1. The document discusses the anatomy and pathways of the pain sensation system. It describes how nociceptors detect painful stimuli and transmit signals to the spinal cord and brain. 2. The spinal cord plays an important role in pain processing. It contains ascending tracts that carry pain signals to the brain and descending tracts that modulate pain. Key nuclei in the spinal cord dorsal horn relay and modulate pain transmission. 3. Pain signals are transmitted from the spinal cord via the spinothalamic tract to the thalamus and then to regions of the cerebral cortex involved in pain perception and modulation like the somatosensory, cingulate, and insular cortices. The periaqueductal

1. PAIN PATHWAY
ANATOMY
MODERATOR: DR FAREED AHMED
PRESENTED BY:DR ANURADHA

2.  Sensation of the affected level of
unpleasantness
 Perception of actual or threatened damage
based on past experience, anxiety, cognitive
factors
 Pain is Subjective

3.  A quality that has complex phenomenological
facets (behavioral, sensory, emotional)
 Pain perception can be modulated by all kinds
of factors, including behavioral states
(stress, sex), cognitive states
(hypnosis), mental states (“trance”), social
norms and drugs.

4.  Nociceptors are special receptors that respond only
to noxious stimuli and generate nerve impulses
which the brain interprets as “pain”
 Free nerve endings
 Tissue damage

5.  Aδ – fast, sensitive to mechanical noxious
stimuli. – small, myelinated. High
conductance speed
 C – slow, sensitive to many noxious stimuli
(chemical, etc.) – small, unmyelinated. Slow
conductance speed
 This distinction has been used to explain
the phenomenon of double-pain

6. Somatosensory
System
Brain Spinal Cord PNS
Somatosensory Dorsal Horn Afferent Neuron
Cortex Ventral Root Efferent Neuron
A-delta Fibers
Thalamus
C-Fibers

7. •Glutamate - Central
Pain •Substance P - Central
Initiators •Brandykinin - Peripheral
•Prostaglandins - Peripheral
•Serotonin
Pain •Endorphins
Inhibitors •Enkephalins
•Dynorphin

8.  1. gray matter
 2. white matter
 3. gray commissure
 4. central canal
 Dorsal and ventral nerve
roots

9.  Ascending and descending fibers are organized in
distinct bundles which occupy particular areas and
regions in the white matter
 Generally long tracts are located peripherally in the white
matter, while shorter tracts are found near the gray
matter
• The TRACT is a bundle of nerve fibers (within CNS) having the same
origin, course, destination & function
• The name of the tract indicates the origin and destination of its fibers
• The axons within each tract are grouped according to the body region
innervated

10.  1. nuclei
 2. horns
a. dorsal -- sensory
b. ventral – motor
c. lateral – autonomic
Spinal grey matters divided into 10 layers

11.  Tracts that serve to join brain to the spinal
cord
 Ascending
 Descending
 Fibers that interconnect adjacent or distant
segments of the spinal cord
 Intersegmental (propriospinal)

12.  Three major pathways carry sensory information
Posterior column pathway (gracile & cuneate
fasciculi)
Anterolateral pathway (spinothalamic)
Spinocerebellar pathway

13.  Monitor conditions both inside the body and in the
external environment
 Sensation-stimulated receptor passes information
to the CNS via afferent (sensory) fibers
 Most sensory information is processed in the spinal
cord , thalamus, or brain stem. Only 1% reaches
the cerebral cortex and our conscious awareness
 Processing in the spinal cord can produce a rapid
motor response (stretch reflex)
 Processing within the brain stem may result in
complex motor activities (positional changes in the
eye, head, trunk)

14. THREE neurons from the
receptor to the cerebral cortex
 First order neuron:
 Cell body located in the dorsal 3
root ganglion. The Axon (central
process) passes to the spinal
cord through the dorsal root of
spinal nerve gives many
collaterals which take part in
spinal cord reflexes runs 2
ipsilaterally and synapses with
second-order neurons in the
cord and medulla oblongata 1

15.  Second order neuron:
◦ Has cell body in the
spinal cord or medulla
oblongata
◦ Axon decussate &
◦ Terminate on 3rd order
neuron
 Third order neuron:
◦ Has cell body in
thalamus
◦ Axon terminates on
cerebral cortex
ipsilaterally

16.  DIRECT---- direct conscious appreciation of
pain
 INDIRECT---affective or arousal impact of
pain via
1) Spino-reticular-thalamic –cortical pathway
(ARAS)
2) Spino-mesencephelic path (affective impact
of pain)

17. Pain information
travels up the spinal
cord through the
spinothalamic track
(2 parts)
•Immediate warning of the
ANTERIOR/VENTRAL presence, location, and
intensity of an injury
•Slow, aching reminder that
LATERAL tissue damage has occurred
Decussates at the
level of spinal
cord

