Spinal Cord- Definition, Anatomy, Function & Disorders

Spinal Cord: definition, meaning, function, diagram, structure

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:49 PM IST

The spinal cord is a vital part of the central nervous system, extending from the brainstem down through the vertebral column. It acts as a communication highway, transmitting signals between the brain and the rest of the body. The spinal cord also coordinates reflex actions and plays a critical role in maintaining posture and movement. In this article, the spinal cord, anatomy of the spinal cord, functions of the spinal cord, spinal cord nerves and their functions, and spinal cord injuries and disorders are discussed. Spinal Cord is a topic of the chapter Neural Control and Coordination in Biology.

This Story also Contains

What is the Spinal Cord?
Anatomy of the Spinal Cord
Functions of the Spinal Cord
Spinal Cord Nerves and their Functions
Spinal Cord Injuries and Disorders

Spinal Cord: definition, meaning, function, diagram, structure

What is the Spinal Cord?

It is a cylindrically shaped bundle of nerves extending from the brainstem down the vertebral column. It acts as that major pathway through which sensory and motor signals are transmitted between the brain and the rest of the body.

The spinal cord plays a crucial role in synchronising reflexes and movements, like walking and catching, with the transmission of information from the body to the brain. Housed within the protective casement of the vertebral column, it provides the basic functions that underlie simple bodily activities as well as complex motor activities, thus being indispensable to human movement, sensation, and general neurological functioning.

Anatomy of the Spinal Cord

The spinal cord is a cylindrical structure comprising nervous tissue extending from the brainstem through the vertebral column and ending near the first or second lumbar vertebra in adults. However, this may vary a bit from one individual to another.

Structure and Location

The length of the spinal cord averages approximately 45 cm (18 inches) in adults.
Its diameter varies along its length, being larger in regions where nerves controlling the limbs originate.
The total vertebral column consists of 33 vertebrae, which encase and protect the spinal cord.
There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral fused into the sacrum, and 4 coccygeal vertebrae.
Each of these vertebrae forms a part of the bony armour surrounding the fragile spinal cord, thereby protecting it from damage.

Regions of the Spinal Cord

The spinal cord is divided into:

Cervical

That part of the spinal cord in the neck region consists of 8 cervical segments (C1-C8).

Thoracic

This lies in the upper back and consists of 12 thoracic segments, T1-T12.

Lumbar

This lies in the lower back and consists of 5 lumbar segments, L1-L5.

Sacral

This is part of the pelvis and consists of 5 sacral segments, S1-S5, fused in the sacrum.

Segments and Nerve Roots

The spinal cord is segmented. Each segment is related to a pair of nerve roots arising from the vertebral column.
Number of Segments: 31 in number. 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.
Each segment gives off nerve roots that arise from the cord and emerge through openings formed by successive vertebrae.
These nerve roots then unite to form peripheral nerves that innervate regions of the body.

NEET Highest Scoring Chapters & Topics

Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis.

Know More

Also Read-

Functions of the Spinal Cord

A large variety of functions are carried out within the spinal cord, which includes transmitting nerve signals, controlling pathways of sensation and movement, and providing reflex actions.

Transmission of Nerve Signals

It acts as a way of conveying nerve impulses from the brain to the body and vice versa.
The spinal cord relays sensory information it picks up from the peripheral sensory receptors towards the brain for processing.
It receives the motor signals from the brain, triggering an outward flow that initiates muscle and other responses
Information on touch, temperature, pain, and proprioception from the body is transmitted to the brain through the spinal cord via the sensory pathways.
They involve sensory neurons that take signals directly up the spinal cord to the brainstem and higher brain centres for perception.
The motor pathways carry commands from the brain down the spinal cord to motor neurons innervating muscles and glands throughout the body.
It's through this that the communication will allow for both voluntary movements, like walking or reaching, and involuntary actions, like regulating the heartbeat.

Reflex Actions

Reflex actions are, therefore, responses that are immediate to certain stimuli, not requiring any conscious processes and directly involving the spinal cord.
The examples include protection of the body against damage, maintenance of posture, and regulation of a variety of physiological processes, all without requiring a single input from the brain.
Reflexes are automatic responses to specific stimuli, controlled by simple neural circuits called reflex arcs made up of sensory neurons and interneurons in the spinal cord, as well as motor neurons.
For instance, during the knee jerk reflex, which is also referred to as the patellar reflex, tapping the patellar tendon initiates involuntary stretching of the leg.
Another example is the withdrawal reflex: the hand is suddenly drawn back from a hot surface.
Reflex arcs are essential to survival and day-to-day functioning.
They provide very quick responses on the part of the body to impending dangers or other environmental changes.
Involving the spinal cord directly allows very rapid responses to happen, thereby preventing injury or allowing immediate reactions to occur—critical in maintaining whole bodily function and coordination.

