Examine the diagram in your text (Smith, Weiss, & Lehmkuhl, 1996, Fig. 6-21, p.212) that explains the terms for thumb movements.
The thumb has four extrinsic muscles:
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:
The ________________________ tendon forms the snuffbox' ulnar border.
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?
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.
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
Estimate the moments (in inch*lbs) that the weight of the laundry basket places on:
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.
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.
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?
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).
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.
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.