Pain Reflex Action YouTube Lecture Handouts
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PAIN
- Word is from Greek word POENA meaning penalty or punishment
- Sherrington defined Pain as:
“The psychical (pertaining to mind) adjunct (joined to) of an imperative (urgent) protective reflex”
- It is unpleasant sensory experience usually associated with emotional disturbances. It also indicates actual or potential tissue damage
- Though unpleasant but has great survival value
Purpose of Pain
- Informs not only about quality of stimulus but
- Has protective function
- Informs that harmful agent is close to body
- The part of body or stimulus should be removed
Types of Pain
- FAST pain eg. Skin is cut with a sharp knife. Usually not in deeper tissues
- Acute pain
- Appear with in 0.1 ms. After the application of stimulus
- Sharp, well localized pricking sensation
- Carried by Aδ Myelinated fibers
- Fibers have topographic representation in cerebral cortex
- It elicits withdrawal reflex
- Sym. Response seen —
- Tachycardia
- Increase in B. P.
- Chemical transmitter … Glutamate
Slow Pain
- Appears after a second or more
- Poorly localized, dull, throbbing or burning sensation
- Carried by Type C unmyelinated fibers
- Produces, nausea, vomiting, lowering of BP
- Feeling of Intense unpleasantness
- Chemical Trans. … substance P
Pain Perception
- Occurs at sub cortical level at Thalamus
- Somatosensory cortex help in exact localization and meaningful interpretation of degree & quality of pain
Visceral Pain
- Characteristics
- Poorly Localized (receptors are few)
- Unpleasant often associated with nausea, vomiting & other Autonomic disturbances
- Usually Radiates
Causes
- Distension of hollow viscera
- Intestinal obstruction
- Inflammation
- Ischemia
- Traction on mesentry
- Spasm of hollow structures eg. Gall bladder, ureter etc.
Viscera Insensitive to Pain
- Parenchyma of liver
- Alveoli of lungs
Neural Pathway
- Afferents reach the Spinal cord via Autonomic nerves
- Cell bodies are in Dorsal Roots
- In CNS path is same as that of somatic sensation
- Visceral pain results in Guarding (contraction of abdominal muscles) which protects underlying viscera
Referred Pain
- Visceral or deep somatic pain is frequently felt not in the viscus but in the somatic structure considerably away from it.
- Radiation of Pain: visceral Pain is both local and Referred
eg.
- Cardiac Pain radiating to the inner aspect of the Lt. Arm
- Irritation of diaphragm causes pain in the tip of shoulder
- Pain of gall bladder stone, tip of rt. shoulder
Mechanisms
- Dermatomal Rule
- Pain is usually reffered to the structure that has developed from the same embryonic segment or dermatome eg. Heart and Arm have same segmental origin
Role of Convergence
Nerves from viscera & somatic structure converge on the same Spin thalamic N.
Since somatic Pain is more common, Brain has learned that activity in a given pathway is caused by pain in a particular somatic structure. Now even if the activity is in viscera, it is projected to somatic area
Facilitation Effect
- Activity in Visceral afferents produce subliminal fringe effect & lowers the excitability threshold of Spin thalamic neurons
- Now any activity in somatic area (which normally dies out) is facilitated and reaches conscious level
Role of Past Experience
- It also plays imp. Role
- The main cause is Plasticity in the CNS and Convergence of somatic & visceral fibers on the second order neurons
- Imp. Visceral Pain initiates reflex spasm of abdominal muscles & make them rigid. It is called guarding & is protective
Pain Suppression System
Observations:
- Reaction to pain varies from person to person
- Rubbing or massaging reduces pain
- Soldiers feels less pain in battle field
- Counter irritants reduce pain
- Acupuncture reduces pain
- (TENS) Trans cutaneous electric Nerve Stimulation
Analgesic Systems
I Analgesia produced by stimulation of nerves. It is at two levels
- Spinal &
- Supraspinal
II Release of Endogenous Opioid Peptides
Spinal System
Gate control theory (Melzack & Wall)
- A hypothetical Gate is in Dorsal Horn
- Interaction is between large diameter proprioceptive fibers & peripheral fibers carrying pain sensation
- Pain signals entering in Lateral Spin thalamic Tract are modified here
- Stimulation of large fibers ‘Close the Gate’
- Stimulation of small fibers ‘Open the Gate’
Supraspinal System
- Mesencephalic Pain Inhibitory System: Fibers arise from Mid Brain and descend down to the Dorsal Horn of Spinal Cord
- Following structures are invol
- Periaqueductal grey & Periventricular area
- Nucleus Raphe Magnus in Medulla
- Dorsal horn of spinal cord
Neurotransmitters
- Periaqueduct neurons … Enkephalin
- Raphae Magnus Nu … Serotonin
- Dorsal horn neuron … Enkephalin
- This neuron in dorsal horn causes Pre & Post Synaptic Inhibition of incoming type C & A δ fibers
Pain signals are blocked at initial entering point
Morphine & Opiate Receptors
It was long known that injection of morphine into periventricular & periaqueductal areas cause exteeme degree of analgesia.
