The spine is a long column of 33 small back bones called vertebrae that are connected together by strong fibrous ligaments and shock-absorbing fibrous discs. The spine is part of the skeleton.

The spine supports the weight of the body, allows the torso to move, anchors many of the muscles, and protects the spinal cord from damage. The spine is also called the vertebral column, spinal column, or backbone.

The five major areas of the spine.¹

Areas of the spine:

• The cervical spine has 7 cervical vertebrae and forms the neck.
• The thoracic spine has 12 thoracic vertebrae and forms the upper and mid back.
• The lumbar spine has 5 lumbar vertebrae and forms the low back.
• The sacrum is made up of 5 sacral vertebrae that are fused together to form a wedge-shaped bone that is part of the pelvis.
• The coccyx is made up of 3 to 5 coccygeal vertebrae that are fused together to form the tailbone.

The spine has a hollow canal in its centre that runs the length of the spine from the base of the skull down to the sacrum called the spinal canal. The spinal canal contains the spinal cord.

The spinal cord is divided into 31 segments, which each give rise to a pair of spinal nerves.³

The spinal cord is a long bundle of nerve tissue that is located in the spine. It is the main pathway for nerve signals travelling between the brain and the rest of the body. It is also the centre for the body’s reflexes.

The spinal cord is made up of millions of microscopic nerve cells. Protective layers of tissue called meninges cover the spinal cord and a special fluid called cerebrospinal fluid cushions the spinal cord within the spine.

The path of the spinal cord

The spinal cord begins at the base of the skull, where it connects to the brain through the brainstem. The spinal cord then runs down through the spine’s hollow central spinal canal.

The spinal cord is shorter than the spine, so it does not travel the full length of the spine. It ends at a point called the conus medullaris near the first or second lumbar vertebra. From this point down, spinal nerves branching from the end of the spinal cord sit within the spinal canal in a bundle called the cauda equina.

Spinal cord segments

Spinal nerves extending from the spine.⁴

The spinal cord is divided into 31 nerve segments from top to bottom:

• 8 cervical segments

• 12 thoracic segments

• 5 lumbar segments

• 5 sacral segments

• 1 coccygeal segment

Each segment is a part of the spinal cord that gives rise to a pair of spinal nerves (one right and one left). The spinal nerves exit the spine through archways between the bones and continue outward to become the nerves of the arms, legs, and body.

The spinal cord is part of the nervous system. The nervous system is the body’s main communication system. It allows messages to be passed from one area of the body to another. This is possible because of special cells called neurons.

Neurons are cells that transmit nerve signals in the body.⁵

Neurons

Neurons are the main cells of the nervous system. Neurons generate, conduct, and pass along nerve signals within the nerves, spinal cord, and brain.

Neurons communicate with other cells (such as other neurons, muscle cells and sensory receptors) through connections called synapses. These connections allow the cells to pass electrical and chemical nerve signals to other cells.

The brain and spinal cord together make up the central nervous system. The central nervous system is the main control system of the body.

• The brain is the command center of the nervous system. It sends commands to the rest of the body which control movement, breathing, and other functions. The brain also receives signals about sensations from the whole body, which it interprets to help manage bodily functions.
• The spinal cord is the main pathway for information travelling between the brain and the rest of the body. It acts like a highway along which nerve signals can travel between distant areas of the body. This includes both commands sent from the brain to the body and sensations from the body to the brain. The spinal cord is also the center for reflexes (a reflex is a muscle response to a touch stimulus).

The main functions of the spinal cord are to pass along information related to movement, sensation, reflexes, and organ function.

Movement

The spinal cord provides a pathway for movement commands to travel from the brain to the muscles. This is called motor function. Neurons that send movement commands are called motor neurons.

Movement begins in special movement (motor) areas of the brain that plan and generate nerve signals to create movements. Motor neurons from this area of the brain have long nerve fibers (axons) that project down the spinal cord, where they pass their signals to other neurons that travel out of the spinal cord and into the body. These neurons connect with muscle cells to pass along movement commands that tell the muscles to contract.

Sensation

The spinal cord is also a pathway for sensations traveling from the body to the brain. This is called sensory function. Neurons that send sensory information are called sensory neurons.

The body’s tissues (like the skin, muscles, and organs) contain special sensory receptors. Sensory receptors detect sensations such as touch, pressure, vibration, or temperature. When a sensation is detected, a signal is sent along the nerve fiber (axon) of a sensory neuron to the spinal cord.

The signal then travels up the spinal cord where it is passed along to other neurons in the brainstem and brain. When these signals reach the sensation centers in the brain, they are interpreted and the person feels the sensation.

Reflexes

Pain signals from touching something hot travels to the spinal cord and back to the muscles without going to the brain first.⁷

Reflexes are automatic responses that happen in the spinal cord and do not travel to the brain first. For example, when the tendon below the knee cap is tapped, it causes the knee jerk reflex.

Spinal reflexes involve neurons for both sensation and movement. When certain sensory receptors are activated, a nerve signal is sent through sensory neurons to the spinal cord. In the spinal cord, the signal is passed on to motor neurons involved in the reflex movement. The motor neurons then send a signal out of the spinal cord to the muscles, causing an immediate muscular response.

Internal organ (autonomic) function

The spinal cord also plays a role in controlling some of the functions of the internal organs through the autonomic nervous system.

The autonomic nervous system

The autonomic nervous system controls largely unconscious bodily processes such as blood pressure, heart rate, breathing rate, body temperature, digestion, bladder, bowel, and sexual function.

It has two divisions:

• The sympathetic nervous system prepares the body for stressful or emergency situations. It is often called the ‘fight or flight’ system, because it prepares the body for action. For example, it increases heart rate and slows digestion.
• The parasympathetic nervous system prepares the body for normal, non-emergency situations. It is often called the ‘rest and digest’ system, because it allows the body to restore itself. For example, it slows heart rate and increases digestion.

The sympathetic and parasympathetic systems have different (and often opposite) effects on the organs and work together to control bodily functions according to the situation.

The autonomic nervous system controls various body functions.^8-11

Neurons that control the function of the autonomic nervous system begin in the brain or brainstem. Some of these neurons leave in the cranial nerves (nerves that arise directly from the brain and brainstem), and the rest travel down the spinal cord, where they branch from certain areas:

• The nerves of the sympathetic nervous system arise from the thoracic and lumbar spinal cord from the levels of T1 to L2.
• Some of the nerves of parasympathetic nervous system arise from the sacral spinal cord, from S2 to S4 (the others leave from the brainstem).

After leaving the spinal cord, the neurons connect (synapse) with other neurons in clusters of nerve cells called ganglia. From these ganglia, motor neurons project out to the organs and signal changes to their function.

Spinal Cord Injury Basics

Bican O, Minagar A, Pruitt AA. The spinal cord: a review of functional neuroanatomy. Neurol Clin. 2013 Feb;31(1):1-18.

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 6th ed. Philadelphia: Lippincott Williams & Wilkins, 2010.

Image credits

1. Image by SCIRE Community Team
2. Spinal cord ©Vectors Market, CC BY 3.0 US
3. Image by SCIRE Community Team
4. BIO 120 Lab Spinal Cord 035 ©djneight, CC BY-NC-ND 2.0
5. Image by SCIRE Community Team
6. Lifting weights ©skeeze, CC0 1.0
7. Imgnotraçat arc reflex eng ©MartaAguayo, CC BY-SA 3.0
8. Lung ©mungang kim, CC BY 3.0 US
9. Heart ©Laymik, CC BY 3.0 US
10. Digestive System ©Design Science, CC0 1.0
11. Excretory system ©Olena Panasovska, CC BY 3.0 US

A spinal cord injury (SCI) occurs when the spinal cord or the nerves at the end of the spinal canal are damaged and causes changes to how the body works.

SCI can be a life-changing injury. It can affect many different body systems and often causes permanent changes to strength, sensation, and other functions below the injury. There are many different types of spinal cord injury and the effects of the injury can be very different from one person to the next.

SCI can have many causes, which are commonly divided into traumatic or non-traumatic causes.

Traumatic spinal cord injury

Traumatic spinal cord injury is damage to the spinal cord that is caused by direct trauma from an outside force. This is usually caused by a sudden blow to the spine (such as something falling on the spine), compression of the spine (from the force of a car of a car accident, for example) or a penetrating injury (such as a gunshot wound).

A broken spinal bone (vertebra) in the neck causes pieces of bone or tissue to move out of place, damaging the fragile nearby spinal cord.²

 

 

How does damage to the spine cause spinal cord injury?

A forceful blow or compression of the spine can cause the spinal bones (vertebrae) or other tissues (such as the gel-like discs between the vertebrae) to break and/or dislocate. The spinal cord is located within the hollow center of the spine, so if pieces of bone or tissue move out of place and pressure and or excessive swelling take place they can put pressure on, tear, or otherwise damage the fragile spinal cord.

Although a large force is usually needed to damage the spine, smaller forces can also cause traumatic injuries in people with certain medical conditions. For example, people with osteoporosis have weak bones that can break from lesser forces, such as a fall from a standing position.

Non-traumatic spinal cord injury

Non-traumatic spinal cord injury is damage to the spinal cord that is caused by anything other than direct trauma. This includes complications from an illness, degeneration of the spine from arthritis, or certain conditions that people are born with (like spina bifida). Non-traumatic injuries often develop gradually over time, compared to the sudden onset of traumatic injuries.

Common causes of spinal cord injury

Spinal cord injury can cause a wide range of different signs and symptoms. The effects of the injury can be very different from one person to the next, depending on the person and the characteristics of the injury. Symptoms can be temporary or permanent and may change over time.

The earliest period after a spinal cord injury often involves a phase of shock. This is usually a temporary period that resolves after a few days or weeks.

After shock resolves, the longer-lasting symptoms of spinal cord injury may be experienced. These may include the following symptoms.

Changes in sensation

Each level of the spinal cord provides sensation to a different part of the body.⁴

Changes in sensation occur below the spinal cord injury. This may include total or partial loss of sensation as well as abnormal sensations like tingling, numbness, or pain.

The amount of sensation affected depends on whether the injury is complete or incomplete and the level of the injury. Each level of injury causes changes to the sensation in a specific area of the body. For example, an injury at C3 affects sensation from the neck down, whereas an injury at L1 affects sensation of the legs and groin.

People with incomplete spinal cord injuries may have only parts of their sensation below the injury affected. Those with complete injuries may also have some sensation in select areas below the injury, which are called zones of partial preservation.

Changes in strength and muscle control

Changes to the strength and control of the muscles also happens below the injury. This can include both paralysis (loss of movement) and weakness of the muscles.

The amount of strength and movement affected depends on whether the injury is complete or incomplete and the level of injury. Each level of injury affects specific muscles. For example, an injury at C3 can cause paralysis from the neck down, whereas an injury at L1 can cause paralysis of the hips and legs.

People with incomplete injuries may have strength in some of the muscles below the injury.

Changes in breathing

Some people with SCI need help with breathing and coughing.⁵                                   

People who have cervical and thoracic spinal cord injuries may experience problems with breathing. This is because the diaphragm (the main muscle of breathing), as well as the muscles of the neck, chest, and abdomen are needed to breathe and cough normally. This can affect the ability to breathe, cough, and clear mucus from the lungs without assistance.

Injuries at C5 and above affect the diaphragm and sometimes people with injuries at these levels cannot breathe long-term without the support of a ventilator or other device. People with lower cervical and thoracic injuries may also experience problems breathing because they cannot control other important muscles of the neck and rib cage that help with breathing and coughing.

Changes in bladder function

There are a number of changes to bladder function after spinal cord injury, including inability to control urination. Many people will use catheters and other treatments to control their bladder functions after spinal cord injury, which may predispose them to developing urinary tract infections if not done carefully.

Changes in bowel function

Bowel problems are also common after spinal cord injury and can include an inability to control bowel functions (bowel incontinence), constipation, and other problems. Many people use a personalized bowel routine, which is a schedule that keeps bowels moving at a regular rate (using special foods or supplements), to maintain healthy bowel function after spinal cord injury.

Changes in control of blood pressure and heart rate

The autonomic nervous system is part of the nervous system that controls the unconscious functions of the internal organs like the heart and circulation (blood vessels). Spinal cord injury can cause changes to how the autonomic nervous system functions, which may alter the body’s ability to control blood pressure, temperature, and heart rate, as well as cause conditions like orthostatic hypotension (a sudden drop in blood pressure when moving into an upright position) and autonomic dysreflexia.

Changes in sexual function

Changes in sexual function are also common after spinal cord injury. This may include difficulties with orgasm, ejaculation, and erection. These changes depend on the individual and their particular injury.

Complete spinal cord injury

The spinal cord, conus medullaris, and cauda equina.⁷

A complete spinal cord injury is when there is a total loss of strength and sensation below the spinal cord injury. This must include complete loss of movement or sensation of the anus (S4 and S5).

In some cases, people with complete injuries may still have some areas of strength or sensation below level of injury (but not including S4 and S5). These areas are known as zones of partial preservation. 

Incomplete spinal cord injury

An incomplete spinal cord injury is when some strength and/or sensation remain below the spinal cord injury. This must include some movement or sensation of the anus (S4 and S5).

Incomplete injuries can have very different symptoms depending how much and in what way the injury has affected the spinal cord. These have traditionally been described as different ‘syndromes’, but more often now are best described by the characteristics of the person’s unique symptoms.

You may hear your healthcare providers use these terms:

Neurological level of injury is the lowest level of the spinal cord that has normal function, which is confirmed using strength and sensation tests. Level of injury is an important classification that, together with whether the injury is complete or incomplete, can be used to describe how much physical function a person is likely to have.

