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Neuroanatomy of Pain
Introduction
What is pain? An unpleasant sensory
and emotional experience associated with actual or potential tissue damage, or described in such terms as tissue damage
Introduction
Pain is subjectiveDoes pain have a purpose?
Types of Pain Acute Pain Chronic Pain Referred Pain Radiating
Neurophysiology of Pain
Afferent Peripheral Receptor Types Special Receptors Visceral Receptors Deep Receptors Superficial Receptors
Afferent Peripheral Receptors
Special Transmit taste, sight, smell
Visceral Receptors Transmit hunger, distention, nausea
Deep Kinesthesia, joint position sense, deep pressure and pain Muscle -- GTO’s, muscle spindles Articular Structures – fast and slow adapting
mechanoreceptor and nociceptors
Afferent Peripheral Receptors
SuperficialWarm/cold, touch, pressure, itch and pain
from skin level
3 categoriesMechanorecptorsThermoreceptorsNociceptors
Mechanorecepetors
Mechanical stimuli Touch, pressure,
stroking
Mechanorecpetors
Mechanical stimuli Touch, pressure,
stroking
Fast-adapting Receptors Pacinian Corpuscles Meissner Corpuscles Respond to pressure
and touch very quickly
Mechanorecpetors
Mechanical stimuli Touch, pressure,
stroking
Fast-adapting ReceptorsSlow-adapting Receptors Merkel Cell Ending Ruffinni Endings Stimulated by
sustained stimuli
Thermoreceptors
Respond to temp and temp changes
Slow-adapting structures
Warm vs cold receptor firing
Nociceptors
Transmit pain impulses
Described as free nerve ending
Stimulated by:MechanicalChemical Thermal
What is the initial response to pain stimulus?
B rad yk in inP ros tag lan d in s
S u b s tan ce P
D eve lop S econ d ary H yp era lg es ia
D eve lop P rim ay H yp era lg es ia
R e lease ch em ica l m ed ia to rs
P a in s tim u lu s
Release of Chemical Mediators
Pain always begin with chemical response
Cell trauma
Release dopamine and NE from Cell membrane
Activates phospholipase
Release Arachidonic Acid Converted to prostaglandin or bradykinin
First Order Neurons
Transmit sensory information from receptors to dorsal horn Types of Primary Receptors in Pain Management A-delta A-beta C fibers
All Types of First-Order Neurons
Closer Analysis of those Receptors Involved in Pain
Management
A-deltaLarge, lightly myelinatedConduction velocitiesRespond to?Protopathic pain (AKA Primary Hyperalgesia)
Closer Analysis of those Receptors Involved in Pain
Management
A-delta
A-betaLarge, myelinated Conduction velocitiesRespond to?
Closer Analysis of those Receptors Involved in Pain
Management
A-delta
A-beta
C-fibersUnmyelinatedConduction velocityRespond toEpicritic pain (AKA Secondary Hyperalgesia)
Dorsal Horn of the Spinal Cord
Spinal Cord Level
SC divided into several LaminaeA-delta and C terminate in Laminae I and IIA-delta has input in V also
Laminae ILaminae IILaminae III and IVLaminae V
Second Order Neurons
Synapse with Laminae I and V cross midline
Synapse with Spinothalmic Tract Immediate warning
of presence, location and intensity of pain
Second Order Neurons
Spinothalamic Tract Receives info from
A-delta in Laminae I and V
Classification of ST Tract Cells
Low-threshold Wide dynamic range High threshold Thermosensitive
Spinoreticulothalamic Tract (FYI)
Input from Laminae VII and VIII
Mostly from C-fibers
A bilateral tract
From reticular formation to thalamus
Behavioral and emotional aspects of pain
Third and Fourth Order Neurons
Second order synapse to higher brain center
3rd = reticular formation to thalamus
4th = between and within higher brain centers
Higher Brain Centers
Reticular Formation
Thalamus
Cortex
Structures involved with Descending Control of
Pain Periaqueductal Grey Matter
Nucleus Raphe Magnus
Corticospinal Tract