Spinal Cord Lec: 4 Assis.Professor Dr. Farah Nabil Abbas MBChB, MSc, PhD

Golgi Tendon Organs Encapsulated sensory receptors. Located in tendons near their junction with the muscle. 10-15 muscle fibers are connected in series with each Golgi tendon organ. Endings of afferent nerve fibers wrapped around collagen bundles in tendon.

Golgi Tendon Organs Contraction of attached extrafusal muscle fibers  pull on the tendon  straightens collagen bundles  distorts receptor endings  activating their afferent neurons Transmission of APs to CNS via type Ib nerve fibers. Inhibit via interneurons, of motor neurons to contracting muscle and its synergists. Stimulate motor neurons of antagonistic muscles.

Inverse Stretch Reflex Golgi tendon organ Sense Organ Ib fiber Afferent Neuron CNS (spinal cord) Synapse Alpha Motor Neuron Efferent Neuron Muscle (extrafusal muscle) Effector

Importance Prevent muscle tearing or tendon avulsion from its attachments to the bone. Equalize contractile forces of separate muscle fibers (fibers which exert excess tension become inhibited by the reflex  spread muscle load over all fibers  prevent damage in isolated areas of a muscle where small numbers of fibers might be overloaded

Polysynaptic Reflexes Withdrawal reflex Crossed-extensor reflex. Abdominal reflex Cremasteric reflex

Withdrawal Reflex Cutaneous sensory stimuli on a limb  contraction of flexor muscles  withdrawing limb “flexor reflex" or "nociceptive reflex" or "pain reflex".  Polysynaptic reflex Contraction of flexor muscles Inhibition of extensor muscles.

Crossed Extensor Reflex Application of strong stimulus to a limb. Response includes: Flexion and withdrawal of that limb Extension of the opposite limb after 0.2-0.5 second.

Abdominal Reflex Superficial reflex Thoracic 7th -12th segments Polysynaptic Subject lie down in the supine position. Gently stroke abdominal skin from lateral to medial aspect in all four quadrant → abdominal muscles contract → umbilicus deviate towards the area stimulated.

Absent Abdominal reflex Physiological (obesity, tolerance, children, multiparous lax abdominal wall). Pathological: Multiple Sclerosis Motor Neuron Disease Neurogenic Bladder Brown-Séquard syndrome Chiari Malformations

Cremaasteric Reflex Area A (orange): area of sensory fibers controlled by the genitofemoral nerve Area B (green): area of sensory fibers controlled by the ilioinguinal nerve Arrow C (red): direction and location where the skin must be stroked to elicit this reflex.

Functions of Stretch Reflex Skeletal Muscle Tone: Maintenance of erect posture against force of gravity, by producing a strong muscle tone in the antigravity muscle. Damping (smoothing) function: Signals discharged to a muscle often have varying intensities  irregular movements. However through muscle spindle and alpha-gamma linkage, signal are adjusted to produce smooth movements.

Functions of Stretch Reflex Servo-Assist Function: servo = force regulator: Stretch reflex assists the brain to produce and regulate force of muscle contraction as follow when the muscle contract: α and γ motor fibers are activated to same degree. Extrafusal & intrafusal muscle fibers equally contracted and shortened to same degree. Central part of intrafusal muscle fibers does not change, and intensity of stretch receptor remains unchanged.

Functions of Stretch Reflex If the muscle tries to left a heavy weight, extrafusal fiber contract isometrically and intrafusal fibers contract at the periphery and lengthen central part. Potentiates stretch reflex leading to strong muscle contraction to help lifting the weight. Antigravity Function: To resist gravity effect which tends to flex muscle of lower limbs and trunk. Stretched muscles respond by reflex contraction to maintain upright position of body and prevent its fall down.

Reflex Action Arrival of stimulus and activation of receptor Stimulus Activation of a sensory neuron Effector REFLEX ARC Dorsal root Ventral Sensation relayed to the brain by collateral motor neuron Information processing in CNS KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron Response by effector Reflex Action

Stretching of muscle tendon stimulates muscle spindles Stretch Contraction Muscle spindle (stretch receptor) REFLEX ARC Spinal cord Activation of motor neuron produces reflex muscle contraction