A pathophysiology diagram illustrating the mechanisms of post-stroke spasticity (PSS) involving the corticospinal tract (CST) and the spinal stretch reflex arc. The diagram is divided into three main levels: the brain, the spinal cord, and the effector muscle. In the brain, an ischemic stroke is depicted, leading to CST axonal injury, represented by solid red lines transitioning into a dashed red line to signify disrupted descending signals. At the spinal cord level, the diagram shows the interaction between the damaged CST and the lower motor neurons. The stretch reflex arc is highlighted, featuring Ia sensory fibers from the muscle spindle synapsing onto an alpha-motor neuron in the anterior horn. A '+' sign next to the alpha-motor neuron and the stretch reflex indicates abnormal hyperexcitability and hyperreflexia due to the loss of descending inhibitory control from the CST. The pathway concludes at the skeletal muscle, where increased muscle tone (+) is indicated, leading to the clinical manifestation of post-stroke spasticity. The illustration serves as an educational tool for neurology and physical medicine, demonstrating the upper motor neuron lesion model.

Anatomical diagrams illustrating the components of the monosynaptic stretch reflex arc in two experimental states. Both panels show a transverse section of the spinal cord (white and gray matter) connected to the gastrocnemius muscle via the sciatic nerve. Panel (a), labeled 'With stretch reflex', depicts an intact neural circuit: a sensory (afferent) pathway, colored green, carries signals from the muscle spindle to the dorsal horn, while a motor (efferent) pathway, colored orange/brown, carries impulses from the ventral horn back to the muscle. Black arrows indicate the direction of signal flow. Panel (b), labeled 'Without stretch reflex', demonstrates a disrupted circuit where the sciatic nerve has been severed, indicated by a red 'X' and the text 'Cut off'. This visualization highlights how the interruption of the peripheral nerve abolishes the reflex arc between the spinal cord and the effector muscle, commonly used in physiological studies to compare muscle response forces with and without neural feedback.

This medical illustration and data plot set depict the pathophysiology of sensorimotor circuit dysfunction, comparing control conditions with chronic oxaliplatin-induced neuropathy (cOIN). The top anatomical diagram illustrates a spinal reflex arc: mechanical muscle stretch triggers sensory input via propriosensory neurons (blue) into the spinal cord, synapsing with interneurons ('in') and alpha-motoneurons (orange, 'α') to produce motor output. Below, comparative waveforms track signal translation through three stages: (A) Population Code, representing peripheral sensory encoding; (B) Synaptic Transmission, representing central processing; and (C) Circuit Translation, the compounded accuracy. Data show that while muscle stretch and physical response remain identical, cOIN specimens exhibit a severe degradation in signal fidelity. Specifically, the sensory population code accuracy drops from 91% to 55%, and central synaptic transmission accuracy falls from 86% to 43%. The total compounded circuit translation accuracy is drastically reduced from 78% in controls to 24% in the cOIN model, illustrating how peripheral and central defects compound to cause sensorimotor disability.

This composite educational graphic illustrates the Repetitive Facilitative Exercise (RFE) technique for hemiplegic fingers, divided into a clinical demonstration and a pathophysiology diagram. Panel (a) shows a three-step manual therapy sequence: (1) quick passive finger flexion to elicit a stretch reflex; (2) simultaneous manual flexion of the metacarpophalangeal (MP) joint with an 'Extend' verbal cue to facilitate voluntary effort; and (3) application of slight resistance during finger extension to maintain the alpha-gamma linkage and muscle contraction. Panel (b) provides a neuroanatomical schematic depicting the hypothesized mechanism. It labels the brain cortex and spinal cord, tracing a dual pathway where the 'intention of the patient' (descending motor tracts) is combined with sensory input from 'stretch reflex by finger flexion' (ascending/local arcs). The integration of these signals at the spinal level is shown to result in 'elicited finger extension.' This visual is intended for rehabilitation specialists and physical therapists focusing on neuroplasticity and motor recovery in stroke or hemiplegic patients.