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Chapter 36 Disorders of Neuromuscular Function

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Chapter 36 Disorders of Neuromuscular Function

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  1. Essentials of Pathophysiology Chapter 36Disorders of Neuromuscular Function

  2. Paralysis refers to weakness or incomplete loss of muscle function.   • Carpal tunnel syndrome is an example of a polyneuropathy. • All levels of spinal cord injury will require assistance to maintain breathing. • Autonomic dysreflexia represents an acute episode of exaggerated sympathetic reflex responses that occur in persons with some types of spinal cord injuries. • The pathophysiology of multiple sclerosis involves the demyelination and subsequent degeneration of nerve fibers in the central nervous system. Pre lecture quiz (True / false) F F F T T

  3. Myasthenia gravis, an autoimmune disorder, is caused by an antibody-mediated destruction of ______________________ receptors in the neuromuscular junction. • Guillain-Barré syndrome is characterized by progressive ascending muscle _____________________ of the limbs, producing a symmetric flaccid paralysis. • Parkinson disease is a degenerative disorder of the basal ___________________ that results in variable combinations of tremor, rigidity, and bradykinesia. • A __________________ is a an irregularly occurring, brief, repetitive movement such as winking, grimacing, or shoulder shrugging. • Muscular dystrophy is a term applied to a number of genetic disorders that produce progressive degeneration and necrosis of skeletal muscle __________________, which are eventually replaced with fat and connective tissue. Pre lecture quiz • Acetylcholine • Fibers • Ganglia • Tic • Weakness

  4. Upper motor neuron cell bodies are in the motor cortex They send their axons down through the internal capsule The axons then run down the white matter of the spinal cord Upper Motor Neurons Are in the Brain and Spinal Cord

  5. Extrapyramidal • Most go to same side of body • Pyramidal • Most cross to other side of body Two Motor Systems Motor cortex neurons Internal capsule Pons Extrapyramidal Pyramidal system system

  6. Lower motor neuron Lower motor neuron’s axon running through peripheral nerves The muscles it innervates Motor Unit Upper motor neurons Send axons down spinal cord tracts Lower motor neurons in spinal cord Peripheral nerves Muscles

  7. Which motor neurons are damaged in patients who have neuromuscular disorders that directly affect skeletal muscle? • Upper • Lower • Both upper and lower • Neither upper nor lower Question

  8. Lower Rationale:The axons of lower motor neurons pass through peripheral nerves to effector tissue in skeletal muscle. Upper motor neurons’ axons travel down the spinal cord. Answer

  9. Muscle stretches Afferent neuron carries impulse to spinal cord Motoneurons cause muscle to contract MuscleTone

  10. Hypotonia Hypertonia Rigidity Clonus Alterations in Muscle Tone

  11. -plegia = stroke or paralysis Paralysis = loss of movement -paresis = weakness Mono- = one limb Hemi- = both limbs on one side Di- or para- = both upper limbs or both lower limbs Quadri- or tetra- = all four limbs Terms to Describe Motor Dysfunction

  12. What would be the terms for the following? • A defect causing weakness in both arms • A weakness in the right arm and leg • Inability to move one leg Discussion

  13. Upper motor neurons • In the brain and spinal cord • Lower motor neurons • Send axons out of the spinal cord Upper vs. Lower Motor Neurons Upper motor neurons Send axons down spinal cord tracts Lower motor neurons in spinal cord Peripheral nerves Muscles

  14. Weakness and loss of voluntary motion • Spinal reflexes remain intact but cannot be modulated by the brain • Increased muscle tone • Hyperreflexia • Spasticity Upper Motor Neuron Damage

  15. Neurons directly innervating muscles are affected • Irritated neurons • Spontaneous muscle contractions: fasciculations • Death of neurons • Spinal reflexes are lost • Flaccid paralysis • Denervation atrophy of muscles Lower Motor Neuron Damage

  16. One lower motor neuron (motoneuron) The neuromuscular junction The muscle fibers it innervates The Motor Unit

  17. Tell whether the following statement is true or false. To increase the strength of a contraction, more motor neurons must be recruited. Question

  18. True Rationale:A motor unit consists of branches of a neuron and the skeletal muscle fibers that they innervate. For stronger contractions, more motor units are required. Answer

  19. Lower motor neuron lesions or infections; peripheral nerve injury Neuromuscular junction disorders Muscle atrophy or dystrophy Possible Problems With the Motor Unit

