Muscles
There are quite a few muscles which act on the spine and help in its different movements. There are short muscles which act directly and long muscles which act indirectly and aid in the movements of the spine. They help to steady the spine. They produce extension, lateral bending and rotation.
Short muscles help to maintain the posture. They contract intermittently, and during an upright posture, there are slow spontaneous swaying movements. They help to initiate flexion and assist the short muscles in further flexion and control of it. It is surprising to know that in incomplete flexion, the short muscles are inactive and controlled by the spinal ligaments. Any imbalance and weakness of these muscles produces a deformity of the spine known as scoliosis.
Side bending is also helped by short muscles. They play a great role in mechanical vertebral pathology. A sudden, enexpected movement can produce a harmful distribution of the forces on the intervertebral joints. If certain parts are compressed or put into a traction beyond their capacity., they can damage the joint to a varying degree, depending on the force causing the painful muscle spasm. Synchronisation of muscular activity is more important than just increasing the strength of these muscles by various spinal exercises. This is why manipulation is an important therepeutic measure.
When the muscles are weak, the ligaments and joints are more strained, thus becoming more vulnerable. Generalised muscle weakness is also the cause of bad posture. Excessive powerful muscle contraction can also damage the bone: for instance, there can be a fracture of the kneecap due to contraction of the high muscles.
Intervertebral Foramen
The intervertebral foramen is a short canal lodged between contiguous. It is ellipsoid in form. Its form changes with the mobility of the intervertebral joint. In the dorsal and lumbar spine it is directed laterally to the right and left. In the cervical spine it is directed slightly to the front, say by fifteen degrees, as compared to the dorsal or lumbar foramen. The canal is covered by a fibrous structure which is connected to the intervertebral disc and capsule of the posterior joints.
Through it passes the spinal nerve which consists of a ventral root and a dorsal root. These appear to be united with each other in the canal, but when seen microscopically they are found to be seperated. The dorsal root contains the spinal ganglion. Each spinal nerve, after coming out of the intervertebral foramen, has an offshoot of a small branach called a meningeal branch which re-enters the vertebral canal through the intervertebral foramen and ennervates the vertebral ligaments and blood vessels of the spinal chord.
The compression or irritation of elements contained in the intervertebral foramen may occur due to the degeneration of the disc, osteoarthritis ofn the intervertebral joints, posterior profusion of the disc, or rupture of the disc with herniation of the nucleus pulposus. This may cause pain, some muscular weakness, lumbago, sciatica and a diminished feeling all over the skin.