Quick Sensory Review

8/8/2019 Quick Sensory Review

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Sensory

Pacinian corpuscle: It is a straight non-myelinated nerve endings surrounded by connective tissue concentric layers giving it an onion like appearance,

first node of Ranvier starts just before leaving the capsule.

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Sensory

Coding Of Sensory InformationIt is the ability of the CNS to recognize the modality (type), locality & intensity of sensation.

[a] Modality of sensation [b] Intensity of sensation [c]Locality of sensationdepends on specificity.

Mullers lawEach receptors give one type of sensation,

irrespective of the method of stimulation.

It is coded by change in:

1. The number of receptors activated (recruitment of receptors).Increase stimulus intensityIncrease number of receptors activated.

2. The frequency of impulses: Stronger stimulus Increasefrequency of impulses.

according to:

Weber-Feshner principleWhich states that sensation felt (interpreted stimulus intensity = log

intensity of the stimulus x constant).i.e. The frequency of impulses

log intensity of the stimulus.

dependson law of projection

Each area in the body e.g. hand or leg isrepresented in a particular area in the cerebral

cortex. So, when an impulse reaches the specific

area in the cortex, the cortex will projects the

sensation to its original site.

Phantom limb;

It occurs in amputees who complain of pain,touch, itching or pressure sensation felt in theabsent limb. This false sensation is due toirritation of the cut ends of the afferent nerves ofthe amputated limb which send impulses up tothe brain. The brain projects the sensation on to

the absent limb as if it were existing.

Classification of receptorsAccording to mode of stimulation According to Adaptation According to Situation

1. Mechanoreceptors. 2. Thermoreceptors.

3.Chemoreceptors. 4.Electromagnetic: Photoreceptors

5. Nociceptors (pain receptors) stimulated by tissue damage.

(1 )Mechanoreceptors:Stimulated by mechanical forms of energy. e.g Touch, pressure,

vibration, acceleration and stretch.

(2 )Thermoreceptors:Respond to changes in temperature. Present in skin and mucous

membranes.

(3 )Chemoreceptors:Stimulated by chemical forms of energy. Osmoreceptors and

glucoreceptors in hypothalamus, Carotid and aortic

chemoreceptors, Taste & smell.

a. Slowly adapting (tonic) receptors:

Baroreceptors, muscle spindle, alveolar stretch receptors.

The slow adaptation keeps the brain continuously alerts due to their

important postural & protective signals.

b. Moderately adapting receptors :

temperature, smell & taste receptors.

c. Rapidly adapting (phasic) receptors)

They discharge while the change is actually taking place.

e.g. Touch receptors (Meissner and paccinian corpuscle).

A) Exteroceptors :- Cutaneous receptors: Pain, touch and

temperature.

- Teleceptors: Vision, hearing, and smell.

B) Interoceptors:

- Proprioceptors: muscle spindle and golgi

tendon organs.

- Visceroceptors: Baroreceptors and

chemoreceptors.

-Hypothalamic receptors: Glucoreceptors and

osmoreceptors.

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Sensory

Somatic sensations[1] Pain sensation. [2] Thermal sensation. [3] Mechano-receptive sensations.

(a)Tactile sensation:Touch : crude & fine.

Pressure. Vibration.(b) Position Senses:

Static : sense of position. Kinetic : sense of movement.

Touch Pressure Sense Vibration Sensea)Crude

touch:Touch sensation

with poor

identification of

site & number of

stimuli..

Tested by a piece

of cotton passed

on the skin.(Cotton wool test)Receptors;Hair

end organs & free

nerve endings.

Afferent: A delta

fibres. (5-30

m/sc)

Tract: Ventral

spinthalamic tact

and some fibres

pass through

dorsal column.

Centre:

Thalamus.

b)Fine touchTouch sensation with accurate identification of site & number of stimuli.Receptors;Meissners & Paccinian corpouscles, Merkels discs & Ruffini

endings.Afferent: A beta fibres (30-70 m/sc).

Tract: dorsal column tract. Centre: sensory cortex.

Fine Touch includes1. Tactile localizationAbility to localize exact point of touch with eyes closed.

2. Tactile discrimination = 2 points discrimination.It is the ability to identify two tactile stimuli applied simultaneously as two

separate points of contact regarding that the distance between these two points is

more thanthreshold distance which is the minimal distance at which the twostimuli are felt as two separate points.

i.e. 2 mm in lips & finger tips & 60 mm in the back.

