Week 6

• Where do upper motor neurons (UMNs) originate in the brain?

  Primary motor cortex (precentral gyrus) and other brain regions
• Where are lower motor neurons (LMNs) located in the nervous system?

  Anterior horn of the spinal cord or motor nuclei of cranial nerves in the brainstem
• What tracts are included in the pyramidal system of motor pathways?

  • Corticospinal tract
  • Corticobulbar tract
• What part of the motor cortex is the main output area for motor commands?

  Primary motor cortex (M1) in the precentral gyrus
• What constitutes a motor unit?

  A single alpha motor neuron and all the skeletal muscle fibers it innervates
• Where are small motor units typically found?

  In muscles requiring fine control, such as eye muscles
• Where are large motor units typically found?

  In muscles generating powerful, gross movements, such as the quadriceps
• Which fibers are innervated by gamma motor neurons?

  Intrafusal fibers of muscle spindles
• What is the primary function of LMNs in the motor control pathway?

  Execute motor commands from upper motor neurons (UMNs)
• What are reflexes in the motor system?

  • Automatic responses to stimuli
  • Mediated by spinal neurons
• What is the purpose of the myotatic reflex (stretch reflex)?

  Maintains muscle length and posture
• Where do sensory (Ia afferent) neurons synapse with alpha motor neurons in the spinal cord?

  In the spinal cord
• What is the purpose of the inverse myotatic reflex?

  Protects muscles from excessive tension
• What effect do sensory neurons have on alpha motor neuron activity in the inverse myotatic reflex?

  • Activate inhibitory interneurons
  • Reduce alpha motor neuron activity
• How do gamma motor neurons adjust muscle spindle sensitivity in the gamma loop?

  • Adjust the sensitivity of muscle spindles
  • Provide feedback to modulate alpha motor neuron activity to maintain muscle tone
• What are the two main types of motor neurons in the motor system?

  Upper motor neurons (UMNs) and lower motor neurons (LMNs)
• What are the functions of upper motor neurons (UMNs) in the motor system?

  • Plan motor activity
  • Initiate motor activity
  • Modulate motor activity
  • Utilize descending pathways like the corticospinal and corticobulbar tracts
• What is the primary function of lower motor neurons (LMNs)?

  To directly innervate skeletal muscles and execute commands from UMNs
• What brainstem pathways are included in the extrapyramidal system?

  • Rubrospinal tract
  • Reticulospinal tract
  • Vestibulospinal tract
  • Tectospinal tract
• What areas assist with planning and coordinating complex movements in the motor cortex?

  • Supplementary motor area
  • Premotor area
• What function do motor units control in the skeletal muscles?

  • Control the strength of muscle contractions
  • Control the precision of muscle contractions
• Which type of muscle fibers are innervated by alpha motor neurons?

  Extrafusal muscle fibers
• What is the role of gamma motor neurons in muscle spindles?

  • Maintain muscle spindle sensitivity during contraction
  • Contribute to muscle tone
• What is another term for the final common pathway in motor control?

  Lower motor neurons (LMNs)
• What are the components of a reflex arc?

  • Receptor
  • Sensory neuron
  • Integration center
  • Motor neuron
  • Effector
• How is muscle stretch detected in the myotatic reflex?

  Stretch is detected by muscle spindles
• What do alpha motor neurons cause in the myotatic reflex mechanism?

  Cause the muscle to contract to oppose the stretch
• Which sensory organs detect tension in the inverse myotatic reflex?

  Golgi tendon organs
• What is the primary purpose of the gamma loop in motor control?

  To regulate muscle tone
• Where do upper motor neurons of the corticospinal tract originate?

  Primary motor cortex
• What voluntary movements does the corticobulbar tract control?

  Voluntary movements of the face, head, and neck
• What are the associated disorders of corticospinal tract damage?

  • Weakness
  • Paralysis
  • Stroke
• What brain areas provide input to the primary motor cortex (M1)?

  • Premotor and Supplementary Motor Areas: Assist with planning movements
  • Sensory Cortex: Provides sensory feedback
  • Basal Ganglia and Cerebellum: Modulate motor activity
• Where does the rubrospinal tract originate in the midbrain?

  Red nucleus
• Where does the reticulospinal tract originate?

  Reticular formation
• From which brainstem nuclei does the vestibulospinal tract originate?

  Vestibular nuclei
• What functions does the vestibulospinal tract control?

  Balance and head stabilization
• Where does the tectospinal tract originate?

  Superior colliculus
• At which medullary structure do most fibers of the corticospinal tract decussate?

  Medullary pyramids
• What is the primary role of the pyramidal system?

  • Controls voluntary movements
  • Especially fine and precise movements