Endogenous Opioids
- Morphine and Opioid Peptides produce analgesia by binding to Opiate receptors
- Three types of receptors
- µ … β- Endorphin
- K … Enkephalins
- δ … Dynorphins
Physiological Significance
- Morphine acts by two mechanisms
- Spinal level … decreases release of substance ‘P’
- Supraspinal level … activates descending pathways
Hyperalgesia
Is decrease in pain threshold
- Two types
- Primary &
- Secondary
Motor Activity of Body
Two motor sy.
- Medial motor system: Phylogenetically old. Includes:
- Axial & girdle Muscles
- Action involves the Axis & Proximal limbs
- Determine Posture & Equilibrium
Tracts Involved
- Ant. Cortico spinal
- Some fibers of Corticobulbar
- Lat. Vestibulospinal
- Medial ″
- Retoculospinal
- tectospinal
Lateral Motor system: phylogenetically new
- Muscles of digits & distal segment of limb
- Regulates skill voluntary movements
Tracts are
- Corticobulbar
- Lateral Corticospinal &
- Rubrospinal
Descending/Motor Tracts
- Pyramidal &
- Extrapyramidal: all other tracts
- Reticulo spinal
- Rubro ″
- Vestibulo ″
- Tecto ″
- Olivo ″
Pyramidal Tract
Salient features:
Longest tract
Fib. Unmyelinated at birth, myelination begins in II postnatal week & is completed by 2 years
80% fib. Are small diameter 1 to 4 µm 20% are large 11 to 22 µm
Large fib. Arise from cells of Betz present in primary motor cortex
Large fib. Have a tendency to disappear at old age causing automatic shaking movement
Phylogenetically ant. Pathway is old
Pathway
- Corticonuclear: begins in cerebral cortex & ends in brain stem (motor cranial nuclei)
- Corticospinal: from cerebral cortex to Spinal ventral horn cells
Origin
- Motor cortex, area 4 … 30%
- Premotor cortex, area 6 … 30%
- Somatosensory area I & II … 40% and adjacent parietal lobe association cortex
Path
- Fibs. Form Corona radiata to reach I. C.
- In Internal Capsule tract lies in the Genu, and ant. 2⟋3 of posterior limb
- Fibs. Are arranged in sequential order
- Mid brain, fibs. Lie ventral to the substantia nigra occupying middle 3⟋5 of this reg.
- Pons, here the tract is broken up into scattered bundles by the nuclei pontis & the fibs. Of middle cerebellar peduncle
- Medulla, fibs. Reunite before entering medulla. They in ventral part producing a bulge the Pyramids (tract named)
- 80% cross – Lateral Corticospinal
- 20% uncrossed — Ant. Corticospinal
Functions
- Controlls, voluntary, fine, precise skilful movements of the limbs
- Fibers are closely packed in Internal capsule & Brainstem small lesion here can cause widespread paralysis
Extrapyramidal Tracts
- Rubrospinal
- Reticulospinal
- Medial & lateral
- Vestibulospinal
- Tectospinal
- Medial longitudinal fasciculus
- Olivospinal
Rubrospinal Tract
- Origin: Red nucleus (magnocellularis)
- Course: crossed, does not extend below thoracic region
- Termination: on interneurons in dorsal horn
- Functions: facilitatory to flexor mus.
Inhibit extensors/antigravity mus.
Reticulospinal
Medial (pontine) Reticulospinal
- Origin: Medial pontine reticular format.
- Course: mostly crossed
- Termination: interneurons terminating on alpha & gamma neurons
Lateral (medullary) reticulospinal
- Origin: Gigantocellular component of medullary reticular formation
- Course: mostly uncrossed
- Termination: interneurons
Functions of ₹
- Two tracts are mostly antagonistic
- Antigravity Mus.
- Pontine … Ex.
- Medullary … Inhi.
- Mus. Tone, act through gamma mn.
- Pontine … Facilitatory
- Medullary … Inhi.
- Can control ANS.
Vestibulospinal
- Origin: lateral vestibular nucleus of cerebellum (Deiters Nu.)
