Download Somatic sensation and pain

SOMATIC SENSATION AND PAIN
Zoltán Pfund, MD, PhD
University of Pécs
Department of Neurology
CONTENTS
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Anatomy and physiology of somatic sensation
Interruption of sensory pathways
Pain and nociception
Anatomy and physiology of pain
Pain disorders
Therapy of pain
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
CUTAN MECHANORECEPTORS
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
CUTAN MECHANORECEPTORS
• Fast Adapting Touch-Pressure Receptors
Hair follicle receptor
Meissner endings – hairless skin – Aβ
Respond to flutter,
flutter, motion
Pacinian corpuscle – dermis – Aβ
Responds to vibration
vibration
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
CUTAN MECHANORECEPTORS
• Slowly Adapting Touch-Pressure Receptors
Free nerve endings - hairy & hairless skin - C fibers
Tickle & light or superficial touch
Merkels discs - in both hairy and hairless skin – Aβ
Pressure, form, texture
Ruffini endings - hairy and some in hairless skin - Aβ
Respond to lateral stretch of the skin and
steady pressure
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
JOINT & MUSCLE RECEPTORS
• Proprioceptive Receptors
Receptors in muscles, tendons and joints
Joint afferents – diverse receptors – Aα
Protective function
Muscle spindle is a major stretch receptor - Aβ
Respond to muscle length
Golgi organs in tendons - Aα
Respond to muscle tension
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
TEMPERATURE RECEPTORS
• Temperature Receptors
Separate warm and cold receptors
Free nerve endings
Warm receptors - C fibers
Respond to increasing temperature
Cold receptors - Aδ fibers
Respond to decreasing temperature
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
NOCICEPTORS
• Nocioceptors
Free nerve endings: mechano and thermoreceptors,
thermoreceptors,
polymodal nociceptors
C fibers – dull/burning pain – slow pain
Aδ fibers - sharp pricking & stinging pain – fast pain
University of Pé
Pécs,
cs, Department of Neurology
SENSORY AFFERENTS
PRIMARY AFFERENT FIBERS
Large
Medium
Small
Unmyelinated
I
II
III
IV
Aα
1212-20 µm
7272-120 m/sec
Aβ
6-12 µm
3636-72 m/sec
Aδ
1-6 µm
4-36 m/sec
C
0.20.2-1.5 µm
0.40.4-2.0 m/sec
University of Pé
Pécs,
cs, Department of Neurology
SOMATOSENSORY PATHWAYS
• Dorsal Column-Medial lemniscal system
Discriminative touch
Vibratory sense
Limb and joint position information
• Anterolateral system
Pain
Temperature
Crude touch
University of Pé
Pécs,
cs, Department of Neurology
DORSAL COLUMN – MEDIAL
LEMNISCAL SYSTEM
• Primary afferents ascend to the medulla
on the ipsilateral side of the cord in the
posterior columns
• Secondary afferents cross in the medulla
and ascend as the medial lemniscus
• In the thalamus they synapse in the VPL
(ventroposterior lateral nucleus) and ascend
to the cortex
University of Pé
Pécs,
cs, Department of Neurology
ANTEROLATERAL SYSTEM
• Primary afferents enter the cord laterally
and synapse in the dorsal horn
• The secondary afferents cross to the
opposite side of the spinal cord and ascend
in the spinothalamic tract
• The spinothalamic tract enters
enters the VPL of
the thalamus,
thalamus, synapses and is finally carried
to cortex by the thalamocortical neurons
University of Pé
Pécs,
cs, Department of Neurology
ANTEROLATERAL SYSTEM
Lissauer`s tract
Pain afferents travel one or two segments up or down the cord
before synapsing.
synapsing. Lissauer's tract is the tract carrying these
migrating axons,
axons, but they are only in the tract for a short time.
time.
Within one or two levels,
levels, they enter the dorsal horn and synapse.
synapse.
University of Pé
Pécs,
cs, Department of Neurology
ANTEROLATERAL SYSTEM
The dorsal horn is a multimulti-layered structure.
structure. The thin outermost layer is
called the posterior marginalis layer.
layer. The wide pale second layer is called
the substantia gelatinosa, and the layer deep to that is called the
the nucleus
proprius.
roprius.
University of Pé
Pécs,
cs, Department of Neurology
ANTEROLATERAL SYSTEM
The two types of pain fibers enter different layers of the dorsal
dorsal horn.
Aδ fibers enter the posterior marginalis and the nucleus proprius, and
synapse on a second set of neurons. The C fibers enter the substantia
substantia
gelatinosa and synapse, but they do not synapse on secondary afferents.
afferents.
Instead they synapse on interneurons - neurons which do not project
out of the immediate area. The interneurons must carry the signal
signal to the
secondary afferents in either the posterior marginalis or the nucleus
nucleus
proprius.
