Reflex arc occurs when a muscle is suddenly stretched  signal to spinal cord  muscle contraction. Deep tendon reflexes test afferent nerve, the synaptic connection, the motor nerves and descending motor pathways.

Testing reflexes:
Have patient relax – position them so that there is a slight stretch on muscle  strike tendon briskly with reflex hammer.
If absent or diminished  reinforce by having patient lock fingers and pull hands against each other (Jendrassik’s manoeuvre)

Grading reflexes:
0 Absent/no response
1 Diminished/slight jerk
2 Average
3 Brisk
4 Hyperactive/hyperreflexia

Patellar reflex:
• innervated by L2-L4
• patient seated with knee flexed
• strike just below patellar

Achilles reflex:
• innervated by S1-S2
• patient supine, flex hip and knee  externally rotate leg so it rests across contralateral leg  examiner dorsiflexes to resistance  strike achilles tendon

Plantar response:
• Babinski sign/extensor plantar response
• patient supine, knee slightly flexed – stroke foot firmly with hard blunt object from lateral heel to lateral forefoot and then medially across forefoot
• if hallux dorsiflexes and toes spread  positive for CNS disorder
• positive Babinski’s sign is normal up to 6 months of age

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