‫بسم هللا الرحمن الرحيم‬
‫﴿و ما أوتيتم من العلم إال قليال﴾‬
‫صدق هللا العظيم‬
‫االسراء اية ‪85‬‬
BY
Dr /Hany M. borg
Assistant professor of physiology
KFS University
Centers
Tracts
Afferents
Receptors
Sensation
1) Def.,
• Sensation is a conscious perception of particular feeling
caused by stimulation of certain type of receptor by its
adequate stimulus.
2) Classifications:
Sensations
General
Special
Organic
1) Special sensations:
• Vision, hearing, taste, smell and equilibrium
2) General sensations:
• Arise from receptors distributed allover the body
• Are classified into;
a) Somatic sensations: from somatic structures e.g.
skin
b) Visceral sensations: from viscera
3) Organic senses: e.g. thirst, hunger and sexual desire
Somatic sensations
Def,
• These sensations arise from somatic structures of all
the body i.e. skin and deep tissues e.g. sk ms
Types:
• They include according to their adequate stimulus:
1. Mechanoceptive sensations: 2 types;
– Tactile e.g. touch, pressure, and vibration
sensations.
– Proprioceptive sensations e.g. sense of position
and movement
2. Thermal sensation; cold and warm.
3. Pain sensation
Somatic sensations
Mechanoreceptive
Tactile
Touch ,
pressure
&vibration
Thermoceptive
proprioceptive
Position &
movement
of joints
pain
According to center of perception
1- Protopathic (crude sensations):
• perceived in the thalamus as slow pain,
extreme grades of temperature & crude
touch.
2- Epicritic (fine sensations):
• Perceived in the cortex as fast pain, fine
grades of temperature, fine touch & deep
sensations
BY
Dr /Hany M. borg
Associate professor of physiology
KFS University
Def :
• Pain is an unpleasant sensory and emotional
experience associated with actual or potential tissue
damage
Significance:
1. Pain is a warning signal for tissue damage. It is the
prominent symptom of tissue damage
2. Pain has a protective function. It initiates protective
reflexes that;
• Get rid of the painful stimulus.
• Minimize tissue injury or damage.
Painless nature of diabetic
foot disease
•Pain Rs are morphologically similar but functionally they
are specific
1) Morphology: are specific free nerve endings
2) Highly specific i.e. respond to tissue damage only
• Classified according to their adequate stimulus into:a) Mechanical Pain Rs:
• Respond to strong mechanical trauma e.g. cutting
b) Thermosensitive pain Rs:
• Respond to excessive changes in temp (above 45°C and
below 10°C).
c) Chemical Pain Rs: respond to noxious chemical stimuli.
d) Polymodal Pain Rs: respond to a combination of
mechanical, thermal, and chemical noxious stimuli
3) Distribution:
a) Abundant in the skin and some internal tissue such as
the periosteum, arterial wall, joint surfaces, and the dura
of the tentorium cerebelli.
b) Few in deep tissues and all viscera. So, for pain to
occur, painful stimulus must by intense and widespread.
The deep & visceral pain is poorly localized.
c) Brain itself and the parenchymal tissues of the liver,
kidneys, and lungs have no pain receptors “pain
insensitive structures”
4) Threshold :
•It is the lowest intensity of injurious agent needed to
stimulate the pain receptors and produced pain
sensation
•Pain receptors are of high threshold: the pain
receptors needs sufficient degree of tissue damage to
be stimulated.
5) Adaptation:
•Slowly adapting receptors even non adapting
receptors
•This is very important because it directs the subject to
get rid of the injurious agent
6) Mechanism of stimulation:
Chemical stimuli
Mechanical stimuli
Thermal stimuli
Strong acids or Alkalies
Cutting or pricking
temp. > 45 C and < 10 C
Tissue damage
1st class
K ions, Histamine,
Serotonin, and Bradykinin
Directly stimulate
Pain Receptors
Release of Pain
Producing
Compounds (PPS)
2nd class
PGE2, leukotriens and
Substance P
Sensitize the pain Rs
by lowering its
threshold to stimuli
Tissue
Damage
Direct
stimulators
Sensitizers
A) According to its mechanism or cause:
•Pain is classified into 3 main types;
1. Physiological
Pain
Also called
Nociceptive pain
Caused by stimulation
of pain receptors by
tissues damage e.g. in
inflammation
2. Pathological
Pain
Also called
neuropathic
pain
Caused by
damage of nerve
pathway
3. Psychogenic
Pain
In depression and
anxiety
Difficult to
differentiate whether
2ry to or actual
cause of pain
B) According to its duration:
•Both nociceptive and neuropathic pains are classified into 2
types;
a) Acute pain: less than 7 weeks
b) Chronic pain : more than 7 weeks
C) According to the quality or character :
•A pain it is classified into 5 types;
a) Pricking or Cutting Pain:
b) Burning Pain:
c) Aching Pain:
d) Throbbing Pain:
e) Colicky Pain:
1. Pricking
pain
• Sharp and localized pain.