- Course: uncrossed, runs entire length of spinal cord
- Termination: some directly on alpha mn. (alpha rigidity)
Functions
- Facilitatory to extensors
- Inhib. To flexors
- MAINTENANCE OF POSTURE
Tectospinal
- Origin: Sup. Colliculi
- Course: crossed, cervical rg.
- Termination: inter neurons
- Functions: Spino Visual Reflex
- Turning of head & moving the arms in response to visual, hearing, & other exteroceptive stimuli
Medial Longitudinal Fasciculus
Origin: from
- Vestibular nu.
- Reticular formation
- Sup. Colliculi
- Interstitial Nu. Of Cajal
- Course: uncrossed, well defined in upper cervical seg.
Functions
- Ocular move. In response to vestibular & auditory stimuli.
- Integration of eye & neck movement.
Olivospinal Tract
- Presence is doubtful
- Functions: exact is not known probably involved in reflex movement.
Applied Aspects
Important points
1 Common Motor path
All motor activities are finally controlled by α motor neuron
2 Total separation of Pyramidal & E. P. is not possible, usually both are affected simultaneously
Common terms:
Monoplegia: paralysis of one limb. Injury to area 4 (fibs. Are scattered)
Hemiplegia: paralysis of one side of body. Injury at Internal capsule.
Paraplegia: paralysis of both the lower limbs. Injury of Spinal cord in lower part
Quadriplegia: paralysis of all 4 limbs. Injury of Spinal cord in upper Cervical rg.
Lesions of the Pyramidal Tracts
- Findings are on the opposite side
- Acute stage/stage of shock
- Hypotonia
- Flaccid paralysis (no reflex movement)
- Vol. muscles are more affected eg. Mus. of face, leg, arm, hand etc.
- Mov. Of respiration, head, trunk & abdominal wall retained
- If corticobulbar fibs. Escape, eyeball mov. Persist
- Emotional mov. Persist & are strong
- All reflexes super. & deep are lost
- Stage of recovery
- The affected mus. Become spastic
- Body assumes characteristic position
- Associated mov. Can be aroused
- All superficial reflexes lost
- Deep reflexes hyperactive
- Babinski sign ‘positive’
- Patient may walk with slight limp
- Power returns in arm & face
- Gait. Spastic hemiplegic gait
Effects of Upper Motor Neuron Lesion and Lower Motor Neuron Lesion
Effects | Upper motor neuron lesion | Lower motor neuron lesion | |
---|---|---|---|
Clinical Observation | 1. Muscle tone | Hypotonia | Hypotonia |
2. Paralysis | Spastic type of paralysis | Flaccid type of paralysis | |
3. Wastage of Muscle | No Wastage of Muscle | Wastage of Muscle occurs | |
4. Superficial reflexes | Lost | Lost | |
5. Plantar reflex | Abnormal plantar reflex … Babinski՚s sign | Plantar reflex — absent | |
6. Deep reflexes | Exaggerated | Lost | |
7. Clonus | Present | Lost | |
Clinical Confirmation | 8. Electrical activity | Normal | Absent |
9. Muscles affected | Groups of Muscles are affected | Individual muscles are affected | |
10. Fascicular twitch in EMG | Absent | Present |
Lesions of Spinal Cord
- Complete transection: Causes
- Gunshot injury
- Dislocation of spine
- Occlusion of blood vessels
- Incomplete Trans. Here some fibers escape
- Hemisection: one lateral half affected
Complete Transection
Clinical stages:
- Stage of Spinal Shock
- Stage of Recovery/Reflex Activity
- Stage of Reflex Failure
Stage of Spinal Shock
Immediately after injury … there is cessation of all activities
Cervical trans … Fatal, because of respiratory paralysis
Transection at Lower level … Patient feels as if he is cut in two parts
Upper part unaffected
Lower part deprived of all sensory & motor activities
Changes in lower part
All sensations lost
Muscle Tone is lost
All Reflexes superficial & deep lost
Change in BP depends on level of transection
If at marked fall in BP.
