Basal Nuclei (Basal Ganglia) Function in Motor Control

Basal Nuclei (Basal Ganglia)

• Several masses of grey matter located deep within cerebral white matter
• Important inhibitory role in motor control
• Inhibiting muscle tone throughout the body
• Maintaining proper muscle tone by balancing excitatory and inhibitory inputs
• Selecting and maintaining purposeful motor activity
• Suppressing useless or unwanted patterns of movement
• Helping monitor and coordinate slow, sustained contractions (especially related to posture)

Functions of Basal Nuclei

• Do not directly influence the efferent motor neurons
• Act by modifying ongoing activity in motor pathways
• Receive and send out large volume of information, as indicated by tremendous number of fibers linking them to brain regions
• One important pathway of strategic interconnections is a complex feedback loop, linking motor cortical regions, basal nuclei, and thalamus

Parkinson's Disease (PD)

• Gradual destruction of neurons that release neurotransmitter dopamine in the basal nuclei
• Characteristic motor disturbances:
  • Rigidity: increased muscle tone
  • Resting tremor: involuntary, useless or unwanted movements
  • Slowness in initiating and carrying out different motor behaviors
• Standard treatment:
  • Administration of levodopa (L-dopa): precursor of dopamine, can enter brain from blood

The Thalamus

• Located deep within the brain, near the basal nuclei
• A midline structure that forms the walls of the third ventricular cavity
• Consists of thalamus and hypothalamus
• Serves as "relay station" for preliminary processing of sensory input
• Screens out insignificant signals
• Routes important sensory impulses to appropriate areas of somatosensory cortex and other brain regions
• Helps direct attention to stimuli of interest along with brain stem and cortical association areas

Role of Thalamus in Motor Control

• Positively reinforces voluntary motor behavior initiated by the cortex
• Modulates activity initiated by the cortex

The Hypothalamus

• Collection of specific nuclei and associated fibers, that lie beneath the thalamus
• Important link between the autonomic nervous system and the endocrine system
• Integrating center for many important homeostatic functions
• Regulates the internal environment
• Functions:
  • Controls body temperature (thermostat)
  • Controls thirst and urine output
  • Controls food intake
  • Controls anterior pituitary hormone secretion
  • Produces posterior pituitary hormones
  • Controls uterine contractions and milk ejection
  • Serves as major ANS coordinating center, affecting all smooth muscles, cardiac muscles, and exocrine glands
  • Plays role in emotional and behavioral patterns
  • Participates in the sleep-wake cycle

The Limbic System

• Functional system (not separate structure), consists of ring of forebrain structures surrounding brain stem and interconnected by intricate neuron pathways
• Includes portions of each of the following:
  • Lobes of cerebral cortex (esp: limbic association cortex)
  • The basal nuclei
  • Hippocampus
  • Thalamus
  • Hypothalamus
  • Amygdala
• Associated with:
  • Emotions
  • Behavior
  • Motivation