deck_5375058 Flashcards
What NM diseases are caused by damage to theanterior horn cells or motor neurons?
so called motor neuron diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis (this also affect the upper motor neurons).In these conditions, the motor axonsand the muscle fibers innervated by them are also secondarily affected.
What are peripheral neuropathies?
these involve not only motor axons, but also other various types of nerve fibers such as those that carry pain and proprioceptive sensations, and autonomic fibers, so peripheralneuropathies also cause sensory or autonomic problems.
What is a commondisease of the neuromuscular junction?
also called disorders of neuromuscular transmission such as myasthenia gravis.
The most common symptom of neuromuscular disease is ____
weakness
What is Gower’s Sign?
In myopathic disease, weakness primarily affects the proximal muscles. Such patients have difficulty arising from the floor because of hip muscle weakness or raising the arms above their head.In this, because of hip muscle weakness, the patient needs to use his hands to raise from the floor shown in figure 1 and then ”climb over his legs” in figures 2, 3, and 4 (Gower’s sign) to achieve the standing position in figures 5 and 6.
What does this image show?
Patients with myopathies also have proximal muscle atrophy and weakness, as is shown in the next patient with shoulder atrophy at arrow 1 and “winging” of the scapula at arrow 2. Winging of the scapula occurs because the weak muscles cannot fix the scapula to the rib cage.
What is a characteristicfindingpoly-peripheral neuopathies?
Distal Leg Wasting. These patients typically also have decreased sensation and depressed reflexes
Patients with _____________do not have sensory deficits as those disorders affect only the motor axons.
motor neuron diseases
What is amononeuropathy?
Neuropathies thataffect individual nerves
What is characteristic of a myasthenia gravis (MG) patient following sustained upward gaze?
Ptosis. This is characteristic of myasthenia gravis, a disease of neuromuscular transmission in which muscle fatigue is a hallmark.
What would a symmetric pattern of muscle weakness, with fasciculations, decreased muscle stretch relfexes, and no sensory loss suggest?
Motor neuron Disease?
What is one motor neuron disease that doesnt present normally?
ALS- still see fasciculations andno sensory loss BUT weakness patterns are asymmetric and muscle stretch reflexes are increased
What categories of NMD would present more commonly with distal patterns of weakness over proximal?
Polyneuropathies
How do Polyneuropathies present?
distal pattern of weakness, with decreased or absent muscle stretch reflexes, sensory loss and fascicualtions sometimes
What are some common characteristics of diseases of neuromuscular junction and myopathies?
both predominantly involve proximal over distal patterns of weakness, and you do NOT see fasciculations or sensory loss
What diseases of the neuromuscular junction present with normal muscle stretch reflexes?
POST-synaptic disorders such as myasthenia gravis
What diseases of the neuromuscular junction present with decreased muscle stretch reflexes?
Lambert-Eaton myastenic syndrome and botulism
Are muscle stretch reflexes present in myopathies?
Normal Initially, may be decreased in later stages (ankle reflexes often preserved until late)
What aremotor unit action potentials (MUAPs).
When the motor neuron depolarizes, it causes the muscle fibers of that motor unit to also depolarize and their individual action potentials summate (A+B+C+D) forming the potentials
What is electromyography?
A diagnostic toolwhich detects MUAPsclose to a needle electrode inserted in the muscle and connected to an oscilloscope. Analysis of the characteristics of the motor unit action potentials, their size, and numbers is a very important diagnostic tool in neuromuscular disease.
What is this?
Normal muscle histology (trichrome stain)
What is this showing?
Normal muscle biopsy stained with alkaline ATPase.Note that the type I muscle fibers stain pale while the type II fibers are dark. Fibers of either type are innervated by one type of motor neuron (motor unit). Here, fibers of various motor neurons, either type I or II, are intermixed in an almost checkerboard pattern.
T or F.A motor neuron and the fibers that it innervates belong to only one type
T,and the physiological and histological characteristics are determined by the motor neuron and its firing pattern. In humans the checkerboard pattern is seen in most muscles, with some having more of one fiber type depending on the muscle function.
Whathappens when a muscle loses it’s innervation through some injury, for example by trauma to its axon,a peripheral neuropathy or damage to the motor neuron?
the muscle fibers become atrophic and angulated.slide: esterase stain
What is fiber type grouping?
When axons are damaged there is sprouting of axons from the other intact neurons that take over and reinnervate previously denervatedfibers, thus more fibers of single neurons remain, forming groups of both fiber types seen histologically.
How does an EMG change in peripheral nerve injury with fiber type grouping?
The action potentials generated by these will be larger, as more muscle fibers innervated by a single motor neuron will be detected by the needle electrode during muscle contractions using EMG recording.However, the total number of action potentials will be decreased (fewer number of motor neurons).Thus, in peripheral nerve injury with denervation and reinnervation there are fewer, but larger, motor unit action potentials on EMG.
T or F.In myopathies, the muscle fibers are not atrophic and angular.
T.In this case, they are necrotic (appearing pale here) from an autoimmune myopathy. In other myopathies, there could be structural abnormalities.
Where is the defect in myopathies?
the individual muscle fibers are ill or nonfunctional (thus when a muscle contracts the motor unit action potentials are smaller)
T or F.In myopathies, the number of motor units is not decreased, unlike neurogenic disorders
T., because the number of motor neurons or axons are normal. (It is the number of individual fibers of the motor unit that are nonfunctional or dead). Even when the muscle contraction is very weak, there is a normal number of motor unit action potentials (this might appear increased for a weak muscle).
What are some serum markers of myopathies?
The sick,necrotic muscle fibers leak some of the sarcoplasmic components such as enzymes like creatine kinase (CK or CPK). Because of this, the enzymes are elevated in serum.
EMG changes in myopathies?
The motor unit action potential is small.This is also polyphasic because the damaged individual fibers fire asynchronously.
Motor Conduction Velocity
stimulation of the ulnar nerve at the wrist on left and the elbow on the right with recordings at the adductor digiti quinti muscle. In the middle, notice the compound muscle action potential (summation of all motor units generated by a maximal nerve stimulation). One can also observe the latencies and measure the amplitudes.Conduction velocities are calculated by dividing the distance between the two stimulation electrodes by the difference of their latencies = distance/latency 1 – latency, 2 = CV (conduction velocity).In the bottom, notice the very slow prolonged latency and small compound muscle action potential in a demyelinating neuropathy.
Serum muscle enzymes are elevated in what kinds of NMD?
mildly in anterior horn disease and elevated in myopaties
