Receptors

• Student should be able to
• understand the types of sensory receptors
• enumerate and understand the properties of
receptors

SENSORY RECEPTORS
• Information about the internal and external environment activates
the CNS via a variety of sensory receptors.
• These receptors are transducers that convert various forms of
energy in the environment into action potentials in neurons.
• Stimulus is an event or particular form of energy that evokes a
specific functional reaction in an organ or receptor. (mechanical,
chemical, EMG, temp)

SENSE ORGANS
• Receptors are dendritic endings of afferent
neurons that are associated with non-neuronal
cells forming sense organs.

• The term Sensory unit
means sensory axon and
all its peripheral
branches.
• The receptive field of
a sensory neuron is the
particular part of the
body surface in which
a stimulus will trigger the
firing of that neuron.

CLASSIFICATION OF SENSORY
RECEPTORSTYPE OF SENSATION
• Mechanoreceptors
• Thermoreceptors
• Nociceptors
• Electromagnetic
• Chemoreceptors
DISTANCE OF
PERCEPTION
• Teleceptors
• Exteroceptors
• Interoceptors
• Proprioceptors

CLASSIFICATION OF RECEPTORS
• Mechanoreceptors
Epidermis & dermis
Joints, tendons, ligaments & muscles
Cochlea
Vestibular apparatus
Baroreceptors in vessels
• Thermoreceptors
Warmth & cold
• Nociceptors
Pain
• Electromagnetic
Rods & cones
• Chemoreceptors
Taste & smell
Carotid &aortic bodies
Hypothalamus
Osmo receptors

TACTILE MECHANORECEPTORSENCAPSULATED
• Meissner’s corpuscles in
dermal papilla
• Pacinian corpuscles in dermis,
ligaments, joint capaules
• Ruffni’s end organs in dermis
and in deeper tissues
NON-ENCAPSULATED
• Free nerve endings in
dermis, ligaments,
cornea, bones
• Hair end organs in hairy
skin
• Merkel’s discs in non
hairy and hairy skin

Mechanoreceptors
Skin (epidermis,
dermis)
Deeper tissues

SENSORY CODING
Receptors encode four elements of stimuli
• Modality
• Location
• Intensity
• Duration

MODALITY OF SENSATION
• Differential Sensitivity of Receptors for particular
stimulus or specific energy for which it is designed
• When nerve fiber from the receptors is stimulated the
perception is that for which the receptor is specialized,
no matter where and how that nerve is stimulated. This
is Muller’s law of specific energy.
• The specificity of nerve fibers for transmitting only one
modality of sensation is called the labeled line principle.

EXPLANNATION
• Each nerve tract terminates at a specific point in the
central nervous system, and the type of sensation felt
when a nerve fiber is stimulated is determined by the
point in the nervous system to which the fiber leads.
• For instance if a pain fiber is stimulated, the person
perceives pain regardless of what type of stimulus
excites the fiber.
• Likewise, if a touch fiber is stimulated by electrical
excitation of a touch receptor or in any other way, the
person perceives touch.

LAW OF PROJECTION
• No matter which part of a pathway you
stimulate between the receptor and the brain
center, your brain will locate the stimulus
where receptors are (e.g. phantom limb)
• reorganization of brain map in somatosensory
cortex
• Some believe it can be blocked by local
anesthetics in spinal cord.

• A phantom limb is the sensation that an amputated
or missing limb is still attached to the body.
• Approximately 60 to 80% of individuals with an
amputation experience phantom sensations in their
amputated limb, and the majority of the sensations
are painful.
• Phantom sensations may also occur after the
removal of body parts e.g. after amputation of the
breast, extraction of a tooth (phantom tooth pain)
or removal of an eye (phantom eye syndrome)

DALE’S LAW
• At one type of synapse only one type of
neurotransmitter is released

TRANSDUCTION OF SENSORY
STIMULI INTO RECEPTOR POTENTIAL
AND NERVE IMPULSESReceptor Potentials
When pressure is
applied to
pacinian corpuscle
, a small non-
propogated
depolarizing
potential develops
called receptor
potential.

