•The vertebral column or the backbone is a stack like arrangement of small bony blocks known as the vertebrae.
•There are a total of 33 vertebrae:
•7 in the neck (cervical vertebrae)
•12 in the upper back (thoracic vertebrae)
•5 in the lower back (lumbar vertebrae)
•5 in the hip area (fused into a single sacrum)
•4 in the tailbone (fused to form a single coccyx)
•Every individual vertebra is separated from the next vertebra by a soft cushion like disc of cartilage called an intervertebral disc.
•Since the sacrum and coccyx are fused, the vertebrae in those are not separated by the intervertebral discs.
•Spinal nerves emerge from the spinal column from gaps between the vertebrae
The spinal column is made up of separate bones each known as a vertebra (plural: vertebrae) and between each vertebra is an intervertebral disc that connects each bone, allows slight movement of the bones and acts as a shock absorber for the spine.
•The sketches here show a typical vertebra
•The vertebral body and laminae form the vertebral foramen, and the vertebral foramen of all the vertebrae form a long vertebral canal that contains the spinal cord
•Cervical vertebrae are smaller and flatter compared to others
•Thoracic vertebrae are larger than the cervical ones and they provide attachment to the rib cage
•Lumbar vertebrae are the largest and thickest
•The brain and spinal cord have 3 layers of wrappings called meninges:
1. Dura mater (outer) latin: 'tough mother'
2. Arachnoid mater (middle) latin: 'spider mother'
3. Pia mater (inner) latin: 'gentle mother'
•The dura mater is the outermost layer and the strongest layer. The space between the dura mater and the vertebrae is known as epidural space.
•The middle layer is called arachnoid layer because it has a web-like network of blood vessels that produces the cerebrospinal fluid (CSF)
•Pia mater is the innermost layer which is tightly attached to the tissue of brain and spinal cord like a transparent, laminating membrane.
•Together all three layers of meninges protect the CNS from any harm.
In a cross-section of the spinal cord you can see the grey and white matter. White matter is white due to the fatty sheaths that are found around the axons of the neuronal cell axon. These are known as myelin sheaths. Grey matter axons do not have myelin sheaths.
•As described before, 31 pairs of spinal nerves emerge from the spinal cord:
•8 cervical, 12 thoracic, 5 lumbar, 3 sacral and 1 coccygeal
•Each spinal segment gives off a nerve root from the front- the ventral root and a root from the back- the dorsal root on both sides. The ventral and dorsal root from each side come together and join each other to form one spinal nerve.
•This way, each spinal segment gives off one pair of spinal nerves, one on each side. Each spinal nerve carries motor fibres from the ventral root sensory fibres to the dorsal root.
•Other than this, spinal nerves from cervical, thoracic and lumbar segments also carry sympathetic nerve fibres that control the autonomic (involuntary) actions.
•Each spinal nerve supplies specific region of the body and specific organs and muscles. The details of this functional distribution is in module 4.
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