Senses 2
 The somatosensory system
 Taste
 Smell
Practical tasks
1. Examination of cutaneous sensitivity
2. Skin localisation
3. Adaptation of skin mechanoreceptors
4. Detection of olfactory sensations
5. Detection of taste sensations
http://1.bp.blogspot.com/_kaQ5P19FVgk/SlYj8SW_S7I/AAAAAAAADSo/cVLxJASLnNo/s400/SomaticSensoryCortex1.JPG
http://1.bp.blogspot.com/-k3FXNezB6eM/Tvjkn5nya5I/AAAAAAAAAKU/7S1QqTSqusE/s1600/Sensory+homunculus.jpg
The somatosensory system
-
allows for sensation of the body and movements of its parts
Sensory receptors of the somatosensory system
1. Exteroceptors – cutaneous sensitivity (skin receptors)
- touch, pressure, vibrations, itching, tickling (mechanoreceptors)
- cold, warmth (thermoreceptors)
- pain (nociceptors)
2. Proprioceptors (Muscle spindle, Goldi tendon organ)
- position of the body
- position of individual parts of the body
- muscle tone
- movement of parts of the body
3. Interoceptors – perceptions from the internal organs
Cutaneous mechanoreceptors
1/ free nerve endings
2/ specialised receptors
– round corpuscles in the skin
– layers of cells surrounded by connective tissue
– branches of afferent nerves among cells
http://users.bergen.org/dondew/bio/anp/anp2/anp2tri3/AnP2Tri3sensor.jpg
Adequate stimulus – mechanic energy
• touch – stimulus of a low intensity
• pressure – stimulus of a higher intensity
• vibration – series of regular repeated stimuli
• various types of receptors exist - differ in:
– location in the skin (superficial, deep)
– sensitivity to different qualities of the stimulus:
- intensity
- direction
- speed
- adaptability – ability to detect duration of the
stimulus
http://t2.gstatic.com/images?q=tbn:ANd9GcQ3iEh08Ir3KUEII9tqp7ZoEeZPtXNOajuji8b4Bq962MIoYvyh
Main types of touch receptors
Receptor
type/adaptability
Merkel’s discs
(slow)
Sensation
Location
Sustained touch and
pressure
Movement of a stimulus
Base of epidermis
Ruffini
Sustained deep pressure
corpuscles (slow)
Texture
Meissner’s
Slow vibrations
corpuscles
2 point discrimination
(rapid)
Pacinian corpus- Deep pressure
Fast vibrations
cles (very rapid)
Deep in dermis and
hypodermis
Hair end organ
Free nerve
endings
Around hair follicles
Light touch
Touch, pressure
(+ heat, cold, nociception)
Upper dermis
Deep in dermis
Throughout the skin
Adaptability of a receptor
- the stimulation continues, but a decline in generator potential and thus frequency of
AP occurs, or disappears
- reduced input to CNS – less intense sensation / no sensation (e.g. clothes - skin)
 receptors
- rapidly adapting
- when the stimulation starts – AP is generated
- although the stimulus is still acting, receptors stop to fire AP after some time
- when the stimulation is ceased, the change causes AP
- slowly adapting – fire AP in as long as the stimulation persists, but
- at the beginning a strong response, then it becomes weaker
- non -adapting – fire constant AP in as long as the stimulation persists
http://virtual.yosemite.cc.ca.us/rdroual/Course%20Materia
ls/Physiology%20101/Chapter%20Notes/Fall%202007/fig
ure_10_03_labeled.jpg
Most sensitive areas of the body
• tip of the tongue, lips
•
fingertips - in proximal direction of hands the sensitivity decreases
Sensitivity of the skin depends on
• receptor count per area (density of receptors)
– higher count = better sensitivity
• one receptor „collects“ stimuli from a smaller
surface – better discrimination
large receptive
fields
small receptive
fields
The receptive field of a cutaneous receptor
– portion of the skin which, when stimulated,
affects the activity of receptor
• large receptive fields – lower sensitivity
• mall receptive fields - higher sensitivity
•
count of nerve fibres – 2 stimuli are perceived
as 2 if 2 receptors are stimulated, each of them
having own sensitive fibre (nerve)
 thickness of the skin
 presence of sweat
 skin temperature
 age
sensed 1 point
sensed 2 points
Cutaneous thermoreceptors
A. Specific (free nerve endings)
