Myotomes and Dermatomes
Examination, Anatomy, and Embryology of Myotomes and Dermatomes
Anonymous EducatorThese flashcards delve into the intricate details of the body's dermatomes and myotomes, highlighting their significance in the realm of neurological assessments. Understanding the structure and function of myotomes and dermatomes is essential for a comprehensive neurological examination, especially in instances involving spinal cord injuries. The arrangement of dermatomes varies across different parts of the body: they form a series of layers across the chest and abdomen, with each layer linked to a distinct spinal nerve. In contrast, along the arms and legs, dermatomes extend longitudinally, tracing the limbs' length. Although the general pattern of dermatomes is consistent among individuals, the specific area each dermatome covers is as unique to an individual as their fingerprints.
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What is the significance of the 3rd week of embryogenesis in the development of dermatomes?
The 3rd week of embryogenesis is crucial for the development of dermatomes because it is during this period that the tri-laminar disc is established, and the mesoderm (the middle layer of the embryo) differentiates into various types. Specifically, the paraxial mesoderm adjacent to the neural tube starts to form somites, which are essential for the development of dermatomes.
What area is characteristically supplied by the dermatome of the T6 spinal nerve?
The intersection of the midclavicular line and the horizontal level of the xiphoid process.
What area is characteristically supplied by the dermatome of the L2 spinal nerve?
The anterior medial thigh, at the midpoint of a line connecting the midpoint of the inguinal ligament and the medial epicondyle of the femur.
What area is characteristically supplied by the dermatome of the T7 spinal nerve?
The intersection of the midclavicular line and the horizontal level at one quarter the distance between the level of the xiphoid process and the level of the umbilicus.
What area is characteristically supplied by the dermatome of the S2 spinal nerve?
The midpoint of the popliteal fossa.
What area is characteristically supplied by the dermatome of the C8 spinal nerve?
The dorsal surface of the proximal phalanx of the little finger.
How is the face and head innervated dermatomally?
The dermatomal innervation of the face and head is primarily provided by the Trigeminal nerve (CN 5). The ophthalmic branch (V1) innervates the scalp, eyes, nose, and forehead, the maxillary branch (V2) innervates the the territory just below the orbits and above the mouth, and the mandibular branch (V3) innervates the lower third of the face, the floor of the mouth, jaw, and the tongue with the caveat that the angle of the mandible is supplied by C2/C3.
What area is characteristically supplied by the dermatome of the T5 spinal nerve?
The intersection of the midclavicular line and the fifth intercostal space, horizontally located midway between the level of the nipples and the level of the xiphoid process.
What area is characteristically supplied by the dermatome of the L5 spinal nerve?
The dorsum of the foot at the third metatarsophalangeal joint.
What area is characteristically supplied by the dermatome of the T10 spinal nerve?
The intersection of the midclavicular line, at the horizontal level of the umbilicus.
What are somites, and how are they related to the formation of dermatomes?
Somites are segments formed from the differentiation of the paraxial mesoderm, beginning around day 20 of embryogenesis. A total of 44 pairs of somites are initially formed, but 13 pairs eventually break down, leaving 31 pairs. These somites differentiate into areas called dermomyotomes, with the dermatome part contributing to the formation of the dermis. This process is linked to the 31 sets of spinal nerves in the body, establishing a basis for segmental innervation patterns observed in dermatomes.
What area is characteristically supplied by the dermatome of the L1 spinal nerve?
Midway between the key sensory points for T12 and L2, which includes the inguinal region and the very top of the medial thigh.
What area is characteristically supplied by the dermatome of the T9 spinal nerve?
The intersection of the midclavicular line and the horizontal level at three quarters of the distance between the level of the xiphoid process and the level of the umbilicus.
What areas are characteristically supplied by the dermatome of the C5 spinal nerve?
The lateral (radial) side of the antecubital fossa, just proximally to the elbow, and the lateral aspect of the lower edge of the deltoid muscle, known as the “regimental badge.”
What area is characteristically supplied by the dermatome of the T3 spinal nerve?
The intersection of the midclavicular line and the third intercostal space.
What area is characteristically supplied by the dermatome of the C6 spinal nerve?
The dorsal surface of the proximal phalanx of the thumb.
What area is characteristically supplied by the dermatome of the T8 spinal nerve?
The intersection of the midclavicular line and the horizontal level at one half the distance between the level of the xiphoid process and the level of the umbilicus.
How many spinal nerves are there in the cervical area, and what is special about the first one?
There are 8 spinal nerves in the cervical area, the first one, C1, doesn't connect to the skin.
What areas does the C2 nerve root supply?
The skin of the neck, temple, forehead, and occiput.
What area is characteristically supplied by the dermatome of the C4 spinal nerve?
The area characteristically supplied by the dermatome of the C4 spinal nerve is over the acromioclavicular joint.
