All spinal cord injury levels receive sensory information from different areas of skin and innervate different muscles.
The spinal cord is the passageway that allows for communication between the brain and body.
After a spinal cord injury, that connection is disrupted, and areas below the level of injury may no longer receive signals from the brain.
This article is going to go over what functions are affected at each level of the spinal cord.
Let’s get started!
Spinal Cord Injury Levels
photo credit: Ralf Stefan
When determining your level of injury, a physician will test your sensory and motor functions with the International Standards Examination.
Each spinal cord segment has a dermatome that receives sensory information from a specific area of the skin.
Additionally, each spinal cord segment has a myotome that innervates specific muscles. Most muscles are innervated by more than one spinal root.
Level of injury refers to the lowest area of the spinal cord where the individuals exhibits normal sensory and motor functions.
The spinal cord is divided into 5 regions (from top to bottom):
The higher your level of injury, the more functions will be affected.
For example, a cervical spinal cord injury is not only going to affect functions innervated at the cervical region, but also functions associated with the thoracic, lumbar, and sacral levels because brain signals cannot pass through the injury site.
Additionally, all functions innervated above the site of injury will be normal and unaffected.
In the next section, we’ll go over what functions are affected at each level of injury.
Cervical Spinal Cord Injury
The cervical region consists of 8 spinal cord segments that make up your neck, but an injury to this region can affect your entire body.
Cervical spinal cord injury the most debilitating type of SCI because all cervical SCIs result in quadriplegia.
Quadriplegia is when both the arms and legs are paralyzed, and it is the result of nearly 60% of all spinal cord injuries.
The cervical nerve roots innervate the neck, shoulders, arms, and fingers.
- C1 – The C1 segment of the spinal cord does not have a dermatome; however, because it is the uppermost segment of the spinal cord, sensorimotor functions throughout the entire body will be affected. C1 spinal cord injuries require immediate medical attention and are typically fatal.
- C2 – The C2 segment is connected to sensation at the back of the head, ears, and upper area of the neck. The muscles directly affected by C2 spinal cord injury affect your ability to nod your head up and down.
- C3 – The C3-C5 nerve roots innervate the diaphragm, which is essential for breathing. Injury to the C3 nerve roots will also affect sensation at the neck as well as the ability to tilt your head right and left.
- C4 – The C4 dermatome affects sensation at the shoulders, upper back, and upper chest. The C4 myotomes affect the ability to raise your shoulders.
- C5 – The C5 nerve roots affect sensation at the outer area of your upper arm and the ability to raise your arm up (shoulder abduction) and bend the elbows (elbow flexion).
- C6 – The C6 dermatome affects sensation at the outer forearms down to the thumbs and part of the index fingers. The C6 myotomes affect elbow flexion and wrist extension.
- C7 – The C7 nerve roots affect sensation at the middle finger. It affects the ability to straighten out your elbows and bend your wrists.
- C8 – The C8 nerve roots affect sensation at the ring and pinky fingers. The myotomes at the C8 level affect the ability to bend your fingers and grab objects.
Thoracic Spinal Cord Injury
After the cervical region is the thoracic region.
This region of the spinal cord is made up of 12 segments labeled T1-T12.
Thoracic spinal cord injuries primarily affect the muscles that make up your trunk and chest, which affect balance, posture, breathing, and coughing.
- T1 – The T1 dermatome affects sensation of the inner forearm. The T1 myotomes affect the ability to separate your fingers (finger abduction).
- T2 – T2 nerve roots affect sensation near the armpit and upper chest.
- T3 – T3 nerve roots affect sensation at the upper chest and back.
- T4 – T4 nerve roots affect sensation at the chest and back. It is generally aligned with the 4th intercostal space (the space between the 4th and 5th ribs), level with the nipples.
- T5 – T5 nerve roots affect sensation at the chest and back between the 4th and 6th dermatomes.
- T6 – T6 nerve roots affect sensation between the 5th and 7th dermatomes. This is generally the area where the abdomen starts.
- T7 – T7 nerve roots affect sensation at the trunk between the 6th and 8th dermatomes.
- T8 – T8 nerve roots affect sensation at the trunk between the 7th and 9th dermatomes.
- T9 – T9 nerve roots affect sensation at the trunk between the 8th and 10th dermatomes.
- T10 – The T10 dermatome generally aligns with the belly button and will affect sensation at the lower trunk between the 9th and 11th dermatomes.
- T11 – T11 nerve roots affect sensation at the lower trunk between the 10th and 12th dermatomes.
- T12 – The T12 dermatome affects sensation at the very bottom of your abdomen.
Lumbar Spinal Cord Injury
Following the thoracic region is the lumbar region, which consists of 5 segments.
Lumbar spinal cord injuries only affect your lower body.
- L1 – The L1 nerve roots affect sensation at the pelvic region.
- L2 – The L2 dermatome affect sensation at the upper thighs. The L2 myotomes affect the hip flexors, which are the muscles near the top of your thighs that allow you to move your upper legs.
- L3 – L3 nerve roots affect sensation at the lower thighs and knees. The L3 myotomes affect the ability to straighten the knees (knee extension).
- L4 – The L4 dermatome affects sensation at the front and inner regions of the lower legs. The L4 myotomes affect the ability to lift the foot upwards (ankle dorsiflexion).
- L5 – The L5 dermatomes affect sensation at the outer areas of the lower legs down to the big, second, and middle toes. The L5 myotomes affect the ability to bend and straighten the big toe.
Sacral Spinal Cord Injury
The sacral region of the spinal cord is consists of 5 spinal cord segments.
- S1 – The S1 dermatome affects sensation at the fourth and pinky toes, heel, and part of the calf. An S1 spinal cord injury will affect the ability to extend the ankle so that the foot points down (ankle plantarflexion)
- S2 – The S2 dermatome affects the majority of sensation at the back of the legs. The S2 myotome affects the ability to bend the knees (knee flexion). The S2, S3, and S4 spinal nerves innervate the pelvic cavity, which is responsible for sexual, bladder, and bowel-related functions.
- S3 – The S3 dermatome affects sensation around the medial buttocks.
- S4 and S5 – The S4 and S5 spinal cord segments affect the perianal area.
Coccygeal Spinal Cord Injury
At the very end of the spinal cord is a single coccygeal nerve.
This nerve innervates the skin around the tailbone.
Understanding Spinal Cord Injury Levels and Functions
Functional loss after spinal cord injury depends on the severity and level of injury.
For example, if you have a severe C4 spinal cord injury, you can experience complete paralysis from the shoulders down.
However, if you have a mild, incomplete C4 spinal cord injury, some neural pathways between the brain and body are spared, and you’ll be able to control some functions below your shoulders.
Generally, the higher your level of injury, the more functions will be affected.
That’s a wrap! Hopefully, this article helped you better understand spinal cord injury levels and what sensorimotor functions they affect.
Featured image: ©iStock.com/sankalpmaya