Muscle and Movement

• Rhythmic behavior


  • Can be maintained by the nervous system via central or peripheral control, neither of which require the brain beyond initialization of movement
• Generation and modulation of movement involves several areas of the brain including

  premotor cortical areas, basal ganglia, cerebellum, primary motor cortex
• Planning and programming of movement


  Separate from the execution of movement
• Categories of muscle cells

  • Striated
  • Smooth
• Sarcomere


  Functional unit of striated (e.g. skeletal) muscle, containing thin and thick filaments which overlap and slide by each other to generate contractions
• Mesencephalic Locomotor Command Region:

  A functional region that can initiate and maintain locomotion upon electrical or pharmacological activation
• Rhythmic behavior (like walking)


  Is generated in the nervous system via central control or peripheral control
• Central control


  Repeated movement is controlled by a central pattern generator
• Peripheral control


  Each movement activates receptors that trigger the next movement in sequence
• Generation of movement


  1. Involves several areas in the vertebrate brain

  2. Electrical stimulation of areas of the primary motor cortex elicit movements of particular parts of the body

  3. There is a point to point correspondence between the stimulated area and movements produced

  4. Body regions are represented in the primary motor cortex by a somatopic map

  5. Primary motor cortex neurons synapse in the brain stem or continue down into the spinal cord (where they activate spinal motor circuits)
• Primary motor cortex


  • Organized by body parts and controls organized movements (rather than individual muscles)
• Premotor cortical areas


  • Mosaic that controls purposeful movements of limbs and face
• Readiness potential


  Rising wave of electrical activity in the brain that occurs prior to an animal being aware of the decision to move
• Cerebellum


  Indirectly involved in the coordination of movement by adjusting motor output of other brain areas
• Basal ganglia


  • Neuron clusters located in the forebrain and midbrain, forming a loop circuit where the output loops back to the site of the circuit's input, most neurons are inhibitory, and the region is important in suppressing unwanted movements
• Planning and programming of movement

  Sensory association cortex funnels activity to premotor cortical areas, including loops through basal ganglia and cerebellum (happens first)
• Execution of movement


  Neural activity passes to primary motor cortex, with correction from the cerebellum loop through spinocerebellum (happens second)
• Muscle


  Tissue that consists of contractile cells
• Myosin


  Molecular motion used by muscle cells to convert chemical ATP to mechanical energy of movement, large protein that interacts with actin
• Actin


  Protein that interacts with myosin to generate force
• Striated muscle


  • Has transverse bands from repeating units of myosin-actin
• Smooth muscle


  • Myosin and actin not organized into sarcomeres
• Connective tissue


  Surrounds individual muscle fibers, bundles of fibers, and the muscle itself
• Tendons


  Attach skeletal muscle to bone, transmitting force generated by muscle contraction to the skeleton
• Myoblasts


  Uninucleated cells that fuse together to form muscle fiber cells
• Myofibrils


  Parallel cylindrical fibers that make up muscle fibers
• Sarcomeres


  Transverse bands in each myofibril, separated by Z discs, the functional unit of striated muscle
• Thin filaments


  Composed of actin
• Thick filaments


  Composed of myosin
• Muscle contraction


  Thin and thick filaments slide over each other and overlap to generate contractions
• Cross-bridges


  Radial projections found in thick filaments, that draw thin filaments toward the center of the sarcomere to cause muscle contraction
• Central Pattern Generator: Neural circuit in the CNS that does not require sensory feedback to trigger next movement