1. Cold receptors
– sensitive to lower than body temperatures
2. Warmth receptors
– sensitive to normal temperatures and higher than body temperature up to 48 ° C
B. Non specific
• nociceptors
– 1. type: sensitive to temperatures higher than 40 ° C
– 2. type: respond to temperatures less than 10 ° C
Adequate stimulus: change in temperature
Non – adequate stimuli: menthol, CO2 (perception of cold)
Receptor count (per unit of skin surface area)
pain > touch > cold > heat
Adaptability of thermoreceptors
- fast - after a few moments we stop to feel the change in temperature in full
extent (e.g. cold is perceived as less cold)
Pain
Somatic pain
- superficial (skin receptors)
- deep (receptors in muscles, joints, connective tissue)
Visceral pain (receptors in viscera)
Fast pain
- begins 0,1 s after stimulation
- sharp, acute, electric
Slow pain
- begins 1 s after stimulation, increases slowly
- burning, nauseous, chronic pain
Pain receptors – nociceptors
 sensitive to high intensity of stimuli
 sensitive to chemical, mechnical, thermic stimuli
 non-adaptable
Referred pain
e.g. patients with heart attack often feel pain of the left arm
= activation of nociceptors in the viscera results in a
perception of pain on the body surface
Explanation
- information from nociceptors (both superficial
visceral) converges to the same synapse in the spinal
cord (spinothalamic tract neurons)
- the brain interprets the information coming from
visceral receptors as having arisen from receptors on
the body surface - since this is typically where
nociceptive stimuli originate
http://www.d.umn.edu/~jfitzake/Lectures/UndergradPharmacy/Sensory
Physiology/Somatosensation/Figures/ReferredPain.jpg
Phantom pain
= pain that feels like it's coming from a body part that was amputated
Explanation
• the nerve endings at the site of the amputation continue to send
pain signals to the brain that make the sensation as thouth the limb
was still there
http://t2.gstatic.com/images?q=tbn:ANd9GcSX2Uqs37A7Th4E
1yi0WvZAglkX9tp0y3Pnsq-NQjWkKSrKNHBF
General somatosensory pathway
3 neurons
1. periphery  spinal cord
- cell bodies in
- dorsal root ganglia
- ganglia of sensory cranial nerves
2. spinal cord (brainstem)  thalamus
- all secondary neurons cross the midline
- shortly after entering the spinal cord (pain,
temperature, coarse touch)
- in medulla oblongata (fine touch, vibration,
proprioception)
- the sensations are processed in
contralateral hemisphere
- projections to reticular system, cerebellum
(balance, movement, activation of CNS)
3. thalamus  postcentral gyrus (parietal
lobe)
Types of afferent nerves transmitting sensory information
• Ab sensory nerves: 30 – 70 m/s (all types of receptors except free
nerve endings)
• tactile sensitivity
• Ad: 5 – 30 m/s (free nerve endings)
• pain
• temperature
• C: less than 2m/s (free nerve endings)
• pain
• temperature
slow pathways
– rough, less precise sensations
fast pathways
– fine, quick, exact sensations
Dermatomes
•
A dermatome is an area of skin
that is mainly supplied by a
single spinal nerve
•
(partial overlapping with
neighbouring areas)
•
Each of these nerves relays
sensation (including pain) from
a particular region of skin to the
brain
•
Dermatomes are useful in
neurology for finding the site of
damage to the spine
The sensory homunculus
Examination of cutaneous sensitivity
Tactile sensitivity
Procedure:
• stamp palmar side of 3. finger (fingertip) – use stamp size 1x1cm
• stamp forearm – use stamp size 1x1cm
• the examined person must not look at the examination
• touch subsequently each of 100 squares in stamped area of the skin with Frey hair,
if the examined person feels a touch, he informs the examiner („yes“)
• for each „yes“ the examiner writes a „+“ into the respective field in the manual
Result
• number of fields marked by „+“ = count
of receptors per 1 cm2 on the fingertip
and the forearm
Conclusion
explain: is the observation normal/expected?