PROPERTIES OF RECEPTOR
POTENTIAL
• It is graded potential
• It is non- propagated
• It doesn't obey all or none law

MECHANISMS OF RECEPTOR
POTENTIALS.
• Different receptors can be excited in one of several ways to cause receptor potentials:
• (1) by mechanical deformation of the receptor, which stretches the receptor
membrane and opens ion channels;
• (2) by application of a chemical to the membrane, which also opens ion channels;
• (3) by change of the temperature of the membrane, which
alters the permeability of the membrane; or
• (4) by the effects of electromagnetic radiation,

RELATION OF THE RECEPTOR
POTENTIAL TO ACTION POTENTIALS
• When the receptor potential rises above the
threshold for eliciting action potentials in the nerve
fiber attached to the receptor, then action potentials
occur.
• More the receptor potential rises above the
threshold level, the greater becomes the action
potential frequency.

RELATION OF THE RECEPTOR
POTENTIAL TO ACTION POTENTIALS
• More the receptor
potential rises above
the threshold level,
the greater becomes
the action potential
frequency.

RELATION BETWEEN STIMULUS
INTENSITY AND THE RECEPTOR
POTENTIAL.
• Amplitude increases
rapidly and then less
rapid rise at high stimulus
strength
• the frequency of
repetitive action
potentials transmitted
from sensory receptors
also increase
• But very strong
stimulation decrease
action potentials as well

ADAPTATION OF RECEPTORS
• Another characteristic of all
sensory receptors is that they
adapt either partially or
completely to any constant
stimulus after a period of time.
• That is, when a continuous
sensory stimulus is applied, the
receptor responds at a high
impulse rate at first and then at a
progressively slower rate until
finally the rate of action potentials
decreases to very few or often to
none at all.

MECHANISMS BY WHICH RECEPTORS
ADAPT
• part of the adaptation results from
readjustments in the structure of the receptor
itself,
• and part from an electrical type of
accommodation in the terminal nerve fibril

SLOWLY AND RAPIDLY
ADAPTING RECEPTORS
• Slowly Adapting Receptors Detect
Continuous Stimulus Strength—The
“Tonic” Receptors.
• impulses from the muscle spindles and
Golgi tendon apparatuses allow the
nervous system to know the status of
muscle contraction
• Receptors of the macula in the
vestibular apparatuses
• pain receptors
• baroreceptors of the arterial tree
• chemoreceptors of the carotid and
aortic bodies.
• Rapidly Adapting Receptors Detect
Change in Stimulus Strength—The “Rate
Receptors,” “Movement Receptors,” or
“Phasic Receptors.”
• Pacinian and meissner’s
• Importance of the Rate Receptors—
Their Predictive Function.

• To classify nerve fibers
• To understand the properties and differences
of nerve fibers

NERVE FIBERS THAT TRANSMIT
DIFFERENT TYPES OF SIGNALS, AND
THEIR PHYSIOLOGIC
CLASSIFICATION
nerve fibers come in all sizes between 0.5
and 20 micrometers in diameter—
the larger the diameter, the greater the conducting
velocity
The range of conducting velocities is between 0.5
and 120 m/sec

GENERAL CLASSIFICATION
OF NERVE FIBERS
In the general classification, the fibers are divided into types
• A, B and C,
• A&B are myelinated. C fibers are not
• the type A fibers are further subdivided into
• A α (annulospiral endings)
• A β (touch and pressure)
• A ɣ (motor to muscle spindles)
• Aδ (Pain and temp)
• B fibers are pre-ganglionic fibers
• C fibers are post ganglionic and also transmit slow pain

ALTERNATIVE CLASSIFICATION
USED BY SENSORY
PHYSIOLOGISTS
• Group Ia
Muscle spindle
• Group Ib
Golgi tendon organs
• Group II
Cutaneous tactile receptors
• Group III
Fibers carrying temperature, crude touch, and pricking pain sensations
• Group IV
Un-myelinated fibers carrying pain, itch, temperature, and crude touch
sensations

Diameter in
micrometers
Conduction
velocity in
m/sec
Motor Fiber Type
Aα 0.12-20 0.72-120 Extrafusal
skeletal muscle
fibers
Aγ 0.12-8.2 0.12-48 Intrafusal muscle
fibers
B 0.21-33 0.86-18 Preganglionic
autonomic fibers
C 0.2-2 0.5-2 Postganglionic
autonomic fibers