18.  Descending pain
pathway
responsible for
pain inhibition
 “affective
sensation”i.e
compulsion to act

19.  Located lateral and ventral to
the ventral horn
 Carry impulses concerned
with pain and thermal
sensations (lateral tract) and
also non- discriminative
touch and pressure (medial
tract)
 Fibers of the two tracts are
intermingled to some extent
 In brain stem, constitute the
spinal lemniscus
 Fibers are highly somato-
topically arranged, with
Information is sent to
those for the lower limb lying the primary sensory
most superficially and those
for the upper limb lying cortex on the opposite
deeply side of the body

20.  Axons of 1st order neurons
terminate in the dorsal horn
 Axons of 2nd order neuron
(mostly in the nucleus
proprius), decussate within
one segment of their origin, by
passing through the ventral
white commissure & terminate
on 3rd order neurons in ventral
posterior nucleus of the
thalamus
 Thalamic neurons project to
the somatosensory cortex

21. SKIN
SPINAL CORD via pseudounipolar cells
SUBSTANTIA GELATINOSA OR NUCLEUS PROPRIUS via LISSAUER TRACT
CROSS OVER VIA ANTERIOR COMMISURE
BRAIN STEM (ROSTRAL VENTROMEDIAL MEDULLA)
THALAMUS (VPL,VPM,MEDIAL DORSAL)
CINGULATE CORTEX,SOMATOSENSORY CORTEX AND INSULAR CORTEX

22. Pseudounipolar cell (dorsal
root ganglion) ,divides
into central and
peripheral branch)
 Head and neck,carried by
5/6/9/10 via gasserian
ganglion,geniculate,super
ior and inferior
petrosal nerve,jugular
ganglion(somatic) and
ganglion nodosum
(viseral)
 Reach brain stem via
cranial nerves

23.  Tip of the posterior
column near posterior
nerve roots
 Centrally projecting
axons carrying
discriminating pain
/temperature info
regarding
location/intensity/qu
ality
 Synapse with second
order neuron,crosses
midline and joins STT

24. SUBSTANTIA GELATINOSA:
 grey horn wid gelatinous
sub which contains
neuroglia and nerve cells
 Rexed lamina 2
 Contains opiod
receptors/ c fibres and
a-delta fibres
NUCLEUS PROPRIUS
 Bulk of dorsal horn
 Rexed 3/4/5
 a/w fine touch and
pressure with nucleus
dorsalis

25. Lamina of Rexed
Lamina I ---------- marginal layer
Lamina II ---------- substantia gelatinosa of Rolando
Lamina III, IV ----- nucleus proprius
Lamina V, VI
Lamina VII --------- intermediate gray
intermediolateral cell column (ILM)
Clarke’s column (Nucleus dorsalis)
intermediomedial cell column (IMM)
Lamina VIII----------motor horn
Lamina IX ---------- anterior horn (motor) cell
Lamina X ----------- gray commissure

26. ANTERIOR WHITE COMMISURE
 alba anterior medullae spinalis
 just anterior to the gray
commissure (Rexed lamina X).
 A δ fibers and C fibers
ROSTRAL VENTROMEDIAL
MEDULLA
 midline on the floor of the
medulla (myelencephalon
 sends descending inhibitory and
excitatory fibers to the dorsal
horn spinal cord neurons
 On-cells, off-cells, and neutral
cells.
 important in the maintenance of
neuropathic pain
 RVM contains high levels of both
the neurokinin 1 receptor and its
endogenous ligand, Substance P
(SP).

28.  Sensory aspects of pain seem to be processed in the
Somatosensory cortex.
 Emotional distress associated with pain seems to be
processed in the Anterior Cingulate Cortex (ACC).
 Subjects with lesions in ACC could still accurately
judge the intensity of pain. But they were not in the
least bothered by it.
• On the other
hand, subjects empathy
for the pain of others
only elicits activity in
ACC, not Somatosensory
cortex.

29. CINGULATE CORTEX
 the medial aspect of the
cortex
 Part of limbic lobe
 Receives input from
thalamus and neocortex
PRIMARY SOMATOSENSORY
CORTEX

30. INSULAR
CORTEX
 deep within the
lateral sulcus
the fissure
separating the
temporal and
the frontal
lobes
 linked to
emotion
 Associated with
addiction

31.  gray matter located around the cerebral
aqueduct within the tegmentum of the
midbrain.
 role in the descending modulation of pain
and in defensive behaviour.
 enkephalin-releasing neurons
 5-HT (serotonin) released from the raphe
nuclei descends to the dorsal horn of the
spinal cord where it forms excitatory
connections with the "inhibitory
interneurons" located in Laminae II (aka
the substantia gelatinosa).
 When activated, these interneurons
release either enkephalin or dynorphin
which bind to mu opioid receptors

