The sacrum is the section located at the base of the spine. It does not have discs separating the vertebrae, because its five levels, S1 to S5, are fused together. The pelvis is connected to the spinal column at the sacrum section. The coccyx is at the very base of the spinal column and is made of four vertebrae that are fused together. The spine is normally a straight line when viewed from the back. If the spine curves to one side or the other, this indicates a condition named scoliosis.
However, the spine does have some normal, gradual curves when viewed from the side. The neck and lumbar sections of the spine have a lordotic curve, which means that they curve inward. These spinal curves help maintain balance while upright and support the weight of the head and upper body. However, too much curvature may cause spinal imbalance, causing spinal conditions that may result in pain or loss of mobility.
Normal adult spines are positioned over the pelvis, so upright posture doesn't strain muscles. However, changes of spinal position can stress muscles and cause spinal deformity. If the spine is injured and unable to function properly, it can be very painful or even disabling. The spine is made of many parts that protect the spinal cord, facilitate movement and support the body. The spinal cord has nerve pathways that carry signals, such as pain, from the arms, legs, and the body to the brain.
Nerve roots are used to transmit information between the spinal cord and the other parts of the body, such as arms, legs and organs.
The flat plates of the lamina create the outer wall of the vertebral canal and help protect the spinal cord. Discs separate the vertebrae. They are made of tough, elastic material that allows the spine to bend and twist naturally. With age, our discs increasingly lose the ability to reabsorb fluid and become brittle and flatter; this is why we get shorter as we grow older. Also diseases, such as osteoarthritis and osteoporosis, cause bone spurs osteophytes to grow. Injury and strain can cause discs to bulge or herniate, a condition in which the nucleus is pushed out through the annulus to compress the nerve roots causing back pain.
On the back of each vertebra are bony projections that form the vertebral arch. The arch is made of two supporting pedicles and two laminae Fig. The hollow spinal canal contains the spinal cord, fat, ligaments, and blood vessels.
Under each pedicle, a pair of spinal nerves exits the spinal cord and pass through the intervertebral foramen to branch out to your body. Surgeons often remove the lamina of the vertebral arch laminectomy to access the spinal cord and nerves to treat stenosis, tumors, or herniated discs.
Seven processes arise from the vertebral arch: the spinous process, two transverse processes, two superior facets, and two inferior facets. The facet joints of the spine allow back motion. Each vertebra has four facet joints, one pair that connects to the vertebra above superior facets and one pair that connects to the vertebra below inferior facets Fig. The ligaments are strong fibrous bands that hold the vertebrae together, stabilize the spine, and protect the discs.
The three major ligaments of the spine are the ligamentum flavum, anterior longitudinal ligament ALL , and posterior longitudinal ligament PLL Fig. The ALL and PLL are continuous bands that run from the top to the bottom of the spinal column along the vertebral bodies. They prevent excessive movement of the vertebral bones. The ligamentum flavum attaches between the lamina of each vertebra.
The spinal cord is about 18 inches long and is the thickness of your thumb. It runs from the brainstem to the 1st lumbar vertebra protected within the spinal canal. At the end of the spinal cord, the cord fibers separate into the cauda equina and continue down through the spinal canal to your tailbone before branching off to your legs and feet. The spinal cord serves as an information super-highway, relaying messages between the brain and the body. The brain sends motor messages to the limbs and body through the spinal cord allowing for movement.
The limbs and body send sensory messages to the brain through the spinal cord about what we feel and touch. Sometimes the spinal cord can react without sending information to the brain. These special pathways, called spinal reflexes, are designed to immediately protect our body from harm. Any damage to the spinal cord can result in a loss of sensory and motor function below the level of injury.
For example, an injury to the thoracic or lumbar area may cause motor and sensory loss of the legs and trunk called paraplegia. An injury to the cervical neck area may cause sensory and motor loss of the arms and legs called tetraplegia, formerly known as quadriplegia. Thirty-one pairs of spinal nerves branch off the spinal cord.
Each spinal nerve has two roots Fig. The ventral front root carries motor impulses from the brain and the dorsal back root carries sensory impulses to the brain. The ventral and dorsal roots fuse together to form a spinal nerve, which travels down the spinal canal, alongside the cord, until it reaches its exit hole - the intervertebral foramen Fig. Once the nerve passes through the intervertebral foramen, it branches; each branch has both motor and sensory fibers.
The smaller branch called the posterior primary ramus turns posteriorly to supply the skin and muscles of the back of the body. The larger branch called the anterior primary ramus turns anteriorly to supply the skin and muscles of the front of the body and forms most of the major nerves. The spinal nerves are numbered according to the vertebrae above which it exits the spinal canal. The 8 cervical spinal nerves are C1 through C8, the 12 thoracic spinal nerves are T1 through T12, the 5 lumbar spinal nerves are L1 through L5, and the 5 sacral spinal nerves are S1 through S5.
There is 1 coccygeal nerve. The spinal nerves innervate specific areas and form a striped pattern across the body called dermatomes Fig. It provides several important functions, including:. The average person is born with 33 individual bones the vertebrae that interact and connect with each other through flexible joints called facets. By the time a person becomes an adult most have only 24 vertebrae because some vertebrae at the bottom end of the spine fuse together during normal growth and development.
Sometimes a person may have an additional vertebra, which is called a transitional body and is usually found at the sixth level of the lumbar area labeled L6. The bottom of the spine is called the sacrum. It is made up of several vertebral bodies usually fused together as one. The remaining small bones or ossicles below the sacrum are also fused together and called the tailbone or coccyx.
The spine above the sacrum consists of:. The spinal column combines strong bones, unique joints, flexible ligaments and tendons, large muscles and highly sensitive nerves. While many of us take the benefits of a healthy spine for granted, spinal pain is a sharp reminder of how much we depend on our back in daily life. Some causes of spinal pain include:.
The spinal column is made up of many parts, all designed to help the back move flexibly, support body weight and protect the spinal cord and nerves.
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