Difference Between Dermatome and Myotome

Main Difference – Dermatome vs Myotome

A spinal nerve is a mixed nerve, carrying motor, sensory, and autonomic nerve impulses between the body and the spinal cord. There are 31 spinal nerve pairs, leaving the spinal cord in humans. Each spinal nerve starts from a nerve root. Dermatome and myotome are two areas of the body that are served by spinal nerves. The main difference between dermatome and myotome is that dermatome is a distinct area of skin innervated by a particular spinal root whereas myotome is a group of muscles innervated by a particular spinal root. Both dermatome and myotome are innervated with a single spinal nerve. The knowledge about the distribution of both dermatome and myotome is important in accessing the spinal lesions while ascertaining the levels of spinal cord injury.     

Key Areas Covered

1. What is a Dermatome
     – Definition, Supply of Spinal Nerves, Importance
2. What is a Myotome
    – Definition, Supply of Spinal Nerves, Importance
3. What are the Similarities Between Dermatome and Myotome
    – Outline of Common Features
4. What is the Difference Between Dermatome and Myotome
    – Comparison of Key Differences

Key Terms: Dermatome, Muscles, Myotome, Senses, Skin, Spinal Nerve, Voluntary Muscular Movements

What is a Dermatome

Dermatome refers to an area of skin innervated by the nerves from a single spinal root. On that account, the skin is a collection of dermatomes. All spinal nerves occur as pairs (left and right). They start with two nerve roots: the ventral nerve root (anterior), innervating the motor functions and the dorsal (posterior) nerve root, innervating the sensory functions. Both anterior and posterior nerve roots combine in order to form a spinal nerve. 31 spinal nerves can be divided into 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerves. Each spinal nerve is composed of a dermatome, except for the first cervical nerve. The dermatomes of the spinal nerves are shown in figure 1.

Figure 1: Dermatomes

The C2 to C4 nerves innervate the regions in the skin of the neck. The C5 to T1 nerves innervate the arms. The T2 to L2 nerves innervate the chest and abdomen. The L3 to S1 nerves innervate the legs. The remaining sacral and coccygeal nerves innervate the groin. The dermatomes of the thorax and abdomen are evenly spaced segments. They are stacked on top of each other. The spinal nerves run longitudinally along the arms and legs. Therefore, they form a pattern of a trunk. However, the dermatome map may slightly differ from person to person. Dermatomes are used to examine the neurological levels in radiculopathy. When an encroachment occurs to a spinal nerve, the corresponding dermatome may exhibit the symptoms.

What is a Myotome

A myotome refers to a group of muscles innervated by the nerves of a single spinal root. Somites of the embryo are developed into the muscles. They are bilaterally-paired blocks of the paraxial mesoderm, occurring along the head-to-tail axis of the embryo during the embryonic development of vertebrates. In the beginning, 44 somites are formed but, only 31 of them remain, each corresponding to the 31 spinal nerves. Each somite comprises a dorsal and a ventral portion; the dorsal portion gives rise to the dermomyotome, which is a precursor of the myotome whereas the ventral portion gives rise to the sclerotome, which is the precursor of the ribs and vertebral column. The nerves of the brachial plexus are shown in figure 2. The brachial plexus is a nerve network formed from the C5 to T1 spinal nerves. It innervates the chest, shoulder, arm, and the hand.

Figure 2: Nerve Innervation of Brachial Plexus

The understanding of the myotome is also important in accessing the spinal lesions while ascertaining the levels of spinal cord injury. A list of common myotomes and their nerve roots are described in table 1.

Common Myotomes and their Nerve Roots

Most muscles in both upper and lower limbs are innervated from more than one spinal nerve root. So, these muscles contain multiple myotomes. As an example, the flexion of the elbow is innervated by the musculocutaneous nerve. This nerve is derived from three spinal nerve roots: C5, C6, and C7. The muscle involved in the flexion of the elbow is the biceps brachii muscle.

Similarities Between Dermatome and Myotome

• Both dermatome and myotome are two types of anatomical structures innervated by a single spinal nerve.
• Both dermatome and myotome are innervated by sensory, motor, and autonomic nerve impulses.
• The knowledge about the distribution of both dermatome and myotome is important in accessing the spinal lesions while ascertaining the levels of spinal cord injury.

Difference Between Dermatome and Myotome

Definition

Dermatome: A dermatome refers to an area of skin innervated by the nerves from a single spinal root.

Myotome: A myotome refers to a group of muscles innervated by the nerves of a single spinal root.

Significance

Dermatome: Dermatome is a region of the skin innervated by a single spinal nerve.

Myotome: Myotome is a group of muscles innervated by a single spinal nerve.

Correlation

Dermatome: Some dermatomes consists of overlapping regions innervated by more than one spinal nerve.

Myotome: Some myotomes are innervated by more than one spinal nerve.

Role

Dermatome: Dermatome is responsible for the coordination of senses.

Myotome: Myotome is responsible for the coordination of voluntary muscular movements.

Conclusion

Dermatome and myotome are two types of regions of the body innervated by a single root of spinal nerves. Dermatome refers to a region of the skin while myotome refers to a group of muscles. Both dermatomes and myotomes play a significant role in the coordination of functions of the body by communicating with the nervous system. The main difference between dermatome and myotome is the structure and the function of each region during coordination of functions.

Reference:

1. “Dermatomes Anatomy.” Overview, Gross Anatomy, Natural Variants, 13 Oct. 2017, Available here.
2. “Myotomes.” TeachMeAnatomy, 4 Feb. 2017, Available here.
3. “Neurological Examination.” The Neurological Examination | Dermatomes | Myotomes | Reflexes, Available here.

Image Courtesy:

1. “Dermatoms” By Ralf Stephan (Public Domain) via Commons Wikimedia
2. “Branches of Brachial plexus” By Madhero88 – Own work (CC BY-SA 3.0) via Commons Wikimedia