2.9: Activity 8

Conducting the patellar reflex - a somatic reflex

• Begin by familiarizing yourself with the components of a reflex arc.
• Pick up a reflex hammer from the supply cart.
• Have your lab partner sit on a high stool and rest their legs with their knees bent. The feet should not touch the floor. Ensure their knee is relaxed and slightly bent.
• Locate the patellar tendon (anatomically patellar ligament) about one inch below the bottom of the patella (knee cap).
• This is where you will apply the stimulus.
• Using the blunt reflex hammer, lightly but firmly tap the patellar ligament. Use the subjective grading system provided below to record the results in the Table \(\PageIndex{1}\).
  • 0 (absent): No visible or palpable quadriceps contraction; no lower-leg movement.
  • 1+ (diminished/trace): Minimal quadriceps twitch; slight or no leg movement. Hyporeflexia is generally associated with a lower motor neuron deficit. Example - Guillain–Barré syndrome.
  • 2+ (normal): Clear quadriceps contraction with knee extension; consistent and symmetric with the other side.
  • 3+ (brisk, super-normal): Larger-than-expected response; obvious kick. Hyperreflexia is often attributed to upper motor neuron lesions eg Multiple sclerosis.
  • 4+ (hyperactive with clonus): Repetitive, rhythmic beats after a single stimulation(tap).

Observation of a hyperactive patellar tendon reflex, on the other hand, generally suggests pathology to the CNS above the L2-L4 spinal cord level, where the patellar tendon reflex is mediated.

• Recorded as sustained clonus when last for several seconds or non - sustained clonus when occur immediately after the stimulus but stop quickly. 

Achilles Reflex Test: (spinal reflex that tests the integrity of spinal nerves L5—S2)

The Achilles (ankle jerk) reflex is a classic deep tendon reflex mediated primarily by the S1 nerve root via the tibial nerve. Tapping the Achilles tendon produces rapid plantar flexion by activating the gastrocnemius–soleus complex.

1. Position The Subject:
   • Seated: legs dangling with knees flexed 90°, ankles free.
   • Prone or supine: foot over edge of table with ankle free.
2. The foot should be visible and the leg must be free of restrictive clothing (i.e., a tightly rolled up pant leg). Expose the posterior ankle and heel; remove shoes/socks.
3. Support the forefoot with your non-dominant hand.
   • Gently bring the ankle into slight dorsiflexion (about a right angle) to preload the tendon.
   • Identify the Achilles tendon just proximal to its insertion on the calcaneus.
4. Hold the reflex hammer by the handle. Allow the reflex hammer to swing loosely between your thumb and forefinger through a 45 to 60 degree arc, while making certain the hammer moves in a horizontal plane (i.e., the broad end of the reflex hammer is perpendicular to the tendon).
5. Deliver a brisk, controlled tap just above the calcaneus at the level of the medial and lateral malleoli.
6. Deliver a brisk, controlled tap to the mid-portion of the Achilles tendon.
7. Observe and feel for plantar flexion at the ankle and contraction of the calf.

Use the subjective grading system (which is beginner-friendly) provided below to record the results in the Table \(\PageIndex{2}\).

• 0: absent
• 1+: diminished/trace (often only with reinforcement)
• 2+: normal
• 3+: brisk (no clonus)
• 4+: hyperactive with clonus

Plantar Reflex Test (spinal reflex that tests the corticospinal tracts of the spinal cord)

The Plantar Reflex is often used to test the integrity of the corticospinal tracts of the spinal cord which carry motor impulses to skeletal muscles. A normal response is curling DOWN of the toes (negative Babinski sign). An abnormal response is dorsiflexion of the big toe and flaring of the other four toes (positive Babinski sign). The presence of the Babinski sign is always abnormal in adults, possibly indicating upper motor neuron lesions such as corticospinal tract damage, multiple sclerosis or amyotrophic lateral sclerosis (Lou Gehrig's disease). It is normal in infants under 1 year of age.