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Dermo-myotomal distribution of lower limb
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Dermo-
myotomal
distribution of
Lower Limb
What is dermomyotome?
Introduction
Dermatome
Dermatome
is an area of skin (sensory) supplied by a single spinal nerve root and its dorsal root ganglion.
Myotome
Myotome
is the group of muscles on one side of the body that are enervated by one spinal nerve root. A myotome may include parts of muscles.
Dermo-
myotome
Dermomyotome:
is an epithelial cell layer constituting of the dorsal part of the somite lying under the ectoderm, it’s all of a mesodermal somite except the sclerotome.
The embryological origin of the dermamyotomes
Developmentثىف
The somite is initially an epithelial sphere, surrounding a mesenchymal core. During the 4th week, the somites differentiate into sclerotomes (ventromedial part) which gives rise to axial cartilages, bones, and tendons and dermomyotomes (dorsolateral part) which contributes to the formation of the dorsal dermis and skeletal muscle.
Trunk
Trunk
Lateral to the notochord, 3 divisions of the mesoderm appear:(Paraxial – Intermediate – Lateral).
-The paraxial mesoderm divides into somites (42-44). Each somite divides into: Sclerotome: Ventromedial part. It surrounds the notochord and neural tube to form the vertebrae.
Dermomyotome: Dorsolateral part, Further divided into:Dermatome and Myotome of the trunk.
-Further into development, somatic sensory fibers originally associated with each somite enter the posterior region of the spinal cord at a specific level and become part of one specific spinal nerve. Therefore, each spinal nerve carries somatic sensory information from a specific area of skin on the surface of the body. -A similar process happens with myotomes and muscle.
Lower limbs
Lower limbs
• Limbs don’t develop from somites. They are derivatives of the lateral mesoderm.
• They develop from buds from the ventrolateral wall of the embryo.
• The leg buds arise at the level of the lower four lumbar and upper three sacral segments (L2 – S3).
• As development continues, limbs further elongate and their attachment to the trunk moves caudally.
Dermatome of the lower limb
Dermatomes
clinical importance
Clinical importance:
Dermatomal innervation of the skin is used in neurological examination of the sensory system to test the integrity of the dorsal root sensory fibers and to detect the site of the lesion.
Myotomes of lower limb
Myotomes
Hip: Flexors, adductors and medial rotators (L2, L3)
Extensors, abductors and lateral rotators (L5, S1)
Knee: Extensors (L3, L4)
Flexors (L5, S1)
Ankle: Dorsiflexors (L4, L5 )
Plantar flexors ( S1, S2)
Foot: Invertors (L4, L5)
Evertors (L5, S1)
Clinical Importance
• Myotomes are useful in neurological examination of the motor system. This can be done by:
• Testing the muscle for any weakness or atrophy
• Performing tendon reflexes. Lower limb tendon reflexes include:
Ankle jerk
(Achilles tendon reflex)
Ankle
jerk
Knee jerk
(patellar tendon reflex)
Knee
jerk
Quiz
A
1- Enumerate the myotomal distribution of the:
Foot: ………………………………..…………….
Ankle: …………………………………………….
-Dermomyotomal distribution of the L2 is:
1-Inguinal region.
2-Medial thigh.
3-P3atellar region.
4-Medial side of the leg & medial malleolus
B
Damage of L1 will lead to paralysis of which muscle:
1- gracilis and adductor longus
2-psoas major
3-Gluteus maximus and peronei
C
حPBL 10
-Karim Ahmed
-Ahmed Helmy
-Ahmed Adel
-Hana Elbealy
-Hania ElDesoukey
-Nehal Tarek
-Mohamed Faiz
-Iman Mariem
-Hassan Alhayek
-Hawraa Bent Abdullah
-Fatema Mamdouh
-Jenan Ali
Thank
you
PBL Tutor:
Dr.Khaled Saad