Dermatomes

Summary

In this educational video, Dr. Morton explains the concept of dermatomes—areas of skin innervated by specific spinal cord levels. He details how dermatomes are tested through touch and provides helpful memory aids for each dermatome. The video emphasizes the importance of understanding common dermatome maps, particularly the red dots representing consistent sensory locations, despite variations in maps. Dr. Morton covers testing points across the body, including the upper and lower limbs, and discusses the relevance of dermatomes in diagnosing conditions like shingles caused by the varicella-zoster virus. Overall, it's a practical guide for students learning human anatomy and dermatome testing.

Takeaways

• 😀 Dermatomes are areas of skin innervated by a single spinal cord level, and they are essential for testing spinal cord function.
• 😀 Dermatomes are also the part of a somite in the developing embryo that forms the dermis of the skin at a specific segmental level.
• 😀 Sensory neurons in a dermatome travel to their associated spinal cord level, allowing for precise testing of sensory function in different body areas.
• 😀 Red dots in dermatome maps represent areas where there is a consistent correlation between sensory neurons and a specific spinal cord level.
• 😀 To test each dermatome, focus on the location of red dots on the body rather than memorizing the entire border of each dermatome.
• 😀 Dermatome maps can vary between different sources, but the red dot locations remain relatively consistent across variations.
• 😀 Common dermatomes include C5 (lateral elbow), C6 (thumb), C7 (middle finger), and T4 (nipple).
• 😀 For lower limb testing, L3 is tested at the medial femoral condyle, L4 at the medial malleolus, and L5 on the dorsum of the foot near the third metatarsal.
• 😀 For testing S1-S2, S1 is assessed at the lateral calcaneus (heel), and S2 at the popliteal fossa (back of the knee).
• 😀 Knowledge of dermatome locations can aid in diagnosing conditions like shingles, where the varicella-zoster virus reactivates in a specific dermatome.
• 😀 Memorizing dermatome landmarks like T4 for the nipple or T10 for the umbilicus helps estimate spinal levels for areas in between, making it easier to test and identify sensory function.

Q & A

What is the definition of a dermatome?

A dermatome is an area of skin that is innervated by sensory neurons from a single spinal cord level. It can also refer to the part of the somite that forms the dermis during embryological development.

How are dermatomes and spinal cord levels related?

Each dermatome corresponds to a specific spinal cord level. Sensory neurons from the skin in a dermatome travel back to the same spinal cord level, allowing clinicians to test nerve function by touching specific areas of skin.

What is the significance of the red dots in dermatome maps?

The red dots on dermatome maps indicate consistent areas of skin where sensory neurons are strongly correlated to specific spinal cord levels. These points are useful for testing and diagnosing neurological issues.

Why is it helpful to memorize the locations of the red dots?

Memorizing the locations of the red dots simplifies the process of learning dermatomes, as these points consistently correspond to spinal cord levels, making them more reliable for clinical testing than trying to memorize the entire borders of each dermatome.

How do you test the C6 dermatome?

The C6 dermatome is tested by touching the dorsal surface of the proximal phalanx of the thumb, specifically the area where the thumbnail is located.

What is a common mnemonic for remembering the T4 dermatome location?

A common mnemonic for remembering the T4 dermatome is 'T4, T4, poor', as it corresponds to the skin at the level of the nipple, which is at the midclavicular line.

How does the L5 dermatome differ from other lower limb dermatomes in testing?

The L5 dermatome is tested by touching the dorsum of the foot over the third metatarsal, which is commonly thought of as the area where shoelaces touch. It differs from other lower limb dermatomes due to its specific location on the foot.

What is the dermatome tested by touching the lateral side of the elbow?

The dermatome tested by touching the lateral side of the elbow is the C5 dermatome, which corresponds to the skin overlying the lateral epicondyle of the humerus.

What does the term 'shingles' refer to in dermatome testing?

Shingles, caused by the varicella-zoster virus (VZV), occurs when the dormant virus in a dorsal root ganglion becomes reactivated, producing a rash along a specific dermatome. The rash follows the pattern of sensory neurons from that spinal cord level.

What does the S2 dermatome correspond to, and how is it tested?

The S2 dermatome corresponds to the skin on the back of the knee, specifically the popliteal fossa. It is tested by gently touching the skin in this area.