreceptors
Sensitive to temperature changes
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Hair follice receptors.
Mechano-receptors like:
Light TouchMeissners
Corpuscle
Krausetouch, light pressure
Pacini-deep pressure, vibration
Rufini-pressure and touch
Strong PressureMerkels Disk
PainNociceptors
Heat/ColdThermoreceptors,
some nociceptors
Skin (cutaneous)
receptors
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Skin
Type
Depth Adaptation
Modality
Touch Pressure
Pacinian
Corpuscles
Glabrous
and Hairy
Deep Rapid Light Vibration
Meissners
Corpuscles
Glabrous Surface Rapid Light Vibration
Merkels
Disk
Glabrous Surface Slow Crude Pressure
Ruffini
Corpuscles
Hairy Deep Slow Crude Pressure
Hair Follice
Receptors
Hairy Deep Rapid Light Neither
Cutaneous Mechanoreceptor Types
Merkels Disk
Ruffini Ending
Mechanical Displacement
Pacinian Corpuscle
Hair Follicle Receptor
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Most mechanoreceptors areencapsulated dendritic endings Encapsulated receptors vary widely in
shape, size, and distribution in the body
The main types are
Meissners corpuscles-tactil, sensing light
touch
Krauses end bulbs-touch, light pressure
Pacinian corpusclesdeep pressure,pressure change, vibration
Ruffinis corpuscles pressure and touch
Proprioceptors (not in the skin but in themuscles
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Meissners Corpuscles In a Meissners
corpuscle (tactilecorpuscle) a few
spiraling dendrites
are surrounded by
Schwann cells,
which in turn are
surrounded by an
egg-shapedcapsule of
connective tissue
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These corpuscles
are found in thedermal papillae
beneath the
epidermis
These corpuscles
are rapidly
adapting receptors
for fine, light touch
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Meissners corpuscles occur insensitive and hairless areas of the
skin, such as the soles of the feet,
palms, fingertips, nipples, and lips Apparently, Meissners corpuscles
perform the same light touch
function in hairless skin that root hairplexuses perform in hairy skin
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Meissners Corpuscles sensing lighttouch
Highly concentrated in areassensitive to light touch.
Fingertips, lips, tongue,
soles, genitals
Located: surface of the skin
highly sensitive Limited. Must
physically be touching.
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Krauses End ulbs Krauses End Bulbs
are a type ofMeissners
corpuscle for fine
touch
Krauses end bulbs
occur in mucous
membranes in the
lining of the mouthand the conjunctiva
of the eye
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Pacinian Corpuscle Pacinian
corpuscles arescattered
throughout the
deep connective
tissues of the body
Occur in the
hypodermis of the
skin Sensing pressure
change, vibration,
deep pressure
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Pacinian Corpuscles Pacinian corpuscles are rapidly adapting
receptors and are best suited to monitor
vibrations which is an on-off stimulus These corpuscles are large enough to be
visible to the naked eye
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Pacinian Corpuscles sensingpressure change, vibrationsIn joints, organs.
Rapidly adaptingresponds
briefly to begining and end of
stimulus
Detects: pressure change, esp.
vibrations
Up to centimeters away
Responds best to sinusoidal
vibrations w/ narrow frequency
range.
~Low pass filter
Result of onion-shaped
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Ruffinis Corpuscle Ruffinis corpuscles
are located in thedermis of the skin
and joint capsules
of the body
The corpuscle
contains an array of
dendritic endings
enclosed in a thinflattened capsule
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Ruffinis corpuscles
respond topressure and touch
They adapt slowly
and thus canmonitor continuous
pressure placed on
the skin
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Ruffini Ending sensing pressure andtouch
Only in glabrous skinSensitive to skin streching.
Contributes to fine motor control.
Contributes significantly to finger positioning.
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Merkels Disk-sensing strong pressureSlow adaptation because of rigid
structure.Sustainable response30 min. in
humans
Irregular firing in sustained.
Large receptive field.Small, sharp pressure: fast firing
rate.
Large, flat pressure: slow rate
Located in hairless skin and in hair
follices.
Not in skin surrounding follicle.
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The Integumentary System Skin)
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Stratum BasaleDeepest of the epidermal strata made of a singlelayer of
cells (consisting of 3 cell types) Keratinocytes
undergo mitosis rapidly to replace the cells that areexfoliated from the surface
as these keratinocytes move up through the moresuperficial strata
Melanocytes
produce the brown pigment melaninto protectagainst UV radiation (sunlight) damage to DNA ofkeratinocytes
Merkel (tactile)cells
touch receptors that provide sensory perception
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Layers of the Dermis: Papillary Layer
Papillary layer
20% of the thickness of the dermis
Its superior surface contains fingerlike projections
called dermal papillaewhich keep it firmly attachedto the superficially located epidermis
Dermal papillae contain sensory receptors such as
tactile corpuscles(touch receptors) and free nerveendings(sense pain)
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Layers of the Dermis: Reticular Layer
Reticular layer
80% of the thickness of the dermis
Elastic fibers provide stretch-recoil properties
Location of:
hair and associated follicles
pacinian corpuscles (pressure receptors)
blood vessels
glands
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The Pacinian Corpuscle: a
Pressure Receptor
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Coding of sensory information on
Paccinian Corpuscle (a skin receptor
for touch and pressure)
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Coding of Stimulus on Paccinian
corpuscle
Mechanical touch-pressure energy affects thereceptor nerve membrane(without myelin)causing its local depolarization, that results in
an appearance of RECEPTOR orGENERATOR POTENTIAL(GP).Whenanother touch pressure stimuli come on thereceptor it causes creation of many local
potentials and their summation . When theamplitude of GP is above10mV then theseries ofACTION POTENTIALS rise uponthe afferent nerve fibre (which is covered with
myelin),that leaves the Paccinian corpuscle.
