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Spinal Cord Sensory Neuron Inter Neuron Motor Neuron NEUROTRAUMA REVIEW constant pressure against the skin. When the sympathetic nervous system is activated, the sympathetic nerves act upon the heart to increase the heart rate, upon the lungs to dilate the bronchi, upon the blood vessels to promote vasoconstriction and upon the skin to stimulate sweat. This is part of the "fght or fight" response that makes the body ready to combat whatever stimulus or stressor has presented itself. In uninjured persons an activated sympa- thetic nervous system is not allowed to just run wild without supervision. In the normal body, whenever the sympathetic nervous system is activated, the brain also activates parasympa- thetic nerves (which decrease the heart rate, constrict the bronchi and promote vasodilation and mucosal drying when stimulated) to keep the sympathetic nervous system in check. If the sympathetic nervous system were permitted to function without controls, it would cause dangerously high heart rates and blood pressures and could even lead to stroke instead of helping the body by increasing the heart rate and blood pressure just a little bit. Spinal Injury: What Happens? In persons who have a severe spinal injury above L2, communication between the brain and the sympathetic nervous system is stopped. The signifcance of this halt in communication depends on how high in the spinal cord the injury lies. Because the sympathetic nerves diverge from the spinal cord at T1–L2, if the spinal cord injury is at the T11, T12 or L1 vertebra (T12 is an easy vertebra to landmark because it is connected to the lowest rib; L1 lies immediately below T12, and T11 lies immedi- ately above), then very few of the sympathetic nervous system nerves are unsupervised by the brain, and so few, if any, problems occur. In fact, amazingly few problems occur until the injury is at T6 or above. Once at or above T6, however, too many of the sympathetic nerves are uninhibited, and autonomic dysrefexia becomes a risk. But if there is spinal cord interruption, then how do the sympathetic nerves get stimulated? In severe spinal injury, sensory nerves still exist; however, with a damaged spinal cord, their pathway to the brain is interrupted. Therefore, they can sense touch, pain, itch, hot, cold, etc., but they cannot transmit sensation to the brain. Some of these sensory nerves are involved in refex arcs. Refex arcs are why we can, for example, hit the patellar tendon with a refex hammer and make the leg move, even when a patient is para- or quadriplegic. The sensory nerve, in the case of a refex arc, goes to the spinal cord and connects to an intermediate neuron called an interneuron. That interneuron connects directly to a motor neuron, which goes back out of the spinal cord and moves the leg… all without interaction from the brain. Refex arcs are not just for motor nerves. There are refex arcs for the sympathetic nerves too. Some sensory nerves connect with inter- neurons in the spinal cord, which connect with sympathetic neurons. This means that if the sensory neurons are stimulated, there is an "automatic" sympathetic response. 1 A True Crisis In patients with injuries at T6 or higher, the action of these refex arcs can cause autonomic dysrefexia. Also known as autonomic hyperre- Are you PREPARED for the next Emergency? Tel: (716) 564-5165 or (800) 414-6474 | Fax: (716) 564-5173 Oxygen Generating Systems Intl. www.ogsi.com | Email: ems@ogsi.com Generate your own OXYGEN On-site 24/7 BEnEFITS OF An OxyGEn SySTEm: Become Completely Self-Suffcient Transportable to Disaster Site Transfll Directly to an Ambulance Fill High Pressure Oxygen Cylinders Generate Oxygen During Power Outages (gen-sets available) Eliminate the cost of oxygen delivery Contact OGSI today to enroll in the FREE grant assistance program. MadE iN thE USa MOGS-100 MObilE OXYGEN trailEr CFP-15+ For More Information Circle 26 on Reader Service Card Tetraplegia is a more common term in Europe, and it may eventually catch on in the U.S. Like quadriplegia, it means paralysis or partial paralysis of four limbs. For you philologists, tetra is the Greek word for four, and plegia means paralysis, also from Greek. Quadri means four as well, but it is from Latin, so quadriplegia combines two languages—a very American thing to do, but perhaps not quite as proper. Tetraplegia A sensory-motor reflex arc. EMSWORLD.com | APRIL 2014 53 EMS_52-55_NeuroP40414.indd 53 3/17/14 7:37 AM