Peripheral nerve
fibers
Afferents Diameter of
nerve fibers in
mm
Conduction
velocity in m/sec
Receptors
Sensory Fiber Type
Aα Ia and Ib 0.13-20 0.80-120 m/sec Primary muscle
spindles, Golgi
tendon organ
Aβ II 0.16-12 0.35-75 Secondary muscle
spindles, skin
mechanoreceptors
Aδ III 0.11-5 0.15-30 Skin
mechanoreceptors,
thermal receptors,
fast pain
C IV 0.2-1.5 0.5-2 Slow pain and temp

Two types of divergence
• Amplifying type in same direction
• Divergence into multiple tracts to enter
multiple areas of brain

CONVERGENCE OF SIGNALS
• Convergence means signals from multiple inputs uniting
to excite a single neuron.
• Convergence from a single source. That is, multiple
terminals from a single incoming fiber tract terminate
on the same neuron.
• Convergence can also result from input signals
(excitatory or inhibitory) from multiple sources

SOMATIC SENSATIONS
AND MECHANICAL
RECEPTORS
DR. SADIA NAZIR
ASSISTANT PROFESSOR PHYSIOLOGY
LMDC

• Classify somatic sensations
• Classify mechanical receptors

Classification of Sensations
• The somatic senses are the nervous mechanisms
that collect sensory information from all over the
body.
• Special senses, which mean specifically vision,
hearing, smell, taste and equilibrium.

CLASSIFICATION OF SOMATIC
SENSES
• The mechanoreceptive somatic senses,
which include both tactile and position
sensations.
• The thermoreceptive senses, which detect
heat and cold
• The pain sense, which is activated by any
factor that damages the tissues.

MECHANORECEPTIVE SOMATIC
SENSES
• The tactile senses include touch, pressure,
vibration, and tickle
• the position senses include static position and rate
of movement

DETECTION AND TRANSMISSION OF
TACTILE SENSATIONS
• Touch, pressure, and vibration are all
detected by the same types of receptors
called tactile receptors.
• There are at least six entirely different
types of tactile receptors

FREE NERVE ENDINGS
• Free nerve endings,
which are found
everywhere in the
skin and in many
other tissues, can
• detect touch and
pressure

MEISSNER’S CORPUSCLE
• Elongated encapsulated nerve
ending of a large (type AB)
myelinated nerve fiber.
• Inside the capsulation are
many branching terminal
nerve filaments.
• These corpuscles are present
in the non hairy parts of the
skin .
• Meissner’s corpuscles adapt in
a fraction of a second after
they are stimulated,
• Detect low frequency
vibration.

MERKEL’S DISCS
• The hairy parts and non
hairy part of the skin also
contain moderate numbers
of expanded tip receptors
• they transmit an initially
strong but partially
adapting signal and then a
continuing weaker signal
• adapts only slowly.
• Therefore, they are
responsible for giving
steady-state signals

IGGO DOME RECEPTOR
• Merkel’s discs are
often grouped
together in a receptor
organ called the Iggo
dome receptor, which
projects upward
against the underside
of the epithelium of
the skin

HAIR END-ORGAN
• This receptor adapts
readily and, like
Meissner’s corpuscles,
detects mainly
• (a) movement of
objects on the surface
of the body or
• (b) initial contact with
the body.

RUFFINI’S END-ORGANS
• Multibranched,
encapsulated endings,
• These endings adapt
very slowly
• They are also found in
joint capsules and help
to signal the degree of
joint rotation
• Found in skin and
deeper tissues

PACINIAN CORPUSCLES
• Lie both immediately
beneath the skin and deep
in the fascial tissues of the
body.
• They are stimulated only by
rapid local compression of
the tissues because they
adapt in a few hundredths
of a second.
• Important for detecting
tissue vibration or other
rapid changes in the
mechanical state of the
tissues.

• Position sense
1. Static
2. Rate of movement called kinesthesia
• Receptors
1. Muscle spindles
2. Golgi tendon organs
3. Ruffni’s endings
4. Pacinian

• Texture meissner & merkel
• Localization meissner & merkel
• Discrimination meissner
• Vibration meissner & pacinian
• Prolonged touch merkel’s
• Prolonged deep touch & pressure
ruffni’s

TRANSMISSION OF TACTILE SIGNALS
IN PERIPHERAL NERVE FIBERS
• Transmit their signals in type A-beta nerve fibers
that have transmission velocities ranging from 30
to 70 m/sec.
• free nerve ending tactile receptors transmit signals
mainly by way of the small type A-delta myelinated
fibers that conduct at velocities of only 5 to 30
m/sec.
• Some tactile free nerve endings transmit by way of
type C unmyelinated fibers (up to 2 m/sec;) these
send signals into the spinal cord and lower brain
stem, mainly the sensation of tickle.