Tactile localization and discrimination are more accurate (less threshold

distance)

a. the more the number of receptors. b. the more the number of afferents.

c. the less the convergence of afferents.

d. the greater the area of cortical representation.

3. StereognosisAbility to know familiar object put in the hand with both eyes closed.

-It depends on:1) All cutaneous & deep sensations. 2) past cortical experience.

- Stereognosis is carried on dorsal column tract.-Its centre mainly insomatic association area (area 5,7).

It enables the person to know

the weights of objects and

discriminate between different

weights.

It is tested by applying different

weights onsupported handof a

blindfolded subject, then he isasked to identify the lighter or

the heavier weight.

Receptors: paccinian and

Ruffini.

Afferent: A beta fibres.

Tract: dorsal column tract.

Is a rhythmic repetitive pressure sensation

which if felt when a vibrating tensing forkis

put opposite body prominences to magnify the

stimulus.

Receptors

-Paccinian corpuscle responds to vibration up

to 500-800 Hz.

-Meissner corpuscle responds to vibration up

to 80 Hz.

Afferent: A beta.

Tract: dorsal column tract.

Centre: sensory cortex.

Importance

Depression of vibration sense is an early

diagnostic sign in degeneration of posterior

column of spinal cord e.g. uncontrolleddiabetes, pernicious anaemia. Also, it localizes

lesions of spinal cord.

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Sensory

Proprioceptive Sensation Thermal SensationsSensation of the position & movement of each part of the body in Relation to eachother & in relation to the space.

Receptors present in joints, ligaments and tissues around ligaments.

-Slowly adaptingmuscle spindle, Golgi tendon organ & Ruffini endings.

-Rapidly adapting

e.g paccinian to detect rate of movement.

Proprioceptive impulses go to the- Cerebellum via spinocerebellar tracts help to keep equilibrium.- Cerebral cortex via dorsal column tracts inform the cortex about the position of different

parts of body (static) & rate of movements (dynamic).

Types

1) Sense of position.

2) Sense of movement.

Loss of proprioception ; leading toSensory ataxia

A) Stamping gait

; patient raises his legs too high & drops them forcefully.

B) +ve Rombergs sign: the patient cannot maintain his erect position with closed eyes.C) Patient cannot walk in the dark .

D) Patient walk with broad base .

The ThermoreceptorsInternal (Central) thermoreceptors:

These are located in the hypothalamus for detection of the core temperature.

External (peripheral) thermoreceptors:

These include cold and warmth receptors and are located under the skin.With the highest density in the face and hands.

Cold receptors Warm receptors

free nerve endings and Krauses end

bulbs

free nerve endings

at tached to C & A delt a fibe rs. a tt ached to C fibe rs.

These receptors respond to

temperature from 10 to 35 C warm

fibers discharge maximal at 25C.

These receptors respond to

temperature from 25 to 45 C, warm

fibers discharge maximal at 35C.

- Cold spots are greater than hot spots

(10 times).

Adaptation of Thermoreceptors- Cold receptors adapt more slowly than warm receptors. (Both moderately

adapting).

- There is no adaptation above 45 C and below 10 C.Range of stimulation of thermal receptors:At O C, there is no action potentials i.e. anaesthesia.O to 10 C, cold pain fibres discharge, maximal at 5C.10 to 35 C, cold fibres discharge, maximal at 25 C.25 to 50 C, warm fibres discharge maximal at 35C.At 50 C, heat pain fibres discharge.Central pathway of thermal sensationThermal signals are transmitted to the higher centres through the lateral

spinothalamic tract.

Sensory pathways

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Sensory

(A) THE ANTERO-LATERAL SYSTEM1. It consists of A-delta nerve fibres (mainly) and also C nerve fibres.2. It transmits the following sensations:

(a) Pain (b) Crude touch (c) Temperature.3. Divided into ventral and lateral spinothalamic tracts.

The ventral spinothalamic tract lateral spinothalamic tractThis tract transmits crude touch as well astickle and itch sensations. Its pathwayconsists of 3 neurons;First order neuronsThese are C afferent nerve fibres. Theyenter the spinal cord via the dorsal roots,ascend or descend a few segments in theLissauer's tract, then terminate at themain sensory nucleus in dorsal horn.Second order neurons These constitute the tract. They start in

the dorsal horn, cross to the opposite side,ascend in the anterior column of spinalcord, and terminate at the ventralposterolateral nucleus.Third order neuronsThese start: in the thalamus, pass in thesensory (thalamic) radiation (in theposterior limb of internal capsule) andterminate at the cortical sensory areas inthe postcentral gyrus.

