Cns 5

The Sensory system

Specific sensation depends upon brain region being stimulated.

Receptor or nerve ending is stimulated. Sensory neuron transmits signal. Brain interprets signal. Sensory adaptation

– Sensory receptors send signal at decreasing rate due to continuous stimulation.

From Sensation to Perception

Survival depends upon sensation and perception

Sensation is the awareness of changes in the internal and external environment

Perception is the conscious interpretation of those stimuli

Organization of the Somatosensory System

Input comes from exteroceptors, proprioceptors, and interoceptors

The three main levels of neural integration in the somatosensory system are:– Receptor level – the sensor receptors– Circuit level – ascending pathways– Perceptual level – neuronal circuits in the cerebral

cortex

Processing at the Receptor Lever

The receptor must have specificity for the stimulus energy

The receptor’s receptive field must be stimulated

Stimulus energy must be converted into a graded potential

A generator potential in the associated sensory neuron must reach threshold

Adaptation of Sensory Receptors

Adaptation occurs when sensory receptors are subjected to an unchanging stimulus– Receptor membranes become less responsive– Receptor potentials decline in frequency or stop

Adaptation of Sensory Receptors

Receptors responding to pressure, touch, and smell adapt quickly

Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood

Pain receptors and proprioceptors do not exhibit adaptation

Processing at the Circuit Level

Chains of three neurons (first-, second-, and third-order) conduct sensory impulses upward to the brain

First-order neurons – soma reside in dorsal root or cranial ganglia, and conduct impulses from the skin to the spinal cord or brain stem

Second-order neurons – soma reside in the dorsal horn of the spinal cord or medullary nuclei and transmit impulses to the thalamus or cerebellum

Third-order neurons – located in the thalamus and conduct impulses to the somatosensory cortex of the cerebrum

Receptive Fields

Area of skin whose stimulation results in changes in the firing rate of the neuron.

– Area of each receptor field varies inversely with the density of receptors in the region.

Back and legs have few sensory endings.– Receptive field is large.

Fingertips have large # of cutaneous receptors.– Receptive field is small.

Two-Point Touch Threshold

Minimum distance at which 2 points of touch can be perceived as separate.

– Measures of distance between receptive fields.

Indication of tactile acuity.– If distance between 2

points is less than minimum distance, only 1 point will be felt.

Lateral Inhibition

Sharpening of sensation.– When a blunt object

touches the skin, sensory neurons in the center areas are stimulated more than neighboring fields.

– No clear, sharp boundary. Will be perceived as a

single touch with well defined borders.

– Occurs within CNS.

Figure 10-6

Sensory Areas

Cortical areas involved in conscious awareness of sensation

Distinct area for each of the major senses

Sensory Areas – Primary Somatosensory Cortex

Located along the postcentral gyrus

Involved with conscious awareness of general somatic senses

Sensory Areas – Primary Somatosensory Cortex

Projection is contralateral – Cerebral hemispheres

Receive sensory input from the opposite side of the body

Sensory homunculus – a body map of the sensory cortex

Sensory Areas – Sensory Homunculus

Sensory Areas – Somatosensory Association Area

Lies posterior to the primary somatosensory cortex

Integrates different sensory inputs– Touch, pressure, and others

Draws upon stored memories of past sensory experiences

White MatterWhite Matter Anterior Funiculus (Anterior White Column)Anterior Funiculus (Anterior White Column)

Posterior Funiculus (Posterior White Column)Posterior Funiculus (Posterior White Column) Fasciculus Gracilis & Fasciculus CuneatusFasciculus Gracilis & Fasciculus Cuneatus

Lateral Funiculus (Lateral White Column)Lateral Funiculus (Lateral White Column)

Gray MatterGray Matter Anterior Horn ------------Anterior Horn ------------------ motormotor

Posterior Horn --------------Posterior Horn -------------- sensorysensory

Lateral Horn -----------------Lateral Horn ----------------- autonomic (sympathetic)autonomic (sympathetic)

