Dermatomes, Myotomes, Plexuses

Question 1

Peripheral Somatic System to CNS Pathway

Answer 1

Receptors in Joints, Skin, Skeletal Muscle –> Somatosensory Fibers (Afferent) –> CNS –> Somatomotor Fibers (Efferent) –> Skeletal Muscle

Question 2

Peripheral Autonomic System to CNS Pathway

Answer 2

Receptors in Viscera/Vessels (Sweat Glands, Erector Pili, Arteries, Veins) –> Viscerosensory Fibers (Afferent) –> CNS –> Visceromotor Fibers (Efferent) –> Glands, Smooth Muscle, Cardiac Muscle

Question 3

What are the Sclerotome, Myotome, & Dermatome derived from?

Answer 3

Paraxial Mesoderm –> Somite –> Sclerotome (Cartilage/Bone), Myotome (Skeletal Muscle), Dermatome (Dermis)

Question 4

Somatic innervation arises how?

Part of each somite gives rise to what?

Cells that migrate anteriorly give rise to what?

Cells that migrate posteriorly give rise to what?

Answer 4

Segmentally along the developing CNS in association with somites

Skeletal Muscle and Dermis of Skin (dermomyotome)

Muscles of limbs and trunk (hypaxial) & associated dermis

Intrinsic muscles of back (epaxial muscles) & associated dermis

Question 5

Describe the progression of spinal nerves from the spinal cord

Which Ramus is Epaxial and which is Hypaxial?

Which areas are differentiated and which are undifferentiated?

Answer 5

Posterior Horn –> Dorsal/Posterior Rootlets –> Posterior Root (Sensory - Differentiated) + Spinal Ganglion –> Mixed Spinal Nerve (Undifferentiated) –> Posterior Primary Ramus (Epaxial)

Anterior Horn –> Ventral/Anterior Rootlets –> Anterior Root (Motor - Differentiated) –> Mixed Spinal Nerve (Undifferentiated) –> Anterior Primary Ramus (Hypaxial)

Question 6

How do the limbs vary from the upper to lower extremities?

Answer 6

Rotation of the LE during development

UE: Flexors in front, Extensors in back

LE: Flexors in back, Extensors in front

Question 7

What is a Dermatome?

Answer 7

Area of skin supplied with afferent nerve fibers by a single posterior spinal root

Question 8

Why is there no C1 dermatome?

Answer 8

C1 only has efferent fibers (suboccipital musculature)

Question 9

What is a nerve map?

Answer 9

Divides areas of the body innervated by multiple nerves

Question 10

What is the difference between Segmental and Plexus Innervation?

Answer 10

Segmental innervation has separate spinal nerves innervating each of the overlapping dermatomes

Plexus innervation has multiple spinal nerves combined into one peripheral nerve

Question 11

What is a Myotome?

Answer 11

All the muscles innervated by single efferent anterior root

Most muscles are composed of more than one myotome