A spinal cord injury typically refers to a fracture or dislocation of the spinal cord vertebrae as a result of a sudden, traumatic blow. This damage, depending upon the state of its severity, may impair the use of the body, especially the torso, which is judged by the strength of a few key muscles and nerves. The torso is defined as the trunk of the body from which the limbs and head extend. It's one of the more likely areas to be paralyzed by a spinal cord injury.
Cause
The damage of a spinal injury begins when displaced bone fragments, disc material or ligaments bruise or tear into the spinal cord tissue. This is likely to cause fractures and compression of the vertebrae, destroying the axons, which are the extensions of nerve cells that carry signals up and down the spinal cord between the brain and the rest of the body. An injury to the spinal cord can damage some or most of the axons. Because the muscles receive chemical signals from the brain, any damage to the spine can affect the strength and movement of the torso.
Segments
The spine is divided and classified according to a few main segments. There are eight cervical spinal nerves --- labeled C1 to C8 --- 12 thoracic spinal nerves --- labeled T1 to T12 --- five lumbar spinal nerves --- labeled S1 to S5 --- and a few sacral spinal nerves. Injury to the cervical spinal nerves usually results in complete paralysis of the torso. Injury to the thoracic spinal nerves will usually cause full or partial paralysis to the lower torso; upper-torso strength varies depending upon injury level, but the upper torso will be stronger if the injury is lower in the spine. Injury to the lumbar spinal nerves can result in full upper torso strength but some impairment to the hip area.
Weakness
Weakness that affects the body below a certain point, such as the torso, is typically indicative of a spinal cord injury. This is due to the vertical arrangement of the vertebrae in the spinal cord. However, weakness can also occur in other patterns, such as those corresponding to one or more peripheral nerves.
Considerations
Weakness or paralysis of a muscle can indicate damage to the muscle itself or a motor nerve and its connection to the synapse, the brain or the spinal cord, states the Merck Online Manuals. Doctors will inspect the torso muscles for such factors as size, tone, strength and dexterity and note the degree of resistance to movement to apprehend the particular problem.
Muscle Strength
Muscle tone in physiology and medicine is defined as the passive contraction of the muscles. A spinal cord injury may be simultaneously responsible for uneven and increased muscle tone, known as spasticity, or even a paucity of muscle tone that has been severely reduced. A muscle can waste away, or atrophy, when the muscles or the nerves are diseased or have not been used for many months, which can itself produce paralysis.
