Lecture 8 - Diseases of the motor unit Flashcards
What are diseases within the skeletal muscle fibres called?
Myogenic diseases/Myopathies
What are diseases within the neuromusclular junction/synapse called?
Neuromusclular transmission diseases
What are diseases within the Motorneurons called?
Neurogenic diseases/Neuropathies
What are the two types of neuropathy? [2]
- Motor neuron diseases (cell body)
- Peripheral neuropathies (axon & myelin)
What are the functional units of a Motor unit?
- Cell body of motor neuron
- Axon of motor neuron
- Neuromuscular junction (synapse)
- Muscle fibres
Name a neuromuscular disease.
Myasthenia gravis
What are the symptoms of Myasthenia gravis?
Reduced number of nicotinic ACh receptors or reduced interaction of ACh with receptors
What is Guillain-Barré Syndrome?
Rapid onset muscle weakness caused by autoimmune damage to the peripheral nervous system
What is a common feature Neuropathies and Myopathies?
Muscle weakness
What are the three types of muscle wasting? [3]
- General wasting
- Distal wasting
- Proximal wasting
What type of muscle wasting is linked to Neurogenic diseases?
Distal limb weakness
What type of muscle wasting is linked to Myopathic diseases?
Proximal limb weakness
What are fibrillations?
- Small spontaneous twitches of single muscle fibres
- Not visible
What are Fasciculations?
- Small visible muscles twitches
- Single motor units firing
What are features of lower motor neuron lesions?
- Primary MNs, innervate skeletal muscle directly
- Weakness, atrophy, decreased tendon relfexes
What are features of upper motor neuron lesions?
- Originate from higher motor centre, synapse with LMNs
- Weakness, increased tendon relfexes
What are tests that can be performed to distinguish Neurogenic and Myogenic disease? [5]
- Measure muscle enzymes in serum
- Electromyography
- Nerve conduction studies
- Muscle biopsy
- DNA analysis
What enzymes are likely to be found in the serum of damaged muscle?
- Creatinine kinase
- Lactate dehydrogenase
How much serum enzyme is expected in Myopathic diseases?
Large increases
How much serum enzyme is expected in Neuropathic diseases?
Small increases
How does electromyography work?
- Intramusclular electrodes
- Records APs of single motor units and groups of motor units
What are the four main measurements taken during Electromyographies?
- Spontaneous activity at rest
- Number of MUs under voluntary control
- Duration and amplitude of MU APs
- Changes over time/stimulations
What is the EMG like in normal muscle?
- No spontaneous activity at rest
- Weak contractions allow for single motor units to be measured
- Maximal` contractions causes interference
What is the EMG like in neurogenic disease?
- Fasciculations/ fibrillations occur at rest
- Reduced interference patterns (some MNs lost)
- Remaining MNs contact more muscle fibres than normal