What area is characteristically supplied by the dermatome of the S1 spinal nerve?
The lateral aspect of the calcaneus.
What area is characteristically supplied by the dermatome of the T2 spinal nerve?
The apex of the axilla.
What is special about the mandibular nerve (V3)?
The mandibular nerve (V3) is the largest branch of the trigeminal nerve and is unique in having both sensory and motor components. The motor root of V3, also known as portio minor, supplies the muscles of mastication (masseter, temporalis, pterygoids), the anterior belly of the digastric muscle, and the mylohyoid muscle.
What area is characteristically supplied by the dermatome of the L3 spinal nerve?
The area at the medial epicondyle of the femur.
What area is characteristically supplied by the dermatome of the L4 spinal nerve?
The area over the medial malleolus.
What area is characteristically supplied by the dermatome of the T11 spinal nerve?
The intersection of the midclavicular line, at the horizontal level midway between the level of the umbilicus and the inguinal ligament.
What areas are characteristically supplied by the dermatomes of the S4 and S5 spinal nerves?
The perianal area, less than one cm lateral to the mucocutaneous zone.
What area is characteristically supplied by the dermatome of the T4 spinal nerve?
The intersection of the midclavicular line and the fourth intercostal space, located at the level of the nipples.
What area is characteristically supplied by the dermatome of the T12 spinal nerve?
The intersection of the midclavicular line and the midpoint of the inguinal ligament.
What area is characteristically supplied by the dermatome of the S3 spinal nerve?
The area over the tuberosity of the ischium or intragluteal fold.
When and by whom was the first comprehensive mappings to illustrate the segmental distribution of dermatomes?
The Keegan and Garrett dermatome map of 1948 holds historical significance as it was one of the first comprehensive mappings to illustrate the segmental distribution of dermatomes.
What areas does the C3 nerve root supply?
The entire neck, posterior cheek, posterior temporal area, and a prolongation forward under the mandible as well as the supraclavicular fossa in the midclavicular line are all innervated by the C3 nerve root.
What area is characteristically supplied by the dermatome of the C7 spinal nerve?
The dorsal surface of the proximal phalanx of the middle finger.
What area is characteristically supplied by the dermatome of the T1 spinal nerve?
The medial (ulnar) side of the antecubital fossa, just distal to the medial epicondyle of the humerus.
Which movements are most associated with the C8 myotome in the upper limb?
Thumb extension is most associated with the C8 myotome in the upper limb.
What movement is primarily associated with the S2 myotome in the lower limb?
Knee flexion is the primary movement associated with the S2 myotome in the lower limb.
How many pairs of somites are there during embryonic development?
Initially, during embryonic development, as many as 44 pairs of somites are formed from the paraxial mesoderm. However, as development progresses, a natural regression occurs, reducing the number to 31 pairs. This reduction corresponds to the 31 pairs of spinal nerves.
What is the significance of the para-axial mesoderm in the development of myotomes?
The para-axial mesoderm is crucial in the development of myotomes because it differentiates into somites, which are segmented blocks that further develop into the skeletal muscles. This process begins around day 20 of embryogenesis, adjacent to the developing neural tube.
What movement is primarily associated with the L4 myotome in the lower limb?
Ankle dorsiflexion is the primary movement associated with the L4 myotome in the lower limb.
What movement is primarily associated with the S1 myotome in the lower limb?
Ankle plantarflexion is the primary movement associated with the S1 myotome in the lower limb.
How do somites contribute to the formation of the skeletal system and muscles?
Somites, which form from the paraxial mesoderm, are segmented into a dorsal and a ventral portion. The ventral portion, known as the sclerotome, develops into the ribs and vertebral column, forming the skeletal framework. The dorsal portion, the dermomyotomes, proliferates and eventually develops into muscle. Thus, somites are essential for both the skeletal system's structure and the formation of muscles.
Which movement is most associated with the C5 myotome in the upper limb?
Shoulder abduction is the primary movement associated with the C5 myotome or nerve root in the upper limb.
What movement is primarily associated with the T1 myotome in the upper limb?
Finger abduction is the primary movement associated with the T1 myotome in the upper limb.
What movement is primarily associated with the L3 myotome in the lower limb?
Knee extension is the primary movement associated with the L3 myotome in the lower limb.
Which movements are most associated with the C6 myotome in the upper limb?
Elbow flexion and wrist extension are the movements most associated with the C6 myotome in the upper limb.
What movement is primarily associated with the L5 myotome in the lower limb?
Great toe extension is the primary movement associated with the L5 myotome in the lower limb.
Which movement is most associated with the L2 myotome or nerve root in the lower extremity?
Hip flexion is the movement most associated with the L2 myotome in the lower extremity.
What movement is primarily associated with the C7 myotome in the upper limb?
Elbow extension is the primary movement associated with the C7 myotome in the upper limb.