Dermatomes and Myotomes Flashcards
The nipples lie along dermatome […], except in individuals with very pendulous breasts.
T4
- In the trilaminar disc (embryo), the neural tube is made of […].
- The […] mesoderm that surrounds the neural tube forms segments called […], which then further divide into […], […], and […]
- Ectoderm
- Paraxial; somites; myotomes (skeletal muscle), dermatomes (skin) and sclerotomes (bones)
Describe the process of dermatome, myotome and sclerotome development.
All arise from somites.
Sclerotomes split into a top half and bottom half that rearrange to form the vertebrae.
Projections from the neural tube protrude between the breaks in the sclerotomes and attach to myotomes and dermatomes. As the myotomes and dermatomes develop into muscle and skin they pull the neural tube projections with them, creating innervation by spinal nerves.
Describe what this image is showing.
As we develop in utero, sections of our limbs are innervated by specific parts of the spinal cord. These associations develop early before our growth in utero has completed. As such, you can see that the implications of this are that as our limbs develop and become shaped in the way that they will be as an adult, the dermatomes and myotomes no longer follow a nice orderly pattern.
What spinal level innervates the dermatome that is shown by the arrow in this image? (the skin of the lateral forearm and the thumb)
The xiphoid process is in the anterior center of dermatome […].
T6
The umbilicus (belly button) is in the anterior center of dermatome […].
T10
The big toe (hallux) is innervated dermatomes […] and […]
L4/L5
Describe the shape of dermatome lines in the trunk.
Dermatomes travel more inferiorly on the anterior side of the trunk compared to the posterior side because they travel along the ribs, which have this shape. As a result, the xiphoid process may be in line with dermatome T6 on the anterior surface of the body, but if a straight line is drawn through the trunk at the xiphoid process, it will be in line with T10 posteriorly. Thus, the posterior segment of dermatome of the umbilicus is coincident with the anterior dermatome of the xiphoid process.
How do you test a dermatome?
Because there is a lot of overlap of the individual dermatomes, only the truly autonomous regions can be tested. These are areas where overlap of innervation is least likely.
What is a myotome?
A muscle or group of muscles that receive somatic and/or motor innervation from a single spinal nerve
What is a dermatome?
Portions of the skin that send somatic sensory information to the brain through a single spinal nerve
The C1 and C2 myotomes produce […]
Cervical anterior/posterior flexion
The C3 myotome produces […]
Cervical lateral flexion
The C4 myotome produces […]
Scapula elevation
The C5 myotome produces […]
Abduction of the shoulder
The C6 myotome produces […]
Elbow flexion + wrist extension
The C7 myotome produces […]
Elbow extension and wrist flexion
The C8 myotome produces […]
Thumb extension
The T1 myotome produces […]
Finger abduction
The L1 and L2 myotomes produce […]
Hip flexion
The L3 myotome produces […]
Knee extension
The L4 myotome produces […]
Ankle dorxiflexion
The L5 myotome produces […]
Hallux extension
The S1 myotome produces […]
Ankle plantarflexion
The S2 myotome produces […]
Knee flexion
The biceps reflex tests sensory and motor function of what spinal levels?
C5 mostly, some C6
The brachioradialis reflex tests sensory and motor function of what spinal levels?
C5 and C6
The triceps reflex tests sensory and motor function of what spinal levels?
C7 mostly, some C6
The patellar reflex tests sensory and motor function of what spinal levels?
Mostly L4, some L3
The calcaneal tendon (achilles) reflex tests sensory and motor function of what spinal levels?
S1
