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step 1 MSK FC-RX
MSK -Anatomy&physio- didn't know
| Question | Answer |
|---|---|
| What is the source of osteoblasts? | Mesenchymal stem cells in the periosteum |
| Which rotator cuff muscle(s) are responsible for external rotation of the humerus/arm? | Infraspinatus muscle and teres minor muscle |
| If a patient presents with a torn PCL, what structures would be directly affected by this injury? | Medial femoral condyle and posterior tibia in PCL injury (LAMP) |
| A patient is unable to oppose his thumb and cannot flex his wrist and the lateral fingers. Which nerve is affected? | Median nerve (C5-T1) |
| A drug is synthesized to prevent calcium binding to NO synthase. What effect would this have on smooth muscle function? | It would prevent relaxation of smooth muscle (calcium required for relaxation as well as contraction on smooth muscle) |
| A man has a tumor invading his brachial plexus. C8 and T1 are compromised. Which nerve distribution is most affected? | The ulnar nerve distribution (C8-T1) |
| Which structures would be directly affected if the ACL were torn? | Lateral femoral condyle and anterior tibia with ACL injury (LAMP) |
| A patient with a proximal ulnar nerve lesion attempts to make a fist. What type of hand gesture do you expect the patient to make? | An "OK" gesture with digits 1–3 flexed (similar to the claw hand of distal median nerve lesions) |
| What is the function of the Golgi tendon organ, a muscle proprioceptor? | It senses tension via the dorsal root ganglion and facilitates inhibition of muscle activation, which reduces tension in the muscle and tendon |
| A woman has a proximal nerve lesion of the right hand. What maneuver during a physical exam can help differentiate median from ulnar nerve injury? | Flexing the fingers; ulnar claw gets prominent, while the median claw disappears |
| What is the role of troponin C in muscle contraction? | It binds intracellular Ca2+, which leads to the conformational change that moves tropomyosin out of the myosin-binding groove on actin |
| What factors activate muscle proprioceptors? | Muscle spindle gets activated by ↑ muscle stretch; Golgi tendon gets activated by ↑ muscle force |
| How does a Pope's blessing distortion arise? | Proximal median nerve lesion causes loss of lateral finger flexion and thumb opposition; distortion arises during attempt to make a fist |
| What happens when ATP binds to a myosin head that is attached to the actin filament? | Release of the myosin head; hydrolysis of ATP to ADP puts myosin in a cocked position for the next contraction cycle; Ca2+ is resequestered |
| A boy fractures the medial epicondyle of the humerus (funny bone), and a nerve is compressed. What deficits in his wrist will likely result? | Radial deviation of the wrist on flexion (seen with proximal lesions such as this; he has injured the ulnar nerve) |
| Which 4 muscles are primarily involved in external rotation of the hips? | Obturator, piriformis, iliopsoas, and gluteus maximus |
| The cells that dissolve bone are derived from what precursor cells? | Osteoclasts are derived from fusion of monocyte and macrophage lineage precursors |
| To diagnose an ulnar claw distortion, what should you ask the patient with a distal ulnar nerve lesion to do? | Extend the fingers (note that attempting finger flexion with proximal median nerve lesions → a similar appearance [Pope's blessing]) |
| During skeletal muscle contraction, what is the result of Ca2+ binding to troponin C? | Shifts tropomyosin to expose the myosin-binding site |
| A patient fractures the medial epicondyle of the humerus. What sensory and motor deficits do you expect on physical exam? | Paresthesia of medial 1½ fingers, inability to flex medial fingers/wrist, inability to abduct and adduct the fingers (this is an ulnar nerve injury) |
| A man who receives an injection to the upper medial gluteal region later demonstrates a Trendelenburg gait. It has what characteristics? | Contralateral hip drops when standing on leg ipsilateral to site of injury (the superior gluteal nerve [L4–S1] was likely injured) |
| What protein can decrease osteoclast activity by binding RANKL, and what is the protein's mechanism of action? | Osteoprotegerin, a RANKL decoy receptor, prevents RANK-RANKL interaction by binding RANKL |
| A man loses sensation over the medial 1½ fingers and hypothenar eminence after a wrist injury. Expected findings on hand motor exam? | Weakness in interossei and medial 2 lumbrical muscles, ulnar claw on digit extension (this is an ulnar nerve injury) |
| In membranous ossification, what is the role of cartilage in the formation of woven bone? | Woven bone is formed directly without cartilage (ie, there is no role for cartilage); woven bone is later remodeled to lamellar bone |
| A patient presents with a herniated disc and posterior hip dislocation. You worry about sciatic nerve impingement. What does physical exam show? | Motor deficits in the semitendinosus, semimembranosus, biceps femoris, and adductor magnus muscles |
| What motor deficits would you expect to find in a patient with damage to the lower trunk of the brachial plexus? | Decreased function of the intrinsic muscles of the hand with a claw-hand deformity |
