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Dermatomes

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Dermatomes of the Human Body: From the Back of head to perianal

Definition: A dermatome is an area of skin that is primarily innervated by the sensory fibres of a single spinal nerve root. These spinal nerves emerge from the spinal cord and are responsible for transmitting sensory information such as pain, temperature, and touch from specific regions of the skin to the brain.

Cervical Dermatomes (C1-C8):
- C2: Back of the head
- C3: Neck region
- C4: Shoulder area
- C5: Lateral aspect of the upper arm
- C6: Lateral forearm and thumb
- C7: Middle finger
- C8: Little finger and medial forearm
Thoracic Dermatomes (T1-T12):
- T1: Medial aspect of the forearm
- T2-T6: Upper chest and back
- T4: Nipples (used as a landmark)
- T7-T9: Mid-abdomen
- T10: Umbilicus (navel)
- T11-T12: Lower abdomen
Lumbar Dermatomes (L1-L5):
- L1: Inguinal region
- L2: Upper anterior thigh
- L3: Knee area
- L4: Medial lower leg
- L5: Lateral lower leg and dorsum of the foot
Sacral Dermatomes (S1-S5):
- S1: Lateral aspect of the foot
- S2: Posterior aspect of the thigh
- S3-S5: Perianal area

Embryological Origin of Dermatomes

Dermatomes develop from specific segments of mesoderm called somites during embryonic development. Each somite differentiates into three main components: the sclerotome, myotome, and dermatome.

Somites: Paired blocks of mesoderm that appear on either side of the neural tube in the developing embryo.
Dermatome Portion of the Somite: Gives rise to the dermis (the deeper layer of skin) and contributes to the overlying epidermis in a specific body region.
Segmentation: As the embryo develops, the dermatomes remain segmented, leading to the formation of distinct bands of skin that are innervated by the sensory nerves corresponding to the specific spinal segments.

The arrangement of dermatomes is a reflection of the segmented nature of the somites, and their distribution patterns align with the spinal nerve roots that innervate specific regions of the body.

Detailed Dermatomes

Region	Spinal Nerve	Description
Face back to vertex	Trigeminal Nerve (CN V)	The trigeminal nerve covers the facial region, including the forehead, cheeks, and jaw.
Back of head	C2	The C2 dermatome covers the posterior aspect of the head and the upper neck.
Tip of the shoulder	C5	The C5 dermatome includes the lateral aspect of the shoulder and the upper arm.
Outside lateral border of arm and hand	C6	The C6 dermatome includes the lateral side of the forearm, thumb, and part of the hand.
Middle finger	C7	The C7 dermatome encompasses the middle finger and the middle part of the hand.
Medial border of hand and arm	C8	The C8 dermatome includes the medial side of the forearm and hand, including the little finger.
Nipple	T4	The T4 dermatome is at the level of the nipples and extends horizontally around the chest.
Umbilicus	T10	The T10 dermatome is located at the level of the umbilicus (navel) and extends horizontally around the abdomen.
Groin	L1	The L1 dermatome covers the groin area and the upper part of the inner thigh.
Knee	L3	The L3 dermatome includes the anterior part of the thigh and the area around the knee.
Back of legs	S1, S2	The S1 and S2 dermatomes cover the sole of foot and posterior aspect of the legs and thighs.
Perianal region	S3, S4, S5	The S3, S4, and S5 dermatomes encompass the perianal area, including the genitals and anus.

Clinical Relevance

Diagnosis of Spinal Cord Injuries:
- Dermatome mapping helps identify the level of spinal cord injury based on sensory loss or changes.
Peripheral Neuropathies:
- Assessment of dermatomes can aid in diagnosing conditions such as shingles, which follows dermatomal patterns.
Nerve Root Compression:
- Conditions like herniated discs can compress spinal nerve roots, leading to dermatomal pain and sensory deficits.

Summary

Understanding the dermatomal distribution of the spinal nerves is crucial for diagnosing and managing various neurological and musculoskeletal conditions. Each dermatome corresponds to a specific spinal nerve, providing a map for sensory innervation of the skin. Accurate knowledge of dermatomes assists in pinpointing the site of nerve injuries and other pathological conditions.

Middle Finger C7

Dermatomes

PLEASE NOTE LEGAL ADVICE: The contents are under continuing development and improvements and may contain errors of omission or fact. Feedback vital and always welcome at drokane at gmail.com. This is not to be used for the assessment, diagnosis or management of patients. It should not be regarded as medical advice. It is only for educational purposes. Please adhere to your local protocols. If you are unwell please seek healthcare advice from your doctor. This does not replace senior or specialist advice. If you do not accept this then please do not use the website. If you need medical advice, please consult a doctor or other appropriate medical professional. If you are a medical professional and you need advice then speak to your senior or colleagues.

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