Spinal Cord Nerves and their Functions

Each of these segments corresponds to a specific pair of spinal nerves supplying different regions of the body. The total overview of the primary spinal nerves and their functions is given below:

Cervical Nerves

C1-C4: The cervical nerves predominantly provide structures for muscles of the neck and respiration. Therefore, the nerves take part in breathing and movements of the head.

C5-C8: These nerves innervate muscles in the shoulders, arms, and hands. They play a very important role in upper limb movements and terms of sensory perception in the line of these parts.

Thoracic Nerves

T1-T12: Thoracic nerves innervate the muscles and skin of the thorax and abdomen. They participate in the movements of the chest wall and the abdominal muscle activity, as well as sensitivity in those areas.

Lumbar Nerves

L1-L5: Lumbar nerves innervate the lower back, buttocks, thighs, legs, and feet. They are responsible for locomotion and sensibilities in these fields, such as walking, standing, and balance.

Sacral Nerves

S1-S5: These nerves are responsible for the innervation of the pelvis, genitals, buttocks and lower limbs and orchestrate acts like bowel and bladder activity, sexual function, movement and sensibility of the lower extremity.

Coccygeal Nerves

Coccygeal Nerve (Co1): The coccygeal nerve is the smallest spinal nerve, and it innervates a small area of skin over the coccyx (tailbone).

Spinal Cord Injuries and Disorders

Trauma or disease can cause spinal cord injuries (SCI), which are divided into two major types: complete and incomplete injuries.

Common Spinal Cord Injuries

Complete injuries: These occur with a total loss of sensation and motor function below the level of injury. The most common cause is cutting or serious damage to the spinal cord.

Incomplete Injuries: It preserves partial communication between the brain and parts of the body below the site of injury. Sensation and motor function may then be partially preserved, depending on the extent of damage to the spinal cord.

Causes

Trauma: This can be caused by everyday events, including road traffic accidents, falls, sporting injuries, and acts of violence.

Disease: All kinds of pathologies may cause spinal cord lesions, such as Tumors, infections, meningitis, and degenerative disorders, especially spinal stenosis.

The spinal cord is prone to many disorders that either diminish its blood flow or harm it directly.

Spinal Cord Disorders

The major spinal cord disorders are:

Multiple Sclerosis

A case of autoimmune neurologic disorder wherein the immune system acts against the protective myelin sheath covering nerve fibres in the brain and spinal cord. It causes problems in communication between the brain and the rest of the body.

Amyotrophic Lateral Sclerosis (ALS)

Lou Gehrig's disease is a neurodegenerative process characterized by progressive destruction of nerve cells in the brain and spinal cord. These nerve cells control voluntary muscle movement; hence, their loss leads to the loss of muscle control, consequently resulting in paralysis.

Spina Bifida

This refers to a congenital condition whereby, before birth, there is an incomplete development of the spinal cord and its covering structures. It generates an extremely vast array of different physical and intellectual disabilities based on severity.

Also Read-

Neuron	Nerve Impulse
Diagram of Neuron	Nerve Fibres
Neuron and Nerves	Action Potential

Frequently Asked Questions (FAQs)

1. What is the primary function of the spinal cord?

The spinal cord's main function is the conduction of sensory information from the body towards the brain and motor commands from the brain towards the body. In addition, it coordinates reflexes, some of the fundamental motor responses that do not require brain involvement or involvement.

2. What are the common causes of spinal cord injuries?

Common causes of spinal cord injuries include traumatic events like motor vehicle accidents, falls, sports injuries, and acts of violence. Nontraumatic events may be caused by diseases that include spinal cord tumours, infections, degenerative disorders, and others.

3. How are spinal cord injuries diagnosed?

The diagnosis of spinal cord injury includes clinical evaluation for imaging tests to visualise damage to the spinal cord; neurological examinations delineate sensory and motor loss below the level of injury.

4. What are the differences between grey matter and white matter in the spinal cord?

Grey matter consists mainly of neuronal cell bodies, dendrites, and unmyelinated axons of the spinal cord. It processes and integrates information from sensory and motor components. White matter consists of myelinated axons that form nerve tracts connecting disparate regions of the spinal cord and convey signals between the brain and the body.