paleospinothalamic pathway Neospinothalamic pathwayThis transports slow pain sensation as well asthermoreceptive sensations specially heat,and it consists of the following 3 neurons; First order neurons: These are mainly C afferent nerve fibres. They enter the spinal cord via the dorsalroots, then terminate at the substantiagelatinosa of Rolandi (SGR) in laminae II & Illof the dorsal horn.Second order neurons:

These constitute the tract. They start: at theSGR, cross to the opposite side close to thecentral canal, ascend in the lateral column ofthe spinal cord and terminate at (a) theperiaqueductal gray area (PAG) (b) thereticular formation (c) the nonspecificthalamic nuclei. Third order neurons: These start at the thalamus and project toalmost all parts of the cerebral cortex (via theinternal capsule). However, they are notessential for perception of the transportedsensations but are essential for arousal of the

nervous system

This transports fast pain as well asthermoreceptive sensations speciallycold, and it consists of the following 3neurons: First order neurons

These are mainly A-delta afferent nervefibres. terminate at laminae I & Vof thedorsal horn.

Second order neurons

These constitute the tract. They start atthe dorsal horns, cross to the oppositeside and ascend in the lateral column ofthe spinal cord. Finally terminate at thethalamicVpLN

Third order neurons These are similar to ventralspinothalamic tract.

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Sensory

(B) THE DORSAL COLUMN LEMNISCAL SYSTEM Gracile and Cuneate tractsThese tracts transport:(1) Fine tactile sensations (tactile localization & discrimination).(2) Stereognosis and texture of material sensation.(3) Fine pressure and muscle tension sensations.(4) Vibration sense.(5) Proprioceptive and kinesthetic sensations.(6) Some crude touch and pressure.

The pathway of the gracile and cuneate tracts consists of the following 3 neurons: First order neuronsThese are mostly A-beta afferent nerve fibres. As They enter the spinal cord, they immediately turn upwards in the ipsilateral dorsal column and ascendwithout relay as the gracile and cuneate tracts till relay at: the gracile and cuneate nuclei in the medulla oblongata.

The gracile tract carries sensations from the lower part of the body and lies medially in the dorsal column, while the cuneate tract carries sensations from the upperpart of the body and lies laterally in the dorsal column.

Second order neuronsThese start at the gracile and cuneate nuclei in the medulla, cross in the sensory decussation to the opposite side, then ascend as the mediallemniscus, and finally terminate at the thalamus specially at the VPLN.

Third order neuronsThese start at the thalamic VPLN and terminate at the cortical sensory areas in the postcentral gyrus.

Sensations from head and neck1st order neuron Trigeminal (Gasserian) ganglion.

Axons enter at pons and divide into 2 parts:-a. Ascending fibres end in Sensory nucleus which is the

2nd order neuron; of fine sensations touch, pr , proprioceptive.crosses to the opposite side & ascends to

b. Descending fibres end in Spinal nucleus. which is the

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Sensory

2nd order neuron of pain and temp.Axons: form the trigeminal lemniscuscrosses to the opposite side & ascends to

3rd order neurone Postro ventral nucleus of thalamusAxons: end in the cerebral cortex.Centre: Face area in the lowest part of post central gyrus.

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Sensory

Pain sensationPain receptors. Free nerve endings

1.Mechanical pain Receptors. 2.Thermal pain Receptor3.Chemical pain Receptors.: stimulated by chemical stimuli.

Distribution of pain receptors

- More: Skin, periosteum, arteries, joint surfaces, & tentorium cerebelli and cranial sinuses.

- Less: deep tissues.

- Absent: liver parenchyma, lung alveoli and brain.Nerve fibres: A delta and C fibres.Adaptation: Slowly (static-tonic) or nonadaptive receptors.

Types of pain Pain is classified according to the:Cutaneous Pain Deep pain Visceral pain

Fast (Immediate, acutesharp or pricking)

Slow (Chronic, burning, achingthrobbing nauseous)

1. Felts within 0.1 second. 1. After one second.

2. Short duration. 2. Prolonged; annoying, intolerable.

4. A delta fibres. 4. C fibres

5. Ends in cerebral cortex. 5. in non specific thalamic nuclei &Reticular formation.

6. Well localized. 6. Poorly localized.

7. Not felt in deep tissues 7.Occurs in skin & deep tissues

9. Neospinothalamic tract 9. Paleospinthalamic tract

Neurotransmitter: Glutamate. Neurotransmitter: Substance P.Reactions to pain(1) Somatic (motor) reflexes:- Spinal reflexes.Flexor withdrawal reflex.(2)Autonomic reactions:-Cutaneous pain: Pressor effects (increased heart rate & ABP).