  20. Disuse atrophy • Denervation atrophy • Muscular dystrophy • Contractile proteins not properly attached to cytoskeleton of muscle cell • Protein movement does not effectively contract muscle cell Skeletal Muscle Problems

  21. Decreased acetylcholine release • Botulism • Decreased acetylcholine effects on muscle cell • Curare • Myasthenia gravis • Decreased acetylcholinesterase activity; acetylcholine has a stronger effect on the muscle cell • Organophosphates Neuromuscular Junction Problems

  22. Tell whether the following statement is true or false. Acetylcholinesterase stimulates the release of acetylcholine (ACh). Question

  23. False Rationale:Acetylcholinesterase breaks down ACh, resulting in relaxation of the skeletal muscle. Answer

  24. Autoimmune disease • Gradual destruction of acetylcholine receptors • Associated with thymus tumor or hyperplasia • Gradual development of weakness • From proximal to distal portions of body • Myasthenia crisis: respiration compromised Myasthenia Gravis

  25. Damage to LMN cell bodies in the spinal cord Damage to axons in the spinal or peripheral nerves Damage to myelin sheath (demyelination) Peripheral Nerve Injuries

  26. Mononeuropathies • Damage to one peripheral nerve • E.g., carpal tunnel syndrome • Polyneuropathies • Damage to many peripheral nerves • E.g., Guillain-Barré syndrome Peripheral Nerve Injuries (cont.)

  27. Peripheral nerve injury at the spinal nerve roots Often due to compression of nerve root by vertebrae or vertebral disk BackPain

  28. Upper motor neuron cell bodies are in the motor cortex They send their axons down through the internal capsule The basalganglia inhibit and modulate movement patterns Motor Impulses Are Modulated by the Basal Ganglia

  29. Tremors • Tics • Hyperkinesia • Choreiform: jerky movements • Athetoid: continuous twisting movements • Ballismus: violent flinging movements • Dystonia: rigidity Basal Ganglia Dysfunction Can Increase Patterned Movement

  30. Which disease is a result of basal ganglia dysfunction? • Myasthenia gravis • Multiple sclerosis • Polio • Tourette syndrome Question

  31. Tourette syndrome Rationale:The tics and hyperkinesia that often accompany Tourette syndrome are typical of basal ganglia dysfunction (the function of the basal ganglia is movement control). Answer

  32. Tremor Rigidity Bradykinesia (slow movement) Loss of postural reflexes Autonomic system dysfunction Dementia Parkinsonism

  33. Vestibulocerebellar disorders • Difficulty maintaining posture • Cerebellar ataxia • Movements divided into separate components • Cerebellar tremor Cerebellum Damage

  34. Damages both upper and lower motor neurons • UMN damage  weakness, lack of motor control • Loss of control over spinal reflexes  stiffness, spasticity • LMN damage • Irritation  fasciculations • Decreased neuron firing  weakness, denervation atrophy, hyporeflexia Amyotrophic Lateral Sclerosis

  35. Destruction of myelin coating on axons Demyelinated or sclerotic patches develop through white matter of CNS Decreased conduction velocity Multiple Sclerosis

  36. Which disorder causes damage to both upper and lower motor neurons? • ALS • MS • Myasthenia gravis • Parkinson disease Question

  37. ALS Rationale:Also known as Lou Gehrig disease, ALS destroys both upper and lower motor neurons. Typical S/S include weakness, lack of motor control, denervation atrophy, and hyporeflexia. Answer

  38. Immediate damage causes: • Spinal cord shock • Temporary complete loss of function below injury • Primary neurologic injury • Irreversible damage to neurons Spinal Cord Injury

  39. Neurons and white matter in area of initial damage are affected • Possible causes include: • Damage to blood vessels supplying the area • Decreased vasomotor tone decreasing blood supply • Local release of substances that cause vasospasm • Release of digestive enzymes from damaged cells Secondary Injury to the Spinal Cord

  40. Central cord syndrome: damage to axons near the gray matter • Arms more affected than legs • Anterior cord syndrome: damage to anterior section of cord • Motor functions affected; touch sensation not affected • Brown-Séquardsyndrome: damage to one side of cord • Motor function lost on that side; pain/temperature sensation lost from other side Partial Spinal Cord Injury

  41. To upper motor neurons (T12 and above) • Spinal reflexes still work • No longer modulated by brain • Hypertonia, spastic paralysis • To lower motor neurons (T12 and below) • Cells in spinal reflex arcs damaged • Flaccid paralysis Complete Spinal Cord Injury