The basic reflex arc and spinal cord circuitry

Basic Spinal Anatomy Transversal cut of the spinal cord

Basic Spinal Anatomy Muscle spindles Motoneurons targetting muscles Golgi tendon organs Soma of the motoneurons Sensory information Tactile, pain, thermic receptors on the skin

How is the sensory-motor circuitry organized? Sensory input ? Motor output

Stretch reflex • Reciprocal innervation and synergist connections

Stretch reflex • Reciprocal innervation and synergist connections • Simplify the commands from higher levels necessary to control of voluntary movements • Corticospinal connexions can modulate the reciprocal connectivity

Withdrawal reflex • Reciprocal innervation and synergist connections • Simplify the commands from higher levels necessary to control of voluntary movements • Corticospinal connexions can modulate the reciprocal connectivity • Cross-connections • Coordination necessary for the control of posture

Vertical Connections • Reciprocal innervation and synergist connections • Simplify the commands from higher levels necessary to control of voluntary movements • Corticospinal connexions can modulate the reciprocal connectivity • Cross-connections • Coordination necessary for the control of posture

Convergence of sensory informations • Reciprocal innervation and synergist connections • Simplify the commands from higher levels necessary to control of voluntary movements • Corticospinal connexions can modulate the reciprocal connectivity • Cross-connections • Coordination necessary for the control of posture • Convergence of sensory input

Are reflexes streotyped ? Corticospinal connections can shape the reflexes in order to adapt to different contexts

Conclusion Spinal cord circuitry forms the infrastructure that is exploited by supraspinal areas in order to coordinat different muscle The input output relation is far from a streotyped relation Since it can be shaped in order to adapt to the behavioral states of the organism