Sensory Nervous SystemSensory Nervous System

Week 11Week 11Dr. Walid DaoudDr. Walid Daoud

A. ProfessorA. Professor

Pain SensationPain Sensation

It is a protective mechanism for the bodyIt is a protective mechanism for the body..

It is produced when there is any tissue It is produced when there is any tissue damagedamage..

It initiates reflexes which aim to remove the It initiates reflexes which aim to remove the painful stimuluspainful stimulus..

Pain ReceptorsPain Receptors

They are free nerve endings of 3 typesThey are free nerve endings of 3 types::

11 - -Mechanosensitive pain receptorsMechanosensitive pain receptors::

Stimulated by mechanical changes toStimulated by mechanical changes to

tissuestissues..

22 - -Thermosensitive pain receptorsThermosensitive pain receptors::

Stimulated by extremes of heat or coldStimulated by extremes of heat or cold..

33 - -Chemosensitive pain receptorsChemosensitive pain receptors::

Stimulated by injurious chemical substancesStimulated by injurious chemical substances

Types of Pain SensationTypes of Pain SensationA- Cutaneous PainA- Cutaneous Pain::

Fast acute painFast acute painSlow chronic painSlow chronic pain

Elicited by mechanical Elicited by mechanical or thermal receptorsor thermal receptors

0.10.1 secsec in Felt in Felt

Carried by A gama fiberCarried by A gama fiber

Not felt in deep tissuesNot felt in deep tissues

Sharp picking painSharp picking pain

Well localizedWell localized

By all types of receptorsBy all types of receptors

Felt after 1 sec or moreFelt after 1 sec or more

Carried by C fibersCarried by C fibers

In skin and deep tissuesIn skin and deep tissues

Dullaching burning Dullaching burning throbbingthrobbing

Poorly localizedPoorly localized

B- Deep PainB- Deep Pain

It is produced in muscles, tendons, It is produced in muscles, tendons, ligaments, joints and periosteum of bonesligaments, joints and periosteum of bones..

It is conducted along C fibersIt is conducted along C fibers..

CausesCauses::

11 - -Inflammation in deep structuresInflammation in deep structures..

22 - -IschemiaIschemia..

33 - -Muscle spasmMuscle spasm..

C- Visceral (referred) PainC- Visceral (referred) PainMost viscera contain only pain receptorsMost viscera contain only pain receptors..

It is transmitted along C fibersIt is transmitted along C fibers..

CausesCauses::

11 - -Ischemia: accumulation of metabolitesIschemia: accumulation of metabolites

22 - -Spasm of hollow viscusSpasm of hollow viscus..

33 - -Overdistension of hollow viscusOverdistension of hollow viscus . .

44 - -Infalmmation of peritoneal coveringInfalmmation of peritoneal covering..

55 - -Chemical irritation as perforated peptic ulcerChemical irritation as perforated peptic ulcer..

Characters:Characters:1- Dull aching1- Dull aching..

22 - -Accompanied by nausea and vomitingAccompanied by nausea and vomiting

33 - -Usually referred to surface areaUsually referred to surface area..

Referred PainReferred PainPain is not felt in the diseased viscus but in the Pain is not felt in the diseased viscus but in the body surface somatic structures supplied by the body surface somatic structures supplied by the same posterior roots as the diseased viscussame posterior roots as the diseased viscus..

11--Cardiac pain:Cardiac pain: ischemia of cardiac muscle ischemia of cardiac muscle

pain is referred to base of neck or left armpain is referred to base of neck or left arm

22--Gastric pain:Gastric pain: referred to body surface referred to body surface

between umbilicus & xiphoid processbetween umbilicus & xiphoid process..

33--Gall bladder pain:Gall bladder pain: felt in mid-epigastrium and tip felt in mid-epigastrium and tip

of right scapulaof right scapula..

44--Appendicitis pain:Appendicitis pain: felt around the umbilicus felt around the umbilicus..

Mechanism of Referred PainMechanism of Referred Pain

Convergence-projection theoryConvergence-projection theory::Pain impulses from diseased viscus Pain impulses from diseased viscus converge on the same cells in the SGR in converge on the same cells in the SGR in spinal cord which receive nerve impulses spinal cord which receive nerve impulses from a particular skin dermatome that from a particular skin dermatome that activate the same cortical neuron. activate the same cortical neuron. Sensory area in cerebral cortex is Sensory area in cerebral cortex is accustomed to receive pain sensation accustomed to receive pain sensation from skin so pain impulses from viscera from skin so pain impulses from viscera are projected to skin are of the same are projected to skin are of the same dermatomal nerve supplydermatomal nerve supply..

Pathway of Pain SensationPathway of Pain Sensation

11 - -Neospinothalamic tractNeospinothalamic tract..

22 - -Paleospinothalamic tractPaleospinothalamic tract..