• Of skin origin (mainly)
• e.g. in pricking or cutting the
skin by sharp object
2. Burning
pain
• Less well localized, has
unpleasant burning nature.
• Usually of skin origin
• Caused by wide spread irritation
of skin
3. Aching pain
4.Throbbing
pain
5.Colicky pain
• disagreeable pain of dull- aching
nature
• More diffuse and felt coming from
deeper tissues e.g. rheumatic
pains
• Fluctuation of its intensity with
arterial pulsations
• localized inflammation in deep
tissues e.g. abscess
• Comes in cramps, so it has a
colicky nature, e.g. intestinal
colic and ureteric colic
• Spasm of smooth ms in the walls
of hollow viscera
D) According to site of origin: 3 types;
Cutaneous
pain
• Pain comes from skin and
subcutaneous tissues
• Usually pricking or burning pain
Deep pain
• Pain comes from structures deep
to the skin e.g. skeletal muscle,
joints, and tendons
• Usually dull aching or throbbing
Visceral pain
• Pain comes from internal viscera
e.g. stomach
• Usually colicky or dull aching
Comparisons Between Slow and Fast Pain
Acute (Fast)
Chronic (Slow)
Source
Skin only
Quality
Onset
Pricking
Within 0.1 sec after
stimulation
Short (one second)
Well –localized
Not summated
Skin, deep tissues,
and viscera
Burning
One or more seconds
after stimulation
Long (few minutes)
Diffuse
Can be summated
A-delta
Neospinothalamic
tract
Cerebral cortex
Glutamate
C
Paleospinothalamic
tract
Thalamus
Substance P
Duration
Localization
Summation
Afferent
Tract
Centre
Chemical trans.
Pathway: Neospinothalamic tract
A) 1st order neuron :
• A delta afferent fibers
• End in lamina I of dorsal horn of spinal cord
B) 2nd order neuron :
• Axons of neurons lamina I of dorsal horn of spinal cord cross
the opposite side in front of central canal and ascend as
neospinothalamic in spinal cord and as spinal leminiscus in
brain stem
• End in posteroventral nucleus of thalamus (PVNT)
Pathway:
C) 3rd order neuron :
• Axons of neurons of PVNT ascend in sensory radiations
• End in primary somatic sensory area (area 3,1,2)
Note:
• The chemical transmitter released at the central end of A
delta fibers that carry fast pain is glutamate
PVNT
Sensory Radiations
Spinal Leminiscus
Lamina I
A delta
Receptors
Free nerve endings
Lateral spinothalamic tract
Pathway: Paleospinothalamic tract
A) 1st order neuron :
• C afferent fibers
• End in lamina II and III (called substantia Gelatinosa of
Rolandi SGR) of dorsal horn of spinal cord
B) 2nd order neuron :
• Axons of neurons SGR of dorsal horn of spinal cord cross
the opposite side in front of central canal and ascend in
spinal cord and as;
1. Spinoreticular tract end in RF of MO and Pons
2. Spinotectal tract end in PAG areas of midbrain
3. Paleospinothalamic tract end in non specific thalamic
nuclei (intralaminar and midline)
Pathway:
C) 3rd order neuron :
• Axons of neurons from RF and NSTN of thalamus
ascend in sensory radiations
• Terminate diffusely in all areas of the cerebral cortex
Note:
• The chemical transmitter released at the central end
of c fibers that carry fast pain is substance P
All cortical areas
Non-specific nuclei
of thalamus
Periaqueductal gray
area (PAG) in
midbrain
Reticular formation
In MO and Pons
SGR
Laminae II, III
Receptors
Free nerve endings
Afferent
C fibers
Paleospinothalamic tracts
Significance of Pain Pathways
Neospinothalamic
Paleospinothalamic
a) Rapidly inform the
C.N.S about the injurious
agent → initiate rapid
protective reflexes as
flexion withdrawal reflex.
a) Continuously inform the
C.N.S about the presence of
tissue damage → direct the
person to remove the
injurious agents.
b) Determines accurately b) Strong arousal state due
the site “locality” of the to potent activation of RAS
painful stimuli.
c)
Initiation
of
the
emotional & autonomic
reactions, through RF
• N.B.
• Damage or removal of the sensory cortex does not
lose pain, but the pain become diffuse, ill defined
and the nature of the painful stimulus cannot be
identified.
• So, CC seems to be concerned with the intensity,
locality & modality discrimination of the painful
stimulus.
THANKS