5. What advancements are being made in spinal cord regeneration research?

Research is being conducted on spinal cord regeneration through various methods to enhance nerve regeneration and regain function, such as stem cell therapy, nerve grafting, and biomaterial scaffolds. In the latest developments, efforts are being made toward inducing axonal growth and enhancing plasticity in the injured spinal cord. That gives hope that shortly, better treatments will be developed, greatly improving outcomes for patients suffering from spinal cord injuries.

6. What is the "gray matter" in the spinal cord?

Gray matter is the inner part of the spinal cord, shaped like a butterfly or letter "H" in cross-section. It contains neuronal cell bodies, interneurons, and the beginning and end points of motor and sensory neurons.

7. What is the "white matter" in the spinal cord?

White matter forms the outer layer of the spinal cord. It consists primarily of myelinated axons, which appear white due to their myelin sheaths. These axons form tracts that carry signals up and down the spinal cord.

8. What is the central canal in the spinal cord?

The central canal is a small, hollow tube that runs through the center of the spinal cord. It contains cerebrospinal fluid and is continuous with the ventricular system of the brain.

9. How does the thickness of the spinal cord vary along its length?

The spinal cord is not uniform in thickness. It has two enlargements: the cervical enlargement (corresponding to the arms) and the lumbar enlargement (corresponding to the legs). These areas contain more neurons to control limb movements.

10. What is the conus medullaris?

The conus medullaris is the tapered, cone-like end of the spinal cord, typically located at the level of the L1-L2 vertebrae in adults. Below this point, the spinal nerves continue as the cauda equina.

11. What are the main functions of the spinal cord?

The spinal cord has three primary functions: 1) Conducting sensory information from the body to the brain, 2) Conducting motor commands from the brain to the body, and 3) Serving as a reflex center for certain automatic responses.

12. How does the spinal cord differ from the brain?

While both are part of the central nervous system, the spinal cord primarily serves as a conduit for nerve signals between the brain and the rest of the body. The brain, on the other hand, is the main center for processing information, decision-making, and controlling bodily functions.

13. How does information travel faster in the spinal cord?

Information travels faster in the spinal cord due to myelination of nerve fibers. Myelin, a fatty substance that wraps around axons, allows for saltatory conduction, where electrical impulses jump between nodes of Ranvier, increasing transmission speed.

14. How does the spinal cord contribute to maintaining posture?

The spinal cord plays a crucial role in posture by continuously receiving sensory input about body position and sending motor commands to muscles. This involves complex reflex circuits and communication with the brain's balance centers.

15. What is the role of glial cells in the spinal cord?

Glial cells in the spinal cord, including astrocytes and oligodendrocytes, provide support and nutrition to neurons, maintain the blood-spinal cord barrier, and produce myelin. They also play a role in immune responses and injury repair.

16. What is a dermatome and why is it important?

A dermatome is an area of skin innervated by sensory fibers from a single spinal nerve. Understanding dermatomes is crucial for diagnosing the level of spinal cord injuries or nerve root problems.

17. How does the spinal cord change as we age?

With aging, the spinal cord may experience some atrophy (shrinkage), decreased blood flow, and loss of some neurons. These changes can affect reflexes, sensation, and motor control to varying degrees.

18. What is a "complete" vs. "incomplete" spinal cord injury?

A complete spinal cord injury results in total loss of sensory and motor function below the level of injury. An incomplete injury means some neural connections remain intact, allowing for some degree of sensation or movement below the injury site.

19. What is the clinical significance of spinal cord levels?

Each spinal cord level corresponds to specific body functions. Understanding these relationships helps clinicians diagnose the location of spinal cord injuries or diseases based on a patient's symptoms.

20. How does the spinal cord protect itself from injury?

The spinal cord is protected by several layers: the bony vertebrae, tough membranes called meninges (dura mater, arachnoid mater, and pia mater), and cerebrospinal fluid that cushions it from impacts.

21. How many segments does the human spinal cord have?

The human spinal cord has 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Each segment gives rise to a pair of spinal nerves.

22. What is a spinal nerve and how many are there?

Spinal nerves are mixed nerves that carry both sensory and motor information between the spinal cord and specific regions of the body. There are 31 pairs of spinal nerves in humans, corresponding to the 31 spinal cord segments.

23. What are the dorsal and ventral roots of a spinal nerve?

The dorsal root contains sensory nerve fibers that carry information from the body to the spinal cord. The ventral root contains motor nerve fibers that carry commands from the spinal cord to the muscles and glands.