Pain ControlPain Control

A-Pain Control SystemA-Pain Control System::

11--Analgesia SystemAnalgesia System::

supraspinal level of pain inhibitionsupraspinal level of pain inhibition::---B endorphin from hypothalamus or pituitaryB endorphin from hypothalamus or pituitary

---Enkephalins from periaqueductal grey area ---Enkephalins from periaqueductal grey area ---Fibers of raphe magnus nucleus secrtete serotonin Fibers of raphe magnus nucleus secrtete serotonin –Serotonin stimulates pain inhibitory complex area –Serotonin stimulates pain inhibitory complex area in dorsal horn of spinal cord that secretes in dorsal horn of spinal cord that secretes enkephalins causing presynaptic inhibition by Ca enkephalins causing presynaptic inhibition by Ca channel blocking preventing release of substance Pchannel blocking preventing release of substance P

Pain ControlPain Control22 - -Gate inhibition theoryGate inhibition theory::

Spinal level of pain inhibition.Spinal level of pain inhibition.SGR cells in layers II & SGR cells in layers II & III act as gate for pain impulses to reach lateral III act as gate for pain impulses to reach lateral spinothalamic tract. It can be closed byspinothalamic tract. It can be closed by::

A-Impulses fromA-Impulses from::

11 - -A beta fibers: rubbing of skin inhibits painA beta fibers: rubbing of skin inhibits pain..

22 - -A gama fibers: counter irritants inhibit painA gama fibers: counter irritants inhibit pain..

B-Endogenous opioid peptidesB-Endogenous opioid peptides::

11 - -Secreted from interneuronsSecreted from interneurons..

22 - -Circulating endorphinsCirculating endorphins . .

Pain ControlPain ControlB- Medical treatmentB- Medical treatment::

11 - -Using painkillersUsing painkillers.. 22 - -Treating the cause of painTreating the cause of pain..

C- Surgical treatment of pain inhibitionC- Surgical treatment of pain inhibition:: 11 - -Antelateral cordotomy to cutAntelateral cordotomy to cut

spinothalamic tractspinothalamic tract.. 22 - -Gyrectomy in frontal lobeGyrectomy in frontal lobe..

D- Electric stimulation for pain inhibitionD- Electric stimulation for pain inhibition:: 11 - -Electric stimulation for analgesia systemElectric stimulation for analgesia system

22 - -Electric stimulation of large sensory fibersElectric stimulation of large sensory fibers

HeadacheHeadache

A type of referred pain to the surface of the A type of referred pain to the surface of the head from deep structureshead from deep structures..Causes of intracranial headacheCauses of intracranial headache::

11 - -MeningitisMeningitis..22 - -Meningeal traumaMeningeal trauma..

33 - -Brain tumorsBrain tumors..44 - -Migraine headacheMigraine headache..

55 - -Low cerebrospinal fluidLow cerebrospinal fluid..66 - -Constipation headacheConstipation headache..

HeadacheHeadache

Headache of extracranial originHeadache of extracranial origin::

11 - -Muscular spasmMuscular spasm..

22 - -Inflammation of nasal sinusesInflammation of nasal sinuses..

33 - -Errors of eye refractionErrors of eye refraction..

44 - -Tooth acheTooth ache..

55 - -Otitis mediaOtitis media..

Sensory Areas of Cerebral CortexSensory Areas of Cerebral Cortex

Somatic Sensory Area ISomatic Sensory Area I::Lies in postcentral gyrus of cerebral cortexLies in postcentral gyrus of cerebral cortexReceives impulses from posteroventral Receives impulses from posteroventral nucleus of thalamus. Characterized bynucleus of thalamus. Characterized by::

--Crossed representationCrossed representation..--Inverted body presentationInverted body presentation..

--Size of represented area is directlySize of represented area is directly proportional to number of receptors in thisproportional to number of receptors in this

area of the bodyarea of the body..

Functions of Somatic Sensory Area IFunctions of Somatic Sensory Area I

It is the center ofIt is the center of::

11 - -Fine touchFine touch..

22 - -Discrimination of weightsDiscrimination of weights..

33 - -Vibration senseVibration sense..

44 - -Sense of position and movements of jointsSense of position and movements of joints..

55 - -Discrimination of various grades ofDiscrimination of various grades of

temperaturetemperature..

Somatic Sensory Area IISomatic Sensory Area II

Lies posterior and inferior to lower end of Lies posterior and inferior to lower end of postcentral gyruspostcentral gyrus..

Receives information from dorsal column, Receives information from dorsal column, spinothalamic tract, visual, auditory and spinothalamic tract, visual, auditory and somatic sensory area Isomatic sensory area I..

FunctionsFunctions::

It begins to make meaning of sensory signalsIt begins to make meaning of sensory signals..

Somatic Association AreaSomatic Association Area

Lies behind the somatic sensory area I and Lies behind the somatic sensory area I and above somatic sensory area IIabove somatic sensory area II..

Receives impulses fromsomatic sensory Receives impulses fromsomatic sensory area I and II, from posteroventral nucleus area I and II, from posteroventral nucleus of thalamusof thalamus..FunctionsFunctions::

It combines information fromsomatic It combines information fromsomatic sensory areas & interpret this information sensory areas & interpret this information to have a meaningto have a meaning..