Anatomy of the Spine - Neuroradiology
C8 emerges between the C7 and T1 vertebrae, and the remaining spinal nerves . The vertebral column is also known as the spinal column or spine (Figure 1). . the opening through which a spinal nerve exits from the vertebral column (Figure 5). . back in relation to its neighbors during movements of the vertebral column. Spinal nerves extend outward from the vertebral column to enervate the . of what these combination nerves do, but there is a thread of relation between them.
This has been caused by a difference in vertebral height and height of the spinal segment.
Thus while the first cervical spinal segment is within C1 vertebra, the T12 cord comes to lie at the T8 vertebra. Similarly, the entire lumbar spinal segment lies between T9 and T11 vertebrae and the sacral cord is between the T12 to L2 vertebrae. C2 root exits at the atlanto-axis. The C3 roots exit between C2 and C3.
The C8 root exits between C7 and T1. The first thoracic root or T1 exits the spinal cord between T1 and T2 vertebral bodies. The T12 root exits the spinal cord between T1 and L1. The L1 root exits the spinal cord between L1 and L2 bodies. The L5 root exits the cord between L1 and S1 bodies. Relation of Spinal and Vertebral Segments — Spinal Level vs Vertebral Level First two cervical cord segments roughly match the first two cervical vertebral levels.
C3 — C8 segments of the spinal cords are situated between C3 through C7 bony vertebral levels. Likewise, in the thoracic spinal cord, the first two thoracic cord segments roughly match first two thoracic vertebral levels. However, T3 through T12 cord segments are situated between T3 to T8. The lumbar cord segments are situated at the T9 through T11 levels while the sacral segments are situated from T12 to L1.
The tip of the spinal cord or conus is situated at L2 vertebral level. Below L2, there is only spinal roots, called the cauda equina. A rough calculation can be done as follow to obtain a relation between vertebral and segmental level.
Axons from different spinal nerves will come together into a systemic nerve. This occurs at four places along the length of the vertebral column, each identified as a nerve plexus, whereas the other spinal nerves directly correspond to nerves at their respective levels. In this instance, the word plexus is used to describe networks of nerve fibers with no associated cell bodies. Of the four nerve plexuses, two are found at the cervical level, one at the lumbar level, and one at the sacral level Figure The cervical plexus is composed of axons from spinal nerves C1 through C5 and branches into nerves in the posterior neck and head, as well as the phrenic nerve, which connects to the diaphragm at the base of the thoracic cavity.
The other plexus from the cervical level is the brachial plexus. Spinal nerves C4 through T1 reorganize through this plexus to give rise to the nerves of the arms, as the name brachial suggests. A large nerve from this plexus is the radial nerve from which the axillary nerve branches to go to the armpit region.
Spinal Cord Injury Levels
The radial nerve continues through the arm and is paralleled by the ulnar nerve and the median nerve. The lumbar plexus arises from all the lumbar spinal nerves and gives rise to nerves enervating the pelvic region and the anterior leg. The femoral nerve is one of the major nerves from this plexus, which gives rise to the saphenous nerve as a branch that extends through the anterior lower leg.
The sacral plexus comes from the lower lumbar nerves L4 and L5 and the sacral nerves S1 to S4.
The most significant systemic nerve to come from this plexus is the sciatic nerve, which is a combination of the tibial nerve and the fibular nerve. The sciatic nerve extends across the hip joint and is most commonly associated with the condition sciatica, which is the result of compression or irritation of the nerve or any of the spinal nerves giving rise to it. These plexuses are described as arising from spinal nerves and giving rise to certain systemic nerves, but they contain fibers that serve sensory functions or fibers that serve motor functions.
This means that some fibers extend from cutaneous or other peripheral sensory surfaces and send action potentials into the CNS. Those are axons of sensory neurons in the dorsal root ganglia that enter the spinal cord through the dorsal nerve root. Other fibers are the axons of motor neurons of the anterior horn of the spinal cord, which emerge in the ventral nerve root and send action potentials to cause skeletal muscles to contract in their target regions.
For example, the radial nerve contains fibers of cutaneous sensation in the arm, as well as motor fibers that move muscles in the arm. Spinal nerves of the thoracic region, T2 through T11, are not part of the plexuses but rather emerge and give rise to the intercostal nerves found between the ribs, which articulate with the vertebrae surrounding the spinal nerve. There are four main nerve plexuses in the human body.
The cervical plexus supplies nerves to the posterior head and neck, as well as to the diaphragm. The brachial plexus supplies nerves to the arm. The lumbar plexus supplies nerves to the anterior leg. The sacral plexus supplies nerves to the posterior leg.
Cranial Nerves The nerves attached to the brain are the cranial nerves, which are primarily responsible for the sensory and motor functions of the head and neck one of these nerves targets organs in the thoracic and abdominal cavities as part of the parasympathetic nervous system. They can be classified as sensory nerves, motor nerves, or a combination of both, meaning that the axons in these nerves originate out of sensory ganglia external to the cranium or motor nuclei within the brain stem.
Sensory axons enter the brain to synapse in a nucleus. Motor axons connect to skeletal muscles of the head or neck.
The anterior divisions of the lumbar nerves rami anteriores increase in size from above downward. They are joined, near their origins, by gray rami communicantes from the lumbar ganglia of the sympathetic trunk.
These rami consist of long, slender branches which accompany the lumbar arteries around the sides of the vertebral bodies, beneath the psoas major. Their arrangement is somewhat irregular: The first and second, and sometimes the third and fourth lumbar nerves are each connected with the lumbar part of the sympathetic trunk by a white ramus communicans. The nerves pass obliquely outward behind the psoas major, or between its fasciculidistributing filaments to it and the quadratus lumborum.
The first three and the greater part of the fourth are connected together in this situation by anastomotic loops, and form the lumbar plexus. The smaller part of the fourth joins with the fifth to form the lumbosacral trunkwhich assists in the formation of the sacral plexus. The fourth nerve is named the furcal nervefrom the fact that it is subdivided between the two plexuses.
Nerve Structures of the Spine
Sacral nerves[ edit ] Plan of sacral and pudendal plexuses The sacral nerves are the five pairs of spinal nerves which exit the sacrum at the lower end of the vertebral column.
The roots of these nerves begin inside the vertebral column at the level of the L1 vertebrawhere the cauda equina begins, and then descend into the sacrum. Each nerve emerges in two divisions: These anastomoses of nerves form the sacral plexus and the lumbosacral plexus. The branches of these plexus give rise to nerves that supply much of the hipthighleg and foot.