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.

To perform the biceps reflex, the index finger of the examiner’s hand that is holding the animal’s elbow is placed on the biceps tendon cranial and proximal to the elbow. The elbow is slightly extended and the finger is struck with the reflex hammer. Normal response is slight flexion of the elbow.

The biceps bracheii is innervated by the musculocutaneous nerve which arises mainly from spinal cord segment C7. The reflex is difficult to attain in normal animals. Absent or decreased reflexes suggest a lesion involving spinal cord segments C6-T2 (LMN). An exaggerated reflex indicates a lesion cranial to spinal cord segment C6 (UMN).

Bicep Reflex Interactive Animation

The triceps reflex is performed with the animal in lateral recumbency. The limb is supported under the radius. The triceps tendon is struck with a reflex hammer just proximal to the olecranon. Normal response is slight extension of the elbow.

The triceps muscle is innervated by the radial nerve, which originates from spinal cord segments C7-T2. The triceps reflex is difficult to elicit in normal animals; thus absent or depressed reflexes may not indicate an abnormality. An exaggerated reflex, if elicited, indicates a lesion cranial to C7 (UMN).

Tricep Reflex Interactive Animation

The extensor carpi radialis (ECR) reflex is performed with the animal in lateral recumbency. The limb is supported under the radius; the elbow is fully extended and the entire leg drawn caudally. The ECR tendon is struck with a reflex hammer at its insertion. Normal response is slight extension of the carpus.

The extensor carpi radialis muscle is innervated by the radial nerve, which originates from spinal cord segments C7-T2. Absent or depressed reflexes indicates a LMN abnormality. An exaggerated reflex, if elicited, indicates a lesion cranial to C7 (UMN).

Extensor Carpi Radialis Reflex Interactive Animation

Thoracic 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.

The forelimb withdrawal reflex primarily involves spinal cord segments C6-T2. Absent or depressed reflexes indicate a lesion of these spinal cord segments or of the peripheral nerves (LMN) Exaggerated reflexes, when associated with other signs of UMN dysfunction, indicate a lesion cranial to spinal cord segment C6 (UMN).

Withdrawl Reflex Interactive Animation