Tendon Reflexes: General Clinical Patterns
- Stimulus
- Elicited by a short, sharp blow to tendon with a tendon hammer
- Potentiation: When muscle is mildly stretched
- Inhibition: Active muscle contraction; Flaccid muscle
- Typical tendon reflexes tested & major afferent root level
- Jaw: Trigeminal
- Biceps: C5
- Pronator: C6
- Triceps: C7
- Finger flexor (Hoffman): C6/C7
- Quadriceps: L4
- Ankle (Gastrocnemius): S1
- Reflexes are lost before weakness with
- Reflexes are lost with weakness
- Reflexes are generally lost in proportion to weakness
- Reflexes may be lost proximally but normal distally in
muscular dystrophies
- Potentiation of Tendon reflexes
- Clinical features
- Tendon reflex may be evoked by low amplitude stimulus
- Motor response with potentiation
- Occurs at somewhat shorter latency
- May have increased amplitude
- Spread: Motor activity occurs in groups of nerighboring neurons
- Jendrassik maneuver (Reinforcement)
- Produces excitatory effect on α-motor neurones
- Upper motor neuron lesion
- Due to reorganization of segmental spinal connections: Especially interneurons
- May be associated with spasticity
- Biceps reflex increased with lesions at or above C3/C4
- Other causes: Anxiety; Hyperthyroidism; Tetany
Other
- Aging: Tendon reflexes at ankles absent in 6% of normals over age 65
- Absent ankle reflexes with upgoing toes (Babinski)
- Suggests combination of spinal & peripheral nerve lesion
Comparison to muscle contraction after direct muscle percussion
- Percussion response > Tendon reflex: Often muscle irritability due to denervation
- Sustained contraction after muscle percussion: See
External link: Medinfo
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Reflex hammer
Pine handled |
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Tendon Tap: Physiology
- Nosology: Phasic stretch reflex; Short latency reflex to stretch
- Initial phase: Phasic stretch stimulates axon terminals in muscle spindles
- Afferent conduction of impulses
- Axon type
- Fastest conducting (Ia) afferents: Terminals respond to phasic changes in muscle length
- NOTE: Group II afferents in spindles respond to static muscle length
- Impulses: Synchronized central conduction
- Motor neuron excitation
- Monosynaptic
- Location: Proximal dendrites & cell body
- Other central pathways involved in tendon reflex
- Stimulation of spinal interneurons by afferents: At same & neighboring segmental levels as motor neuron
- Excitation & Inhibition of segmental neurons: Via reticulospinal, vestibulospinal & corticospinal pathways
H-reflex
- Definition: Electrical equivalent of the tendon jerk
- Elicited by electrical stimulation of afferent 1a axons
- Stimulus is low amplitude
- 1a axons have lower electrical threshold than motor axons
- High amplitude stimulus stimulates motor neurons & inhibits H reflex
- No role of muscle spindle or fusimotor drive in stimulation of H reflex
- Modulated by central excitation & inhibition
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