Chapter 50 Disorders of Motor Function

1. Chapter 50Disorders of Motor Function

2. Motor Cortex • Highest level of motor function • Precise, skillful, intentional movements • Speech, flexor muscles of limbs, etc. • Controlled by the primary, premotor and supplementary motor cortices in the frontal lobe • Receives information from the Thalamus, cerebellum and basal ganglia

3. Motor Cortex Primary motor cortex Responsible for execution of a movement. Adjacent to central sulcus Motor Humunculus Premotor cortex (areas 6 and 8) Generates intricate plan of movement. Throwing a ball or picking up a fork

4. Motor Cortex Supplementary motor cortex • Involved in the performance of complex, skillful movements • (areas 6 and 8)

5. Homunculus

7. Basal Ganglia • A group of deep, interrelated subcortical nuclei that play an essential role in control of movement • Receives indirect input from the cerebellum and from all sensory systems, including vision, and direct input from the motor cortex • Functions in the organization of inherited and highly learned and rather automatic movement programs • Also involved in cognitive and perception functions

8. Structural Components of the Basal Ganglia • Caudate nucleus • Putamen • Globuspallidusin the forebrain • SubstantiaNigra (midbrain) • Subthalamic nucleus

10. Structural Components of the Basal Ganglia • Caudate + Putamen =Striatum • Putamen + GlobusPallidus = Lentiform nucleus

11. Motor System Overview • Cortex sends messages to the caudate and putamen of the basal ganglia • Acts on the Thalamus • Then to the supplementary motor cortex for review and editing • Then to the primary motor cortex, premotor cortex and primary somatosensory cortex • Then to the brain stem and spinal cord • The cerebellum – ensures the desired movements occur smoothly

13. Basal Ganglia • Basal Ganglia monitors sensory information coming into the brain • sends it to the right place to be stored as a memory

14. Four Functional Pathways Involving Basal Ganglia • A dopamine pathway from the substantianigra to the striatum • A γ-aminobutyric acid (GABA) pathway from the striatum to the globuspallidus and substantianigra • Acetylcholine-secreting neurons, which are important in networks within the neostriatum • Multiple general pathways from the brain stem that secrete norepinephrine, serotonin, enkephalin, and several other neurotransmitters in the basal ganglia and the cerebral cortex

16. Thalamus • It relays to the cerebral cortex information received from other regions of the brain and spinal cord. • Sends information down spinal cord to the body • a brain “switching station”

17. Thalamus • The cerebral cortex is interconnected with the Thalamus • Excitatory circuit • If unmodulated would cause hyperactivity = stiffness and rigidity with a continuous tremor (tremor at rest) • Basal Ganglia modulates the Thalamic excitability by an inhibitory loop

18. The cerebellum receives continuous information about the sequence of muscle contractions from the brain • Receives sensory information from the peripheral parts of the body • Proprioception • sequential changes in the status of each body part

19. Brain Stem Midbrain • Associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation Pons • Nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture

20. Brain Stem Medulla • Contains the cardiac, respiratory, vomiting and vasomotor centers dealing with autonomic, involuntary functions • Breathing, heart rate and blood pressure

21. Spinal Cord Structure and Function • White Matter Pathways • Myelinated axons surrounding gray matter = cell bodies and their synaptic interconnections • Central Butterfly of Gray Matter • Collections of motor neurons with related function in the anterior horns • Sensory relay neurons in the posterior horn

22. Dorsal Ventral

23. Ascending (Sensory) Pathways • AnterolateralSpinothalamic Tract • Carries information from pain, temperature and crude touch receptors to the thalamus (relay station of the brain) • First neuron synapses in the dorsal horn • Second neuron crosses the cord to the region ventral to the central canal and travels in the spinothalamic tract to the thalamus

24. Ascending Pathways

25. Ascending (Sensory) PathwaysDorsal Columns • Medial Leminiscal Pathways • Carries information from the skin of the lower and upper limbs (light touch, vibration, ability to discriminate between adjacent stimuli, pressure) • Carries information from shoulder, arm and finger on position and tension in muscles and tendons, movement, etc. • Dorsal root ganglion to the cord, to the dorsal column of white matter, to a nucleus in the medulla to the thalamus to the cortex for conscious perception

26. Descending Pathway

27. Descending (Motor) Pathways • Lateral Corticospinal Tract (Pyramidal Tract) • Carries movement signals from the cerebral cortex to the motor neurons in the spinal cord • Crosses over in the medulla • Travels down the cord in a lateral position • Passes into the gray matter in the cord to synapse with the motor neuron

28. Descending (Motor) Pathway • Extrapyramidal Pathways (Multineuronal Pathways) • Provides for the support of movements of the lateral corticospinal tract • Movements of the trunk, proximal limb muscles, balance, posture, orienting to sight or sound and more.