DETECTION OF VIBRATION
• Pacinian corpuscles can detect signal
vibrations from 30 to 800 cycles per second
and they also transmit their signals over type
A-beta nerve fibers.
• Meissner’s corpuscles detect vibrations from 2
to 80 cycles per seconds

TICKLE AND ITCH
• rapidly adapting mechanoreceptive free nerve
endings elicit only the tickle and itch
sensations.
• These sensations are transmitted by very small
type C, unmyelinated fibers similar to those
that transmit the aching, slow type of pain.

• Receptors afferents
dorsal root ganglia gray column
ascending tracts thalamus
sensory cortex

SENSORY PATHWAYS
• Dorsal Column-medial lemsiscus pathway
• Sensations carried:
• Light touch
• pressure
• Tactile localisation
• 2 point discrimination
• Flutter and vibration
• Stereognosis
• Propioception
• Graphesthesia
• Large myleinated nerve fibres (fast)
• Spatial orientation

•DORSAL COLUMN MEDIAL
LEMNISCUS PATHWAY
•Nerve fibres enters through
dorsal roots divides into
medial +lateral barnches
•Medial ascends in dorsal
columns
•Lateral further branches
and synapse with local
neurons
•Some fibres are given
off to the dorsal column
•Some form local
reflexes
•Others form

•Ascending fibres terminate on cuneate and gracile nuclei
•Decussate to the opposite side immediately medial
lemniscus
•Fibers terminate in the thalamic sensory relay area, called
the ventrobasal complex.
•third-order nerve fibers project, mainly to
• the postcentral gyrus of the cerebral cortex, (called somatic
sensory area I)
•also project to a smaller area in the lateral parietal cortex
called somatic sensory area II).

• the fibers from the lower parts
of the body lie toward the
center of the cord, whereas
new fibres enter laterally.
• In the thalamus, the tail end of
the body represented by the
most lateral portions of the
ventrobasal complex and the
head and face represented by
medial areas of the complex.
• because of the crossing of the
medial lemnisci in the medulla,
the left side of the body is
represented in the right side of
the thalamus, and the right
side of the body in the left
side of the thalamus.
Spatial Orientation

ANTEROLATERAL SYSTEM
Transmits sensory signals that DO NOT require highly
discrete localization
• Composed of smaller, myelinated nerve fibers
(transmission speeds 40 m/sec)
• Less spatial orientation
• Sensory modalities – wide range
• Comprise of:
• Anterior spinothalamic tract
• Lateral spinothalamic tract

ANTEROLATERAL SYSTEM
• Pain
• Thermal sensations
(including warmth & cold)
• Crude touch and pressure
sensations
• Tickle and itch sensations
• Sexual sensations

•From receptors (free nerve
ending enter dorsal horn
(cell bodies of these first
order neurons are in the
dorsal root ganglion)
•Synapse with 2nd order
within 1-2 segments
•Second order neurons
dorsal horn (at all levels).
Their axons decussate in the
anterior white and gray
commisure
•Joined by trigeminothalmic
fibers in medulla, send
collaterals to reticular
formation (alertness to pain)

•3rd order neurons VPL
nucleus of thalamus. Their
fibres ascend through the
posterior limb of internal
capsule corona radiate
•4th order neurons of the
cerebral cortex (Broadmans
areas 3,1.2
Somatosensory cortex)
•Some fibers from the
second order neuron
decussate and ascend as
anterior spinothalmic tract
•Both anterior & lateral
spinothalamic tracts unite
in MO forming spinal
lemniscus

ANTERIOR AND
LATERAL
SPINOTHALMIC
TRACTS
Some fibers carrying crude
touch, tickle may ascend 8-10
spinal cord segments before
synapsing with secondary
neurons. Ascend more
anteriorly as the anterior
spinothalmic tract
Secondary fibers decussate in
anterior gray or white
commissures. Acend to the
medulla together spinal
lemniscus

• Dorsal Column–Medial
Lemniscal System
• 1. Touch sensations
requiring a high degree of
localization of the stimulus
• 2. Touch sensations
requiring transmission of
fine gradations of intensity
• 3. Phasic sensations, such as
vibratory sensations
• 4. Sensations that signal
movement against the skin
• 5. Position sensations from
the joints
• 6. Pressure sensations
having to do with fine
degrees of judgment of
pressure intensity
• Anterolateral System
• 1. Pain
• 2. Thermal sensations,
including both warmth and
cold sensations
• 3. Crude touch and pressure
sensations capable only of
crude localizing ability on
the surface of the body
• 4. Tickle and itch sensations
• 5. Sexual sensations

Cortex: Broadmann’s
areas (50)
Central fissure: anterior
to it motor cortex
Posterior sensory
cortex
Occipital lobe visual
Tempral Lobe Auditory
SS1 and SS2
Located  aneterior part
of parietal lobe
SS1-high degree of
localization

Molecular layer
External granular layer
External pyramidal layer
Internal granular layer
Internal pyramidal layer
Polymorphic layer

FUNCTIONS OF
SOMATOSENSORY AREA I
• Localize and discriminate
discretely the different
sensations in the different
parts of the body
• judge critical degrees of
pressure against the body
• judge the texture,
BILATERAL EXCISION OF
SOMATOSENSORY AREA
Pt is unable to
• Localize and discriminate discretely the
different sensations in the different parts of the
body
• judge critical degrees of pressure against the
body
• judge the texture, weights, shapes or forms of
objects. This is called astereognosis.
• Judge the shape by drawing. Agraphaesthesia

Effect of Removing the Somatosensory Association
Area—(5,7) Amorphosynthesis
• The person loses ability to recognize
complex objects and complex forms felt on
the opposite side of the body.
• He or she loses most of the sense of form of
his or her own body parts on the opposite
side and forgets that it is there .
• When feeling objects, the person tends to
recognize only one side of the object and
forgets that the other side even exists.

LESIONS OF DORSAL COLUMN
TRACT
• Sensory ataxia
• Loss of vibration
• Loss of tactile discrimination
• Loss of tactile localization

• Dorsal Column–Medial
Lemniscal System
• Touch sensations requiring a
high degree of localization of
the stimulus
• Touch sensations requiring
transmission of fine
gradations of intensity
• Phasic sensations, such as
vibratory sensations
• Sensations that signal
movement against the skin
• Position sensations from the
joints
• Pressure sensations having to
do with fine degrees of
judgment of pressure intensity
• Anterolateral System
• Pain
• Thermal sensations, including
both warmth and
cold sensations
• Crude touch and pressure
sensations capable only of
crude localizing ability on the
surface of the body
• Tickle and itch sensations
• Sexual sensations

• Dermatome
Segment of skin supplied by the spinal nerve

PAIN AND
ANALGESIA SYSTEM
DR. SADIA NAZIR
ASSISTANT PROFESSOR PHYSIOLOGY
LMDC

PAIN IS A PROTECTIVE
MECHANISM
• Pain occurs whenever any tissues are being
damaged, and it causes the individual to react
to remove the pain stimulus.

TYPES OF PAIN
• Fast Pain
• Slow Pain
• Fast pain is felt within about 0.1 second after a
pain stimulus is applied
• Slow pain begins after 1 second or more and then
increases slowly over many seconds and
sometimes even minutes.

QUALITIES OF PAIN
• Fast pain is also described by many alternative
names, such as sharp pain, pricking pain,
acute pain, and electric pain
• Slow pain also goes by many names, such as
slow burning pain, aching pain, throbbing
pain, nauseous pain, and chronic pain

PAIN RECEPTORS
• Are Free Nerve Endings
• They are widespread in the superficial layers of
the skin as well as in certain internal tissues,
such as the periosteum, the arterial walls, the
joint surfaces, and the falx and tentorium in
the cranial vault.
• Non-adapting Nature of Pain Receptors

Three Types of Stimuli Excite Pain Receptors—
• Mechanical
• Thermal
• Chemical

• Some of the chemicals that excite the chemical
type of pain are bradykinin, serotonin,
histamine, potassium ions, acids,
acetylcholine, and proteolytic enzymes
• In addition, prostaglandins and substance P
enhance the sensitivity of pain endings but do
not directly excite them

DUAL PATHWAYS FOR
TRANSMISSION OF PAIN SIGNALS
INTO THE CENTRAL NERVOUS
SYSTEM
• Peripheral Pain Fibers—
• “Fast” (A delta) and “Slow” Fibers (C fibers)
• The two pathways mainly correspond to the two
types of pain—
• a fast-sharp pain pathway and
• a slow-chronic pain pathway.