| How are osteoclasts activated? | RANKL (RANK ligand expressed on osteoblasts) stimulates RANK receptors on osteoclasts |
| What role do osteoclasts and osteoblasts play in endochondral ossification? | They replace the cartilaginous model with woven bone and later remodel it into lamellar bone |
| What presentation is associated with an injury to the genitofemoral nerve (L1–L2)? | Decreased sensation in upper medial and anterior thigh beneath the inguinal ligament (the lateral portion of the femoral triangle) and absence of cremasteric reflex |
| A patient sustained a midshaft humerus fracture damaging the extensor compartment. He has a wrist drop. What sensory deficit is expected? | Deficit over the posterior arm/forearm and dorsal hand (diagnosis: radial nerve [C5-T1] dysfunction) |
| A man with a fibular neck fracture cannot evert or dorsiflex his foot. He has a "steppage gait." What spinal nerve roots are impaired? | L4–S2 (common peroneal nerve), causing foot drop (PED = Peroneal Everts and Dorsiflexes; if injured, foot dropPED) |
| After falling from a tree, a woman has no sensation over her shoulder and cannot abduct her arm. What could her injury be? | She likely has a fractured surgical neck of the humerus or an anterior humeral head dislocation, damaging the axillary nerve (C5-C6) |
| Ryanodine receptors couple with which receptors on the cell membrane? | Dihydropyridine receptors |
| Inability to invert the foot is due to damage to what nerve? | Tibial nerve (L4–S3) (TIP = Tibial Inverts and Plantarflexes; if injured, can’t stand on TIPtoes) |
| A patient sustains a fracture of the medial malleolus. What nerve and artery may be damaged as a result? | The tibial nerve and the posterior tibial artery |
| A man is struck from behind by a thrown javelin; it lands in his popliteal fossa. What major nerve and artery are at risk for damage? | The tibial nerve and the popliteal artery |
| What nerves supply the rotator cuff muscles? | Suprascapular nerve supplies supraspinatus and infraspinatus; axillary nerve supplies teres minor; upper and lower subscapular nerves supply subscapularis |
| What unusual movement typically causes anterior talofibular strains? | Overinversion/supination of the foot |
| During the power stroke, what happens to myosin? | Myosin releases ADP and Pi and becomes displaced on the actin filament |
| What are the actions of the gluteus medius and gluteus minimus muscles? | Abduction and internal rotation of the hip |
| A patient with lung cancer develops atrophy, pain, and edema in his right hand. Where is his tumor most likely invading? | The lower trunk of the brachial plexus and the subclavian vessels (usually within the scalene triangle); the patient likely has a right-sided Pancoast tumor |
| How does estrogen deficiency (eg, due to surgery or menopause) lead to osteoporosis? | Excess remodeling cycles and bone resorption occur without the protective effects of estrogen |
| In patients unable to stand on their tiptoes, which nerve is damaged? | Tibial nerve (L4–S3) (TIP = Tibial Inverts and Plantarflexes; if injured, can’t stand on TIPtoes) |
| A patient has a supracondylar humerus fracture and sensory loss on the dorsal and palmar aspects of the lateral fingers. The damaged nerve arises from which roots? | C5-T1 (the median nerve is damaged) |
| A man's hip dislocates posteriorly. He cannot rise from a seat or climb stairs. What are the spinal roots of the injured nerve? | L5–S2 (inferior gluteal nerve), with impairment of the gluteus maximus muscle |
| What is the function of the muscle spindle, a type of muscle proprioceptor? | It senses speed and length of stretch via the dorsal root ganglion and facilitates muscle agonist contraction and antagonist relaxation, which prevents overstretching |
| What opens the presynaptic voltage-gated Ca2+ channels, inducing the release of acetylcholine into the synaptic space? | Action potential |
| Name the major nerves that innervate the arm | Axillary, radial, musculocutaneous, median, ulnar |
| During skeletal muscle contraction (power stroke), which bands of the sarcomere decrease in length? | H band and I band between the Z lines (HIZ shrinkage); ADP is released at end of power stroke |
| What type of injury to the wrist could lead to acute carpal tunnel syndrome? | A dislocation of the lunate bone (median nerve injury) |
| A man has a palmar laceration. A hand surgeon notes a transected recurrent branch of the median nerve. What exam findings do you expect? | Ape hand with preserved sensation (loss of opposition, abduction, and flexion of thumb) |
| What 3 markers can you use to measure the activity of osteoblasts? | Osteocalcin, bone ALP, and type 1 procollagen propeptides |
| Name the muscles that are innervated by the femoral nerve (L2–L4). | Quadriceps, iliacus, pectineus, and sartorius (extensor) |
| Explain how type I slow-twitch muscle fibers utilize oxidative phosphorylation. | They have a relative increase in oxidative phosphorylation, which leads to sustained muscle contractions (think "1 slow red ox") |
| A woman giving birth receives a pudendal nerve block. What landmark does the anesthesiologist use to locate the site of the block? | The ischial spine |
| How does a genitofemoral nerve injury affect female patients? | Sensation is lost in the labia majora and medial thigh (L1-L2) |
| How does a genitofemoral nerve injury affect male patients? | Sensation is lost in the scrotum and medial thigh, and the cremasteric reflex is absent |
| An experimental drug prevents the human body from breaking down old bone cells. Which enzyme does this drug most likely inhibit? | Collagenase, as osteoclasts release H+ and collagenases to dissolve old bone |
| A man falls down the stairs and lands on the medial heel of his hand while it is outstretched. What nerve might he have injured? | Ulnar nerve (C8-T1) from fractured hook of hamate |
| Which bones are formed by membranous ossification? | Bones of the calvarium (skull roof), face, and clavicle vs base of skull=endochondral ossification |
| A man can no longer adduct his thigh and has a sensory deficit in his medial thigh. What type of intervention may be responsible for this? | Pelvic surgery, associated with lesions of the obturator nerve (L2–L4) |
| What type of bone is formed by healed fractures? | Woven bone (as opposed to lamellar bone) |
| How do molecules such as acetylcholine and bradykinin induce smooth muscle cell relaxation? | They bind to endothelial cell receptors, increasing Ca2+; the Ca2+ activates NO synthase, and the NO diffuses in smooth muscle, triggering relaxation |
| A poison affects the release of certain molecules (breakdown products), such that myosin cannot be detached from the actin filament. What molecules are these? | ADP and inorganic phosphate |
| After presynaptic neuron neurotransmitter release, postsynaptic acetylcholine binding leads to the depolarization of which membrane? | The motor end plate of the muscle cell (postsynaptic membrane) |
| What are muscle proprioceptors? | Specialized sensory receptors that transmit information regarding muscle dynamics |
| Are type I red muscle fibers found in slow- or fast-twitch muscles? | They are found in slow-twitch muscles ("1 slow red ox") |
| A patient presents with a knee injury. You notice that the tibia moves forward relative to the femur at 30°. What is the most likely diagnosis? | n ACL injury; the Lachman test was used, which is more sensitive than the anterior drawer sign test |
| Name the muscles innervated by the deep peroneal nerve that are affected by a period of lateral leg compression | Tibialis anterior (sensory deficit occurs in webspace between hallux and 2nd digit) |
| A weight trainer benches on a daily basis. He is inducing hypertrophy of which type of muscle fiber? | Type II muscle fibers, which are white fast-twitch fibers |
| Why are type I muscle fibers red? | They have high concentrations of mitochondria and myoglobin for sustained contraction |
| During muscle contraction, which of the muscle bands remains the same length? | The A band (A band is Always the same length) |
| A diagnosis of carpal tunnel syndrome is made. Which lumbricals are affected by the nerve that is affected by this syndrome? | The lumbricals of the index and middle fingers are affected by the median nerve |
| What are T-tubules, and what is their relation to the muscle? | Extensions of muscle plasma membrane in contact with sarcoplasmic reticulum; this enables coordinated contraction of striated muscles |
| A patient reports decreased sensation to the anterior and lateral thigh. What are risk factors for this condition | Tight clothing, obesity, pelvic procedures, and pregnancy can affect the lateral femoral cutaneous nerve (L2–L3) |
| A man with back pain has weak left knee extension and left patellar hyporeflexia. Herniation at which level is to blame? | Left posterolateral herniation of the L3–L4 intervertebral disc, impinging on the left L4 nerve root |
| What deficits do you expect on exam in a patient with damage to the musculocutaneous nerve? | Difficulty flexing the arm at elbow (by bicep brachii) , variable sensory loss over the lateral aspect of the forearm. |
| How is parathyroid hormone involved in normal bone physiology? | At low, intermittent levels, it exerts anabolic (bone-building) effects by activating osteoblasts directly and osteoclasts indirectly |
| Generally speaking, for distortions of the hand caused by nerve injuries, which subtype has deficits that are less pronounced? | Proximal lesions |
| What is the function of the most commonly injured rotator cuff muscle? | Supraspinatus, the most commonly injured rotator cuff muscle, serves to abduct the arm initially (before the action of the deltoid) |
| Why are disc herniations more likely to occur posterolaterally as opposed to anteriorly? | Because the posterior longitudinal ligament is thin and the anterior longitudinal ligament is thick along the midline of vertebral bodies |
| What nerve innervates the supraspinatus muscle, and what are the degrees of motion? | Suprascapular nerve; 0°–15° of abduction |
| A patient presents with avascular necrosis and nonunion in a wrist bone. The fracture has retrograde blood supply. What part of the wrist is fractured? | The proximal portion of the scaphoid |
Created by:
ema1437
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