Lecture 13: Motor System

• What does the motor system direct?

  Voluntary control of muscles
• Why is even the simplest movement complex?

  It requires inputs from various nervous system areas
• What is the primary function of the motor system?

  Initiation and regulation of locomotion
• What are the components of the motor system?

  • Cerebral motor cortex
  • Basal nuclei
  • Cerebellum
  • Brainstem
  • Spinal cord
  • Peripheral nerves
• How do the components of the motor system work together?

  They integrate signals into motor patterns
• What are the three key components of body movements in locomotion?

  • Voluntary
  • Reflex
  • Rhythmic
• Which part of the brain directs voluntary movement?

  Primary motor cortex
• What does the primary motor cortex synthesize?

  Numerous signals into patterns of action
• Which areas coordinate with the primary motor cortex?

  Cerebral cortex, basal nuclei, cerebellum
• What do the descending motor tracts control?

  Motor neurons innervating skeletal muscles
• What do motor tracts act on to maintain posture?

  Local reflex circuitries
• What is the role of the central pattern generator in the spinal cord?

  To initiate, modify, or terminate locomotor activity
• What initiates voluntary movements in the brain?

  Cerebral cortex
• What information does the motor cortex rely on to initiate movement?

  Body position, goals, and past experiences
• What does the cerebral cortex feed to the basal nuclei and cerebellum?

  A signal for feedback to the primary motor cortex
• What are the three descending motor tracts from the cerebral motor cortex?

  Corticonuclear, corticopontine, corticospinal
• What does the corticonuclear tract mediate?

  Voluntary actions like eye movements and facial expressions
• Where does the corticopontine tract terminate?

  In the pons
• What is the function of the corticospinal tract?

  Controls precise movements of extremities
• What is unique about the corticospinal tract in dogs?

  75% of fibers cross at pyramidal decussation
• What does the rubrospinal tract control?

  Flexor motor system and fine movements
• What do the pontine and medullary reticulospinal tracts maintain?

  Muscle tone against gravity
• How does the pontine reticulospinal tract affect motor neurons?

  Facilitates extensor muscles, inhibits flexor muscles
• What does the medullary reticulospinal tract do?

  Inhibits extensor muscles, facilitates flexor muscles
• What do the vestibular nuclei in the medulla oblongata control?

  Balance by facilitating extensor muscles
• How are motor neurons classified?

  As upper and lower motor neurons
• What do upper motor neurons regulate?

  Voluntary muscle control and posture
• What do lower motor neurons innervate?

  Skeletal muscles
• What are the components of the basal nuclei?

  Caudate nucleus, putamen, globus pallidus
• How do basal nuclei influence movements?

  By coordinating with the cerebral motor cortex
• What role do basal nuclei play in motor skills?

  Regulate the learning of motor skills
• What is a reflex?

  An involuntary response to a sensory stimulus
• What is the role of reflexes in muscle tone?

  Integral part of maintaining muscle tone
• What are the two types of reflexes?

  Monosynaptic and polysynaptic
• What characterizes a monosynaptic reflex?

  Involves one synapse between sensory and motor neurons
• What does a polysynaptic reflex involve?

  One or more interneurons connecting signals
• What is the purpose of the withdrawal reflex?

  To protect the body from damaging stimuli
• How do voluntary and reflex motor control interact?

  • Produce coordinated patterns of rhythmic activity
  • Descending motor signals are not required for all muscle activity
• How is walking defined?

  Using four legs alternately for support
• What does the gait cycle describe?

  The activity of locomotion from heel placement