Neuroanatomy/Pain ReviewNeuroanatomy/Pain Review

AnatomyAnatomy

Cell body (in ganglion)Cell body (in ganglion)nucleusnucleusDendritesDendrites

axon

Dendrite

Body

Synapse

Anatomy Cont. Anatomy Cont.

Axons (actual nerve fibers)Axons (actual nerve fibers)peripheral nervous system: may be covered peripheral nervous system: may be covered

by myelin sheath (schwann cell) which allows by myelin sheath (schwann cell) which allows for regrowthfor regrowth

CNS: oligodendrocytes are the “myelin” but it CNS: oligodendrocytes are the “myelin” but it doesn't allow for regrowthdoesn't allow for regrowth

Anatomy Cont.Anatomy Cont.

Nodes of Ranier: breaks in myelin. Action Nodes of Ranier: breaks in myelin. Action potentials jump from node to node potentials jump from node to node (salutatory condition) myelin acts as (salutatory condition) myelin acts as resistance and insulation and thus needs resistance and insulation and thus needs nodes for function. nodes for function.

Nerve TypesNerve Types Afferent; sensory nerves (ascending tracts)Afferent; sensory nerves (ascending tracts)

AAA Beta): sensory, large diameter with myelin A Beta): sensory, large diameter with myelin (Fastest)(Fastest)

A delta: pain fibers, smaller with less myelin (4-30m/s)A delta: pain fibers, smaller with less myelin (4-30m/s)C: pain, smallest, non myelinated (.5-2m/s) dull slow C: pain, smallest, non myelinated (.5-2m/s) dull slow

painpainSee Prentice Table 1-2 for Classes of Afferent NeuronsSee Prentice Table 1-2 for Classes of Afferent NeuronsNote: First pain is from Adelts (faster), second pain is CNote: First pain is from Adelts (faster), second pain is C

Nerve Types Cont.Nerve Types Cont.

Efferent Nerves: motor nerves Efferent Nerves: motor nerves (descending tracts)(descending tracts)Gamma: motor neuronGamma: motor neuron

Ascending and descending tracts:Ascending and descending tracts:myelination increases conduction velocitymyelination increases conduction velocityDiameter increases conduction velocity (less Diameter increases conduction velocity (less

resistance)resistance)

Nerve Types:Nerve Types:

Afferent NervesAfferent Nerves

CNSA BetaAdeltaC

PhysiologyPhysiology

Excitable Tissue: only nerves and muscles Excitable Tissue: only nerves and muscles are excitable tissue due to the fact only are excitable tissue due to the fact only they have a resting membrane potentialthey have a resting membrane potential

Physiology Cont.Physiology Cont.

Resting membrane Potential: a Resting membrane Potential: a chemical and electrical balance with a chemical and electrical balance with a pump to aid in return to homeostasis.pump to aid in return to homeostasis.at rest membrane in -70 mV to -90 mVat rest membrane in -70 mV to -90 mVsemipermeable membrane which is semipermeable membrane which is

impermeable to Sodium at restimpermeable to Sodium at rest

Physiology Cont.Physiology Cont.

Sodium Potassium pump keeps the potential Sodium Potassium pump keeps the potential by pump in K+ in and Na+ outby pump in K+ in and Na+ outNa+ want in the cell but if it gets in an action Na+ want in the cell but if it gets in an action

potential is formedpotential is formedto +30 mV (a 100 mV difference)to +30 mV (a 100 mV difference)hormone , chemical, electrical, thermal or hormone , chemical, electrical, thermal or

mechanical factors may create action potentialsmechanical factors may create action potentials

As athletic trainers we try and change this status As athletic trainers we try and change this status and create an action potentialand create an action potential

ThresholdThreshold

The minimum amount of stimulus The minimum amount of stimulus necessary to create an action potentialnecessary to create an action potential

Polar: refers to negativePolar: refers to negativedepolarize: less negativedepolarize: less negative repolarize: becoming negativerepolarize: becoming negativehyperpolarize: more negativehyperpolarize: more negative

Physiology Cont.Physiology Cont.