University of Pé
Pécs,
cs, Department of Neurology
INTERRUPTION OF SENSORY
PATHWAYS
Hemispheric lesion:
Contralateral side of the body
University of Pé
Pécs,
cs, Department of Neurology
INTERRUPTION OF SENSORY
PATHWAYS
Brainstem:
Alternate syndromes
University of Pé
Pécs,
cs, Department of Neurology
INTERRUPTION OF SENSORY
PATHWAYS
Spinal cord:
Segmental
University of Pé
Pécs,
cs, Department of Neurology
INTERRUPTION OF SENSORY
PATHWAYS
Peripheral:
Root,
Root, plexus
plexus or peripheral nerve
University of Pé
Pécs,
cs, Department of Neurology
PAIN AND NOCICEPTION
• Pain is a subjective experience that accompanies
nociception, but can also arise without any stimuli. It
includes the emotional response.
• Nociception is a neurophysiologic term and denotes the
activity in the nerve pathways. These pathways transmit
the unpleasant signals that are not always painful.
• Pain is a critical component of the body's defense system
• Cognitive and emotional factors might dramatically
influence painful sensations
• According to WHO one human being out of five suffers
from chronic pain
University of Pé
Pécs,
cs, Department of Neurology
PAIN AND NOCICEPTION
• Pain is a subjective experience that accompanies
nociception, but can also arise without any stimuli. It
includes the emotional response.
• Nociception is a neurophysiologic term and denotes the
activity in the nerve pathways. These pathways transmit
the unpleasant signals that are not always painful.
• Pain is a critical component of the body's defense system
• Cognitive and emotional factors might dramatically
influence painful sensations
• According to WHO one human being out of five suffers
from chronic pain
University of Pé
Pécs,
cs, Department of Neurology
NOCICEPTION
• Nociceptors are the free nerve endings of neurons that
have their cell bodies outside the spinal column in the dorsal
root ganglion
• When the nociceptors are stimulated, they transmit signals
through sensory neurons in the spinal cord
• Signals release glutamate, an exicitory neurotransmitter
that relays signals from one neuron to another and ultimately
to the thalamus, in which pain perception occurs
• From the thalamus, the signal travels to the cerebrum,
at which point the individual becomes fully aware of the pain
University of Pé
Pécs,
cs, Department of Neurology
ANATOMY AND PHYSIOLOGY
OF PAIN
– Neurotransmission by C neurons involves substance P
– A-δ transmitters at terminals: glutamate, aspartate,
adenosin triphosphate
– Opiates (receptors in lamina II) decreases substance P and
lamina II neurons release enkephalins, endorphins and
dynorphins
University of Pé
Pécs,
cs, Department of Neurology
ANATOMY AND PHYSIOLOGY
OF PAIN
Spinal afferent tracts
– Lateral spinothalamic tract (fast conducting
pathway) via anterior comissure, termination in
brainstem and thalamic structures
– Medial spinothalamic tract; paleospinothalamic
pathway (slow-conducting multineuron system),
mediates poorly localized pain from deep somatic
and visceral structures. Connections to medulla,
parabrachial region, midbrain reticular formation
and hypothalamus
University of Pé
Pécs,
cs, Department of Neurology
ANATOMY AND PHYSIOLOGY
OF PAIN
Thalamic terminus and thalamocortical projections
– Lateral division terminates in the ventrobasal and
posterior groups of nuclei; projections to the primary
sensory cortex and Sylvian fissure
– Medial divisions terminates in the intralaminar complex;
projections to hypothalamus, amygdaloid nuclei and
limbic cortex (arousal and autonomic responses)
– Paleospinothalamic fibers project onto the medial
intralaminar nuclei; cortical projection is not well known
University of Pé
Pécs,
cs, Department of Neurology
DESCENDING PAIN-MODULATING
SYSTEMS
–
–
–
–
Projections from the frontal cortex and
hypothalamus to the periaqueductal region of
the midbrain and medulla
From the medulla it descends to the lateral
funiculus and posterior horn
Modulate activity of nociceptive pathways
Other descending pathways (serotoninergic,
noradrenergic) project to locus ceruleus, dorsal
raphe nucleus
University of Pé
Pécs,
cs, Department of Neurology
DESCENDING PAIN-MODULATING
SYSTEMS
Opiate interneurons in the spinal cord can be activated by descending
descending
projections from the brainstem (especially the raphe nuclei and periaqueductal
grey), and can block pain transmission at two sites. 1.,
1., They can prevent the
primary afferent from passing on its signal by blocking neurotransmitter
neurotransmitter release,
and 2.,
2., they can inhibit the secondary afferent so it does not send the signal up
the spinothalamic tract.
