Why patellar, Achilles, and pupillary reflex checks together map neurological health during a complete neurological exam

Three taps, three stories: what your nervous system is trying to tell you

When a clinician taps the knee, then the ankle, and shines a light to watch the eyes react, it might feel like a simple sequence. But those quick taps and faint observations are really tiny conversations with the nervous system. They tell a clinician where signals are flowing smoothly and where they might be getting tangled. If you’ve ever wondered how a single exam can cover so much ground, here’s the heartbeat of it: multiple reflex checks, each peeking at a different part of the nervous system, all together painting a full picture.

Why check more than one reflex?

Think of the nervous system as a busy city with many bridges and tunnels. A single test can hint at a specific neighborhood, but to understand the whole map, you need several checks. The knee-jerk, the ankle-jerk, and the pupil response each spotlight a different piece of the puzzle:

• The knee-jerk taps into the L2-L4 spinal segments and the lower motor neurons in the legs.

• The ankle-jerk focuses on the S1-S2 region and nearby nerves that run down into the feet.

• The pupil response reaches up to the brainstem and taps into autonomic pathways that govern the brain’s little light-dimming reflex.

Put together, they help a clinician decide whether a problem lies in the lower spinal cord, in the nerves of the leg, or somewhere higher up in the brainstem. It’s a practical way to triage symptoms—pain, numbness, weakness, or vision changes—without jumping to conclusions.

Knee-jerk reflex: the patellar tap

Let’s start with the knee-jerk, the patellar reflex. The patient typically sits with legs dangling, relaxed. The clinician taps just below the kneecap with a small hammer—often a Taylor-type reflex hammer or a similar tool—while watching the lower leg for a quick kick. A normal response is brisk but controlled.

What if it’s absent? A missing patellar reflex can signal issues with the L2-L4 segment of the spinal cord, or a peripheral nerve problem in the thigh or leg. On the flip side, an exaggerated response—hyperreflexia—might hint at an upper motor neuron issue, such as a lesion higher in the spinal cord or brain. It’s not a diagnosis by itself, but it’s a strong hint that guides further questions and tests.

And if the knee doesn’t respond at all but the patient makes up for it with other signs—tremors, muscle weakness, or gait changes—that pattern matters. One reflex is rarely the whole story, but it’s a critical clue in the bigger narrative.

Ankle-jerk reflex: the Achilles tap

Moving down, we get to the Achilles reflex—the ankle jerk. With the patient’s foot relaxed, the clinician taps the Achilles tendon just above the heel. The expected result is a subtle up-and-down movement of the foot. It’s a similar idea to the knee-jerk, but it focuses on the lower spinal levels, specifically S1-S2, and the nerves that run toward the foot.

Like the knee-jerk, abnormal results here can point to different problems. A diminished or absent Achilles reflex might indicate issues along the lower spinal cord or peripheral nerves in the leg. An exaggerated response could also arise from certain central nervous system disorders or even from factors like distracted patient posture or anxiety. That’s why clinicians often pair this test with others and consider how the patient feels, moves, and stands.

The pupil reflex: a window into the brainstem

Pupillary light reflex is a little different in tone from the leg taps. A light is briefly shone in one eye, and the clinician watches both pupils for constriction. A normal pupil responds briskly to light, with both eyes narrowing in unison. That quick, coordinated response relies on the midbrain and brainstem pathways and involves autonomic nerves that regulate pupil size.

Changes in this reflex can hint at problems higher up in the brain or with pressure on the brainstem. For example, slowed or unequal pupil responses might signal an injury, swelling, or other intracranial processes that deserve prompt attention. It’s not just about vision; it’s a window into how the brain is balancing the body’s automatic functions.

Reading the reflex map: patterns matter

So, what does it mean when you see all three checks together? Here’s the practical takeaway:

• All three reflexes normal: The nervous system appears to be functioning well across multiple levels. This is reassuring, but it’s still part of a larger clinical picture—neuro status isn’t judged by one test alone.

• One reflex off, others normal: This pattern narrows the field. For instance, a single abnormal knee-jerk with a normal ankle reflex and normal pupillary response might point to a peripheral nerve issue or a localized spinal segment problem. It invites targeted follow-up, not panic.

• More than one reflex abnormal: When several reflexes are out of sync, clinicians start thinking broader—could there be a central issue in the brainstem or higher? It signals the need for more detailed imaging, imaging-adjacent tests, or additional neuro checks.

These checks aren’t about diagnosing a single condition on the spot. They’re about constructing a believable story from the body’s signals, then testing that story with more clues. And that’s where the real art of the neurological exam shows up: linking what you see with what you suspect, then moving toward clarity with thoughtful questions and tests.

Beyond the basics: other clues in the neuro exam

The knee, ankle, and pupil checks are important, but modern neuro exams are a little like a well-rounded toolkit. Clinicians often supplement these with other quick observations:

• Cranial nerves: A quick look at facial movement, taste, hearing, and swallowing can reveal more about cranial nerve integrity.

• Motor strength and coordination: Pushing against resistance, evaluating gait, and checking finger-to-nose coordination add depth to the picture.

• Sensory testing: Light touch, vibration sense, and proprioception help map how well the sensory pathways are carrying information.

• Reflexes in other areas: The jaw jerk, biceps, triceps, and plantar reflexes (Babinski) can offer extra detail in certain scenarios.

All of these pieces together help them decide where to look next. It’s less about nailing a single label and more about narrowing the possibilities so the right questions can be asked and the right care shared.

Tools of the trade and the human side of the exam

Two practical notes you might find interesting: the tools and the atmosphere. The reflex hammer isn’t glamorous, but it’s a sturdy, trusted tool. The clinician’s touch matters, too. The patient’s comfort and relaxation can influence reflex results—tension can blunt a response, while calm, focused attention helps. This is where the human element shines through: listening, reassuring, and guiding, not just testing.

And yes, there are a few small reminders that keep the exam accurate. Consistency in technique, a quiet room, and clear communication with the patient all matter. A patient who understands what’s happening tends to respond more naturally, which makes the findings more trustworthy. It’s a collaboration—a tiny, precise dance between clinician and patient.

Relatable takeaways you can carry forward

If you’re studying neurology or just curious about how clinicians think, here’s the core you can hold onto:

• The body speaks in many dialects. The knee-jerk, ankle-jerk, and pupil response are three distinct dialects of the nervous system. Listening to all of them gives you a richer understanding.

• Patterns matter more than solo signals. A single off reflex can have many explanations; multiple abnormal findings point you toward more serious possibilities.

• Testing is a skill, not a guess. Technique, patient cooperation, and thoughtful interpretation turn simple taps into meaningful information.

• It’s about the story, not a single moment. Each test adds a chapter to the patient’s neurological narrative, guiding care decisions and next steps.

A few quick digressions that fit here-and-now

If you’ve ever watched a clinician in action, you might notice how the exam blends science with storytelling. The patient’s daily life—how they move around the house, work, or with family—often reveals clues you might miss in a sterile checklist. And, of course, technology is quietly part of the scene too: imaging, nerve conduction studies, and autonomic tests can extend the picture long after the initial reflexes have given you their first hints.

Cultural and human nuance matter, too. In some cultures, people may pause before answering questions or describing symptoms. A good clinician recognizes that pause as part of the dialogue, not a barrier. Patience, clear explanations, and a little empathy go a long way in getting accurate information and helping patients feel seen.

A final thought: why all three reflexes still belong in the toolkit

The idea that all the listed reflexes are checked—patellar, Achilles, and pupillary—reflects a practical, thorough approach. It isn’t about catching a rare anomaly; it’s about ensuring nothing slips through the cracks. Each reflex tests a different link in the nervous chain. Together, they form a quick, reliable snapshot of the nervous system’s health, from spinal segments you can feel to brainstem pathways you can’t.

If you’re exploring the topics that commonly show up in NCLEX-style questions, this triad is a perfect example of how clinical reasoning works: start with the basics, observe patterns, and expand your thinking with context. The reflexes aren’t just about reflexes; they’re about understanding how the nervous system runs, moment by moment, in real life.

In the end, three taps can tell you a lot. When you see them working together—knee, ankle, and pupil—you’re witnessing a concise tour of the nervous system’s highways and byways. It’s a reminder that in medicine, as in life, paying attention to small details often helps you see the bigger picture clearly, with honesty, care, and a touch of curiosity.