3. ⚫ Each single motor neuron and the muscle fibers it
innervates constitute a MOTOR UNIT.
⚫ No .of muscle fibers in a motor unitvaries.
⚫ HAND,MOTION OF EYE – 3-6 muscle fibers.
⚫ LEG MUSCLES – 600 muscle fibers.
⚫ Groupof muscle fibers (forming a motor unit ) can be
intermixed in a muscle.
⚫ ALL THE MUSCLE FIBERS IN A MOTOR UNIT ARE OF
SAME TYPE.
4. ⚫Based on typeof muscle fibers innervated ,durationof
twitchcontraction
Motorunitsare divided into
⚫S- slow -- small units
⚫FR – fast resistant to fatigue
⚫FF fast fatiguable --- large units
⚫RECRUITMENTof motorunits followssize principle:
⚫S muscle units – relatively slow contraction,controlled
contraction ---FR more powerful response –FF muscle
units mostdemanding tasks..
9. ⚫ Differ byactivity
⚫ Increased activity – muscle hypertrophy –type IIa ,IIb
fibers
⚫ Inactivity –atrophy – type I fibers aresusceptible
If nerve to slow
muscle is cut,the
nerve toa fast
muscle is spliced to
thecutend
The fast nerve
growsand
innervates the
previously slow
muscle
Muscle becomes
fast,changes in
portein
isoforms,changes in
myosin ATPase
activity
13. ⚫ Amyotrophic comes from thegreek language:
A- means "no", myo refers to "muscle", and trophic means
"nourishment"; amyotrophic therefore means "no muscle
nourishment," which describes the
characteristic atrophicationof thesufferer'sdisused
muscle tissue.
⚫ Lateral identifies theareas in a person's spinal cord where
portions of the nervecells thatareaffected are located.
⚫ As thisarea degenerates it leads to scarring or hardening
(“sclerosis") in the region.
21. ⚫HALLMARK-deathof LMN ,.UMN
⚫LMN-ant.horncellsof spinal cord,bulbar muscles
⚫UMN—layer 5 of motorcortex,descending via
pyramidal tracts.
⚫Other motor neuron disease involvesonly subsetof
motor neurons.
22.
23.
24.
25. ⚫Onset-----UMN or LMN-----Involves both---absence
of them ?diagnosis.
⚫Accof lipid pigmented—LIPOFUSCHIN.
⚫Normallyseen in aged cells.
⚫Focal enlargementsare frequent –SPHEROID—accof
neurofilamentproteins.
⚫Proliferation of astrocytes,microglia.
⚫Combined grey and white matterdisease.
⚫Motorcellsand motorfibre tracts.
⚫ATROPHY,DEGENERATION.LOSS OF MOTOR
NEURONS OF CN..
26. Death of the peripheral motor neurons in brainstem,spinal
cord.
Denervation
Consequentatrophyof the muscle fibres
Histo chemical,electrophysiological
Earlystages
Reinnervation
Less than poliomyelitis.peripheral neuropathy
27.
28. ⚫Progressivedegeneration –muscleatrophy is readily
recognised in muscle biopsiesand on clinical exam,---
AMYOTROPHY.
⚫Thinning of corticospinal tracts
⚫Lossof fibers in the Lateral columns—fibrillary
gliosis-LATERAL SCLEROSIS.
⚫SELECTIVITY OF NEURONAL CELL DEATH.
29. ⚫UBIQUITIN-marker fordegeneration is seen.
⚫Nucleusof Onuf –innervates bowel ,bladder is not
involved.
⚫Max involvement in cervical spinal cord
⚫Lossof large pyramidal cells BETZ cells in motor
,premotorcerebral cortex.
⚫Gliosisof lateral cords
⚫NONE ARE PATHOGNOMONIC.
30. ⚫Cause notwell defined..
⚫Excitatory neurotransmitters.
⚫Glutamateparticipate in death of motor neurons in
ALS.
⚫EAAT2.
⚫SOD1—cellulardefenseagainstexcitotoxicity
⚫When mutated—catalytic.
⚫Non neuronal cells –influences thediseasecourse.
31. ⚫Variable on motor neurons involved.
⚫Asymmetricweakness ,usuallydistally in one of the
limbs.
⚫Insidiousonset
⚫Developmentof cramps with volitional movements in
early hoursof morning.
⚫Weakness
⚫Wasting
⚫ Atrophy
32. ▣ Spontaneus twitching of motorunitsor fasciculation
▣ EXTENSORS >FLEXORS in upper limbs
▣ Difficulty in chewing ,swallowing,movementsof face
and tongue.
▣ Early involvementof resp.muscles—death
▣ Hyperactivityof musclestretch reflexes
▣ Spasticresponse topassive movements
▣ Musclestiffnessoutof proportion
▣ Exaggeration of motorexpression of emotion—
weeping,laughing—pseudobulbareffect
33. ⚫Asymmetric—symmetric
⚫Whether UMN or LMN atonset—both later
⚫Sensory,bowel,bladder–not involved.
⚫Cognitive function,ocularmotility –preserved
⚫Dementia is nota componentof sporadic ALS
⚫Familial—ALS+ FRONTO TEMPORAL DEMENTIA.