DUAL PATHWAYS FOR TRANSMISSION OF
PAIN SIGNALS INTO THE CENTRAL
NERVOUS SYSTEM
FAST PAIN
(NEOSPINOTHALAMIC
PATHWAY)
1. Mechanical or thermal pain
stimuli
2. A delta fibers at velocities
between 6 and 30 m/sec.
3. They terminate mainly in
lamina I (lamina
marginalis)
SLOW PAIN
(PALEOSPINOTHALAMIC
PATHWAY)
1. Mostly by chemical types
of pain stimuli but
sometimes by persisting
mechanical or thermal
stimuli.
2. C fibers at velocities
between 0.5 and 2 m/sec.
3. laminae II and III of the
dorsal horns, which
together are called the
substantia gelatinosa,

Fast pain
4. most pass all the way to the
thalamus (Ventrobasal)
• Project to somatosensory cortex.
5. can be localized much more
exactly in the different parts of
the body than can slow-chronic
pain.
6. Glutamate, the Probable
Neurotransmitter of the Fast
Pain Fibers
SLOW PAIN
4.most terminate in one of
three areas:
(a) reticular nuclei
(b) tectal area of the
mesencephalon
(c) periaqueductal gray region
(d) Intralaminar nuclei and
hypothalamus
5.Poorly localized.
6.Type C pain fiber terminals
entering the spinal cord

Pain Suppression (“Analgesia”) System in the Brain
and Spinal Cord
• Inhibition of pain signals at spinal cord by
descending brain fibers
• Encephalin secreting neurons in cord and brain stem
• Inhibition of pain fibers by tactile incoming fibers

Acupuncture analgesia (AA)
• technique of relieving pain by
inserting and manipulating
threadlike needles at key points
• acupuncture endorphin hypothesis
• Acupuncture needles activate
specific afferent nerve
fibersCNSblocking pain
transmission at both
• the spinal-cord and brain levels
through use of endorphins and
closely related endogenous opiates.

• The periaqueductal gray and periventricular
areas of the mesencephalon and upper pons
surround the aqueduct of Sylvius and portions
of the third and fourth ventricles. Neurons from
these areas send signals to
• The raphe magnus nucleus, a thin midline
nucleus located in the lower pons and upper
medulla, and the nucleus reticularis
paragigantocellularis, located laterally in the
medulla. From these nuclei, second-order
signals are transmitted down the dorsolateral
columns in the spinal cord to
• Pain inhibitory complex located in the dorsal
horns of the spinal cord.

INHIBITION OF PAIN TRANSMISSION BY
SIMULTANEOUS TACTILE SENSORY
SIGNALS
• Stimulation of large type A beta sensory fibers
from peripheral tactile receptors can depress
transmission of pain signals from the same body
area.
• This presumably results from local lateral
inhibition in
the spinal cord.
• It explains why such simple maneuvers as rubbing
the skin near painful areas is often effective in
relieving pain.
• It also explains why liniments are often useful for
pain relief.

• Allodynia
Non painful stimulus causes pain (Lesion of VPL of
thalamus)
• Hyperalgesia
Hypersensitivity to pain
A pain nervous pathway sometimes becomes excessively
excitable;.
• Possible causes of hyperalgesia are
• Excessive sensitivity of the pain receptors themselves,
which is called primary hyperalgesia (Burns)

REFERRED PAIN
• Often a person feels pain in a part of the body
that is fairly remote from the tissue causing
the pain. This is called referred pain. For
instance, pain in one of the visceral organs
often is referred to an area on the body
surface.

