Anatomy clinical correlates: Vertebral canal

Our spinal cord is protected by a strong vertebral canal; however, it’s still vulnerable to a variety of clinical conditions. Being able to recognize and identify these clinical conditions can help us understand the functional deficits that coincide with those conditions, and ultimately allow us to treat them.

The spinal cord transmits information from both motor neuron branches and sensory neuron branches between the brain and the rest of the body.

One way we can test whether there is injury to the spinal cord and disruption of these neuronal pathways is eliciting the autonomic tendon reflexes, you know, when the doctor hits your knee with a tendon hammer you automatically kick him?

This occurs because when you hit the tendon with a tendon hammer, stretch receptors in the muscle tendon send afferent impulses to the spinal cord, through their cell bodies in the dorsal root ganglion, which synapse with alpha motor neurons in the anterior horn.

These alpha motor neurons then transmit an automatic efferent signal back to the muscle leading to a contraction in the muscle.

All you have to do is locate the muscle tendon, get the individual to fully relax the muscle, and strike the tendon with a tendon hammer. Testing tendon reflexes can give important information about a patient’s condition.

Eliciting testing tendon reflexes can tell us if there is damage to a particular nerve route, to an area of the spinal cord or brain, or the general state of a patient’s entire peripheral nervous system which can be affected in things such as diabetes and motor neuron disease.

Testing tendon reflexes can also help us to determine different myotome levels that may be affected during nerve dysfunction.

Now remember, a myotome is a group of muscles innervated by a single spinal level, however it is difficult to test a single myotome as each muscle is innervated by multiple spinal levels.

Therefore, clinically when we test tendon reflexes we are gaining information on multiple myotomes.

The commonly affected tendon reflexes and their associated myotomes tested in clinical practice, as well as a little memory trick, are: The brachioradialis and biceps tendon which test myotome C5 and C6 to ‘pick up sticks’, the triceps tendon which tests C6, C7 and C8 to ‘make your arm straight’, the patellar tendon which tests L2, L3 and L4 to ‘kick the door’, and the achilles tendon which tests S1,S2 to ‘buckle your shoe’.