Diffuse, Dull aching andDepressor effects.Causes:- inflammation, ischaemia ormuscle spasm.- Bone fractures; due tostimulation of periosteal painreceptors.

Ischaemic pain Type of deep pain felt inmuscles when their bloodsupply is decreased.

The Patients complains ofsevere pain in the musclesupon walking or runningdue to accumulation of painproducing substances as

Most of viscera contain only painreceptors.Pain from viscera is carried a long;C fibres.Pain from peritoneum, pleura orpericardium:A delta.It differs from cutaneous pain. Sharp cut in the viscera does notcause pain (why).. Diffuse stimulation of pain nerve

endingsevere pain.Causes Of Visceral Pain

1. Ischaemia: increased acidicmetaboli tes, bradykinin &proteolytic enzymes.2. Inflammation of peritonealcovering.3. Irritation (chemical irritation by

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Sensory

Deep & visceral pain: Depressor effects (decreased heart rate & ABP).(3) Emotional reactions:--Acute pain: Crying and anxiety.(4) Hyperalgesia:- mainly due to skin lesion. (increased pain sensibility).

lactic acid.Examples1. Cardiac muscle: anginapectoris.2. Skeletal muscle:

intermittent claudication.

HCI in peptic ulcer).4. Overdistension of a hollowviscus.5. Spasm of a hollow viscus.

Referred painDefinition Examples Mechanism of referred pain

Pain originatingfrom viscerabut felt insomaticstructureswhich suppliedby the samespinal dorsalroot (the samedermatome) ofthe diseasedviscus.

1. Cardiac pain: is felt in leftshoulder.2. Gall bladder pain: is felt intip of right shoulder.3. Appendicular pain: is feltaround the umbilicus.4. Gastric pain: is feltbetween the umbilicus &xiphoid process.5. Renal pain: is felt in theback, inguinal region &testicles.6. Teeth pain: referred toother teeth.

a. Convergence projection theory

Afferent pain fibres from the skin and viscous converge on the same cells of SGR

or thalamus and will finally activate the same cortical neurons. Whatever the

source of pain, the cortex will project it to the skin being the commonest source of

pain.

b. Facilitation theory

Afferents of diseased viscera, give facilitation to cutaneous pain cells in Substantia

Gelatinosa of Rolandi (SGR), Which leads to facilitation of their stimulation.

So that minor activity in the pain pathway from somatic areas which would

normally die out in the spinal cord passes on to the brain

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Sensory

Pain Control SystemsThere are three control systems:

I) Gate theory. II) Anaelgesic system. III) Brain opiate system.

(I) Gate theoryVarious relay stations in pain pathway act as gates whichcan be opened or closed.The most important gates are located in: SGR, thalamus &Reticular formation.1) Spinal gate:SGR (substantia gelatinosa of Rolandi) in spinal cord.At this level, there is a group of inhibitory interneuronswhich block the transmission of pain sensation bypresynaptic inhibition of pain-conducting fibers. This gatecan be closed by Impulses from:1.A beta fibres: (rubbing of skin inhibits pain).2. A delta fibres; counter irritant and acupuncture inhibitpain.

(II) Analgesicsystem

Areas in thebrain containopiatereceptorsa) Periventriculararea ofhypothalamus.b) Periaqueductal

gray area in themidbrain.c) Substantia nigrain the midbrain.d) Raphe magnusnucleus in the

(III) Brain Opiate SystemMorphine like substances in CNS when bind toOpiate receptors in the brain cause inhibition ofthe pain pathway.

Sites of opiate receptors1. Periaqueductal gray area. 2.Periventricular aea.3. Raphe magnus nucleus in medulla. 4.Substantia nigra.

Opioid peptides(1) EnkephalinsAct as neurotransmitters at the analgesicsystem, adrenal medulla & GIT.(2) Endorphins- In hypothalamus act as neurotransmitters.

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Sensory

They stimulate cutaneous receptors which send impulsesthroughA delta fibres.3. Cortico-fugal fibres: from certain higher centers(thinking decrease pain).

All these fibers causes presynaptic inhibition of pain

by activating an interneurone which secrete GABA &enkephalin which are inhibitory neurotransmitters.2) Thalamic gate:The same "gating" mechanism for pain is found also at thethalamus where pain signals could be blocked bycorticofugal fibers or facilitated by intralaminar thalamicnuclei. In this way, the thalamus considered as asecondary gate far pain transmission.

medulla.e)Inhibitoryinterneurones inspinal cord.

