Spinal cord circuit and motor control Overview of

Spinal cord circuit and motor control Overview of the motor system Topographic relationship between spinal motor neurons and muscles Motor unit and muscle force Reflex circuit Spinal cord circuit and motor control Planning, initiation of voluntary movement

Sensory-motor integration, motor learning Simple movement, reflex Basic movement, posture Dorsal horn

Ventral horn Motor neuron pool In a mature animal, each muscle fiber receives input from a single motor neuron Each motor neuron innervates multiple muscle fibers All motor neurons innervating a muscle is

called a motor neuron pool All motor neurons in a motor neuron pool are clustered together in spinal cord Motor neuron pool muscle Topographical relationship

between motor neurons and muscles Motor neuron pools are organized within the ventral horn with those innervating distal muscle groups located laterally and those innervating the proximal muscles located medially Different segments of the spinal cord innervate muscles in different parts of the body (see

diagram on the right) Motor Unit A motor unit consists of a motor neuron and all the muscle fibers it innervates Three types: Fast fatigable (FF) Powerful, but fatigue with repetitive stimulation muscle fiber thick, large number

Motor neuron large, fast conduction, but higher firing threshold Slow (S) (opposite to FF) Fast, fatigue-resistant (FR)

Muscle force Firing rate of motor neurons Progressive recruitment of motor units S FR FF Stretch reflex Muscle stretch activation of dorsal root

ganglion neuron (1) Alpha motor neuron activation contraction of same or synergistic muscle (2) Interneuron activation inhibition of another motor neuron reduced contraction of antagonist muscle { he dorsal root ganglion neuron (proprioceptor) is activated hen intrafusal muscle fiber (spindle) detects changes in

uscle length nother example of stretch reflex: Knee je