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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 liningblood 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 showinga 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
Directionof 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 pressurereceptor 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 causessodium channels to
open
pressure
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Pressure on the skin is transmitted toto the corpuscle in the dermis The shape of the corpuscle is changed
Causing sodium ion channels in theneurone 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 isreached
An action potential develops and is
transmitted along the sensory neurone
pressure
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Pressure causes sodium channels inthe neurone membrane to openNa+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Neurone ending
in corpuscle
pressure
pressure
Pressurecauses sodium channels to open
Sodium ions diffuseinto the neurone
Down the concentration gradient
Creating a generator potential
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The greater the pressure the moresodium channels open
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Neurone ending
in corpuscle
pressure
pressure
pressure
More sodium ions diffuseindown theconcentration gradient
A larger generator potentialis created
If the threshold is reached an action potentialdevelops
Action potentials will continue to be developedwhile the generator potential is at or above thethreshold
The greater the pressure the greater the
frequency of nerve impulsesalong the neurone
The maximum frequency is limited by
the refractory period
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Pacinian Corpuscles Show AGraded Response
time
Potentialdifferenceacrossmembrane
threshold
restingpotential
Generatorpotential
Action potentialsat low frequency
pressure
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Greater pressure results in a higherfrequency of impulses along the neurone
time
Potentialdifferenceacrossmembrane
threshold
restingpotential
Generatorpotential
Action potentials at highfrequency and for alonger time
Greaterpressure
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Laws of Sensory Perception:
Weber-Fechners Law of Perception: is a basic psy-
chophysical Law. The bigger is the intensity of sti-mulation, the higher is the magnitude of sensation.Magnitude of sensation E = log S, ( S - intensity ofstimulation )or in a modified form :
Stevensons Law: FAP= k . Sn
(FAP is rate of APs froma receptor, k- constant, n=1 is valid formechanoreceptors, n1, for fotoreceptors, n 1, forpain receptors.
The Law of Projection:Each sense occupies the uniq-ue and separated site within the brain cortex.Therefore, we are able to distinguish the individualstimuli - like touch, pressure, pain sensations, lightor sound.
The Law of Adaptation
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The Law of Adaptation Adaptation-is an internal electric property(caused by
membrane properties of the receptor) to respond whenthe long-term stimulus of a constant intensity is applied.Actualy, it is a drop of the receptor excitability to giverise the GP and then the APs
Receptors with Rapid Adaptationof theirBurst Activity - their fire just for a short time, during
the constant (maintained ) stimulation ( as typically seenin touch, pressure, taste and smell receptors.)
Receptors with Low Adaptation of theirBurst Activity-they fire for a long time with only a lowdrop of their firing activity (as seen in the pain, cold, heat
receptors, baroreceptors, in pulmonary stretch recepors,the chemoreceptors, carotid baroreceptors or in thepulmonary stretch receptors).
The receptors with Low Adaptation areinvolved in a control of blood pressure, in control of
breathing , in responses of body to the pain, etc.
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Receptor Adaptation
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Sensory perception
- it is an ability to distinguish, detect, utilize
some feelings , and answer to many informa-tion that come to the brain through the reflexarc.
- The reflex arcconsists of receptor, afferent
nerve pathway, the central nervous sys tem(brain and spine),efferent pathwayand effector(muscle...)
- Information from an environment come to our
body and are processed by our senses (Touch,Taste, Smell, Vision, Hearing).Reaching thebody the information are coded in 2 forms: asa local electric response (local potential), andthe general action potential (AP)
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Reflex arc
l ( R) d A i
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Local response (LR) and Action
potential (AP)
Local electric response-takes local place, it does notspread to the vicinity, when its magnitude reachesmore than 10 mV then, in turn AP is produced. Thistype of coding is so called AMPLITUDE. (i.e. the
stronger is stimulus, the higher is amplitude ofresponse (examples: receptor potential (generatorpotential), EPSP and IPSP or end-plate potential).
Action potentialis a generally spreading electricity,
being under the Law All or NoneThis type of coding isnamed FREQUENCY. I.e.the stronger is stimulus thehigher is a rate of APs from the receptors. The brainknows that a higher frequency of action potentialsmeans a stronger stimulus (and vice versa)
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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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Questions1. 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 checkyour answers
Click here to finish
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Answer Q1 In the dermis of the skin, tendons and
jointsBack 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 alower generator potential
If this is lower than the threshold there
will be no action potentials/no impulses tothe 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 anincrease in the frequency of impulses
sent along the neurone
Back to question
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Answer Q5 Continuousstimulation of a sensory
neurone can result in a decreased
frequency of impulses and even stopthem, this is known as adaptation.
It is useful as it prevents overloading the
nervous system with insignificantinformation 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
Respirationenergy required fromrespiration to restore receptors after
transduction / presence of mitochondria