24. What is a spinal reflex and how does it work?

A spinal reflex is a rapid, automatic response to a stimulus that doesn't require brain involvement. It involves a reflex arc: a sensory neuron detects a stimulus, an interneuron in the spinal cord processes the signal, and a motor neuron triggers a response.

25. What is the difference between ascending and descending tracts in the spinal cord?

Ascending tracts carry sensory information from the body up to the brain, while descending tracts carry motor commands from the brain down to the body's muscles and glands.

26. What is the spinal cord and where is it located?

The spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem to the lower back. It is located within the vertebral column (spine), protected by the surrounding bones called vertebrae.

27. How does the spinal cord change during embryonic development?

During embryonic development, the spinal cord forms from the neural tube. It undergoes neurogenesis, cell migration, and differentiation. Initially longer than the vertebral column, it experiences "ascension" relative to the vertebrae as the body grows.

28. How does the blood-spinal cord barrier function?

Similar to the blood-brain barrier, the blood-spinal cord barrier is formed by tight junctions between endothelial cells in blood vessels. It selectively allows nutrients to enter while keeping out potentially harmful substances, maintaining a controlled environment for spinal cord tissue.

29. What is a spinal cord "tract" and how is it organized?

A spinal cord tract is a bundle of axons carrying similar types of information. Tracts are organized into columns: dorsal (posterior) for ascending sensory information, lateral for both ascending and descending signals, and ventral (anterior) primarily for descending motor commands.

30. What is the cauda equina and why is it named this way?

The cauda equina ("horse's tail" in Latin) is a bundle of spinal nerve roots that extend beyond the conus medullaris. It's named for its resemblance to a horse's tail, with nerve roots branching out from the end of the spinal cord.

31. How does the concept of neuroplasticity apply to the spinal cord?

Neuroplasticity, the brain's ability to reorganize itself, also occurs in the spinal cord. After injury, remaining neural circuits can be strengthened or reorganized to compensate for lost functions, forming the basis for rehabilitation strategies.

32. What is spinal shock and how does it differ from spinal cord injury?

Spinal shock is a temporary loss of all reflex activity below the level of a spinal cord injury, lasting hours to weeks. It differs from the injury itself in that some functions may return as the shock subsides, even if the injury is permanent.

33. How do proprioceptive signals from muscles and joints interact with the spinal cord?

Proprioceptive signals from muscle spindles and joint receptors enter the spinal cord through dorsal roots. They contribute to reflexes and ascend to the brain, providing crucial information about body position and movement for coordinated motor control.

34. What is the significance of the corticospinal tract in the spinal cord?

The corticospinal tract is a major descending pathway that carries motor commands from the cerebral cortex to the spinal cord. It's crucial for voluntary movement, especially fine motor control of the hands and fingers.

35. How does the autonomic nervous system interact with the spinal cord?

The spinal cord contains autonomic neurons in the thoracic and lumbar regions (sympathetic) and sacral region (parasympathetic). These neurons receive input from higher brain centers and regulate involuntary functions like heart rate, digestion, and blood pressure.

36. How does the spinal cord contribute to pain perception?

The spinal cord is crucial in pain perception. Nociceptive (pain) signals enter through dorsal roots and can trigger immediate reflexes. The signals are also processed and modulated in the dorsal horn before being sent to the brain for conscious perception.

37. What is the role of interneurons in the spinal cord?

Interneurons in the spinal cord play a vital role in processing and integrating sensory information, coordinating motor outputs, and mediating reflexes. They form complex circuits that can modify incoming signals before they reach motor neurons or ascend to the brain.

38. What is syringomyelia and how does it affect spinal cord function?

Syringomyelia is a disorder where a fluid-filled cavity (syrinx) forms within the spinal cord. It can disrupt sensory and motor pathways, leading to symptoms like pain, weakness, and loss of temperature sensation, often in a cape-like distribution on the upper body.

39. How do spinal cord stimulators work in managing chronic pain?

Spinal cord stimulators are implanted devices that send low-level electrical pulses to the spinal cord. These pulses interfere with pain signal transmission to the brain, based on the "gate control theory" of pain, potentially providing relief for certain chronic pain conditions.

40. What is the significance of the spinothalamic tract?

The spinothalamic tract is a major ascending pathway that carries information about pain, temperature, and crude touch from the body to the thalamus in the brain. It's crucial for our ability to perceive and respond to these sensory inputs.