All or none theory: If stimulus meets the All or none theory: If stimulus meets the threshold, action potential will always go to threshold, action potential will always go to +30mV, even if supra-threshold stimulus is +30mV, even if supra-threshold stimulus is givengiven

Physiology Cont.Physiology Cont.

Refractory period: membrane potential goes Refractory period: membrane potential goes below the resting potential of -70mV and below the resting potential of -70mV and may not be stimulated for a given period of may not be stimulated for a given period of time. This limits how many action potentials time. This limits how many action potentials may be producedmay be producedAbsolute refractory period: NO stimulus will Absolute refractory period: NO stimulus will

create a response no matter how strongcreate a response no matter how strongRelative refractory period: resting potential is Relative refractory period: resting potential is

much lower, therefore a higher stimulus is much lower, therefore a higher stimulus is neededneeded

PainPain

How is this class How is this class affecting your pain affecting your pain

receptors?receptors?

PainPain

The purpose of pain is as a protective The purpose of pain is as a protective mechanism. Pain is an unpleasant mechanism. Pain is an unpleasant sensory and emotional experience sensory and emotional experience associated with actual or potential tissue associated with actual or potential tissue damage:damage:

The types of pain areThe types of pain areAcuteAcuteChronicChronicReferredReferred

Acute PainAcute Pain

First pain: carried in A-delta fires: larger First pain: carried in A-delta fires: larger diameter fibers contain myelin, reflex to diameter fibers contain myelin, reflex to get off source, goes to cognitive level get off source, goes to cognitive level (more discrete - very localized)(more discrete - very localized)

Second Pain: carried in C fibers. Smaller Second Pain: carried in C fibers. Smaller diameter, non myelinated, slower. (less diameter, non myelinated, slower. (less discrete - more diffuse)discrete - more diffuse)

Acute Pain TreatmentAcute Pain Treatment

GoalGoalblock the pain through:block the pain through:

inhibitioninhibitionblocking A fibers (Gate Control)blocking A fibers (Gate Control)

Chronic Pain: Chronic Pain:

Any pain which lasts for six months or more Any pain which lasts for six months or more (in athletes we may consider chronic pain to (in athletes we may consider chronic pain to be pain which is continue from months but is be pain which is continue from months but is not in proportion to tissue injury or activity... not in proportion to tissue injury or activity... i.e... chronic tendinitis may be long lasting but i.e... chronic tendinitis may be long lasting but have organic root)have organic root)No real purpose (?)No real purpose (?)numerous by-passes. Also goes to limbic system numerous by-passes. Also goes to limbic system

(emotional control)- learned response(emotional control)- learned response

Chronic PainChronic Pain

Goals in treatingGoals in treatingunlearn the Painunlearn the PainAcute pain control techniques are usually Acute pain control techniques are usually

ineffectiveineffectiveExercise my affect pain by distractionExercise my affect pain by distraction Important to have guidance under a physicianImportant to have guidance under a physician

Referred Pain (projected pain)Referred Pain (projected pain)

Felt at other site than injured areaFelt at other site than injured areaDermatome (skin represented by nerve root)Dermatome (skin represented by nerve root)Myotome (muscle innovated by nerve root)Myotome (muscle innovated by nerve root)Sclerotome (bones innovated by nerve root)Sclerotome (bones innovated by nerve root)

Pain TransmissionPain Transmission

Acute Pain

Noxious Stimulus travel Via A-Delta and C-delta Fibers to Dorsal Horn (spinal Cord)

Doral HornA-BetaC-Delta

Pain Transmitted to Higher Brain Centers

Acute Pain

STT (Spinal thalamic Tract)Thalamus and Cortex

location and discrimination

Retinacular Formation & Periaquductal Gray (PAG)

Motor, sensory and autonomic Response

Discrimination and Location of pain occurs during this sequence

Limbic System& Cortex

Descending Control Mech. Activated here once noxious stimuli reaches higher centers of brain. Incoming stimuli can be inhibited at various levels and endoginous opiates released