Gray Commissure -------- Gray Commissure -------- anterior and posterior anterior and posterior

White MatterWhite Matter Anterior Funiculus (Anterior White Column)Anterior Funiculus (Anterior White Column)

Posterior Funiculus (Posterior White Column)Posterior Funiculus (Posterior White Column) Fasciculus Gracilis & Fasciculus CuneatusFasciculus Gracilis & Fasciculus Cuneatus

Lateral Funiculus (Lateral White Column)Lateral Funiculus (Lateral White Column)

Gray MatterGray Matter Anterior Horn ------------Anterior Horn ------------------ motormotor

Posterior Horn --------------Posterior Horn -------------- sensorysensory

Lateral Horn -----------------Lateral Horn ----------------- autonomic (sympathetic)autonomic (sympathetic)

Gray Commissure -------- Gray Commissure -------- anterior and posterior anterior and posterior

Spinal Cord Spinal Cord Internal StructureInternal Structure Spinal Cord Spinal Cord Internal StructureInternal Structure

Lamina I Posteromarginal NucleusLamina I Posteromarginal Nucleus

Lamina II Lamina II Substantia Gelatinosa of RolandoSubstantia Gelatinosa of Rolando

Lamina IIILamina III

Lamina IV, V, VI ----- Nucleus PropriusLamina IV, V, VI ----- Nucleus Proprius

Lamina VIILamina VII

- Intermediate Gray- Intermediate Gray

- I- Intermediolateral cell column (ILM)ntermediolateral cell column (ILM)

- - Clarke’s column (Nucleus dorsalis)Clarke’s column (Nucleus dorsalis)- I- Intermediomedial cell column (IMM)ntermediomedial cell column (IMM)

Lamina VIIILamina VIII

Lamina IX ---------- Lamina IX ---------- Anterior Horn (Motor) CellAnterior Horn (Motor) Cell

Lamina X ----------- Gray CommissureLamina X ----------- Gray Commissure

Lamina I Posteromarginal NucleusLamina I Posteromarginal Nucleus

Lamina II Lamina II Substantia Gelatinosa of RolandoSubstantia Gelatinosa of Rolando

Lamina IIILamina III

Lamina IV, V, VI ----- Nucleus PropriusLamina IV, V, VI ----- Nucleus Proprius

Lamina VIILamina VII

- Intermediate Gray- Intermediate Gray

- I- Intermediolateral cell column (ILM)ntermediolateral cell column (ILM)

- - Clarke’s column (Nucleus dorsalis)Clarke’s column (Nucleus dorsalis)- I- Intermediomedial cell column (IMM)ntermediomedial cell column (IMM)

Lamina VIIILamina VIII

Lamina IX ---------- Lamina IX ---------- Anterior Horn (Motor) CellAnterior Horn (Motor) Cell

Lamina X ----------- Gray CommissureLamina X ----------- Gray Commissure

Lamina of RexedLamina of RexedLamina of RexedLamina of Rexed

Spinal Nerves

A series of connective tissue layer surrounds each spinal nerve.

Epineurium-outermost layer, consists of a dense network of collagen fibers.

Perineurium-extend inward from the epineurium, dividing the nerve into a series of compartments.

Endoneurium-delicate connective tissue fibers.

Ventral and Dorsal Roots

In the vicinity of the cord, each spinal nerve divides into a ventral (anterior, motor) root and a dorsal (posterior, sensory) root.

Ventral roots contain mostly efferent nerve fibers and convey motor information.

Dorsal roots contain afferent nerve fibers and convey sensory information.

The axons of motor neurons whose cell bodies are located within the CNS in the ant. Horn emerge from the spinal cord to form ventral roots (motor).

Groups of sensory neurons , whose axons make up the dorsal roots lie outside the cord in the dorsal root ganglia or spinal ganglia of the PNS.