+
+
+
+
+
+
+
+
Thermal sensitivity – examination of cold receptor count
Procedure:
•stamp palmar side of 3. finger – use stamp size 1,5x1,5 cm (2,25 cm2)
•stamp forearm – use stamp size 1,5x1,5 cm
•touch subsequently each of 100 squares of the stamped area of skin with cold
metal stick, the examined person must not look at the examination
•after each stimulus dip the stick into ice in order to maintain it cold
•if the examined person feels cold (not a touch), he informs the examiner
• for each „yes“ the examiner writes a „+“ into the respective field in the manual
Result
•count of receptors per 1 cm2
(result divided by 2,25) on fingertip
and forearm
+
+
Conclusion:
explain: is the observation normal/expected?
+
+
+
+
+
+
Thermal sensitivity – examination of warmth receptor count
Procedure:
• stamp the palmar side of 3. finger – use stamp size 1,5x1,5 cm (2,25 cm2)
• stamp forearm – use stamp size 1,5x1,5 cm
• touch each of 100 squares in stamped area with a warm metal stick
(the examined person must not look at the examination)
• after each stimulus dip the stick into warm water in order to maintain it cold
• if the examined person feels warmth (not a touch), he informs the examiner
• for each „yes“ the examiner writes a „+“ into the respective field in the note book
Result
+
•count of receptors per 1 cm2
+
(result divided by 2,25)
on fingertip and forearm
Conclusion:
• explain: is the observation normal/expected
+
+
+
+
+
+
Examination of discrimination sensitivity (2 point discrimination)
(i.e. what is the smallest distance in which 2 tactile stimuli are
recognized as 2 and not as 1 ?)
Procedure:
• touch the skin with both spikes of a compass at one time
• start with small distance of spikes, increase the distance gradually
• measure and record the minimum distance when the examined person can
recognize 2 stimuli
• make this examination on
•
•
•
•
•
fingertip (3rd finger)
dorsum manus
palm of the hand
forearm
upper arm
Result: distance in mm (cm)
Conclusion: is the observation normal/expected?
Weber's experiment
Procedure:
• prepare 3 containers
• fill them with water – temperature 15,25, 35°C
• put one hand into the container with 15 °C, the other one into
the container with 35 °C for approx 30 s
• put both hands into the middle container with 25 °C water
Result: describe your observation
Conclusion: explain the observation (adaptability...)
1
2
15°C
2
25°C
1
35°C
Accuracy of tactile localization
Procedure
• mark 3 points with a marker
- fingertip
- dorsum manus
- forearm
• patient closes his eyes
• the examiner touches a dot and asks the patient to touch the
same place (for all dots)
Result:
did the patient indicate exactly the same place?
if not, what was the distance between the marked point and the point
shown by the examinee?
Conclusion:
explain the observation
2
Adaptation of skin mechanoreceptors
Procedure:
- put a cork on the forearm of the examined person and leave it there
(the patient must not look at the arm)
 after putting the cork on the arm the volunteer feels touch of the cork
 in a few seconds adaptation occurs - the person does not „feel“ the
presence of the cork any more
- remove the cork quickly
 the volunteer is supposed to feel the change – that the cork was removed
- repeat the experiment with a metal object
Result:
- describe your observation
Conclusion
- explain your observation (adaptation .....)
Sense of taste
Sense of taste
 taste receptors – sensitive to different chemical stimuli
 adequate stimulus – chemical substances dissolved in water
Elementary (primary) tastes /stimuli
1. sour - acids (H+ concentration)
2. salty - ionized salts, mainly Na+
3. sweet - sugars, aldehydes, glycols, some amino acids, etc.
