Nmj
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NEUROLOGY NEUROMUSCULAR JUNCITON SEPTEMBER 21, 2005
• •
NEUROMUSCULAR JUNCTION • Junction is found in the middle of the bulk of the muscle fiber • Motor point – where the nerve will enter the muscle • Each muscle has its own myoneural junction
•
MYELINATED FIBERS • Nerve fibers becomes unmyelinated as it enters the myoneural junction
•
PRESYNAPTIC • From the nerve • Numerous mitochondria • Has synaptic vesicles which enclose the preformed acetylcholine POSTSYNAPTIC • From the muscle (sarcolemma) • Has synaptic clefts to increase the surface area • Has ligand-dependent receptors NOTE: the terminal portion of the nerve bulges to increase the surface area of the myoneural junction so that acetylcholine can bind to more receptors. PHYSIOLOGY • CALCIUM leaks out into the synaptic cleft through the calcium channels in the presynaptic area. • Calcium gets inside the terminal button (presynaptic) to facilitate the release of acetylcholine. • Acetylcholine in the synaptic area attaches to the receptor (postsynaptic) that leads to a conformational change in the receptor. • Sodium and calcium can now enter the receptors to depolarize the muscle. MYASTHENIA GRAVIS • Has normal myoneural junction • Presence of antibodies block the acetylcholine receptors thereby inhibiting its effect
There is normal secretion of acetylcholine CLINICAL FEATURES: occurs in all ages, affects female than males, fluctuating weakness, affects cranially innervated muscles (diplopia, difficulty in swallong, facial and limb weakness, generalized weakness and respiratory failure), easy fatigability. DIAGNOSTIC TESTS: tensilon test, decrement on repetitive nerve stimulation, positive Ach receptor antibody TREATMENT: anticholinesterase, steroid, plasmapharesis, thymectomy
DISORDERS OF MUSCLE • If there is hemiparesis, think of the CNS • If there is weakness in four extremities, think of the PNS PNS Anterior horn cells in the spinal cord Peripheral nerve Myoneural junction Muscle ANTERIOR HORN CELL • Affects the motor function • There is segmental weakness (the level of myotome involved can be identified) • There is progressive weakness • From segemental to generalized weakness • Will not present any sensory symptoms PERIPHERAL NERVE • Motor plus sensory component • Generalized weakness • Symmetrical and distal in distribution
janesa – D2007
1
•
Example: difficulty in buttoning shirt, use of utensils but can lift arms
MUSCLE • Motor component • Distribution is proximal • Can be symmetric or asymmetric • Example: can’t get up from the chair CLINICAL MANIFESTATIONS OF WEAKNESS: 1. inability to ambulate/ atrophy of proximal muscles • pelvic and shoulder girdle muscles • example: difficulty in getting up from stool or toilet bowl, difficulty in combing hair 2. gower’s maneuver • generalized muscle weakness • example: difficulty in getting up from sitting on the floor (Indian sit) 3. respiratory embarrassment/failure • severe disorder NOTE: sensory is still intact DIAGNOSTIC TEST: 1. Creatinine Kinase • Normally found inside the muscle and normally leaks out from it in small amounts specially during exercise • Normal value: <14 iu • Increased when there is destruction of muscle membrane 2. electromyography • done by inserting a needle into a muscle • take note of the response of the muscle 3. pedigree/chromosomal studies • to assess the inheritance pattern • to indicate the transmission of disease • affects 50% of children if sex-linked • 50% are carriers
•
non-specific changes
5. biochemical exam • genetic markers NOTE: one muscle fiber is like one strand of hair (about 50um) PROGRESSIVE MUSCLAR DYSTROPHY CLINICAL PATTERN USUAL INHERITANCE DUCHENNE DYSTROPHY X-LINKED BECKER’S DYSTROPHY X-LINKED LIMB-GIRDLE AUTOSOMAL RECESSIVE SCAPULOHUMERAL AUTOSOMAL RECESSIVE FASCIOSAPULOHUMERAL AUTOSOMAL DOMINANT OCULOPHARYNGEAL AUTOSOMAL DOMINANT NOTE: becker’s is less severe than duchenne. : autosomal recessive – male and female are both affected, will not spare a generation DUCHENNE MUSCULAR DYSTROPHY • dystrophinopathies (chromosome xp21) • peculiar way of walking (waddling gaitprotruding abdomen due to weak spinal muscles • progressive muscle weakness • onset is around 5-7 y/o • wheelchair bound by the age of 12-15 • usual complication is respiratory infxn STUDY: • duchenne • beckers • limb-girdle • inflammatory myopathy • dermatopolymyositis • periodic paralysis – associated flaccidity, tendency of remission and relapse
4. muscle biopsy aestimateo anima D2007 janesa – D2007
2
• •
NEUROMUSCULAR JUNCTION • Junction is found in the middle of the bulk of the muscle fiber • Motor point – where the nerve will enter the muscle • Each muscle has its own myoneural junction
•
MYELINATED FIBERS • Nerve fibers becomes unmyelinated as it enters the myoneural junction
•
PRESYNAPTIC • From the nerve • Numerous mitochondria • Has synaptic vesicles which enclose the preformed acetylcholine POSTSYNAPTIC • From the muscle (sarcolemma) • Has synaptic clefts to increase the surface area • Has ligand-dependent receptors NOTE: the terminal portion of the nerve bulges to increase the surface area of the myoneural junction so that acetylcholine can bind to more receptors. PHYSIOLOGY • CALCIUM leaks out into the synaptic cleft through the calcium channels in the presynaptic area. • Calcium gets inside the terminal button (presynaptic) to facilitate the release of acetylcholine. • Acetylcholine in the synaptic area attaches to the receptor (postsynaptic) that leads to a conformational change in the receptor. • Sodium and calcium can now enter the receptors to depolarize the muscle. MYASTHENIA GRAVIS • Has normal myoneural junction • Presence of antibodies block the acetylcholine receptors thereby inhibiting its effect
There is normal secretion of acetylcholine CLINICAL FEATURES: occurs in all ages, affects female than males, fluctuating weakness, affects cranially innervated muscles (diplopia, difficulty in swallong, facial and limb weakness, generalized weakness and respiratory failure), easy fatigability. DIAGNOSTIC TESTS: tensilon test, decrement on repetitive nerve stimulation, positive Ach receptor antibody TREATMENT: anticholinesterase, steroid, plasmapharesis, thymectomy
DISORDERS OF MUSCLE • If there is hemiparesis, think of the CNS • If there is weakness in four extremities, think of the PNS PNS Anterior horn cells in the spinal cord Peripheral nerve Myoneural junction Muscle ANTERIOR HORN CELL • Affects the motor function • There is segmental weakness (the level of myotome involved can be identified) • There is progressive weakness • From segemental to generalized weakness • Will not present any sensory symptoms PERIPHERAL NERVE • Motor plus sensory component • Generalized weakness • Symmetrical and distal in distribution
janesa – D2007
1
•
Example: difficulty in buttoning shirt, use of utensils but can lift arms
MUSCLE • Motor component • Distribution is proximal • Can be symmetric or asymmetric • Example: can’t get up from the chair CLINICAL MANIFESTATIONS OF WEAKNESS: 1. inability to ambulate/ atrophy of proximal muscles • pelvic and shoulder girdle muscles • example: difficulty in getting up from stool or toilet bowl, difficulty in combing hair 2. gower’s maneuver • generalized muscle weakness • example: difficulty in getting up from sitting on the floor (Indian sit) 3. respiratory embarrassment/failure • severe disorder NOTE: sensory is still intact DIAGNOSTIC TEST: 1. Creatinine Kinase • Normally found inside the muscle and normally leaks out from it in small amounts specially during exercise • Normal value: <14 iu • Increased when there is destruction of muscle membrane 2. electromyography • done by inserting a needle into a muscle • take note of the response of the muscle 3. pedigree/chromosomal studies • to assess the inheritance pattern • to indicate the transmission of disease • affects 50% of children if sex-linked • 50% are carriers
•
non-specific changes
5. biochemical exam • genetic markers NOTE: one muscle fiber is like one strand of hair (about 50um) PROGRESSIVE MUSCLAR DYSTROPHY CLINICAL PATTERN USUAL INHERITANCE DUCHENNE DYSTROPHY X-LINKED BECKER’S DYSTROPHY X-LINKED LIMB-GIRDLE AUTOSOMAL RECESSIVE SCAPULOHUMERAL AUTOSOMAL RECESSIVE FASCIOSAPULOHUMERAL AUTOSOMAL DOMINANT OCULOPHARYNGEAL AUTOSOMAL DOMINANT NOTE: becker’s is less severe than duchenne. : autosomal recessive – male and female are both affected, will not spare a generation DUCHENNE MUSCULAR DYSTROPHY • dystrophinopathies (chromosome xp21) • peculiar way of walking (waddling gaitprotruding abdomen due to weak spinal muscles • progressive muscle weakness • onset is around 5-7 y/o • wheelchair bound by the age of 12-15 • usual complication is respiratory infxn STUDY: • duchenne • beckers • limb-girdle • inflammatory myopathy • dermatopolymyositis • periodic paralysis – associated flaccidity, tendency of remission and relapse
4. muscle biopsy aestimateo anima D2007 janesa – D2007
2