29. Pyramidal motor system • Originates in the motor cortex • Controls all of our voluntary movements • Consists of upper motor neurons in the Primary Motor Cortex and lower motor neurons in the anterior horn of the spinal cord Extrapyramidal motor system • Originates in the basal ganglia • Includes the substantianigra, caudate, putamen, globuspallidus, thalamus, and subthalamic nucleus. • Provides background for the more crude, supportive movement patterns

31. Amyotrophic Lateral Sclerosis (ALS) • Rapidly progressive weakness, muscle atrophy, spasticity, dysphagia • Early symptoms: muscle weakness in an arm or leg, twitching, slurred speech • Death within 2-3 years due to respiratory compromise • Sensory and cognitive function are unaffected

32. Locations of MotorneuronsAffected by ALS • The anterior horn cells of the spinal cord are affected • Death of LMNs leads to denervation, with subsequent shrinkage of musculature and muscle fiber atrophy. • The UMNsof the cerebral cortex are affected later • Lastly the motor nuclei of the brain stem, particularly the hypoglossal nuclei are affected Lou Gehrig

33. xv Steven Hawking

34. http://vimeo.com/27944955 http://www.youtube.com/watch?v=-qFSMXEYC3c

35. Spinal Cord Trauma • Often leads to paraplegia or quadriplegia depending on the location and extent of the injury • Hyperextension Injury • When the forehead is struck and driven posteriorly • Diving impact in shallow water • May tear the anterior spinal ligament and spinal cord may contact the vertebral body

36. Trauma to the Spinal Cord • Hyperflexion Injury • When the head of shoulders are struck from behind by an object of considerable weight or from a fall

38. Spinal Cord Trauma • Concussion • Mild injury, transient and reversible • Contusion • Severe trauma with hemorrhagic necrosis, edema and softening of the cord – Myelomalacia, • or blood in the cord – Hematomyelia • Laceration or Tansection

39. Cervical Contusion

40. Disorders Arising in the Basal Ganglia • Characteristics of Disorders of the Basal Ganglia • Involuntary movements • Alterations in muscle tone • Disturbances in body posture

41. Characteristics of Disorders of the Basal Ganglia • Involuntary movements • Alterations in muscle tone • Disturbances in body posture

42. Types of Involuntary Movement Disorders • Tremor = Trembling or vibrating • Tics = A habitual spasmodic contraction of the muscles, most often in the face • Chorea = Irregular writhing movements • Athetosis = Wormlike twisting of limb • Ballismus = Violent flinging motion of limbs • Dystonia = Abnormal posture • Dyskinesias = Bizarre wriggling movements • TardiveDyskinesia • Develops due to use of antipsychotic medications

43. Parkinson Disease • Characteristics • 0.3% of the general population has Parkinson Disease = 80,000 people • Usually begins after 50 years of age • Affects men twice as often as women • Course of the disease is 10-20 years • Clinical syndrome • Parkinsonism • James Parkinson, 1817 = ‘shaky palsy’

44. Parkinson Disease • Degeneration of pigmented neurons (containing dopamine) in the substantianigra • Cause unknown: May be environmental/genetic • Early symptoms: tremor, rigidity, slow movement • Later: cognitive problems, dementia, dyskinesia • Gross: atrophy of substantianigra • Microscopic: Lewy bodies (inclusions in neurons)

45. Parkinson Disease • Cogwheel-type motion • Ratchet-like movements • Bradykinesia • Slowness initiating and performing movements • Difficulty walking • Neuropsychiatric disorders

46. xv Parkinson disease (R) : atrophy of substantianigra

47. xv Parkinson disease: Lewy body

48. xv Michael J. Fox and Muhammad Ali

49. http://www.youtube.com/watch?v=xuVY7wS25rc&feature=related

50. Huntington Disease • Degeneration of basal ganglia and cerebral cortex • Early symptoms: lack of coordination, unsteady gait • Later: chorea (involuntary writhing), psychiatric symptoms, dementia • Autosomal dominant mutation on chromosome 4 • Begins in 30s-40s; slow progression over 10-20 years