ms Lecture 5
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How do you call diseases of
a) Nervous tissue
- a) neuropathies
- b) myasthenia gravis/syndrome
- c) myopathies
Motor unit functional components
- ⋅MN cell body
- ⋅MN axon
- ⋅NMJ, synapses
- ⋅Muscle fibres
General features of neurogenic and myopathic diseases (see on notes sheet)
No answer given
Fasciculation VS Fibrillation
- Fasciculation = small visible muscle twitches (single MUs firing)
- Fibrillation = small spontaneous twitches of single muscle fibres, not visible, require EMG analysis.
A patient has distal limb weakness and fibriallations. Neurogenic or myopathic?
Neurogenic : Myopathic would include proximal limb weakness.
LOWER MOTONEURONES (LMNs) + Lesion effects
- ⋅Primary MNs
- ⋅Innervated skeletal muscle directly
- ⋅Located in spinal cord ventral horn/ cranial nerve nuclei
- Lesion: weakness, atrophy, ↓ tendon reflexes, ↓ tone, fasciculation
UPPER MOTONEURONES (UMNs) + Lesion effects
- ⋅Originate in higher motor centre (eg. celebral cortex)
- ⋅Synapse with LMN
- ⋅Relay descending commands
- Lesion : Weakness, (no paralysis, no/little citrophy), ↑ tendon reflexes, ↑ tone (spasticity), Babinski (extensor plantor responses)
What does the presence of both LMN and UMN lesion signs indicate?
Amyotrophic lateral sclerosis (LGU Gehrig disease; motor neurone disease)
Tests to distinguish Neurogenic & myogenic diseases
- ⋅Measurement of muscle enzymes in serum.
- ⋅Nerve conduction studies
- ⋅Muscle biopsy
- ⋅DNA analysis
DIAGNOSTIC SERUM ENZYME MEASUREMENT
- ⋅ Cell membrane integrity is lost in diseased/ damaged muscle cells
- ⋅Soluble enzymes in sacroplasm leak out and can be detected in serum
- Neuopathy - Small increase in enzyme serum
- Myopathy - Large increase in serum enzyme
Examples of enzymes that can be detected via serum enzyme measurement
- - Creatine kinase (CK)
- - Serum glutamic-oxaloacetic transaminase (SGOT)
- - Lactate dehydrogenase (LDH)
Electromyography (in diagnosis of neurogenic/myopatic disease)
- Action potentials of single or groups of neighboring motor units using intramuscular electrodes
- Main measurements:
- -spontaneous activity at rest
- -number of MUs under voluntary control
- -duration & amplitude of motor unit APs
Electromyography : Normal muscle
- ⋅ No spontaneous activity at rest
- ⋅ During weak voluntary contraction a series of MU potentials are recorded.
- ⋅ in fully active muscles, potentials overlap so much that it's impossible to identify single potentials.
Electromyograph: Diseased (neurogenic)
- ⋅ Denervated muscle is spontaneously active at rest
- ⋅ Muscle MAY still contract
- ⋅ Reduced interference pattern (possible MN loss)
- ⋅ Gian potentials -> remaining motor neurones contact more muscle fibres than normal.
Electromyography: Diseased (myogenic/myopathic)
- ⋅ No activity in muscle at rest
- ⋅ Number of motor units firing under voluntary action unchanged
- ⋅ Motor unit potentials reduced in size : each MU has fewer surviving muscle fibres.
Nerve conduction studies
- - Record surface EMG- Electrically stimulate motor nerve at 2 sites- Measure latencies of muscle APs from each site (t1,t2)
- - Distance(D) between stimulation sites
- - Conduction velocity = D/(t2-t1)
- CV slowed = demyelination/nerve compression.
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