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