1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 36 Disorders of Neuromuscular Function

2. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Upper Motor Neurons Are in the Brain and Spinal Cord 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

3. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Two Motor Systems Extrapyramidal –Most go to same side of body Pyramidal –Most cross to other side of body Motor cortex neurons Internal capsule Pons Extrapyramidal system Pyramidal system

4. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Motor Unit Lower motor neuron Lower motor neuron’s axon running through peripheral nerves The muscles it innervates upper motor neurons send axons down spinal cord tracts lower motor neurons in spinal cord peripheral nerves muscles

5. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which motor neurons are damaged in patients who have neuromuscular disorders that directly affect skeletal muscle? a.Upper b.Lower c.Both upper and lower d.Neither upper nor lower

6. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b.Lower 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.

7. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Muscle Tone Muscle stretches Afferent neuron carries impulse to spinal cord Motoneurons cause muscle to contract

8. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Alterations in Muscle Tone Hypotonia Hypertonia Rigidity Clonus

9. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Terms to Describe Motor Dysfunction -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

10. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion 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

11. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Upper vs. Lower Motor Neurons Upper motor neurons –In the brain and spinal cord Lower motor neurons –Send axons out of the spinal cord upper motor neurons send axons down spinal cord tracts lower motor neurons in spinal cord peripheral nerves muscles

12. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Upper Motor Neuron Damage Weakness and loss of voluntary motion Spinal reflexes remain intact but cannot be modulated by the brain –Increased muscle tone –Hyperreflexia –Spasticity

13. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Lower Motor Neuron Damage 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

14. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Motor Unit One lower motor neuron (motoneuron) The neuromuscular junction The muscle fibers it innervates

15. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: To increase the strength of a contraction, more motor neurons must be recruited.

16. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True A motor unit consists of branches of a neuron and the skeletal muscles fibers that they innervate. For stronger contractions, more motor units are required.

17. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Possible Problems With the Motor Unit Lower motor neuron lesions or infections; peripheral nerve injury Neuromuscular junction disorders Muscle atrophy or dystrophy

18. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Skeletal Muscle Problems Disuse atrophy Denervation atrophy Muscular dystrophy –Contractile proteins not properly attached to cytoskeleton of muscle cell –Protein movement does not effectively contract muscle cell

19. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuromuscular Junction Problems 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

20. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: Acetylcholinesterase stimulates the release of acetylcholine (ACh).

21. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer False Acetylcholinesterase breaks down ACh, resulting in relaxation of the skeletal muscle.

22. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Myasthenia Gravis 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

23. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Peripheral Nerve Injuries Damage to LMN cell bodies in the spinal cord Damage to axons in the spinal or peripheral nerves Damage to myelin sheath (demyelination)

24. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Mononeuropathies –Damage to one peripheral nerve –For example, carpal tunnel syndrome Polyneuropathies –Damage to many peripheral nerves –For example, Guillain-Barre syndrome Peripheral Nerve Injuries (cont.)

25. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Back Pain Peripheral nerve injury at the spinal nerve roots Often due to compression of nerve root by vertebrae or vertebral disk

26. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Motor Impulses Are Modulated by the Basal Ganglia Upper motor neuron cell bodies are in the motor cortex They send their axons down through the internal capsule The basal ganglia inhibit and modulate movement patterns

27. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Basal Ganglia Dysfunction Can Increase Patterned Movement Tremors Tics Hyperkinesia –Choreiform: jerky movements –Athetoid: continuous twisting movements –Ballismus: violent flinging movements –Dystonia: rigidity

28. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which disease is a result of basal ganglia dysfunction? a.Myasthenia gravis b.Multiple sclerosis c.Polio d.Tourette syndrome

29. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer d.Tourette syndrome The tics and hyperkinesia that often accompany Tourette syndrome are typical of basal ganglia dysfunction (the function of the basal ganglia is movement control).

30. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Parkinsonism Tremor Rigidity Bradykinesia (slow movement) Loss of postural reflexes Autonomic system dysfunction Dementia

31. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Cerebellum Damage Vestibulocerebellar disorders –Difficulty maintaining posture Cerebellar ataxia –Movements divided into separate components Cerebellar tremor

32. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Amyotrophic Lateral Sclerosis 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

33. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Multiple Sclerosis Destruction of myelin coating on axons Demyelinated or sclerotic patches develop through white matter of CNS Decreased conduction velocity

34. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which disorder is caused by damage to both upper and lower motor neurons? a.ALS b.MS c.Myasthenia gravis d.Parkinson

35. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer a.ALS Also known as Lou Gehrig’s disease, ALS is the result of damage to both upper and lower motor neurons. Typical S/S include weakness, lack of motor control, denervation atrophy, and hyporeflexia.

36. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Spinal Cord Injury Immediate damage causes: –Spinal cord shock ºTemporary complete loss of function below injury –Primary neurologic injury ºIrreversible damage to neurons

37. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Secondary Injury to the Spinal Cord 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

38. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Partial Spinal Cord Injury 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-Sequard syndrome: damage to one side of cord –Motor function lost on that side; pain/temperature sensation lost from other side

39. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

40. Complete Spinal Cord Injury 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

41. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins