9.2: Reflex Tests
- Page ID
- 124982
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Knee-Jerk (Patellar) Reflex Test
The knee-jerk (patellar) reflex tests the femoral nerve. View the video showing an example of the patellar reflex test.
- Allow the subject to sit comfortably with their legs hanging. Their feet should NOT touch the ground.
- Strike the ligament portion of the patellar tendon just below the patella (kneecap) and observe the resulting contraction of the quadriceps muscles and extension of the lower leg.
Ankle-Jerk Reflex
The ankle-jerk reflex tests nerves within the sacral plexus. View the video showing an example of the ankle-jerk reflex.
- Have the subject sit comfortably on the table with his or her legs free over the edge.
- With the shoe off, hold and push the subject’s foot upward slightly then strike the Achilles (calcaneal) tendon (Figure \(\PageIndex{2}\)) at the level of the ankle and observe the resulting plantar flexion of the foot. Plantar flexion is seen as a downward movement of the foot, as occurs when a person points their toes.
Figure \(\PageIndex{2}\) Achilles (calcaneal) tendon: The red square indicates the region of the achilles tendon that should be struck with the mallet to conduct the ankle-jerk reflex test. (Image credit: Grey's Anatomy by Henry Gray is public domain CC0 1.0) / Red square added by Harmony Folse
Biceps-Jerk Reflex
The biceps-jerk reflex will test nerves of the brachial plexus. View the video showing an example of the biceps-jerk reflex.
- Have the subject sit comfortably on the table with the arm relaxed and fully extended.
- Gently press the biceps tendon in the antecubital fossa with the thumb and strike the thumb with the mallet.
- If this procedure is performed correctly, the biceps muscle will shorten and should produce a slight flexion of the forearm.
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Triceps-Jerk Reflex
The triceps-jerk reflex will test nerves of the brachial plexus. View the video showing an example of the triceps-jerk reflex.
- Have the subject sit comfortably on the table with the arm relaxed and abducted (Figure \(\PageIndex{4}\))
- Strike the triceps tendon about 2 inches above the elbow. If there is no response, repeat this procedure, striking to either side of the original point.
- If this procedure is performed correctly, the triceps muscle will shorten and should produce a slight extension of the forearm.