Peripheral distribution of Spinal Nerves

A typical spinal nerve has a white ramus(this contains myelinated axons), and a gray ramus (unmyelinated fibers that innervate glands and smooth muscles in the body wall or limbs)

A dorsal ramus(providing sensory and motor innervation to the skin and muscles of the back), and a ventral ramus (supplying the ventrolateral body surface, structures in the body wall and the limbs).

Each pair of nerves monitors a region of the body surface called a dermatome.

Nerve Plexuses

A complex, interwoven network of nerves is a nerve plexus.

The three large plexuses are the cervical plexus, the brachial plexus and the lumbosacral plexus. The latter can be further divided into the lumbar plexus and the sacral plexus.

White Matter of the Spinal Cord

Sensory and Motor Pathways

Most motor pathways:– Decussate at some point along their course– Consist of a chain of two or three neurons– Exhibit somatotopy

Tracts arranged according to the body region they supply

All pathways are paired– One of each on each side of the body

Fasciculus cuneatus and Fasciculus gracilis

Figure 12.33a

Posterior White Column-Medial Lemniscal PathwayPosterior White Column-Medial Lemniscal Pathway

(Tract of gall and burdach)(Tract of gall and burdach) Modality: Modality: Discriminative Touch Sensation (include Vibration) and Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation, Kinesthesia)Conscious Proprioception (Position Sensation, Kinesthesia)

Receptor: Most receptors except free nerve endingsReceptor: Most receptors except free nerve endings

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion)

Posterior Root - Posterior White ColumnPosterior Root - Posterior White Column

2nd Neuron: 2nd Neuron: Dorsal Column NucleiDorsal Column Nuclei (Nucleus Gracilis and Cuneatus)(Nucleus Gracilis and Cuneatus)

Internal Arcuate Fiber - Lemniscal Decussation Internal Arcuate Fiber - Lemniscal Decussation

- Medial Lemniscus- Medial Lemniscus

3rd Neuron: 3rd Neuron: Thalamus (VPLc)Thalamus (VPLc) Internal Capsule ----- Corona Radiata Internal Capsule ----- Corona Radiata

Termination: Termination: Primary Somesthetic Area (S I)Primary Somesthetic Area (S I)

Posterior White Column-Medial Lemniscal PathwayPosterior White Column-Medial Lemniscal Pathway

(Tract of gall and burdach)(Tract of gall and burdach) Modality: Modality: Discriminative Touch Sensation (include Vibration) and Discriminative Touch Sensation (include Vibration) and Conscious Proprioception (Position Sensation, Kinesthesia)Conscious Proprioception (Position Sensation, Kinesthesia)

Receptor: Most receptors except free nerve endingsReceptor: Most receptors except free nerve endings

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion)

Posterior Root - Posterior White ColumnPosterior Root - Posterior White Column

2nd Neuron: 2nd Neuron: Dorsal Column NucleiDorsal Column Nuclei (Nucleus Gracilis and Cuneatus)(Nucleus Gracilis and Cuneatus)

Internal Arcuate Fiber - Lemniscal Decussation Internal Arcuate Fiber - Lemniscal Decussation

- Medial Lemniscus- Medial Lemniscus

3rd Neuron: 3rd Neuron: Thalamus (VPLc)Thalamus (VPLc) Internal Capsule ----- Corona Radiata Internal Capsule ----- Corona Radiata

Termination: Termination: Primary Somesthetic Area (S I)Primary Somesthetic Area (S I)

Spinal Cord Ascending TractsSpinal Cord Ascending Tracts Spinal Cord Ascending TractsSpinal Cord Ascending Tracts

Lateral spinothalamic tract

Spinothalamic TractSpinothalamic Tract Modality: Modality: Pain & Temperature Sensation, Light Touch Pain & Temperature Sensation, Light Touch

Receptor: Receptor: Free Nerve Ending Free Nerve Ending

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion) Posterior Root Posterior Root

2nd Neuron: 2nd Neuron: Dorsal Horn Dorsal Horn (Lamina IV, V, VI)(Lamina IV, V, VI)

