Motor Neurons and Muscles
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What areas of the central nervous system are involved in control of movement?
• basal ganglia • cerebellum • descending systems (motor cortex and brainstem centers)
What areas of the peripheral nervous system are involved in control of movement?
• local circuit neurons • motor neuron pools • sensory inputs and skeletal musccles
What is the general motor function of the basal ganglia?
• gating proper initiation of movement - suppresses unwanted movements, prepares upper MN circuits for movement initiation
What is the general motor function of the motor cortex?
• planning, initiating and directing voluntary movements
What is the general motor function of the brainstem centers
• basic movements and postural control
What is the general motor function of local circuit neurons?
• lower motor neuron integration
What is the general motor function of the cerebellum?
• sensory motor coordination of ongoing movement - detects and attentuates “error” signals
What is the spinal cord organized into?
• dorsal sensory and ventral motor regions
Where do upper motor neurons from the brainstem innervate and why?
• both sides of midline • lower motor neurons in medial ventral horn • for axial and proximal limb muscles • for posture, balance and coordination
Where do upper motor neurons from the cerebral cortex innervate and why?
• lower motor neurons in lateral ventral horn • distal limb muscles • skilled movements
What is the general motor function of upper motor neurons in the superior colliculus?
• to initiate orienting movements of head and eyes
Where do lower motor neurons receive from and innervate on?
• send axons out of brainstem and spinal cord to innervate the skeletal muscles of head and body
Where do local circuit neurons receive from and innervate on?
• receive input from upper motor neurons and sensory inputs - innervate lower motor neurons
Where do upper motor neurons synapse?
• mainly with local circuit neurons and sometimes lower motor neurons
What are upper motor neurons involved in?
• the initiation of voluntary movements and spatio-temporal sequences of skilled movements
Where does planning initiation and directing sequences of movements occur?
• several motor cortical areas including the primary motor cortex and pre-motor cortex
Which parts of the spinal cord are for motor and for sensory?
• ventral spinal cord: motor - dorsal spinal cord: sensory
What is a motor unit?
• motor neuron and the fibers it innervates
What is a motor pool?
• group of motor neurons that innervate a group of muscle fiber
What experiment displays evidence for motor pools?
• retrograde labeling muscle to cord
What is the relationship of number of fibers/motor neuron?
• less fibers/unit equals more control and fine movements
Polyinnervated to mononeural?
?
What influences contraction strength of a muscle?
• increased firing rate of motor neurons - recruitment of additional motor units
What are the different “stages” of contraction when you increase the firing rate?
• single muscle twitches • temporal summation • unfused tetanus • fused tetanus