Pain theoriesPain theories

Specificity TheorySpecificity TheoryPattern TheoryPattern TheoryGate Control TheoryGate Control Theory

Specificity theory: specific Specificity theory: specific stimulus has a specific receptor stimulus has a specific receptor which goes to a location in the which goes to a location in the

brain The specific location brain The specific location identifies the pain’s quality. Thus identifies the pain’s quality. Thus any noxious stimulus applied to any noxious stimulus applied to

the surface of the skin results in a the surface of the skin results in a pain sensation. The evaluation of pain sensation. The evaluation of

the type of pain occurs in the the type of pain occurs in the brain.brain.

Pattern Theory: a pattern or Pattern Theory: a pattern or coding of sensory information coding of sensory information

is created by different is created by different sensations. This theory is sensations. This theory is faulty due to the number of faulty due to the number of different types of receptors different types of receptors

proven to exist.proven to exist.

Gate Control Theory (1965)Gate Control Theory (1965) Melzack and Wall originally described a Melzack and Wall originally described a

neurophsiologic mechanism which involved the neurophsiologic mechanism which involved the concept of peripheral and central “gating”. The concept of peripheral and central “gating”. The gate theory utilizes the specificity theory and gate theory utilizes the specificity theory and the pattern theory and added the interaction of the pattern theory and added the interaction of peripheral afferents with a modulation system peripheral afferents with a modulation system in the spinal cord gray matter. Additionally in the spinal cord gray matter. Additionally Melzack and Wall believed there also exists a Melzack and Wall believed there also exists a descending modulation system.descending modulation system.

Gate Control TheoryGate Control TheoryFirst Order neurons: the theory focuses First Order neurons: the theory focuses

on the first order neurons (primary on the first order neurons (primary afferents): the A-beta (large diameter afferents): the A-beta (large diameter sensory neurons) and A-delta and C sensory neurons) and A-delta and C neurons (both small diameter sensory neurons (both small diameter sensory neurons).neurons).

A non-painful stimulus can block the A non-painful stimulus can block the transmission of a noxious stimulustransmission of a noxious stimulus

Brain/Pain centersC delta noxious stimulus

A-betanon-painful

stimulusBlocking entry of c-delta Fibers

Gate Control Theory Cont.Gate Control Theory Cont.

The second order neuron, the T-cell and the The second order neuron, the T-cell and the substantia gelatinosa (Rexed’s laminae II and substantia gelatinosa (Rexed’s laminae II and II of the dorsal horn of the spinal gray matter) II of the dorsal horn of the spinal gray matter) can exert affects on the primary afferentcan exert affects on the primary afferent

Works on the premise that the SG (located in Works on the premise that the SG (located in dorsal horn) modulates afferent nerve dorsal horn) modulates afferent nerve impulses and influence transmission of T impulses and influence transmission of T cells. This activates a central controlling cells. This activates a central controlling mechanismmechanism

Gate ControlGate Control

In Dorsal Horn of Spinal CordIn Dorsal Horn of Spinal Cord

T

Brain. A-BetaSensory, Proprioception, Etc

A-Delta, C FibersPain Transmission

SG

Facilitator Synapse

Inhibitory Synapse

The second order neuronThe second order neuron

When the substantia gelatinosa is active When the substantia gelatinosa is active the “gate” is closed and there is a the “gate” is closed and there is a decrease in the amount of sensory input to decrease in the amount of sensory input to the T-cellthe T-cell

If the S.G. is relatively inactive the “gate” is If the S.G. is relatively inactive the “gate” is openopen

the balance of activity in the large and the balance of activity in the large and small diameter sensory neurons small diameter sensory neurons determines the position of the “gate”determines the position of the “gate”

Gate Control TheoryGate Control Theory

Large diameter afferents cause an initial Large diameter afferents cause an initial increase in the T-cells followed by a increase in the T-cells followed by a reduction of activity. The initial increase reduction of activity. The initial increase is due to direct activation of the second-is due to direct activation of the second-order neuron by primary afferents. The order neuron by primary afferents. The reduction is an indirect result due to large-reduction is an indirect result due to large-diameter afferents also activating the s.g. diameter afferents also activating the s.g. cells which causes the gate to closecells which causes the gate to close

Gate Control Theory Cont.Gate Control Theory Cont.