Spinothalamic Tract - (Spinal Lemniscus)Spinothalamic Tract - (Spinal Lemniscus)

3rd Neuron: 3rd Neuron: Thalamus (VPLc, CL & POm)Thalamus (VPLc, CL & POm) Internal Capsule ----- Corona Radiata Internal Capsule ----- Corona Radiata

Termination: Termination: Primary Somesthetic Area (S I) &Primary Somesthetic Area (S I) &

Diffuse Widespread Cortical RegionDiffuse Widespread Cortical Region

Spinothalamic TractSpinothalamic Tract Modality: Modality: Pain & Temperature Sensation, Light Touch Pain & Temperature Sensation, Light Touch

Receptor: Receptor: Free Nerve Ending Free Nerve Ending

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion) Posterior Root Posterior Root

2nd Neuron: 2nd Neuron: Dorsal Horn Dorsal Horn (Lamina IV, V, VI)(Lamina IV, V, VI)

Spinothalamic Tract - (Spinal Lemniscus)Spinothalamic Tract - (Spinal Lemniscus)

3rd Neuron: 3rd Neuron: Thalamus (VPLc, CL & POm)Thalamus (VPLc, CL & POm) Internal Capsule ----- Corona Radiata Internal Capsule ----- Corona Radiata

Termination: Termination: Primary Somesthetic Area (S I) &Primary Somesthetic Area (S I) &

Diffuse Widespread Cortical RegionDiffuse Widespread Cortical Region

Spinal Cord Ascending TractsSpinal Cord Ascending Tracts Spinal Cord Ascending TractsSpinal Cord Ascending Tracts

Spinocerebellar TractSpinocerebellar Tract

Modality: Modality: Unconscious Proprioception Unconscious Proprioception

Receptor: Receptor: Muscle spindle, Golgi tendon organMuscle spindle, Golgi tendon organ

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion) Posterior Root , [Posterior Column]Posterior Root , [Posterior Column]

2nd Neuron: 2nd Neuron: 1. Clarke’s column (Lamina VII)1. Clarke’s column (Lamina VII) Posterior Spinocerebellar TractPosterior Spinocerebellar Tract

22. Posterior Horn. Posterior Horn Anterior Spinocerebellar TractAnterior Spinocerebellar Tract

Termination: Termination: Cerebellar CortexCerebellar Cortex

Spinocerebellar TractSpinocerebellar Tract

Modality: Modality: Unconscious Proprioception Unconscious Proprioception

Receptor: Receptor: Muscle spindle, Golgi tendon organMuscle spindle, Golgi tendon organ

Ist Neuron: Ist Neuron: Dorsal Root Ganglion (Spinal Ganglion)Dorsal Root Ganglion (Spinal Ganglion) Posterior Root , [Posterior Column]Posterior Root , [Posterior Column]

2nd Neuron: 2nd Neuron: 1. Clarke’s column (Lamina VII)1. Clarke’s column (Lamina VII) Posterior Spinocerebellar TractPosterior Spinocerebellar Tract

22. Posterior Horn. Posterior Horn Anterior Spinocerebellar TractAnterior Spinocerebellar Tract

Termination: Termination: Cerebellar CortexCerebellar Cortex

Spinal Cord Ascending TractsSpinal Cord Ascending Tracts Spinal Cord Ascending TractsSpinal Cord Ascending Tracts

Spinocerebellar TractSpinocerebellar TractSpinocerebellar TractSpinocerebellar Tract

Inferior cerebellarInferior cerebellar pedunclepeduncle

posteriorposterior spinocerebellarspinocerebellar tracttract

Clarke’sClarke’s columncolumn

posteriorposterior white columnwhite column

posterior rootposterior root

Posterior SCbllTPosterior SCbllT

Inferior Inferior cerebellarcerebellar pedunclepeduncle

cuneocerebellarcuneocerebellar tracttract (upper body)(upper body)

posteriorposterior white columnwhite column

posterior rootposterior root

Anterior SCbllTAnterior SCbllT

superiorsuperior cerebellarcerebellar pedunclepeduncle

anterioranterior spinocerebellarspinocerebellar tracttract

anterior whiteanterior white commissurecommissure

posterior rootposterior root

Spinocerebellar TractSpinocerebellar TractSpinocerebellar TractSpinocerebellar Tract

What is pain?

