Spinal reflexes (myotactic reflexes) test the integrity of sensory and motor components of the reflex arc and the influence of descending motor pathways on the reflex. An absent or depressed reflex indicates complete or partial loss of either the sensory or motor nerves responsible for the reflex (lower motor neuron [LMN]) A normal reflex indices that sensory and motor nerves are intact. An exaggerated reflex indicates an abnormality in the descending pathways from the brain and spinal cord that normally inhibit the reflex (upper motor neuron [UMN]). In general, forelimb reflexes are not as reliable for localizing lesions as rear limb reflexes.

The sciatic reflex is performed with the animal in lateral recumbency. The area between the greater trochanter and the tuber ischii is located with the thumb or forefinger. When the thumb is struck briskly with a reflex hammer, the response is a flexion of the stifle and hock.

The sciatic nerve originates form L5-L7 S1-S2 nerve roots. An exaggerated reflex indicates a lesion above these segments. Unilateral loss of the reflex suggests a sciatic nerve lesion, whereas bilateral loss suggests a segmental spinal cord lesion.

Sciatic Reflex Interactive Animation

The patellar reflex is the most reliable pelvic limb reflex. It is performed with the animal in lateral recumbency. The uppermost leg is supported by holding the hock with the stifle slightly flexed. When the patellar ligament is struck briskly with a reflex hammer, the response is a single, quick extension of the stifle.

Absence or depression of the patellar reflex (hypo-patellar reflex) and decreased muscle tone (flaccidity) indicate a lesion of the sensory or motor component of the reflex arc (LMN). Unilateral loss of the reflex suggests a femoral nerve lesion, whereas bilateral loss suggests a segmental spinal cord lesion involving spinal cord seg-ments L4-L6. Exaggerated reflexes (hyperpatellar reflex) and increased muscle tone (spasticity), when associated with other signs of UMN dysfunction, suggest a lesion cranial to the L4 spinal cord segment (UMN). Alternatively, loss of the sciatic nerve can result in an exaggerated patellar reflex.

Patella Reflex Interactive Animation

The cranial tibial reflex is performed with the animal in lateral recumbency. The uppermost leg is supported by placing a hand under the hock with the stifle and hock slightly flexed. When the insertion of the cranial tibial muscle is struck briskly with a reflex hammer, the response is slight flexion of the hock.

The cranial tibial reflex is mediated via the peroneal branch of the sciatic nerve.

Cranial Tibial Reflex Interactive Animation

The gastrocnemius reflex is performed with the animal in lateral recumbency. The uppermost leg is supported by placing a hand under the metatarsal bones with the hock slightly flexed. When the gastrocnemius tendon is struck briskly with a reflex hammer, the response is extension of the hock followed by flexion.

The gastrocnemius reflex is mediated via the tibial branch of the sciatic nerve, and cord segments L5 to L7 and S1.

Pelvic limb withdrawal reflex is performed with the animal in lateral recumbency. The least harmful stimulus possible is applied to the foot; the normal response is flexion of the entire limb. Note the examiner pinches both medial and lateral toes.

The rear limb withdrawal reflex primarily involves spinal cord segments L6 to S1 and the sciatic nerve. Absence or depression of the reflex indicates a lesion of these spinal cord segments or nerves (LMN). Unilateral absence of the reflex is most likely the result of a sciatic nerve lesion, whereas bilateral absence or depression is more likely the result of a spinal cord lesion. An exaggerated withdrawal reflex indicates a lesion cranial to spinal cord segment L6 (UMN).

Rear Withdrawl Reflex Interactive Animation