Dermatomes & Myotomes Made Easy

Summary

In this video, Dr. A provides an overview of dermatomes and myotomes, explaining the role of the nervous system, including the central and peripheral nervous systems. The spinal cord acts as a bridge between them, with spinal nerves extending from it to innervate different areas of the body. Dr. A outlines the dermatome map, describing sensory points for various spinal nerves, and discusses how myotomes control muscle movements. He also explains how clinicians assess the function of these nerves through specific movements and resistance testing. The video offers clear, concise insights into this crucial aspect of anatomy and clinical assessment.

Takeaways

• 😀 The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS), with the spinal cord acting as the link between them.
• 😀 The spinal cord has 33 vertebrae, but only 31 pairs of spinal nerves that extend from it, each corresponding to specific areas of the body.
• 😀 The cervical spinal nerves (C1-C8) exit the spinal column above their corresponding vertebrae, while other spinal nerves exit below their respective vertebrae.
• 😀 The **dorsal roots** of spinal nerves carry sensory information from the peripheral nervous system to the central nervous system.
• 😀 **Dermatomes** are areas of skin that are innervated by specific spinal nerves, each having a corresponding key sensory point (e.g., C5 at the lateral elbow, C6 at the back of the thumb).
• 😀 The **brachial plexus** includes spinal nerves C5 to T1 and innervates the upper extremities, while T1-T12 innervate the thoracic and abdominal regions.
• 😀 The **lumbar and sacral nerves** provide sensory information to the lower extremities, with key sensory points for L1 at the inguinal area, L5 at the top of the foot, and S2 at the popliteal fossa.
• 😀 **Myotomes** refer to the muscle groups innervated by specific spinal nerves, and their functionality is tested through movements and resistance (e.g., C5 for shoulder abduction, S1 for plantar flexion).
• 😀 Specific movements associated with spinal nerve levels include **C4** for shoulder shrug, **C6** for wrist extension, and **L3** for knee extension.
• 😀 Clinical assessment of myotomes involves both voluntary muscle movements and resistance testing to check the integrity of nerve function and diagnose potential issues.

Q & A

What is the difference between the central nervous system (CNS) and the peripheral nervous system (PNS)?

The central nervous system (CNS) includes the brain and spinal cord, while the peripheral nervous system (PNS) includes all the nerves outside the CNS, such as cranial and spinal nerves.

How does the spinal cord link the CNS and PNS?

The spinal cord acts as a bridge, connecting the central nervous system to the peripheral nervous system. It transmits information between the brain and the spinal nerves.

What are the components of the spinal column, and how many vertebrae are there?

The spinal column consists of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, the sacrum (five fused vertebrae), and four fused coccygeal vertebrae, totaling 33 vertebrae.

Why is there a discrepancy between the number of cervical vertebrae and cervical nerves?

The first cervical nerve exits above the first cervical vertebra, while the eighth cervical nerve exits below the seventh cervical vertebra. The rest of the nerves exit below their corresponding vertebrae.

What are dorsal roots, and what role do they play in the nervous system?

Dorsal roots are extensions from the posterior median sulcus of the spinal cord that transmit sensory information from the peripheral nervous system to the central nervous system.

What is a dermatome, and how is it related to spinal nerves?

A dermatome is an area of skin that is innervated by a specific spinal nerve. It helps identify the regions of the body affected by the activity of particular spinal nerves.

Can you describe the sensory points for the C5, C6, C7, C8, and T1 dermatomes?

For C5, it's the lateral aspect of the elbow; C6 is on the back of the thumb; C7 is on the back of the middle finger; C8 is on the back of the pinky finger; and T1 is on the medial aspect of the elbow.

What are the key sensory points for the lower extremities?

For L1, it is the inguinal area; L2 is the medial aspect of the thigh; L3 is the medial aspect of the knee; L4 is the medial malleolus; L5 is the top of the foot at the third metatarsal; S1 is the lateral aspect of the calcaneus; and S2 is the popliteal fossa.

What is the significance of the T4 and T10 spinal nerves in dermatome distribution?

The T4 spinal nerve crosses just over the pectoral region, while the T10 spinal nerve crosses directly over the umbilicus, making them key landmarks in dermatome distribution.

How are myotomes tested clinically?

Myotomes are tested by asking a person to perform specific movements (e.g., shoulder abduction, knee extension) and applying resistance to assess the functioning of the corresponding spinal nerves.