A sensory and emotional experience of discomfort.

Single most common medical complaint.

Perceiving Pain

Algogenic substances – chemicals released at the site of the injury

Nociceptors – afferent neurons that carry pain messages

Referred pain – pain that is perceived as if it were coming from somewhere else in the body

Peripheral Nerve Fibers Involved in Pain Perception

A-delta fibers – small, myelinated fibers that transmit sharp pain

C-fibers – small unmyelinated nerve fibers that transmit dull or aching pain.

Three Chronic Pain Conditions

Neuralgia – an extremely painful condition consisting of recurrent episodes of intense shooting or stabbing pain along the course of the nerve.

Causalgia – recurrent episodes of severe burning pain. Phantom limb pain – feelings of pain in a limb that is no

longer there and has no functioning nerves.

Pain 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 Cortexlocation 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 endogenous opiates released

Pain Nerve Fibers

Acute Pain Fibers: conduct impulses rapidly. Sharp pain. Restricted area of skin. Seldom continues after stimulation stops.

Chronic Pain Fibers: slower, dull, aching pain. Diffuse and difficult to pinpoint. May continue after stimulus ceases. May be felt in deeper tissues.

An event usually triggers both acute and chronic pain fibers (dual sensation)

Acute Pain

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

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

Acute Pain Treatment

Goal– block the pain through:

inhibition blocking A fibers (Gate Control)

Chronic Pain:

Any pain which lasts for six months or more – numerous by-passes. Also goes to limbic

system (emotional control)- learned response

Referred Pain (projected pain)

Felt at other site than injured area– Dermatome (skin represented by nerve root)

Pain theories

Specificity Theory Pattern Theory Gate Control Theory

Specificity theory: specific stimulus has a specific receptor which goes to a location in the brain The specific location identifies the pain’s quality. Thus any noxious stimulus applied to the surface of the skin results in a pain sensation. The evaluation of the type of pain occurs in the brain.

Pattern Theory: a pattern or coding of sensory information is created by different sensations. This theory is faulty due to the number of different types of receptors proven to exist.

Gate Control Theory (1965)

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

Gate Control Theory

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

A nonpainful stimulus can block the transmission of a noxious stimulus

Brain/Pain centersC delta noxious stimulus

A-betanon-painful

stimulusBlocking entry of c-delta Fibers

Gate Control Theory Cont.

The second order neuron, the T-cell and the substantia gelatinosa can exert affects on the primary afferent

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

Gate Control

In Dorsal Horn of Spinal Cord

T

Brain. A-BetaSensory, Proprioception, Etc

A-Delta, C FibersPain Transmission

SG

Facilitator Synapse

Inhibitory Synapse

The second order neuron

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

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

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

Gate Control Theory

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

Gate Control Theory Cont.

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

Gate Control Theory

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

Gate Control Theory

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

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

Pain modulation: Levels Theory of Pain Control

Spinal Levels of Pain Control– Gate Control Theory– Central Biasing (hyperstimulation analgesia)– Endogenous Opiate (Pituitary level)

Level I: Presynaptic inhibition Gate Control Theory

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

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

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

PAIN INHIBITORY COMPLEX: PRESYNAPTIC INHIBITION

PAINRECEPTOR

BRAIN STEM.NEURON

INHIBITORY NEURON

ANTEROLATERALPATHWAY

DORSAL HORN OFSPINAL CORD

+

-

PAIN TRANSMISSION AND INHIBITION

SUBSTANCE P IS THE NEUROTRANSMITTER: BUILDS UP SLOWLY IN THE JUNCTION AND IS SLOWLY DESTROYED

PRESYNAPTIC INHIBITION BY INHIBITORY NEURON BLOCKS THE RELEASE OF SUBSTANCE P (ENKEPHALIN)

