The human spinal cord consists of nerves that connect the brain to nerves in the body. It is a superhighway for messages between the brain and the rest of the body. The spinal cord is surrounded for most of its length by the bones (vertebrae) that form the spine.
Your spinal cord is protected by the vertebral column (also known as the spinal column or backbone).
The human spinal column is made up of 33 bones - 7 vertebrae in the cervical region, 12 in the thoracic region, 5 in the lumbar region, 5 in the sacral region and 4 in the coccygeal region.
The outer layer of the human spinal cord consists of white matter, i.e., myelin-sheathed nerve fibers.
These are bundled into specialized tracts that conduct impulses triggered by pressure, pain, heat, and other sensory stimuli or conduct motor impulses activating muscles and glands. The inner layer, or gray matter, is mainly composed of nerve cell bodies. Within the gray matter, running the length of the cord and extending into the brain, lies the central canal through which the cerebrospinal fluid circulates.
A spinal cord injury (SCI) can occur anywhere along the spinal cord. It is the result of damage to cells in the spinal cord and causes a loss of communication between the brain and the parts of the body below the injury.
Effects of a SCI may include low blood pressure, inability to regulate blood pressure effectively, reduced control of body temperature, inability to sweat below the level of injury, and chronic pain.
Picture of the human spinal cord
Incomplete Spinal Cord Injury: An incomplete spinal cord injury does not result in complete loss of movement and sensation below the injury site. These injuries are usually classified as:
Anterior cord syndrome: Damage to the front of the spinal cord, affecting pain, temperature and touch sensation, but leaving some pressure and joint sensation. Often motor function is unaffected.
Central Cord Syndrome: Form of incomplete spinal cord injury in which some of the signals from the brain to the body are not received, characterized by impairment in the arms and hands and, to a lesser extent, in the legs. Sensory loss below the site of the spinal injury and loss of bladder control may also occur. This syndrome, usually the result of trauma, is associated with damage to the large nerve fibers that carry information directly from the cerebral cortex to the spinal cord. These nerves are particularly important for hand and arm function. Symptoms may include paralysis and/or loss of fine control of movements in the arms and hands, with relatively less impairment of leg movements. The brain's ability to send and receive signals to and from parts of the body below the site of trauma is affected but not entirely blocked.
Brown-Sequard syndrome: Injury to the lateral half of the spinal cord. The condition is characterized by the following clinical features found below the level of the lesion - contralateral hemisensory anesthesia to pain and temperature, ipsilateral loss of propioception, and ipsilateral motor paralysis. Tactile sensation is generally spared.
Spinal contusions: The most common type of spinal cord injury. The spinal cord is bruised but not severed. Inflammation and bleeding occurs near the injury as a result of the injury.
Injuries to individual nerve cells: Loss of sensory and motor functions in the area of the body to which the injured nerve root corresponds.
The spine is surrounded by many muscles and ligaments to give it strength
The Atlas is the topmost vertebra, and along with C2, forms the joint connecting the skull and spine. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra.
C2 or axis
Forms the pivot upon which C1 rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.
Injuries to C-1 and C-2 can result in a loss of many involuntary functions including the ability to breathe, necessitating breathing aids such as ventilators or diaphragmatic pacemakers.
C4 (cervical vertebra)
The fourth cervical (neck) vertebra from the top. Injuries above the C-4 level may require a ventilator for the person to breathe properly.
5th cervical vertabrae down from the base of the skull, found in the neck. C5 injuries often maintain shoulder and biceps control, but have no control at the wrist or hand.
C6 (cervical vertebra)
The sixth cervical (neck) vertebra from the top. The next-to-last of the seven cervical vertebrae. An injury to the spinal cord between C6 and C7 vertebrae is called a C6-7 injury. These injuries generally allow wrist control, but no hand function.
C7 or vertebra prominens
The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens. In some subjects, the seventh cervical vertebra is associated with an abnormal pair of ribs, known as cervical ribs. These ribs are usually small, but may occasionally compress blood vessels (such as the subclavian artery) or nerves in the brachial plexus, causing unpleasant symptoms. C-7 and T-1 can straighten their arms but still may have dexterity problems with the hand and fingers. Injuries at the thoracic level and below result in paraplegia, with the hands not affected.
Although there are seven cervical vertebrae (C1-C7), there are eight cervical nerves (C1-C8). All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emerges below the C7 vertebra. In other words C8 is a nerve root not a vertebrae.
Thoracic Vertebrae (T1- T12)
Human vertebra picture
Paralysis of the legs is called paraplegia.
Paralysis of the arms AND legs is called quadriplegia.
T-1 to T-8
Most often control of the hands, but poor trunk control as the result of lack of abdominal muscle control.
T-9 to T-12
Allow good trunk control and abdominal muscle control. Lumbar and Sacral injuries yield decreasing control of the hip flexors and legs. Individuals with SCI also experience other changes. For example, they may experience dysfunction of the bowel and bladder.
Lumbar Vertebrae (L1- L5)
The lumbar vertebrae graduate in size from L1 through L5. These vertebrae bear much of the body's weight and related biomechanical stress.
The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body.
Some individuals have four lumbar vertebrae, while others have six. Lumbar disorders that normally affect L5 will affect L4 or L6 in these individuals.
The first lumbar vertebra is at the level as the ninth rib. This level is also called the important transpyloric plane, since the pylorus of the stomach is at this level.
L3 - L5
A lot of motion in the back is divided between these five motion segments with segments L3 - L4 and L4 - L5 taking most of the stress. L3 - L4 and L4 - L5 segments are most likely to breakdown from wear and tear causing such conditions as Osteoarthritis.
L4 - L5 and L5 - S1
The most likely to herniate (herniated disc, bulging disk, compressed disk, herniated intervertebral disk, herniated nucleus pulposus, prolapsed disk, ruptured disk, slipped disk). The effects of this can cause pain and numbness that can radiate through the leg and extend down to the feet (sciatica).
The fifth lumbar vertebra is the most common site of spondylolysis and spondylolisthesis.
Sacral Spine (s1 - S5)
The Sacrum is located behind the pelvis. Five bones (abbreviated S1 through S5) fused into a triangular shape, form the sacrum. The sacrum fits between the two hipbones connecting the spine to the pelvis located just below the lumbar vertebrae.
It consists of four or five sacral vertebrae in a child, which become fused into a single bone after age 26. The sacrum forms the back wall of the pelvic girdle and moves with it.
The first three vertebrae in the sacral have transverse processes which come together to form wide lateral wings called alae. These alae articulate with the blades of the pelvis (ilium).
As part of the pelvic girdle, the sacrum forms the back wall of the pelvis and also forms joints at the hip bone called the sacroiliac joints. The sacrum contains a series of four openings on each side through which the sacral nerves and blood vessels run. The sacral canal runs down the center of the sacrum and represents the end of the vertebral canal.
Back pain or leg pain (sciatica) can typically arise due to injury where the lumbar spine and sacral region connect (at L5 - S1) because this section of the spine is subjected to a large amount of stress and twisting.
People with rheumatoid arthritis or osteoporosis are inclined to develop stress fractures and fatigue fractures in the sacrum.
The sacrum is shaped diferent in males and females. In females the sacrum is shorter and wider than in males.
The bottom of the spinal column is called the coccyx or tailbone. It consists of 3-5 bones that are fused together in an adult. Many muscles connect to the coccyx.