VISCERAL PAIN AND SURFACE
PAIN
VISCERAL PAIN
• Highly localized types of
damage to the viscera seldom
cause severe pain.
• True visceral pain is
transmitted via pain sensory
fibers within the autonomic
nerve bundles, and the
sensations are referred to
surface areas of the body
often far from the painful
organ.
SURFACE
PAIN/PARIETAL PAIN
• Parietal sensations are
conducted directly into
local spinal nerves from
the parietal
peritoneum, pleura, or
pericardium, and these
sensations are usually
localized over painful
area.

VISCERAL” AND THE “PARIETAL”
PAIN
TRANSMISSION PATHWAYS

CAUSES OF TRUE VISCERAL PAIN
• Any stimulus that excites pain nerve endings in diffuse areas of the viscera
can cause visceral pain.
• Such stimuli include
• ischemia of visceral tissue,
• chemical damage to the surfaces of the viscera,
• spasm of the smooth muscle of a hollow viscus,
• excess distention of a hollow viscus, and stretching of the connective
tissue surrounding or within the viscus.
• Essentially all visceral pain that originates in the thoracic and abdominal
cavities is transmitted through small type C pain fibers and, therefore, can
transmit only the chronic-aching-suffering type of pain.

Hyperalgesia
• A pain nervous pathway sometimes becomes
excessively excitable; this gives rise to hyperalgesia,
which means hypersensitivity to pain.
• Possible causes of hyperalgesia are
• (1) excessive sensitivity of the pain receptors
themselves, which is called primary hyperalgesia
• (2) facilitation of sensory transmission, which is
called secondary hyperalgesia.

• Herpes Zoster (Shingles)
• Herpesvirus infects a dorsal root ganglion.
• This causes severe pain in the dermatomal segment
served by the ganglion, thus eliciting a segmental
type of pain that circles halfway around the body.
• The disease is called herpes zoster, or “shingles,”
because of a skin eruption that often ensues.

• Tic Douloureux
• Lancinating pain occasionally occurs in some people
over one side of the face in the sensory distribution
area (or part of the area) of the fifth or ninth nerves;
This phenomenon is called tic douloureux
(trigeminal neuralgia or glossopharyngeal
neuralgia).
• The pain feels like sudden electrical shocks, and it
may appear for only a few seconds at a time or may
be almost continuous.

• Headache
• Headaches are a type of pain referred to the surface
of the head from deep head structures.
• Pain-Sensitive Areas in Cranial Vault.
• Tugging on the venous sinuses around the brain,
• Damaging the tentorium,
• Stretching the dura at the base of the brain can
cause intense pain that is recognized as headache
• Middle meningeal artery is a pain sensitive structure

TYPES OF INTRACRANIAL
HEADACHE
• Brain tumors
• Headache of Meningitis.
• Headache Caused by
Low Cerebrospinal Fluid
Pressure.
• Migraine Headache
• Alcoholic Headache
TYPES OF EXTRACRANIAL
HEADACHE
• Headache Resulting
from Muscle Spasm.
Irritation of Nasal and
Accessory Nasal
Structures.
Eye Disorders

THERMAL SENSATIONS
• The human being can perceive different gradations of
cold and heat,
• from freezing cold
• cold
• cool
• Indifferent
• to warm
• hot
• burning hot.

• Thermal gradations are discriminated by at
least three types of sensory receptors:
• cold receptors,
• warmth receptors,
• and pain receptors.

BROWN-SÉQUARD SYNDROME
• If the spinal cord is transected on only one side, the Brown-Séquard syndrome occurs.
• All motor functions are blocked on the side of the transection in all segments below
the level of the transection and at the level.
• The sensations of pain, heat, and cold— sensations served by the spinothalamic
pathway—are lost on the opposite side of the body in all dermatomes two to six
segments below the level of the transection.
• The dorsal and dorsolateral columns—kinesthetic and position sensations, vibration
sensation, discrete localization, and two-point discrimination—are lost on the side of
the transection in all dermatomes below the level of the transection.

BROWN-SÉQUARD SYNDROME
At the level Below the
level
Above the
level
LMN paralysis same side UMN paralysis same
side
Cutaneous anesthesia in
the dermatomal
segment of ipsilateral
side
Loss of pain and temp
of contralateral side 2
to 5 segments below
the level of lesion
Altered sensations
Loss of vibration, fine
touch, tactile
localization and
discrimination in all

Receptors

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Receptors