Motor areas in the brain

Motor areas in the brain

1. Classes of movement

   • Reflexes
     • Travel up afferent sensory nerve into SC, synapses with interneuron & moves down efferent pathway immediately
     • Involuntary, innate, initiated by stimulus, stereotypical movement
   • Rhythmic motor pattern
     • Combines voluntary & reflexive acts e.g. chewing, walking
       • Initiation & termination voluntary; once initiated, action is repetitive & reflexive
   • Complex & voluntary actions
     • Largely reliant on cortical areas to send efferent signals
       • Complex, purposeful, learnt & improvable
         • Writing, speaking, piano, etc.
     • Higher centres required (motor cortical region)
       • Contraction/relaxation of muscles to move joints
         • Signalling system accurately times contractions & adjusts throughout movement
           • Sensory inputs help plan & refine movement

2. Higher cortical centres involved in movement

   • Basal ganglia; cerebellum; primary & secondary motor cortices; primary & secondary somatosensory cortices; visual & auditory cortices

3. Primary motor cortex

   • Pre-central gyrus in frontal lobe
   • Voluntary control of skeletal muscle on contralateral side of body
   • Selects appropriate motor neurons responsible for EXECUTION (after planning of movement)
   • Somatopically organised (homunculus)

4. Modulators of primary motor cortex

   • Primary somatosensory cortex: sensations for moving & planning
   • Premotor cortex
   • Supplementary motor area
   • Help plan & program movements; sent to primary motor cortex for execution

5. Secondary motor areas

   • Pre-motor cortex
     • Lateral + in frontal lobe
     • Planning movement, rehearsing, instructions to M1
   • Supplementary motor cortex
     • Prepares complex sequences e.g. finger placement to turn a key; feeds correct sequences in order to M1
     • Anterior to primary motor cortex (frontal lobe)
   • Broca's area
     • Left side in frontal lobe
     • Production of speech