Question

Figure 1: Testing the stretch reflex of the biceps brachii

MATERIALS 1. a blinded volunteer…use a blindfold…you don’t have to find someone who is blind! 2. two textbooks PROCEDURE:- 1. Have the volunteer balance a heavy textbook on his or her hand (eyes closed). 2. Take a second book and drop it from a short height onto the first book. Tell the volunteer when you are going to drop the book (similar to Fig 1). 3. Record what happens to the arm and forearm. 4. Repeat step two a number of times. As alternatives to step two:- a) Snatch the first book away and record what happens. b) Just tap the first book instead of dropping the second.

Why…ie Describe why the volunteer responded in the way they did when you repeated step 2

Answer 1

The volunteer responded in this way because when the step 2 is repeated, the stretch receptors of the biceps brachii are activated and the message is passed to the cervical spinal nerve 5 entering into branchial plexus, completely & cervical spinal nerve 6 entering into the distal arm partially. This message induces the involuntary reflex action of contraction in biceps musle and the fore arm jerking through reflex arc.