32. Melzack & Wall (1965)
A gate, where pain
impulses can be “gated” descending nerve
fibers from brain
The synaptic junctions
between the peripheral
nociceptor fiber and the
dorsal horn cells in the
spinal cord are the sites
of considerable
plasticity. pain pathways
axons from
touch
receptors
axons from
“THE PAIN GATE” nociceptors
opioid-releasing
interneuron

33. Stimulation of touch fibres for pain relief:
◦ TENS (transcutaneous electrical nerve stimulation)
◦ Acupuncture
◦ Massage
Release of natural opioids
◦ Hypnosis
◦ Natural childbirth techniques

34. MEDIAL SPINOTHALAMIC TRACT:
 MEDIAL THALAMUS
 MEDIATES AUTONOMIC AND UNPLEASANT
PERCEPTION OF PAIN PATHWAY
 FEW TO PERIAQUEDUCTAL GRAY
 COLLATERAL FIBRES TO RAS AND
HYPOTHALAMUS-AROUSAL TO PAIN

35.  ran additional route by which dull, aching pain is
transmitted to a conscious level
 Some 2nd order neurons terminate in the reticular
formation of the brain stem, mainly within the
medulla
 Reticulothalamic fibers ascend to intralaminar nuclei
of thalamus, which in turn activate the cerebral
cortex

36.  Located in
periaqueductal grey
matter of the
brainstem,amygdala,
corpus striatum nd
hypothalamus
 Spinal
cord(substance
gelatinosa)
 Endorphins inhibit
release of excitatory
neurotransmitters

37.  Mu,kappa and delta
 Superfamily of G protein
coupled receptors
 Brain,spinal cord and
peripheral recetors
 Mimic endogenous ligands
 l/t hyperpolarisation

38. • Pain receptors are the only receptors in viscera whose stimulation produces
sensations
• Pain receptors respond differently to stimulation
• Pain receptors are not well localized
• Pain receptors may feel as if coming from some other part of the body
• Known as referred pain…
38

39. Afferent innervation of the viscera.
Often anatomical separation nociceptive innervation (in
sympathetic nerves) from non-nociceptive
(predominantly in vagus).
Many visceral afferents are specialized nociceptors, as
in other tissues small (Ad and C) fibers involved.
Large numbers of silent/sleeping nociceptors, awakened
by inflammation.
Nociceptor sensitization well developed in all visceral
nociceptors.

40.  Pain originating
from organs
perceived as
coming from skin
 Site of pain may be
distant from organ

41. Referred pain
Convergence theory:
This type of referred pain occurs
because both visceral and somatic
afferents often converge on the same
interneurons in the pain pathways.
Excitation of the somatic afferent
fibers is the more usual source of
afferent discharge,
so we “refer” the location of visceral
receptor activation to the somatic
source even though in the case of
visceral pain.
The perception is incorrect. The convergence of
nociceptor input from the
viscera and the skin.

42. • Thalamus
• Allows person to be aware of pain
• Cerebral cortex
• Judges intensity of pain
• Locates source of pain
• Produces emotional and motor responses to pain
• Pain inhibiting substances:
• Enkephalins
• Serotonin
• Endorphins
42

43. Left
spinothalamic pathway spinal cord injury
. Anaesthesia will normally
Loss of sense of: begin 1-2 segments below
•Touch the level of
•Pain
•Warmth/cold lesion, affecting all caudal
in right leg body areas.

44. Hyperalgesia:
The skin, joints, or muscles that have already
been damaged are unusually sensitive. A light
touch to a damaged area may elicit excruciating
pain;
Primary hyperalgesia occurs within the area of
damaged tissue;
Secondary hyperalgesia occurs within the
tissues surrounding a damaged area.

45.  Melzack (1992) 7 features
1. Phantom limb feels real. Sometimes amputees try
to walk on their phantom limb.
2. brain contains neuromatrix of the body image –
neurosignature like a hologram

46.  A well-known case of congenital insensitivity
to pain is a girl referred to as 'miss C' who
was a student at McGill university in Montreal
in the 1950s.
 She was normal in every way, except that she
could not feel pain. When she was a child she
had bitten off the tip of her tongue and had
suffered third-degree burns by kneeling on a
radiator.

47.  Aspirin and ibuprofen block formation of
prostaglandins that stimulate nociceptors
 Novocain blocks conduction of nerve
impulses along pain fibers
 Morphine lessen the perception of pain in
the brain.

48. 1. Prevents serious damage. If you touch
something hot, you are forced to withdraw
your hand before it gets seriously burnt.
2. Teaches one what to avoid
3. If pain is in joints, pain limits the activity, so
no permanent damage can occur.
 but pain can become the problem, and
cause people to want to die.