Which spinal levels correspond to the biceps muscle stretch reflex?

The biceps muscle stretch reflex, commonly tested during neurological examinations, primarily involves the spinal segments C5 and C6. This reflex is elicited by tapping the biceps tendon, which leads to a contraction of the biceps muscle via the activation of the associated nerve root levels.

C5 corresponds to the motor innervation that activates the biceps muscle, while C6 is involved in the afferent sensory pathway that relays information from the biceps tendon back to the spinal cord. This pathway encapsulates the essence of a reflex arc, combining both sensory input and motor output, thereby confirming that the reflex function is local to these two spinal levels.

Other choices reference spinal levels that are not involved in the biceps reflex; for instance, the lumbar and sacral segments are responsible for different muscle groups and reflexes, which do not pertain to the biceps muscle stretch reflex, further reinforcing that C5 and C6 are the relevant levels for this particular reflex assessment.