Upper extremity anatomy and function

Each lab group needs:

  1. Thumb movements

    Examine the diagram in your text (Smith, Weiss, & Lehmkuhl, 1996, Fig. 6-21, p.212) that explains the terms for thumb movements.

    • Abduction and abduction occur in a plane that is perpendicular to the palm. Locate and mark the axes for this motion at the carpometacarpal (CMC) joint, and at the MP joint.

    • Flexion and extension occur in the plane of the palm. Abduction and abduction occur in a plane that is perpendicular to the palm. Locate and mark the axes for this movement at the CMC, MP,and IP joints.

    • Opposition involves an automatic rotation of the thumb that occurs whenever we combine abduction and flexion. You can detect the rotation if your monitor the orientation of the thumbnail as you combine flexion and abduction.

    • Reposition is the "opposite of opposition."

  2. Extrinsic thumb muscles

    The thumb has four extrinsic muscles:
    • flexor pollicis longus
    • extensor pollicis longus
    • extensor pollicis brevis
    • abductor pollicis longus

    Tendons of three of the muscles form the borders of the "anatomical snuff box," located on the hand's radiodorsal surface. Two tendons form the snuffbox' radial border:

    _______________________ and _______________________

    The ________________________ tendon forms the snuffbox' ulnar border.

    anatomical snuffbox

    The muscles move the thumb in the plane of the palm but also but also radially or ulnarly (choose one) deviate the wrist.

    To move the thumb without also moving the wrist, the "snuffbox" muscles must act in a synergy with what carpal muscles?

  3. Demonstration of a passive grasp that involves the thumb

    Observe how, when you passively extend the wrist, the thumb's MP and IP joints flex. The thumb may flex enough that its tip contacts the side of the second digit, producing a grasp, albeit a weak one. The thumb flexion does not depend on muscle activity, but results from passive forces that develop when the wrist extends.

    • In which extrinsic thumb muscle does passive force develop as a result of the wrist extension?

    • Why is an extrinsic, and not an intrinsic thumb muscle, the source of this passive force?

  4. Sensory innervation of the hand

    map of hand's sensory innervation

    Consider a person who describes paresthesia (numbness and tingling) in the fourth and fifth fingers of both hands, and who comments that the symptoms are exacerbated when he goes for long bike rides. What might be the problem?

    Alternatively, consider a patient who is referred to you after undergoing surgery to repair a midshaft humerus fracture that resulted from a gunshot wound. He describes paresthesia over the dorsum of his hand. What nerve is damaged, and what muscle function might the person lack.

    What sensory symptoms might alert you to the beginning stages of carpal tunnel syndrome? What muscles might eventually lose innervation if the condition is untreated

  5. Moments around the lateral axes of the glenohumeral and elbow joints as one lowers a laundry basket to the floor

    Estimate the moments (in inch*lbs) that the weight of the laundry basket places on:

    1. the glenohumeral joint's lateral axis
    2. the elbow's lateral axis

    The figure illustrates each axis with an 'x.'

    What movement does gravity cause at the glenohumeral joint? Name three muscles that cross the glenohumeral joint and that may act as the person lowers the basket to the floor.

    What movement does gravity cause at the elbow? Name three muscles that cross the elbow and that may act as the person lowers the basket to the floor.

    lowering a basket to the floor

  6. Activity in the triceps brachii during forceful gripping

    Palpate the triceps brachii just superior to the olecranon process, and note that it is active when you grip an object firmly in your fisted hand. Your text (Smith, Weiss, & Lehmkuhl, 1996, Fig. 4-4C, p.134) also illustrates EMG evidence for this triceps activity. Explain why the elbow extensors are part of a synergy for forceful gripping.

    Hint: the elbow extensors counteract the tendency of another muscle, which participates in the gripping synergy, to flex the elbow. What muscle participates in the gripping synergy and contributes to elbow flexion?

  7. The wrist's role in opening the hand

    Open your fingers quickly and forcefully while you observe your wrist. Note that the wrist flexes.

    The only muscle that extends the second, third, fourth, and fifth MP joints is the ________________. However, this muscles also extends or flexes (choose one) the wrist.

    What carpal muscles must counteract this unwanted effect on wrist motion? Choose one or more carpal muscles that might be part of the "hand opening" synergy and palpate their tendons near the wrist while you forcefully open the hand.

    When one opens the hand forcefully, the neuromotor system recruits all these muscles in a synergy that is difficult to override voluntarily. What is the synergy's purpose?

  8. The intrinsic muscles' role in opening the hand

    To understand the muscular synergies involved in opening the hand (and in the next problem, which involves closing the hand), you should examine the extensor mechanism and the muscles that attach to it. Refer to a popular anatomy atlas like Netter (1997, Plate 433 - Flexor and extensor tendons in fingers), to your text's reproductions of Netter's drawings of the extensor mechanism (Smith, Weiss, & Lehmkuhl, 1996, Fig 6-12), or to adaptations of Netter's drawings.

    The extensor digitorum "is mechanically capable of extending the MCP, PIP, and DIP joints but not at the same time. When the extensor digitorum contracts alone, ... the MCP joints extend but the IP joints remain semiflexed in a clawhand position (Smith, Weiss, & Lehmkuhl, 1996, p.205-6)." The authors also explain that the extensor digitorum combines with the lumbricales in a muscle synergy to open the hand. Unless the hand must be opened forcefully or against resistance, the interosseous muscles are inactive (pp. 206-207).

    1. How can the lumbricales contribute to hand opening?

    2. How can the interossei contribute to forceful opening of the hand?

  9. Forceful closing of the hand

    According to Smith, Weiss, and Lehmkuhl (1996, p. 201), "forceful closure of the hand or power grip elicits high-level activity of the flexor digitorum superficialis, the interossei, and the flexor digitorum profundus."

    Explain why we use the interosseous muscles in hand closure, even though they can contribute to PIP and DIP extension.

  10. Adaptations for a person with a weak grasp

    Consider a person whose grasp is so weak that he or she cannot grip a spoon to eat or a pen to write. How might you modify implements like eating utensils or tools to facilitate this person's function.

    Hint: even weak muscles develop more force when they are elongated.

Last updated 11-27-01 Dave Thompson PT
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