Small diameter afferents increase T-cell Small diameter afferents increase T-cell activity by these primary afferents also activity by these primary afferents also activate inhibitory interneurons that reduce activate inhibitory interneurons that reduce activity in the s.g which open the gateactivity in the s.g which open the gate

Gate Control TheoryGate Control Theory

When the balance of small to large When the balance of small to large diameter sensory neuronal input is no diameter sensory neuronal input is no longer maintained and reaches a critical longer maintained and reaches a critical value the second-order neurons are value the second-order neurons are activated. This activation is of the activated. This activation is of the ascending system and leads to the ascending system and leads to the perception of pain and the subsequent perception of pain and the subsequent behavioral responses.behavioral responses.

Gate Control TheoryGate Control Theory

The Descending control system in which The Descending control system in which emotion and past experience evoke emotion and past experience evoke descending input, impinging upon the descending input, impinging upon the gating mechanism to block pain sensation gating mechanism to block pain sensation at the spinal level.at the spinal level.

PAINPAIN is an excellent “bible” for those is an excellent “bible” for those working clinically with pain controlworking clinically with pain control

Pain modulation: Levels Theory Pain modulation: Levels Theory of Pain Controlof Pain Control

Spinal Levels of Pain ControlSpinal Levels of Pain ControlGate Control TheoryGate Control TheoryCentral Biasing (hyperstimulation analgesia)Central Biasing (hyperstimulation analgesia)Endogenous Opiate (Pituitary level)Endogenous Opiate (Pituitary level)

Level I: Presynaptic inhibition Level I: Presynaptic inhibition Gate Control TheoryGate Control Theory

The concept that when several sensory The concept that when several sensory stimuli reach the spinal cord at the same stimuli reach the spinal cord at the same location and time. one of them becomes location and time. one of them becomes dominant.dominant.

As long as the stimulation is causing firing of As long as the stimulation is causing firing of the sensory nerve, the gate to pain should be the sensory nerve, the gate to pain should be closedclosed

If accommodation occurs (electrical stimulus) If accommodation occurs (electrical stimulus) the gate is then open and pain returnsthe gate is then open and pain returns

Level 2: Descending inhibitionLevel 2: Descending inhibitionCentral BiasingCentral Biasing

A theory of pain A theory of pain modulation where modulation where higher centers such as higher centers such as the cerebral cortex the cerebral cortex influence the influence the perception of and perception of and response to painresponse to pain

Impulses from higher Impulses from higher centers act to close the centers act to close the gate and block gate and block transmission of the pain transmission of the pain message at the dorsal message at the dorsal horn synapsehorn synapse

Transmission of sensory input ot higher brain centers

Transmission Cell

Substantia gelitinosa

A-beta fiber Afferents

A-Delta & Cfiber afferents

CentralControl

+-

+ -

+-

Level 3: Level 3: -Endorphin -Endorphin modulationmodulation

Endogenous OpiateEndogenous Opiate Opiate like substance made by the bodyOpiate like substance made by the body

NorepinephrineNorepinephrineSeratoninSeratonin

These opiates inhibit the depolarization of These opiates inhibit the depolarization of second order nociceptive nerve fibers (thus second order nociceptive nerve fibers (thus no pain)no pain)Found in substantia gelatinosa - activated in tractFound in substantia gelatinosa - activated in tractCauses degeneration of prostaglandin and Causes degeneration of prostaglandin and

dorsal horn inhibitiondorsal horn inhibition

The purpose of knowing all The purpose of knowing all the pain control theories is the pain control theories is to use modalities to assess to use modalities to assess

these pain theories and these pain theories and decrease the decrease the

athlete/patient’s painathlete/patient’s pain