What is the spinal cord?
This may seem to be a silly question, but until people get a spinal cord injury or know somebody who has, most pay little attention to their spinal cords. Most people don’t know the different parts of the spinal cord, what each part does, and how the spinal cord transmits sensory and motor information. Many think that the spinal cord conducts information like a telephone wire and the spinal cord can be fixed by reconnecting it. Some people mistakenly believe that the spinal cord is the vertebral column. While almost everybody knows that spinal cord injury causes paralysis, many are not aware that the spinal cord also controls the bladder and bowel, sexual function, blood pressure, skin blood flow, sweating, and temperature regulation.
The spinal cord connects the brain to the body. The spinal cord resides in a bony spinal or vertebral column that has 24 segments. Seven vertebra in the neck are called cervical (C1-C7), twelve chest or thoracic (T1-T12) segments by the rib cage, five segments for the lower back or lumbar (L1-L5), and five segments form the tail or sacral (S1-S5) vertebrae. The vertebral bodies are in the front of the spinal column. Spinal discs are located between the vertebral bodies. The front of the spinal cord is referred to as anterior while the back is referred to as posterior. The sides of the spinal cord are called lateral. Note that in animals that walk on four legs, posterior is dorsal and anterior is ventral.
Each segment has four spinal roots (left and right, posterior and anterior) that send and receive information from each side of the body. Posterior roots receive sensation while anterior roots send motor signals to muscles. For example, the C1-C3 segments send and receive information from the back of the head and neck, C4 covers the shoulder and deltoid muscles, C5 the biceps, C6 the wrist extensors, C7 the triceps, C8 the wrist flexors, and T1 the intrinsic muscles of the hand. The spinal roots leave the vertebral column between the bony segments through openings in the vertebral column called foramina. Note that there are only seven cervical vertebrae but eight sets of cervical roots because the C1 roots are between the skull and C1.
The spinal cord is shorter than the vertebral column and occupies the spinal canal from the C1 to L1 vertebral levels. In general, the bony vertebral segments are lower than the spinal cord levels. The spinal cord stops just below the L1 vertebral level and only spinal roots are present from L1 to S5 vertebral spinal column. The end of the cord is called the conus. Spinal roots below the conus are called the cauda equina because they resemble a horse’s tail.