- In pituitary act as hormone.(3) DynorphinVery potent analgesic secreted from many areasin nervous system.Types of opiate receptorsDelta, Mu, Kappa, Sigma & Epislon.

Stress analgesia; During stress, Pain is blocked- It occurs during stressful conditions.- Such analgesia produced by impulses discharged from cerebral cortex and hypothalamus, which excite the supraspinal pathway of pain inhibition

secreting endorphins which inhibit pain.- It occur by the following mechanism:a) The neurons of the periaqueductal gray area are stimulated by B endorphin reaching them from hypothalamus (neurons of periventricular area)or pituitary (through blood).b) Fibres of periaqueductal and substantia nigra secrete (Dopamine) which stimulate raphe magnus nucleus.c) Fibres of raphe magnus nucleus secrete (Serotonin) which stimulate Pain inhibitory complex area (in the dorsal born of sp.cd).d) Pain inhibitory complex area (in the dorsal born of sp.cd ) It consists of many interneurones which release enkephalin.

They cause presynaptic inhibition of pain nerve terminals, the latter, in turn, will stop releasing P substance.

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HeadacheBrain is insensitive to pain.Pain sensitive intracranial structure;(Arteries, Veins,Nerves and Dura at the base of the brain)

Headache is referred pain

a. Supratenterial is referred along the ophthalmic n frontal Headache.b. Infratentorial is referred along Cervical 2 occipital Headache.

Causes of intracranial headache: 5%

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1. Meningeal irritation; meningitis; generalized.Brain tumour; localized.

2. Migraine headache; Abnormal vascular phenomenon.

3. Hypertension: Headache pulse Pressure.

4. Low CSF pressure:

Removal of 20 ml of CSF. brain descent traction of the dura & headache.

5. Alcoholic headache

alcohol produces direct meningeal irritation.

6. Constipation.

Absorption of toxins produces direct meningeal irritation.

Causes of extra-cranial headache 95%1. Muscular spasm of scalp and neck muscles due to emotions.2. Irritation of the nasal sinuses.3. Errors of refraction .

4. systemic disorders as anaemia.5. Toothache.

Somato-Sensory cortexSomatic sensory area I Somatic association area sensory area II

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Sensory

Site: Post central gyrus ( area 3,1,2)Representation

Crossed representationi.e receives sensation from the opposite . Inverted representationi.e body is represented upside down

Large areas for thumb & lipsi.e area number of receptors.Modality orientation

- Anterior columns for proprioceptive sensations .- posterior columns for touch & pressure.Functions It receive the following sensations.1. Fine touch: Tactile localization & discrimination, stereognosis& texture of materials.2. Discrimination of various weights (pressure sense). 3.Vibration sense.4. Sense of position and movements of joints.5. Discrimination of various grades of temperature. 6.Localization of pain and temp.Destruction of sensory area I

A) The person loses ability for:

1. Discrete (fine) but not crude localization.2. perception of the above sensations.

B) Temperature & Pain;sensation is poorly affected. (perceived atthe level of thalamus).

Site . behind the lower parts of sensory area Ii.e area 5,7Receives signals from;a. Somatic sensory area I&IIb. Ventro-basal nuclei of the thalamusc. Other areas of the thalamus

Function. Collects information to understandthe meaning.

Effect of removal(Amorphosynthesis)

a. Inability to recognize complex objects that arefelt.b. Denial of the existence of the opposite half ofthe body.c. When felling objects fell only one side.

Site. Behind and below thelower part of sensory area I.

Spatial orientation. Faceanterior, trunk and legsposterior.

Receives impulses:-Dorsal columns & spino-reticulo-thalamic fibres ofboth sides,Sensory area I,visual and auditory areas.

Functions1- Potentiate function of SI.2- It gives meaning for thesensory signals e.g shape, ortexture of objects

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ThalamusThalamus Thalamic syndrome

[I]Non specific nuclei Midline & intralaminar- Relay impulses from reticular activating system to all parts of the

neocortex, so responsible for consciousness and alertness- Act as higher centre for crude (protopathic) sensations.

[II]Specific nuclei: to specific portions of cortex.a. Ventral nuclei:

I.Ventrolateral. (Motor nuclei)Receive impulses from BG & cerebellum & project to motor cortex.II. Postero-ventral nuclei: relay impulses to postcentralgyrus.PVMN; from the face (trigeminal leminsicus) to the cortex.PVLN; from the body (spinal & medial leminsci) to the cortex.

b. Dorsal nuclei:I. Dorso-lateral nuclei project to cortical association areas.

