Anatomy and Physiology of Spine1

The human skeleton is the body's framework or scaffolding system. Skeletal bones are classified as long, short, flat, or irregular and vary in length, width, and depth. The function of the skeletal system is to support the body against the force of gravity, protect soft body parts, produce red blood cells, store inorganic calcium, and phosphorus salts, and to provide sites for muscle attachment to enable body movement. The bones in the spine are irregular in shape and provide places to connect to other bones.

The spinal column is also called the vertebral column. The bones in the spine are called vertebrae (ver-ta-bray). The column starts at the base of the skull and continues to the pelvis. Alternate layers of bone (vertebrae) and cartilage (car-til-ledge, the inter-vertebral disks) stack vertically one on top of the other in the spinal column. The lattice-like structure of the cancellous bone (cancel-lus, the spongy interior) in a vertebra absorbs external pressure. The cartilaginous disks between vertebrae absorb and distribute shock and keep the vertebrae from grinding together during movement. The spinal column (or vertebral column) extends from the skull to the pelvis and is made up of 33 individual bones termed vertebrae. The vertebrae are stacked on top of each other group into four regions.

The spine has four natural curves. Two are lordotic (lor-dot-ick) and two are kyphotic (kye-fah-tick). The cervical and lumbar curves are lordotic. The thoracic (thor-as-ick) and sacral (say-kral) curves are kyphotic. In the womb and for a period of time following birth, a baby's spine is shaped like the letter C. This curve is termed a primary curve, which is kyphotic. During the time the baby is learning to lift his head and eventually walk, muscles develop. As muscular strength and ability is gained, the baby's activity will shift body weight to the spine. Gradually secondary curves develop in the cervical and lumbar regions; lordotic curves. These curves will continue to develop until growing stops.

The cervical spine is further divided into two parts; the upper cervical region (C1 and C2), and the lower cervical region (C3 through C7). C1 is termed the atlas and C2 the axis. The occiput (CO), also known as the occipital bone, is a flat bone that forms the back of the head.

The atlas is the first cervical vertebra and therefore abbreviated C1. This vertebra supports the skull. Its appearance is different from the other spinal vertebrae. The atlas is a ring of bone made up of two lateral masses joined at the front and back by the anterior arch and the posterior arch.

The axis is the second cervical vertebra or C2. It is a blunt tooth-like process that projects upward. It is also referred to as the ‘dens’ (Latin for ‘tooth’) or odontoid process. The dens provides a type of pivot and collar allowing the head and atlas to rotate around the dens.

The cervical bones - the vertebrae - are smaller in size when compared to other spinal vertebrae. The purpose of the cervical spine is to contain and protect the spinal cord, support the skull, and enable diverse head movement (e.g. rotate side-to-side, bend forward and backward).

Nerve impulses travel to and from the brain through the spinal cord to a specific location by way of the peripheral nervous system (PNS). The PNS is the complex system of nerves that branch off from the spinal nerve roots. These nerves travel outside of the spinal canal or spinal cord into the organs, arms, legs, fingers - throughout the entire body.

C1: Head and neck

C2: Head and neck

C3: Diaphragm

C4: Upper body muscles (e.g. Deltoids, Biceps)

C5: Wrist extensors

C6: Wrist extensors

C7: Triceps

C8: Hands

The thoracic vertebrae increase in size from T1 through T12. They are characterized by small pedicles, long spinous processes, and relatively large inter-vertebral foramen (neural passageways), which result in less incidence of nerve compression.

The lumbar vertebrae graduate in size from L1 through L5. These vertebrae bear much of the body's weight and related biomechanical stress. The pedicles are longer and wider than those in the thoracic spine. The spinous processes are horizontal and more squared in shape. The inter-vertebral foramen (neural passageways) are relatively large but nerve root compression is more common than in the thoracic spine.

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 hip bones connecting the spine to the pelvis. The last lumbar vertebra (L5) articulates (moves) with the sacrum. Immediately below the sacrum are five additional bones, fused together to form the coccyx (tail bone).

Although vertebrae range in size; cervical the smallest, lumbar the largest, vertebral bodies are the weight bearing structures of the spinal column. Upper body weight is distributed through the spine to the sacrum and pelvis. The natural curves in the spine, kyphotic and lordotic, provide resistance and elasticity in distributing body weight and axial loads sustained during movement.

The vertebrae and disks are held together by groups of ligaments. Ligaments connect bone to bone, where as tendons connect muscle to bone. In the spine, tendons connect muscles to the vertebrae. The ligaments and tendons help to stabilize the spine and guard against excessive movement in any one direction.

The spine also has joints—similar to knees, elbows, and other joints. The spinal joints are called facet joints. The facet joints have been described as finger-like and link the vertebrae together. The facet joints are located at the posterior area of the spinal column. In addition, the facet joints help to make the spine flexible.

Medical professionals often refer to sections of the body in terms of anatomical planes (flat surfaces). These planes are imaginary lines - vertical or horizontal - drawn through an upright body. The terms are used to describe a specific body part.

Listed below are general anatomical terms and their meanings:

In the center of the spinal column is a vertical hole called the spinal canal; it contains the spinal cord. The bones that create the spinal canal serve as armour to help protect the spinal cord from injury. Small nerve roots branch off from the spinal cord through spaces on between each vertebra and extend out into the entire body. The spinal cord and the nerves are part of the central nervous system that includes the brain. The nerves are the body's neural message system.

The central nervous system is composed of the brain and spinal cord. The brain has 12 cranial 7nerves. The spinal cord, which originates immediately below the brainstem, extends to the first lumbar vertebra (L1). Beyond L1 the spinal cord becomes the Cauda Equina (see below). The spinal cord provides a means of communication between the brain and peripheral nerves.

The CNS extends to the peripheral nervous system, a system of nerves that branch beyond the spinal cord, brain, and brainstem. The PNS carries information to and from the CNS.

Cerebrospinal fluid is a clear fluid found in the brain chambers (Ventricles), spinal canal, and spinal cord. This fluid is secreted from the choroids plexus, a vascular part in the ventricles of the brain. CSF bathes and circulates among these tissues and acts as a shock absorber to protect against injury. The fluid contains different electrolytes, proteins, and glucose. In an average adult the total volume of CSF is about 150 milliliters.

Meninges are membranes that cover and protect the brain and spinal cord. There are three primary types: (1) Dura mater (2) Arachnoid mater, and (3) Pia mater.

A dermatome is an area of skin supplied by fibers from a single spinal nerve root.

60% of adults suffer back problems annually. Of those 50% will have another attack within a year and 30% will become chronic sufferers. 80% of western country workers are back pain sufferers. We begin to deteriorate in moving and handling ability between the ages of 25–40 years.

There are two main risk factors for back injury among nurses: Lifting and transferring patients, and bed-making. During a typical shift, on average a hospital staff nurse will lift 20 patients into bed, and transfer 5–10 patients from bed to a chair. Patients typically weight in excess of 100lbs, which puts this load well above the weight that would be considered ‘safe’ for industrial workers for this frequency of lifting. As with many hospitality workers, bed-making also increases the risks of back injury because of the bending and stretching involved in putting sheets onto a bed.