Myotomes

Question 1

What is a myotome?

Answer 1

The anatomical term myotome (Greek: myo=muscle, tome= a section, volume) refers to the muscles served by a spinal nerve root. Myotomes are, therefore, a group of muscles that are innervated by the same spinal nerve. The term is also used in embryology to describe the part of the somite which develops into the muscles.

Question 2

What is the function of a myotome?

Answer 2

Myotomes play a crucial role in movements such as flexing and extending the spine, bending and straightening the arms, and bending and extending the legs.
Myotomes are part of somatic nervous system and the somatic nervous system is part of peripheral nervous system
16 of the 31 spinal nerves has a specific myotome that controls voluntary muscle movement.

Question 3

Describe myotome distribution

Answer 3

Most muscles in the limbs receive innervation from more than one spinal nerve root, and are hence comprised of multiple myotomes.
E.g Biceps Brachii muscle,which flexes the elbow, It is innervated by the musculocutaneous nerve, which is innervated by C5, C6 and C7 nerve roots.
All three of these spinal nerve roots can be said to be associated with elbow flexion.

Question 4

Allocate the spinal nerves to their corresponding myotome function

Question 5

What is the purpose/importance of myotomes?

Answer 5

Myotomes are mainly useful for clinical evaluation of patients in understanding the pattern in neurological deficit after a complex nerve injury . Injury to each or a combination of spinal myotomes, lesions may be localized to the spinal nerve or trunk level.
Myotome testing is an essential part of neurological examination when suspecting radiculopathy or sometimes myelopathy
Testing of myotomes, in the form of isometric resisted muscle testing, gives information about the level in the spine where a lesion may be present.
During myotome testing, the aim is to identify any muscle weakness within a specific set of muscles.
Results may indicate lesion to the spinal chord nerve, or the intervertebral disc herniation pressing on the spinal nerve roots. The muscle strength grading scale, which assigns a rating to the degree of muscle weakness, is often used.
Myotomes are much more complex to test than dermatomes, since each skeletal muscle is innervated by nerves derived from more than one spinal chord level

Question 6

Describe the correlation between a herniated disc and a myotome

Answer 6

Herniated disc
This happens when components of the intervertebral disc space become displaced outside of the intervertebral disc space. Because the intervertebral disc is very close to the spinal nerves and result in myelopathy. The spinal cord level of myelopathy can be determined through myotome testing.
Common causes of disk herniation is aging,trauma, congenital disorders(short pedicles) and connective tissue disorder

Question 7

Describe the correlation between a foot drop and a myotome

Answer 7

Problem lifting your foot or “foot drop’’ can be a sign of concern in the lower part of the spine (L4-S3). To make a diagnosis, a power test will be done to the muscles and to resist some movements.

Question 8

claw hand, wrist drop