You go to the movies after a long day and you begin to nod off as soon as the movie starts. Your head starts to lower a little, but a reflex causes your head to rise. This is called the reflex.

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You go to the movies after a long day and you begin to nod off as soon as the movie starts. Your head starts to lower a little, but a reflex causes your head to rise. This is called the reflex.

A. tendon

B. crossed extension

C. withdrawal

D. stretch (myotatic)

E. flexor (withdrawal)

This is called the D. stretch (myotatic) reflex.

Explanation:

Myotatic reflexes are stretch reflexes that function to maintain the muscle at a constant length. They cause the muscle to contract after it is stretched. This type of reflex does not rely on cerebral input for function. When the muscle lengthens, its spindle is stretched. That increases the nerve activity which, in its turn, increases alpha motor neuron activity. The fibers of the muscle then contract. That is precisely what causes your head to rise when you start to nod off.