1. Deep Tendon Reflex The reflex arc Myotatic Reflex

2. Introduction… The spinal cord mediates local spinal reflexes. The spinal reflexes consist of involuntary responses to appropriate stimuli transmitted to the spinal cord. They depends on the integrity of the reflex arc.

3. Reflexes can be : ◦ Monosynaptic reflex : e.g., knee jerk reflex. ◦ Multisynaptic reflex: e.g., withdrawal reflex

4. The Reflex Arc of Monosynaptic reflex Consist of: ◦ A receptor organ: Muscle spindle. ◦ Sensory (afferent) fibers of the spinal nerves: carry sensory impulses from sensory receptors to the spinal cord. ◦ Motor (efferent) fibers of the spinal nerves: that activate muscles. ◦ The effector organ: the muscle.

5. Within the spinal cord; the afferent fibers affect the efferent fibers either directly or indirectly via interneurons. When the reflex arc involves only one synapse, this is referred to as monosynaptic reflex arc.

7. The deep tendon reflexes The best example of these reflexes is the stretch (myotatic) reflex. The stretch reflex consist of involuntary muscular contraction in response to stretching of muscle tendon.

8. Mechanism of the myotatic reflex Tapping of a muscle tendon leads to elongation (stretching) of the fibers of that muscle. This leads to stimulation of muscle spindles within the muscle. The muscle spindles are sensory receptors present within the skeletal muscles.

9. The sensory (afferents) fibers of the spinal nerves carry the sensory impulses from the muscle spindles to the spinal cord. In the spinal cord, the sensory fibers stimulate the motor neurons that send their motor fibers (efferents) to the muscle causing its contraction.

11. Important stretch reflexes and their spinal segments Spinal segmentStretch reflex C5,6Biceps reflex C5,6Brachioradialis reflex C6,7Triceps reflex L3,4Patellar reflex (Knee jerk) S1,2Achilles tendon reflex (Ankle jerk)

12. Importance of a stretch reflex A protective measure to prevent tearing. Important in posture: because a slight lean to either side causes a stretch in the spinal, hip and leg muscles to the other side, which is quickly countered by the stretch reflex

13. Clinical applications of the stretch reflex Physicians use the knee jerk and other muscle jerks to determine the sensitivity of the stretch reflexes and to assess the degree of facilitations of the spinal cord centers.

14. When large numbers of facilitatory impulses are being transmitted from the upper regions of the central nervous system into the cord, the muscle jerks are greatly exacerbated. On the other hand, if the facilitatory impulses are depressed or abrogated, the muscle jerks are considerably weakened or absent.

15. Hyperreflexia Vs. Hyporeflexia Stretch reflexes increase in case of lesions in the pyramidal and extrapyramidal spinal motor tracts. The reflexes decrease or disappear (areflexia) in case of reflex arc lesions.

16. Stretch reflex and Jendrassik maneuver Patient flexes both sets of fingers into a hook-like form and interlocks fingers together.