Below no significant effect
Urinary bladder & rectum are paralysed
The penis is flaccid & erection is impossible
Cause of Spinal shock: sudden stoppage of excitatory impulses from higher centers
- Duration & severity depends on degree of encephalization (evolution of animal) higher the animal longer the period
- Frog … few minutes
- Cats & dogs … few hours
- Monkeys … few days
- Humans … about 3 weeks
Stage of Recovery/Stage of Reflex Activity
- Smooth muscles are First to recover
- Sphincter of UB gets tone very soon
- Retention of urine
- Reflex evacuation of bladder & Ref. defecation
- Next tone of blood vessels regained
- BP becomes normal
- Skin becomes normal
- Bed sores if any heals rapidly
- Skeletal mus. Tone recovers after ~3 weeks
- Tone returns first in flexors, paraplegia of flexion
- Limbs cannot support body weight
- No wasting of muscles
- Reflex activity returns few weeks after return of muscle tone
- First reflex to return is Babinski positive
- Extensor reflex appears after some time
- Mass reflex established
Stage of Reflex Failure
- Due to malnutrition, infection, toxaemia
- Gen. Condition deteriorates
- Threshold of stimulus increases
- Reflexes more difficult to elicit
- Mass reflex abolished
- Muscles become flaccid
- Wasting present
Incomplete Transection of SC
- There is partial lesion involving both the sides of spinal cord
- SC. is gravely injured, but does not suffer from complete division
- Effect occurs in three stages
- Stage I & III are similar to complete Transection
- Stage II differs remarkably
SN | Complete Transection | Incomplete Transection |
1 | TONE returns in Flexor muscles First | In Extensor muscles first because some descending fib. may escape injury (Vestibul ospinal & Ret. Spinal) |
2 | Paraplegia in Flexion (higher tone in flexor muscles) | Paraplegia in Extension (higher tone in extensor mus) |
3 | Flexor Reflexes return first eg. Withdrawal Reflex | Extensor Reflexes return first eg. Stretch Reflex. |
- In incomplete transection range of reflex activity is greater & movement of locomotion can be carried out to some extent. Stepping movements can be seen (Phillip sons Reflex)
Brown Squared Syndrome Hemisection of S. C
Lateral half of S. C. is involved
- Immediate effect – Spinal shock
- Late effects-
- Changes below the level
- Changes at the level
- Change above the level
Below the Level
- Same side
- Sensory: Loss of fine touch, tactile localization, tactile discrimination, vibration sense, kinaesthetic sense & Stereognosis.
- Motor
- UMN paralysis
- Vasomotor
Temporary loss of tone, leads to fall in BP.
- Opposite side
- Sensory: Total loss of Crude touch, temp. & pain sensation
- Motor
Not much, UMN paralysis of few muscle fibs. May be because of damage to direct pyramidal fibers
In Nutshell
- Same side: extensive motor loss little sensory loss.
- Opposite side: extensive sensory loss little motor loss.
At the Level
Same side:
Sensory … all sensations lost
Motor … LMN paralysis
Flaccid paralysis
all reflexes lost
no muscle power
Wasting & degen. Seen
Vasomotor system … complete & permanent failure
Opposite side:
Sensory
Some loss of pain & temp. (Horizontal fibs.)
Tracts of Gall & Burdach not affected
Motor
Usually no change
Above the Lesion
- Same side
- Sensory, a band of hypaesthesia can be seen because of irritation of damaged ends of nerve fibers
- Motor, twitching of muscles can be present due to irritation of nerves
- Opposite side
- Not much changes
Tabes Dorsalis
Causes: Usually caused by Syphilis, bilateral degeneration of post. Nerve roots & post. Funiculi. (Sp. Fas. Gracilis) Characteristic features
- Lightning pain due to stimulation of pain fib. in DNR with pain free intervals
- Pain sensitivity decreases, resulting in trophic changes
- Perforated ulcers of skin at pressure points
- Charcot joints deformation due to repeated trauma caused by loss of pain sensation
- Loss of sensation: on same side at and below the lesion. Position sense, vibration, Stereognosis, discriminative touch lost
- Reflexes: tendon reflexes lost
- Sensory ataxia due to lack of co-ordination of muscles Romberg՚s Sign positive
Syringomyelia
Causes: Excessive over growth of glial tissue along with cavitation in grey matter around central canal of spinal cord. Cervical enlargement is more frequent site effected
Characteristic features:
- Sensory: dissociated anaesthesia. Loss of pain & temp. With retention of touch
- Symptoms are bilateral usually hands & arms affected due to predilection for cervical region
- Motor: occurs with further spread of gliosis & cavitation
- Flaccid paralysis LMN type
- Progressive spastic paralysis, if diseases progresses to involve Pyramidal & Extrapyramidal tracts
Sub-Acute Combined Degeneration
- Cause: usually associated with Pernicious Anaemia, lack of Intrinsic Factor essential for Vit. absorption
- Bilateral degeneration of white fibs. Of the dorsal & lateral column of S. C. lumbo sacral region is especially involved
- Manifestation: loss of position & vibration sense of lower extremities
- UMN type paralysis, Babinski positive
Disseminated (Multiple) Sclerosis
- Widespread demyelination in CNS.
- Nerve cells are replaced by Glial cells.
- Crippling disease
- Both sensory & motor symptoms may be present
- Sign & symptoms depend on Asc. or Des. Tracts involved