The International Standards for Neurological Classification of Spinal Cord Injury (ISCNSCI) exam (often called the American Spinal Injury Association (ASIA) exam) is a physical exam that is used to classify spinal cord injuries. It determines both the neurological level of injury and the completeness of the injury.

During this exam, a health provider such as a doctor or physiotherapist will carefully test for sensation and strength at specific points on the body and use the exam findings to determine the characteristics of the injury. These tests include:

• Testing for ‘light touch’ sensation (if you can feel the touch of a cotton swab or tissue and whether it feels normal)
• Testing for ‘pin prick’ sensation (if you can feel whether the touch of a safety pin is sharp or dull and whether it feels normal)
• Testing for muscle strength of specific muscles (if you can resist against certain movements applied by the health provider)
• Testing for movement and sensation of the anus. This is a very important test because it is the only way we can determine if a person’s injury is complete or incomplete). It is testing the last nerves to leave the spinal cord (S4 and S5).

Testing muscle strength as part of the ISCNSCI Exam.¹¹

ASIA Impairment Scale (AIS)

The ASIA Impairment Scale (AIS) describes the completeness of the injury. This scale identifies whether a person has any movement or sensation in the lowest levels of the spinal cord (S4 and 5) and what movement or sensation they have below the neurological level of injury. If you are interested in learning how healthcare providers are trained to do the test, you can visit http://asialearningcenter.com/.

Spinal cord injury is a relatively rare condition. Although estimates vary by country and study, it is estimated 86,000 people were living with SCI in Canada in 2010. New injuries were estimated to be 4,300 per year in 2010.

It is best to discuss all treatment options with your health providers to find out which treatments are suitable for you.

For a review of what we mean by ‘strong’, ‘moderate’, and ‘weak’ evidence, please see SCIRE Community Evidence Ratings.

Spinal Cord Anatomy

Understanding Rehabilitation

Brodell DW, Jain A, Elfar JC, Mesfin A. National trends in the management of central cord syndrome: an analysis of 16,134 patients. Spine J. 2015 Mar 1;15(3):435-42. doi: 10.1016/j.spinee.2014.09.015. Epub 2014 Sep 28.

Van Middendorp JJ, Goss B, Urquhart S, Atresh S, Williams RP, Schuetz M. Diagnosis and Prognosis of Traumatic Spinal Cord Injury. Global Spine Journal. 2011;1(1):1-8. doi:10.1055/s-0031-1296049.

Kirshblum SC, Burns SP, Biering-Sorensen F, Donovan W, Graves DE, Jha A, Johansen M, Jones L, Krassioukov A, Mulcahey MJ, Schmidt-Read M, Waring W. International standards for neurological classification of spinal cord injury (revised 2011). J Spinal Cord Med. 2011 Nov;34(6):535-46. doi: 10.1179/204577211X13207446293695.

American Spinal Injury Association (ASIA) Learning Center. International Standards for Neurological Classification of spinal cord injury (ISNCSCI). Available from: http://lms3.learnshare.com/Images/Brand/120/ASIA/International%20Standards%20Worksheet.pdf. Accessed April 13, 2016.

Noonan VK, Fingas M, Farry A, Baxter D, Singh A, Fehlings MG, Dvorak MF. Incidence and prevalence of spinal cord injury in Canada: a national perspective. Neuroepidemiology. 2012;38(4):219-26.

New PW, Cripps RA, Bonne Lee B.Global maps of non-traumatic spinal cord injury epidemiology: towards a living data repository. Spinal Cord. 2014 Feb;52(2):97-109.

Farry A, Baxter D. The Incidence and Prevalence of Spinal Cord Injury in Canada: Overview and estimates based on current evidence. Rick Hansen Institute and Urban Futures Institute 2010.

McCammon JR, Ethans K. J Spinal Cord Med. 2011;34(1):6-10. Spinal cord injury in Manitoba: a provincial epidemiological study.

Warren S, Moore M, Johnson MS. Traumatic head and spinal cord injuries in Alaska (1991-1993). Alaska Med. 1995 Jan-Mar;37(1):11-9.

Image credits

1. Spinal cord ©Vectors Market, CC BY 3.0 US
2. Image by SCIRE Community Team
3. Blood Pressure ©Alexander Panasovsky, CC BY 3.0 US
4. Dermatoms © Ralf Stephan, CC0 1.0
5. Image by SCIRE Community Team
6. Excretory system ©Olena Panasovska, CC BY 3.0 US
7. Image by SCIRE Community Team
8. Blausen 0822 SpinalCord ©BruceBlaus, CC BY 3.0
9. Arm ©Jacqueline Fernandes, CC BY 3.0 US
10. Leg ©Bakunetsu Kaito. CC BY 3.0 US
11. Image by SCIRE Community Team