41. How does the spinal cord contribute to thermoregulation?

The spinal cord plays a role in thermoregulation by relaying temperature information from the skin to the hypothalamus and by carrying commands from the hypothalamus to effectors like sweat glands and blood vessels. It also contains some local circuits involved in immediate responses to temperature changes.

42. What is a "central pattern generator" in the spinal cord?

Central pattern generators are neural circuits within the spinal cord that can produce rhythmic motor patterns, such as those involved in walking or swimming, without input from the brain. They demonstrate the spinal cord's ability to generate complex motor outputs independently.

43. How does the spinal cord change in conditions like multiple sclerosis?

In multiple sclerosis, the immune system attacks the myelin sheaths in the central nervous system, including the spinal cord. This demyelination can disrupt signal transmission, leading to various sensory and motor symptoms depending on the affected areas.

44. What is the role of neurotransmitters in spinal cord function?

Neurotransmitters in the spinal cord, such as glutamate, GABA, glycine, and various neuropeptides, mediate communication between neurons. They play crucial roles in transmitting sensory information, coordinating motor outputs, and modulating pain signals.

45. How does the spinal cord contribute to proprioception?

The spinal cord receives proprioceptive information from muscles, tendons, and joints through dorsal root ganglia. This information is processed in the dorsal column nuclei and sent to the brain, contributing to our sense of body position and movement. Some proprioceptive reflexes are also mediated at the spinal level.

46. What is a "brown-séquard syndrome" and what does it tell us about spinal cord organization?

Brown-Séquard syndrome results from a hemisection (injury to one side) of the spinal cord. It causes ipsilateral loss of proprioception and motor function, with contralateral loss of pain and temperature sensation. This pattern demonstrates the crossed nature of certain spinal tracts.

47. How does the spinal cord contribute to the stretch reflex?

The stretch reflex, like the knee-jerk reflex, is mediated by the spinal cord. When a muscle is stretched, sensory neurons in muscle spindles activate, synapsing directly onto motor neurons in the spinal cord. This causes rapid contraction of the stretched muscle, all without involving the brain.

48. What is the clinical significance of the "spinal cord level of injury"?

The spinal cord level of injury refers to the lowest spinal cord segment with normal function. It's crucial for predicting what bodily functions may be affected, potential for recovery, and appropriate treatment strategies. Higher-level injuries generally result in more extensive paralysis and loss of function.

49. How does the concept of "spinal cord plasticity" influence rehabilitation strategies?

Spinal cord plasticity refers to the ability of spinal neural circuits to adapt and reorganize. This concept has led to rehabilitation strategies that aim to strengthen and retrain remaining neural pathways after injury, potentially improving function even in chronic spinal cord injury cases.

50. What is the role of the spinal cord in the "fight or flight" response?

The spinal cord contains preganglionic sympathetic neurons in the thoracolumbar region. During a "fight or flight" response, these neurons receive signals from the brain and activate the sympathetic nervous system, leading to increased heart rate, blood pressure, and other stress responses.

51. How does the spinal cord contribute to bladder control?

The spinal cord contains neural circuits that regulate bladder function. Sensory neurons detect bladder fullness, and motor neurons control the bladder muscles. The sacral spinal cord contains the main micturition center, which coordinates voluntary control with reflex mechanisms for urination.

52. What is a "spinal cord concussion" and how does it differ from other injuries?

A spinal cord concussion is a transient neurological deficit following trauma, without detectable structural damage to the spinal cord. Unlike more severe injuries, symptoms typically resolve completely within 48 hours. It demonstrates the spinal cord's sensitivity to mechanical forces even without permanent damage.

53. How does the spinal cord contribute to chronic pain conditions?

The spinal cord can play a role in chronic pain through several mechanisms: central sensitization (increased responsiveness of pain circuits), altered inhibitory controls, and structural changes in neural circuits. Understanding these processes is crucial for developing targeted pain therapies.

54. What is the significance of the "spinal shock" phase after spinal cord injury?

Spinal shock is a temporary loss of all reflexes below the level of injury, typically lasting days to weeks. It's significant because it can mask the true extent of injury initially. As spinal shock resolves, some reflexes may return, providing important prognostic information.

55. How does the concept of "neuronal pools" apply to spinal cord function?

Neuronal pools in the spinal cord are groups of interconnected neurons that work together to perform specific functions. These pools can integrate multiple inputs, amplify signals, and coordinate complex motor patterns. Understanding neuronal pools is crucial for comprehending how the spinal cord processes information and generates outputs.