NCBTMB Exam Applied Science and Anatomy 5

Question 1

A client presents with weakness in shoulder abduction beyond 90° and atrophy of the supraspinatus and infraspinatus fossae. Which specific nerve entrapment is most likely responsible for this pattern?

Accepted Answer

Suprascapular nerve entrapment at the suprascapular notch

Answer

The suprascapular nerve innervates both the supraspinatus (initiates abduction 0–15°) and infraspinatus (external rotation). Entrapment at the suprascapular notch affects both muscles, causing the described atrophy and weakness pattern. The axillary nerve affects the deltoid (abduction 15–90°), the long thoracic nerve causes winging scapula, and upper trunk compression produces a broader deficit including biceps and brachialis.

Question 2

During the cell cycle, a therapist studying pathophysiology learns that cyclin-dependent kinases (CDKs) are regulated by cyclin proteins. At which checkpoint would a cell with irreparable DNA damage most critically be halted to prevent oncogenesis?

Accepted Answer

G2/M checkpoint via p53-mediated upregulation of p21

Answer

The G2/M checkpoint is the last opportunity to halt a cell with damaged DNA before mitosis. p53, activated by DNA damage sensors (ATM/ATR kinases), transcriptionally upregulates p21, a CDK inhibitor that blocks CDK1/cyclin B activity, preventing entry into mitosis. Rb phosphorylation at G1/S controls proliferation entry but occurs earlier. The spindle assembly checkpoint monitors kinetochore attachment, not DNA integrity. G0 re-entry is not a damage checkpoint.

Question 3

A massage therapist is treating a client with chronic compartment syndrome of the anterior leg. Which combination of muscle actions would be MOST compromised, and which nerve is at greatest ischemic risk within that compartment?

Accepted Answer

Dorsiflexion and toe extension; deep fibular nerve

Answer

The anterior compartment of the leg contains tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius — all responsible for dorsiflexion and toe extension. The deep fibular (peroneal) nerve traverses this compartment and is highly vulnerable to ischemic injury from elevated intracompartmental pressure, causing foot drop. The tibial nerve runs in the deep posterior compartment, the superficial fibular in the lateral compartment, and the sural nerve is cutaneous.

Question 4

When a massage therapist applies sustained pressure to a hypertonic muscle, the Golgi tendon organ (GTO) fires and the muscle relaxes. This response is mediated by which precise neural pathway?

Accepted Answer

Ib afferent → interneuron inhibition → alpha motor neuron suppression (autogenic inhibition)

Answer

GTOs are innervated by Ib afferent fibers. When tension in the tendon exceeds a threshold, Ib afferents synapse on inhibitory interneurons in the spinal cord that suppress the alpha motor neurons innervating the same muscle — this is autogenic inhibition. The Ia afferent mediates the classic stretch (myotatic) reflex and excites the agonist. Type II afferents (flower-spray endings) contribute to tonic stretch responses. Reciprocal inhibition involves Ia afferents inhibiting antagonist motor neurons, not autogenic suppression.

Question 5

A client recovering from anterior cervical discectomy at C5–C6 reports persistent paresthesia along the lateral forearm and thumb. Which dermatome and its associated myotome reflex are MOST specifically implicated?

Accepted Answer

C6 dermatome; brachioradialis reflex (C5–C6)

Answer

The C6 dermatome covers the lateral forearm, thumb, and index finger. The brachioradialis reflex is the most specific clinical test for C6 root integrity (though the biceps reflex also has C5–C6 contribution, it is more C5-dominant). A C5–C6 discectomy directly threatens the C6 nerve root, making the brachioradialis reflex the most diagnostically specific indicator. C5 sensory distribution covers the lateral arm (deltoid patch), C7 the middle finger, and C8 the ring and little fingers.

NCBTMB Exam Practice Test

NCBTMB Exam Practice Test

NCBTMB Exam Applied Science and Anatomy 5