Concerned with complex integrative functions as language.II. Dorso-medial nuclei project to frontal lobe &hypothalamus.Concerned with Thinking and autonomic functions

c. Anterior nuclei project to limbic cortex.Concerned with recent memory and emotion.d. Medial geniculate body: relays impulses to auditory cortex.e. Lateral geniculate body: relays impulses to visual cortex..

Functions of thalamus[1] It contains relay nuclei for all sensory pathways except of olfaction.[2] Sensory centre for slow pain, extremes of temp & crude touch.[3]Non specific thalamic nuclei are responsible for excitability of the

cortex.[4] It is part of limbic circuits concerned with emotion & recent

memory.[5] It affects motor function as it is part of the circuits between BG,

cerebellum and motor cortex.

Cause: Thrombosis of the thalamo-geniculate artery branchof the

posterior cerebral artery.

LesionPostroventral nucleus & Lateral ventral nucleus.

Effects1. At frist:

- Loss of all sensations on the opposite side of the body

initially,

- Sensory ataxia: due to loss of proprioceptive sensations.

2. Later on: after few weeks or months

- Return of some crude sensations later on.

- Return of pain i.e thalamic pain; which is characterized by

severe and prolonged. This pain may occur spontaneously

or in response to trivial stimuli.

- It is due to facilitation of intralaminar and medial nuclei of

the thalamus.

3. Emotional disturbance

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Lesions of the Sensory SystemHyperalgesia Syringomyelia Tabes dorsalis Peripheral nerveprimary Secondary Widening of the central

canal of the sp cord (usuallycervical)

Damage:pain & temp fibres, later oncrude touch & pressurefibres as they cross in frontof the central canal.

Effects;Loss of pain, temp, crudetouch on both sides.

At the level of the lesion jacket like Dissociatedsensory loss- LMNL due to damage ofAHCs at the level of thelesion.-Autonomic manifests ; duedamage of LHCs in theaffected segments

CauseIt attacks the dorsal roots central to thedorsal root ganglion of lumbo-sacral regionof spinal cord.Manifestations1. Severe pain as it irritates pain fibers atfirst due to irritation of pain conductingnerve fibres.2. Later on pain fibers degenerate leadingto loss of pain in correspondingdermatomes.3. Then, degeneration of gracile and

cuneate tracts leading to loss of fine touch,pressure, vibration sense andproprioceptive sensation.- Loss of Proprioceptive sensationleading to; Ataxia:Inco-ordination of voluntary movement inabsence of paralysis characterized by thefollowing manifestations;A) Stamping gait; patient raises his legstoo high &drops them forcefully.B) +ve Rombergs sign: the patientcannot maintain his erect position withclosed eyes.C) Patient walk with broad base.

[a] Mono-neuropathyloss o all sensation inthe area of supply.

[b] Poly-neuropathy(peripheral neuritis)i.e all peripheralnerves.

Loss of sensations fromthe distal parts of the

limbs e.g gloves andstock anaesthesiaespecially for pain.

[c] Lesion of thedorsal roots

loss of sensations fromthe correspondingdermatomes alsodecrease of deepreflexes.

It occurs intheinflammedskin due todecreasedthresholdof painreceptorsbybradykinin,K,Histamineandprostaglandins. Sonon painfulstimulibecomepainful.

It occurs in normal skindue to increasedthreshold of painreceptors. So painreceptors needstronger stimulus, butonce pain is elicited, itis very severe.It can be explained by(Convergencefacilitation theory).Impulses from theinjured area facilitate acentral neuron.Impulses from the areaof secondaryhyperalgesia convergeon same centralneuron. Theconvergence on acentral facil itatedneuron explains theexaggerated painsensibility.

Brown Sequard syndrome i.e Hemisection of the sp. cd.1- At the level of the lesion same side

Sensory: loss of all sensations at the corresponding dermatome.

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Sensory

Motor: Lower motor neuron lesion & loss of all reflexes mediated by affected segments.

2- Below the level of the lesion

On the same side1.Sensory: loss of dorsal column sensations i.e fine touch, Pressure, vibration, sense of position & sense of movements.

2.Motor: Upper motor neuron lesion (UMNL).

On the opposite side1.Sensory; loss of spinothalamic sensations i.e pain & temperature,2.Motor: No loss.

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Quick Sensory Review