Spinal column

Key takeaways

Spinal column belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Spinal column to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Spinal column from memory before moving on to harder problems.

Reference excerpt

The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmented column of vertebrae that surrounds and protects the spinal cord. The vertebrae are separated by intervertebral discs in a series of cartilaginous joints. The dorsal portion of the spinal column houses the spinal canal, an elongated cavity formed by the alignment of the vertebral neural arches that encloses and protects the spinal cord, with spinal nerves exiting via the intervertebral foramina to innervate each body segment. There are around 50,000 species of animals that have a vertebral column. The human spine is one of the most-studied examples, as the general structure of human vertebrae is fairly typical of that found in other mammals, reptiles, and birds. The shape of the vertebral body does, however, vary somewhat between different groups of living species. Individual vertebrae are named according to their corresponding region including the neck, thorax, abdomen, pelvis or tail. In clinical medicine, features on vertebrae such as the spinous process can be used as surface landmarks to guide medical procedures such as lumbar punctures and spinal anesthesia. There are also many different spinal diseases in humans that can affect both the bony vertebrae and the intervertebral discs, with kyphosis, scoliosis, ankylosing spondylitis, and degenerative discs being recognizable examples. Spina bifida is the most common birth defect that affects the spinal column.

Structure The number of vertebrae in a region can vary but overall the number remains the same. In a human spinal column, there are normally 33 vertebrae. The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone. The articulating vertebrae are named according to their region of the spine. From top to bottom, there are 7 cervical vertebrae, 12 thoracic vertebrae and 5 lumbar vertebrae. The number of those in the cervical region, however, is only rarely changed, while that in the coccygeal region varies most. Excluding rare deviations, the total number of vertebrae ranges from 32 to 35. In about 10% of people, both the total number of pre-sacral vertebrae and the number of vertebrae in individual parts of the spine can vary. The most frequent deviations are: 11 (rarely 13) thoracic vertebrae, 4 or 6 lumbar vertebrae, 3 or 5 coccygeal vertebrae (rarely up to 7). There are numerous ligaments extending the length of the column, which include the anterior and posterior longitudinal ligaments at the front and back of the vertebral bodies, the ligamentum flavum deep to the laminae, the interspinous and supraspinous ligaments between spinous processes, and the intertransverse ligaments between the transverse processes.

Vertebrae

The vertebrae in the human vertebral column is divided into different body regions, which correspond to the curvatures of the vertebral column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are essentially alike, with minor variation. These regions are called the cervical spine, thoracic spine, lumbar spine, sacrum, and coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae, and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region, however, is only rarely changed. The vertebrae of the cervical, thoracic, and lumbar spines are independent bones and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head rests.

A typical vertebra consists of two parts: the vertebral body (or centrum), which is ventral (or anterior, in the standard anatomical position) and withstands axial structural load; and the vertebral arch (also known as neural arch), which is dorsal (or posterior) and provides articulations and anchorages for ribs and core skeletal muscles. Together, these enclose the vertebral foramen, the series of which align to form the spinal canal, a body cavity that contains the spinal cord. Because the vertebral column will outgrow the spinal cord during child development, by adulthood the spinal cord often ends at the upper lumbar spine (at around L1/L2 level), the lower (caudal) end of the spinal canal is occupied by a ponytail-like bundle of spinal nerves descriptively called cauda equina (from Latin "horse's tail"), and the sacrum and coccyx are fused without a central foramen. The vertebral arch is formed by a ventral pair of pedicles and a dorsal pair of laminae, and supports seven processes, four articular, two transverse and one spinous, the latter also being known as the neural spine. The transverse and spinous processes and their associated ligaments serve as important attachment sites for back and paraspinal muscles and the thoracolumbar fasciae. The spinous processes of the cervical and lumbar regions can be felt through the skin, and are important surface landmarks in clinical medicine. The four articular processes for two pairs of plane facet joints above and below each vertebra, articulating with those of the adjacent vertebrae and are joined by a thin portion of the neural arch called the pars interarticularis. The orientation of the facet joints restricts the range of motion between the vertebrae. Underneath each pedicle is a small hole (enclosed by the pedicle of the vertebral below) called intervertebral foramen, which transmit the corresponding spinal nerve and dorsal root ganglion that exit the spinal canal. From top to bottom, the vertebrae are:

Cervical spine (neck): 7 vertebrae (C1–C7) Thoracic spine (chest/upper back): 12 vertebrae (T1–T12) Lumbar spine (lower back): 5 vertebrae (L1–L5) Sacrum (pelvis region): 5 (fused) vertebrae (S1–S5) Coccyx (tailbone): 4 (3–5, fused) vertebrae

Combined vertebral regions

For some medical purposes, adjacent vertebral regions may be considered together:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Spinal column

Start with the simplest possible case. Write down what Spinal column claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Spinal column before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Spinal column ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Spinal column

In research: Spinal column appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Spinal column in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Spinal column is common in secondary-school and first-year university syllabi. It links to neighbouring topics Back anatomy, Bones of the thorax, Bones of the vertebral column, so understanding it makes those chapters shorter.
In everyday life: Look for Spinal column outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Spinal column in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Spinal column means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Spinal column out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Spinal column in simple terms?

The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate.

Why does Spinal column matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Spinal column?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Spinal column.