The level of a spinal cord injury refers to the lowest region of the spinal cord where normal motor control and sensation exist. Knowing one’s level of injury will help individuals determine what functions may be affected after an injury.
To help you understand what functions correspond to each of the spinal cord injury levels, this article will discuss:
- What your level of injury means
- Cervical spinal cord injury levels (C1-C8)
- Thoracic spinal cord injury levels (T1-T12)
- Lumbar spinal cord injury levels (L1-L5)
- Sacral spinal cord injury levels (S1-S5)
- Coccygeal spinal cord injury
What Your Level of Spinal Cord Injury Means
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 be able to effectively send or receive communication from the brain. Therefore, it’s essential to understand what your level of injury is to determine which functions may or may not be affected.
When determining your level of injury, a physician will test your sensory and motor functions using the International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), also called the ASIA exam.
Each level of the spinal cord receives sensory information from a different area of skin called a dermatome. This information travels through the spinal cord to the brain for processing and to allow the brain to decide how to appropriately respond.
Additionally, each level of the spinal cord sends motor signals from the brain to different muscles throughout the body. The muscles designated to each level of the spinal cord are called myotomes.
In the next section, you’ll learn more about how different levels of spinal cord injuries affect different dermatomes and myotomes. Before we get there, let’s discuss the anatomy of the spinal column.
The spinal cord is protected by the spine, which is composed of 33 vertebrae. Peripheral nerves (which connect the central nervous system to the rest of the body) branch out from the spinal cord in pairs and exit above or below their corresponding vertebrae (C1-C7 spinal nerves exit above the corresponding vertebrae, while the rest of the spinal nerves from C8 downward all exit below). For example, the C3 spinal nerves exit above the C3 vertebrae, while the T5 spinal nerves exit below the T5 vertebrae.
For each spinal cord level, there is a pair of spinal nerves (31 pairs in total), with one nerve going to the left side of the body and one going to the right. Furthermore, for each spinal nerve within the pair, there is a sensory nerve root that sends messages from the body to the brain, and a motor nerve root that sends messages from the brain to the corresponding area of the body. To give an example, at the C3 level of the spinal cord, there are nerve roots coming to (sensory) and from (motor) the spinal cord on both the right and left sides of the spine.
Additionally, the spinal cord is divided into 5 regions (from top to bottom):
The higher your level of injury, the more functions will be affected. This occurs because motor signals from the brain and sensory signals from the body cannot travel past damaged regions of the spinal cord. As a result, all motor functions and sensations innervated below the level of injury may be affected, depending on the severity of the injury (whether the spinal cord was completely severed or if some connections were left intact).
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.
However, 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 Level of Spinal Cord Injury
The cervical region of the spinal cord consists of 8 pairs of cervical nerves in your neck area. Generally, a cervical-level spinal cord injury is the most debilitating because it has the potential to affect the entire body. Nearly 60% of all spinal cord injuries are cervical-level injuries.
Complete cervical spinal cord injuries result in quadriplegia, which describes paralysis in both the upper and lower limbs. The peripheral nerves that branch out of the cervical region of the spinal cord primarily innervate the neck, shoulders, arms and hands, providing both muscular control and sensation to these areas.
However, because all functions innervated below the level of injury can also be affected, individuals with cervical spinal cord injuries will frequently experience weakness or paralysis in the trunk and lower body as well.
Below, we’ll discuss which functions correspond to each specific level of the cervical spinal cord:
- C1 – The C1 segment of the spinal cord is unique in that it does not typically have a dermatome; however, because it is the uppermost segment of the spinal cord, most sensory and motor functions throughout the body may be affected.
- 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 myotome affects 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 Levels of Spinal Cord Injury
Below the cervical region is the thoracic region of the spinal cord. This region of the spinal cord consists of 12 levels.
Thoracic-level spinal cord injuries primarily affect the muscles that make up your trunk and chest. As a result, individuals may experience difficulties with balance, posture, breathing, and coughing. The thoracic nerves primarily affect sensation of the chest and abdomen, with T3-T12 innervating progressively lower areas of the trunk.
Because the thoracic region is located below the cervical region, all functions innervated by the cervical region will be unaffected. Therefore, individuals with SCIs below the T1 level should be able to use their hands and arms normally.
The functions directly affected at each level of thoracic spinal cord injury include:
- 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 T4 and T6 dermatomes.
- T6 – T6 nerve roots affect sensation between the T5th and T7th dermatomes. This is generally the area where the abdomen starts.
- T7 – T7 nerve roots affect sensation at the trunk between the T6 and T8 dermatomes.
- T8 – T8 nerve roots affect sensation at the trunk between the T7 and T9 dermatomes.
- T9 – T9 nerve roots affect sensation at the trunk between the T8 and T10 dermatomes.
- T10 – The T10 dermatome generally aligns with the belly button and will affect sensation at the lower trunk between the T9 and T11 dermatomes.
- T11 – T11 nerve roots affect sensation at the lower trunk between the T10 and T12 dermatomes.
- T12 – The T12 dermatome affects sensation at the very bottom of your abdomen.
Lumbar Levels of Spinal Cord Injury
Following the thoracic region is the lumbar region. This region of the spinal cord consists of 5 levels.
Lumbar spinal cord injuries only affect the lower body, so individuals should have unaffected motor control and sensation in their hands, arms, and trunk. Because individuals with lumbar spinal cord injuries experience weakness or paralysis in their legs, they may struggle with walking and balance.
The functions affected at each level of the lumbar spinal cord include:
- 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 raise your upper legs (such as during walking or marching).
- 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 front and 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 consists of 5 levels. Individuals with sacral-level spinal cord injuries have unaffected upper body functions and partial leg functions.
Because bowel and bladder functions are innervated by the bottommost segments of the sacral spinal cord, individuals with nearly any level of spinal cord injury are likely to experience bowel and bladder problems.
Functions linked to sacral levels of the spinal cord include:
- 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. As a result, individuals may experience pain, discomfort, or complete loss of sensation in the tailbone area.
However, because this nerve makes up the lowest level of the spinal cord, individuals should have normal motor control and sensation throughout most of their bodies.
Spinal Cord Injury Levels and Functions: Key Points
Functional loss after spinal cord injury depends on the severity and level of injury. The severity of your SCI will determine to what extent functions innervated below your level of injury are affected. Likewise, the level of injury will determine which functions may or may not be affected.
We hope this article helped you better understand spinal cord injury levels and what sensorimotor functions they affect.
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