Level 2: Descending inhibition

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

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

Transmission of sensory input to higher brain centers

Transmission Cell

Substantia gelitinosa

A-beta fiber Afferents

A-Delta & Cfiber afferents

CentralControl

+-

+ -

+-

Level 3: -Endorphin modulationEndogenous Opiate

Opiate like substance made by the body Norepinephrine Seratonin

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

horn inhibition

Gate-Control Theory

Brain

Spinal Cord

GatingMechanism

TransmissionCells

Frompainfibers

FromotherPeripheralfibers

Tobrain

Brain

Spinal Cord

GatingMechanism

TransmissionCells

Frompainfibers

FromotherPeripheralfibers

Tobrain

Gate is open Gate is closed

Three Factors Involved in Opening and Closing the Gate

The amount of activity in the pain fibers. The amount of activity in other peripheral

fibers Messages that descend from the brain.

Conditions that Open the Gate

Physical conditions– Extent of injury– Inappropriate activity level

Emotional conditions– Anxiety or worry– Tension– Depression

Mental Conditions– Focusing on pain– Boredom

Conditions That Close the Gate

Physical conditions– Medications– Counter stimulation (e.g., heat, message)

Emotional conditions– Positive emotions– Relaxation, Rest

Mental conditions– Intense concentration or distraction– Involvement and interest in life activities

Types of Pain Medications

Peripherally active analgesics – work at the periphery (e.g., aspirin).

Centrally active analgesics – narcotics that bind to the opiate receptors in the brain (e.g., codeine, morphine, heroin).

Local analgesics – can be injected into the site of injury or applied topically (e.g., novocaine).

Indirectly acting drugs – affect non-pain conditions such as emotions that can exacerbate pain experience.

Psychological Pain Control Methods

Biofeedback – provides biophysiological feedback to patient about some bodily process the patient is unaware of (e.g., forehead muscle tension).

Relaxation – systematic relaxation of the large muscle groups.

Hypnosis – relaxation + suggestion + distraction + altering the meaning of pain.

Psychological Pain Methods

Acupuncture – – Counter-irritation – may close the spinal gating

mechanism in pain perception.

Referred pain

Visceral pain may feel as if it is coming from some part of the body other than the part being stimulated. May arise from common nerve pathways.– Example: Pain originating in the heart may be

referred to the left shoulder and left upper limb.

Pain originating in the heart may feel as if it is coming from the skin because sensory impulses from those two regions follow common nerve pathways to the brain.

Surface regions to which visceral pain may be referred

Theories

A. Convergence theory B. Facilitation theory

Other sensations

Hyperalgesia Itch (pruritus) Vibration sense Two point discrimination Stereognosis

Headaches

Nervous tissue of the brain lacks pain receptors but nearly all other tissues of the head including meninges and blood vessels are richly innervated

Many headaches are associated with stressful life situations that cause fatigue, emotional tension, anxiety, or frustration

Tension Headache

Triggered by various physiological changes such as prolonged contraction of skeletal muscles in forehead, sides of head, back of neck.

Contractions stimulate pain receptors

Vascular Headache

Accompanies constriction or dilation of cranial blood vessels.

Ex. Throbbing headache of “hang-over” from drinking too much alcohol may be due to blood pulsating through dilated cranial vessels

Migraine

Form of vascular headache Certain cranial vessels constrict producing a localized cerebral

blood deficiency Variety of symptoms: seeing patterns of bright light that

obstruct vision, numbness in limbs or face Vasoconstriction subsequently leads to vasodilation of affected

vessels causing severe headache usually on one side of the head.

Can last several hours or more

Other Causes of Headaches

Sensitivity to food additives High blood pressure Increased intracranial pressure due to tumor

or hematoma Decreased cerebrospinal fluid pressure

following lumbar puncture Sensitivity to or withdrawal from certain drugs