University of Pé
Pécs,
cs, Department of Neurology
PAIN THRESHOLD
• The threshold for perception of pain is approximately
the same in all person
• It is lowered by inflammation (sensitization)
• It is raised by local anesthetics, certain lesions of the
nervous system and centrally acting analgesic drugs
University of Pé
Pécs,
cs, Department of Neurology
DIFFERENT TYPES OF PAIN
• Acute pain is defined as short-term pain or pain with
an easily identifiable cause
• Chronic pain is medically defined as pain that has
lasted 6 months or longer
• Cutaneous pain is caused by injury to the skin or
superficial tissues
• Somatic pain originates from ligaments, tendons,
bones, blood vessels, and even nerves themselves
• Visceral pain originates from body organs
• Phantom limb pain is the sensation of pain from a
limb that one no longer has
• Neuropathic pain can occur as a result of injury or
disease to the nerve tissue itself
University of Pé
Pécs,
cs, Department of Neurology
DIFFERENT PAIN TYPES
• Skin pain: fast pain is transmitted by A-δ fibers, slow
and longer-lasting pain is transmitted by C fibers
• Deep pain: visceral and skeletomuscular structures;
sharp, penetrating and burning type (e.g. heartburn
and angina pectoris)
• Referred pain: deep pain projects fix site
University of Pé
Pécs,
cs, Department of Neurology
PAIN INTENSITY
fast pain
longerlonger-lasting pain
Intensity
Time
University of Pé
Pécs,
cs, Department of Neurology
REFERRED PAIN
Diaphragm C4
Heart T3T3-4
Esophagus T4T4-5
Stomach T6T6-9
Liver, gallbladder T8T8-11
Small intestines T10T10-L1
Large intestines T11T11-L1
Kidney, testicles T10T10-L1
Urinary bladder T11T11-L1
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Peripheral nerve pain (neuropathic, neurogenic)
– Pain arises from direct stimulation of nervous tissue,
pain is due to stimulation of sensitized C fibers
– Mono and polyneuropathies
– Plexus lesion
– Trigeminal neuralgia
– Root irritation
– Herpes zoster
– Deafferentation pain
– Reflex sympathetic distrophy
– Fibromyalgia
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Carpal tunnel syndrome (mononeuropathy)
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Carpal tunnel syndrome
• Due to excessive use of hand
• Dysesthesias and pain in the
fingers
• Paresthesias are worse during
the night
• Pain radiates into the forearm
• Sensory loss, atrophy, motor
weakness
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Polyneuropathy:
similar symptoms,
different etiology
PAIN DISORDERS
Brachial plexus neuritis (Parsonage-Turner syndrome)
– The illness develops abruptly in healthy individuals
– Shoulder and neck ache
– Pain becomes rapidly more severe
– After a period of 5 to 14 days there is a rapid development
of muscular weakness, sensory and reflex impairment
– Atrophy
– CMV infection, AIDS, Coxsackie virus, vaccines
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Low-back pain
- Local pain: periosteum, capsule of apophyseal
joints, muscles, ligaments, annulus fibrosus
- Referred pain: projected from the spine to viscera
- Radicular or root pain: distal radiation to the
territory of root
- Pain secondary to muscle spasm
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Normal
Abnormal
Disc degeneration
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
L5 disc: axial view
S1 root irritation
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Herpes zoster:
• segmental distribution of rash
• inflammatory reaction in cranial
or spinal sensory ganglia (root)
• radicular pain
• varicella zoster virus
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Central pain
– Spinal cord lesion: intolerable pain below the level of lesion;
deafferentation of secondary neurons in the posterior horns
or of sensory ganglion cells; deafferented cells become
continuously active
– Thalamic pain syndrome (Déjerine-Roussy) and parietal
lobe infarction (Schmahmann and Leifer), lateral medullary
and pons lesion: intractable pain; loss of descending
inhibitory systems and/or altered sensitivity and
hyperactivity of central neurons
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Primary headaches
– Migraine: trigeminovascular headache
– Cluster: trigemino-autonomic headache
– Tension headache: contraction of craniocervical muscles
University of Pé
Pécs,
cs, Department of Neurology
PAIN DISORDERS
Secondary headache
- Headaches related to medical diseases
- Pain-sensitive cranial structures:
1. Skin, subcutaneus tissue, muscles, extracranial arteries,
periosteum of the skull
2. Delicate structures of eye, ear, nasal cavities, sinuses
3. Intracranial venous sinuses
4. Parts of dura and intracranial arteries
5. Optic, oculomotor,
oculomotor, trigeminal,
trigeminal, glossopharyngeal,
glossopharyngeal, vagus,
vagus,
first three cervical nerves
University of Pé
Pécs,
cs, Department of Neurology
ANEURYSM RUPTURE
University of Pé
Pécs,
cs, Department of Neurology
SINUS THROMBOSIS
University of Pé
Pécs,
cs, Department of Neurology
BRAIN TUMOR
University of Pé
Pécs,
cs, Department of Neurology
THERAPY OF PAIN
• (specific treatment)
• Nonopioid analgesics: e.g. Acetylsalicylic acid, Indomethacin,
Naproxen
• Narcotic analgesics: e.g. Codeine, Morphine, Fentanyl
• Anticonvulsants: e.g. Carbamazepine, Gabapentin, Pregabalin
• Tricyclic and SSRI antidepressants: e.g. Amitriptylin, Sertaline
• Anesthetics: e.g. Lidocaine, Mexiletine
• Root blocks, epidural injection, ganglion infiltration
• Ablative surgery: rhizotomy, spinothalamic tractotomy, bilateral
cordotomy, stereotactic surgery on the thalamus
• Spinal cord stimulation, deep brain stimulation
• Other treatments: biofeedback, acupuncture, transcutaneous
electrical stimulation
University of Pé
Pécs,
cs, Department of Neurology