4. bitter - long chain organic substances, alkaloids (e.g. quinine, caffeine, nicotine)
- causes rejection of food – many deadly toxins are bitter
5. umami – taste of foods rich in monosodium glutamate
(„meaty“ taste, chinese food taste)
6. kokumi
hundreds of different tastes can be perceived – all are combinations of
elementary taste sensations
 individual receptors generate receptor potential/action potential of varying
intensity – the sum of potentials results in a particular taste senastion
Taste buds
Location
• mainly - in papillae of the tongue
• palate, pharynx, larynx
Composition
• supporting cells
• sensory cells
• their tips are arranged around a taste pore
• microvilli of the tips protrude into the taste
pore = receptor surface
Specificity of the taste buds
- individual taste buds respond mostly
to one of the primary tastes
Threshold for taste
- bitter taste – the most sensitive
- detectable concentrations
Bitter (quinin)
Sour (HCl)
Salty (NaCl)
Sweet (sucrose)
0,000008 mole
0,0009 mole
0,01 mole
0,01 mole
• taste receptors are partially (slowly) adaptable
– when stimulated a strong immediate signal is transmitted by the taste nerve
– later a weaker continuous signal is transmitted
The complec taste experience depends on stimulation of
- taste receptors
- pain receptors (e.g. pepper)
- touch receptors (texture of the food)
(+ smell of the food)
Gustatory pathway
Somatosensory cortex, frontal cortex –
conscious perception of tase
Hippocampus
- memory of taste
Amygdala, hypothalamus
– emotional quality of taste
Thalamus
Med.oblongata
Taste buds
http://www-psych.stanford.edu/~lera/psych115s/notes/lecture11/images/tstoverview.jpg
Detection of gustatory sensation
Procedure A
• pour a sample of sweet, sour, salty and bitter solution
into separate glass containers
use a set of containers with solutions of different
concentration of
a/ saccharose
b/ citric acid
- dip a stick into the container and touch the tongue
of the examinee
- find the threshold concentration (the examinee
can detect the taste) – for both tastes
(record the number of the container)
Result and conclusion
compare the sensitivity of your examinee to both tastes
Procedure B
• test the threshold
• dip a stick with cotton swab in one solution (the patient
must not know the taste !!)
• touch different regions of tongue with the stick
• at the end of examination the patient has to determine
– what taste he felt (sweet, salty.....)
– in which part of tongue he felt the taste maximally
• repeat the procedure for all elementary tastes
(use the bitter taste at the end)
• after testing of each taste, the examinee has to wash
his mouth with water
Result and conclusion
describe your observations
Sense of olfaction
Sense of olfaction (smell)
•
•
adequate stimulus – chemical substances present in air
human – microsmate – less sensitive sense of olfaction
• receptors in superior part of each nostril (2,4 cm2) – regio olfactoria
• sensory cells (olfactory cells) = bipolar nerve cells
• project olfactory cilia into mucus that covers mucosa of the nasal cavity (secreted
by Bowmans glands)
• cilia capture the chemical
stimuli (odours) – the substance
must be dissolved in mucus
• Henning´s theory - six elementary odours :
– flowers
– fruit
– resin
– spices
– putrid
– burns
• i.e. smell receptors are specialized to indiviual odours
• all other odours are a combination of elementary odours
• there are also othes classifications :
–
–
•
•
•
•
camphoraceous, musky, floral, pepperminty, ethereal, pungent, putrid
50 or even 100 elementary odours
threshold concentrations – very low
poor discrimination of intensites of stimuli (gradations)
adaptation of receptors: very fast in 1st second, then proceeds only slowly
affective component od odours (pleasant, unpleasant)
Olfactory pathways
Detection of olfactory sensations
Principle
• by sniffing the solutions of olfactory substances we examine the
ability to distinguish primary odours and determine their
thresholds
Procedure
A. by sniffing get familiar with the 4 available primary odours – flowers,
fruit, resin, spices (use bottles 1)
B. test the threshold for odours
•
•
•
•
from a set of 10 bottles with increasing concentration select the least concentrated
solution (bottle 10)
remove the stopper from one of the bottles and hold it about 4 cm under your partner's
nose about 2 seconds
ask your partner to identify the odor, and then replace the stoppe
record the number of bottle in which the examinee can recognize
the odour = threshold
Result: record the threshold values
Conclusion: compare the sensitivity to different odours
C. Test the memory for odours
•
let the examinee sniff to an „unknown“ odour
•
the examinee has to determine the odour
Result and conclusion: describe your observation