Reflexes
Reflexes
Reflex action – a sensory stimulus provoking an involuntary motor response – is a useful way of assessing the integrity of neurological function, since disease in the afferent (sensory) limb, synapse, or efferent (motor) limb of the reflex arc may lead to dysfunction, as may changes in inputs from higher centres.
Different types of reflex may be distinguished. Muscle tendon reflexes (myotactic reflexes) may be either tonic (in response to a static applied force: "stretch reflex") or phasic (in response to a brief applied force, for example a blow from a tendon hammer to the muscle tendon). The latter are of particular use in clinical work because of their localizing value (see Table). However, there are none between T2 and T12, and thus for localization one is dependent on sensory findings, or occasionally cutaneous (skin or superficial) reflexes, such as the abdominal reflexes.
| Reflex | Root Value |
|---|---|
| Jaw jerk Supinator (Brachioradialis, Radial) Biceps Triceps Finger flexion (Digital) Abdominal Cremasteric Knee (Patellar) Hamstring Ankle (Achilles) Bulbocavernosus Anal |
Trigeminal (V) nerve C5, C6 C5, C6 C7 C8, T1 T7 to T12 L1, L2 L3, L4 L5, S1 (L5) S1 (S2) S2, S3, S4 S4, S5 |
Tendon reflex responses are usually graded on a five point scale:
− absent (areflexia; as in lower motor neurone syndromes, such as peripheral nerve or anterior horn cell disorders; or acute upper motor neurone syndromes, e.g., "spinal shock")
+/− present only with reinforcement (Jendrassik’s maneuver);
hyporeflexia
+ normal
++ brisk norma
+++ pathologically brisk (hyperreflexia, as in upper motor neurone syndromes)
Reflex "spread", or "recruitment", for example a finger jerk when eliciting the supinator or biceps jerk, is suggestive of corticospinal pathway (upper motor neurone) pathology, producing an enlarged receptive field for the reflex response; concurrent disruption of the local reflex arc may result in inverted reflexes (q.v.).
Reflex responses may vary according to the degree of patient relaxation or anxiety (pre-contraction). Moreover, there is interobserver variation in the assessment of tendon reflexes (as with all clinical signs): a biasing effect of prior knowledge upon reflex assessment has been recorded.
There is also a class or "primitive", "developmental", or "psychomotor" signs, present in neonates but disappearing with maturity but which may re-emerge with ageing or cerebral (especially frontal lobe) disease, hence sometimes known as "Frontal Release Signs." References
Dick JPR. The deep tendon and the abdominal reflexes. Journal ofNeurology, Neurosurgery and Psychiatry 2003; 74: 150-153
Donaghy M, Compston A, Rossor M, Warlow C. Clinical diagnosis. In: Donaghy M (ed.). Brain’s diseases of the nervous system (11th edition). Oxford: OUP, 2001: 1-59 [at 26-32]
Stam J, van Crevel H. Reliability of the clinical and electromyographic examination of tendon reflexes. Journal of Neurology 1990; 237: 427-431
Cross References
Age-related signs; Areflexia; Crossed adductor reflex; Facilitation; Frontal Release Signs; Hyperreflexia; Hyporeflexia; Inverted reflexes; Jendrassik’s maneuver; Lower motor neurone (LMN) syndrome; Primitive reflexes; Pupillary reflexes; Upper motor neurone (UMN) syndrome; Woltman’s sign. See also specific (named) reflexes
