2.7: Activity 6

Integrated Human Anatomy and Physiology Lab Manual II: Neural and Cardiopulmonary Systems · LibreTexts

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    Spinal Nerve Plexus and Muscle Actions: Case Study

    The objective of this activity is to develop students' critical thinking skills by analyzing case-based scenarios involving the spinal nerve plexus and associated muscle actions. Students will identify the roles of different nerve plexuses, understand their anatomical connections, and relate these to specific muscle functions and movements.

    Introduction

    The 31 pairs of spinal nerves are bundles of sensory and motor neurons wrapped in connective tissue. Since they carry both sensory and motor signals, the spinal nerves are “mixed” nerves, unlike the cranial nerves which can be sensory, motor or mixed. The sensory axons enter the spinal cord as the dorsal nerve root. The dorsal root ganglion for each nerve is an enlargement of the spinal nerve. The motor fibers, both somatic and autonomic, emerge as the ventral nerve root. A motor signal causes a response, such as signaling a muscle to contract. This signal may initiate from the motor cortex of the cerebrum, then travels down the spinal cord along a vertical tract (or
    column).

    In the thoracic region, the ventral rami of spinal nerves T2-T12 form intercostal nerves that supply the ventral and lateral areas of the chest and superior abdomen. For every other spinal nerve, the axons of the ventral rami combine with those of nearby spinal nerves to form a plexus.

    • Cervical plexus - innervates the head and neck, and extends from the cervical region of the spinal column.
    • Brachial plexus - innervates the arm, and extends from the cervical region of the spinal column.
    • Lumbar plexus – innervates the anterior and medial portions of the thigh and extends from the lumbar region of the spinal column.
    • Sacral plexus – innervates the posterior of the thigh, the lower leg and most of the pelvis, and it includes nerves with extends from the lumbar region of the spinal column and from the sacrum.

    Context

    Understanding the spinal nerve plexus is crucial for comprehending how nerves facilitate muscle actions and movements throughout the body. Each plexus, such as the cervical, brachial, lumbar, and sacral plexuses, serves distinct regions and influences various muscular activities. Through case-based scenarios, students will explore real-world applications of this knowledge, enhancing their ability to diagnose potential nerve injuries and predict functional outcomes.

    Instructions

    • Review available online and offline resources on the anatomy and function of the spinal nerve plexuses, focusing on their connections to muscles and regions they innervate.
    • Activate prior knowledge about  with skeletal muscles, their actions and innervation (specific prime mover and related plexus). Nerve plexuses are networks of these spinal nerves that redistribute nerve fibers, allowing for more complex muscle innervation patterns. Each muscle receives innervation from specific spinal nerves, and understanding these connections is crucial for diagnosing and treating neurological conditions

    Case Study Analysis - link nerve, plexus, and muscle action

    • Case 1 Scenario: Alex is unable to flex his elbow after an accident.
      • Question: Which muscle responsible for elbow flexion is likely affected in Alex's case? Identify the spinal nerve and plexus involved in innervating this muscle and discuss how loss of function impacts daily activities.
      • Discuss your findings and reasoning with peers to verify your conclusions.
    • Case 2 Scenario: Jamie experiences difficulty in extending the knee, especially when standing up from a seated position.
      • Question: What muscle is primarily responsible for knee extension? Identify the corresponding spinal nerve and plexus that innervate this muscle, and explain the significance of this movement in mobility and stability.
      • Discuss your findings and reasoning with peers to verify your conclusions.
    • Case 3 Scenario: Taylor notices an inability to raise their arm above shoulder height.
      • Question: Which muscle is likely responsible for shoulder abduction? Determine the relevant spinal nerve and plexus, and analyze how this limitation affects Taylor’s ability to perform various tasks.
      • Discuss your findings and reasoning with peers to verify your conclusions.
    • Case 4 Scenario: Morgan struggles to lift their leg when walking, particularly when trying to step up onto a curb.
      • Question: Identify the muscle responsible for hip flexion that may be impaired in Morgan’s case. Discuss the spinal nerve and plexus associated with this muscle and how this loss of action influences ambulation.
      • Discuss your findings and reasoning with peers to verify your conclusions.
    • Case 5: Scenario: Casey finds it difficult to lift their foot (dorsiflex) while walking, causing tripping hazards.
      • Question: Which muscle is involved in dorsiflexion of the foot? Identify the associated spinal nerve and plexus, and consider the implications of this impairment on balance and walking.
      • Discuss your findings and reasoning with peers to verify your conclusions.

    This page titled 2.7: Activity 6 was last modified on Sat, 08 Nov 2025 01:38:07 GMT and is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Lakshmikanta Sengupta and Susmita Sengupta.