Neurophysiological Basis of Movement

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Neurophysiological Basis of Movement
World VI Motor Disorders
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Lecture 30 Peripheral Muscular and Neurological
Disorders
Sites of Damage in Nerve and Muscle
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Muscular Dystrophies

• Genetic diseases progressive weakness and
  degeneration of skeletal muscles
• Duchenne and Becker dystrophy1 in 3,500 to 5,000
  births
• Mostly males are affected

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Muscular Dystrophies Duchenne Dystrophy

• Mutation of a gene responsible for dystrophin, a
  protein involved in maintaining integrity of
  muscle fibers
• Clinical symptoms at 2 to 6 years all muscles
  are affected
• Late to walk waddling, unsteady gait
• Respirator dependence by the age of 20

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Muscular Dystrophies Becker Dystrophy

• Similar to Duchenne dystrophy mutation of a gene
  responsible for dystrophin
• Clinical symptoms appear at adolescence
• Slower disease progression longer life expectancy

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Muscular Dystrophies Myotonic Dystrophy

• Most common adult form of muscular dystrophy
• Myotonia prolonged episode of muscle activity
  after its voluntary contraction
• Commonly in finger and facial muscles
• High-stepping, floppy-footed gait
• Long face drooping eyelids

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Myotonic Discharge
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Stiff Person Syndrome

• Excessive motoneuron excitation
• Starts at 30 to 60 years of age
• Leads to boardlike rigidity of trunk muscles

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Stiff Person Syndrome
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Continuous Muscle Fiber Activity Syndromes
Tetanus (induced by tetanus toxin)

• The toxin blocks postsynaptic inhibition at the
  spinal level.
• EMG bursts can be stopped by neuromuscular or
  peripheral nerve block.
• Discharges are attenuated during sleep and under
  general or spinal anesthesia.

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Continuous Muscle Fiber Activity Syndromes
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Neuromyotonia
Small potentials on the background on voluntary
activation
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Myasthenia Gravis
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Myasthenia Gravis Epidemiology

• 3 to 4 new cases per million annually
• Prevalence 60 cases per million
• Can start at any age
• Women are affected 21 over men
• Death rate in the 1930s was 40 death rate in
  the 1970s1980s was 7

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Myasthenia Gravis Physiology

• Autoimmune process (the body produced antibodies
  to ACh receptors)
• Reduction of ACh receptors
• Reduction of postsynaptic potentials

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Myasthenia Gravis Increased Duration of Action
Potentials in the Muscle
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Myasthenia Gravis Treatment

• ACh-esterase inhibitors (neostigmine, distigmine)
• Thymectomy to suppress autoimmune processes
• Plasmapheresis to remove autoimmune antibodies
• Side effects with any treatment

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Peripheral Neuropathies Mononeuropathies

• Slowed conduction in a single nerve
• Reduced amplitude of motor and/or sensory
  potentials
• Signs of denervation
• Carpal tunnel syndrome entrapment of the median
  nerve at the wrist
• Ulnar nerve can be entrapped near the elbow
• Brachial plexus lesions mostly seen in muscles
  innervated by median and ulnar nerves
• Peroneal peroneal pressure palsy
• Tibial tarsal tunnel syndrome
• Sciatic

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Carpal Tunnel Syndrome
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Peripheral Neuropathies Multiple Mononeuropathies

• Diabetes mellitus
• Polyarteritis nodosa (connective tissue disorder,
  vasculitis)
• Leprosy

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Diabetes (Diabetes Mellitus) Impaired Ability to
Metabolize Glucose

• Total number of cases in the U.S. 16 million
• Yearly increase 650,000 new cases
• Long-term complications

• Peripheral sensory neuropathy
• Peripheral motor neuropathy
• Loss of autonomic nerve function
• Atrophy of peripheral tissues

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Diabetes
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Diabetes
Reorganization of postural control switch to
alternative sources of information
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Consequence of Diabetes Atrophy of Peripheral
Tissues

• Is it a consequence of inadequate blood supply?
• Is it a consequence of abnormal pressure
  distribution with foci of high pressure?
• Studies by the group of Peter Cavanagh

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Diabetes
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Peripheral Neuropathies Polyneuropathies

• May be associated with demyelinating neuropathies
• Guillain-Barré syndrome reduced recruitment
  conduction block may result in permanent axonal
  loss
• Chronic inflammatory demyelinating
  polyneuropathy common recovery, but nerve
  conduction velocity may remain slow

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Peripheral Neuropathies Polyneuropathies

• Axonal neuropathies (mostly of toxic origin)
• Neuronal degenerations

• Amyotrophic lateral sclerosis (Lou Gehrigs
  disease)
• Poliomyelitis (enterovirus destroying anterior
  horn cells EMGs show chronic denervation may
  lead to weakness and paina postpolyo syndrome)

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ALS

• 20,000 Americans have ALS (one in 15,000).
• 5,000 people in the United States are diagnosed
  with ALS each year.
• Men are affected more often than women.
• ALS most commonly strikes people between 40 and
  60 years of age.
• About 5 to 10 percent of all ALS cases are
  inherited.
• About 20 percent of all familial cases result
  from a specific genetic defect mutation of
  superoxide dismutase 1 (SOD1).

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ALS

• The earliest symptoms may include twitching,
  cramping, or stiffness of muscles muscle
  weakness affecting an arm or a leg slurred and
  nasal speech or difficulty chewing or
  swallowing.
• Patients have increasing problems with moving,
  swallowing (dysphagia), and speaking or forming
  words (dysarthria).
• Patients have tight and stiff muscles
  (spasticity) and exaggerated reflexes
  (hyperreflexia).