What is the action of the masseter?

Correct Answer: B

Rationale: The masseter, a powerful jaw muscle, elevates the mandible for chewing, originating from the zygomatic arch and inserting on the mandibular ramus, key in mastication. Swallowing involves pharyngeal muscles (e.g., constrictors), not masseter. Lip movement is orbicularis oris's role. Eye closure is orbicularis oculi's function. Masseter's role in biting and grinding, a primary masticatory action, makes 'b' the correct answer.

Correct Answer: D

Rationale: The hyoid bone, in the anterior neck, is unique as it doesn't articulate with any other bone, suspended by ligaments and muscles (e.g., suprahyoid, infrahyoid) to support the tongue and larynx. The mandible articulates with the temporal bone at the TMJ. Nasal bones articulate with each other and the frontal/maxilla. The cricoid cartilage , not a bone, connects to the thyroid cartilage. The hyoid's free-floating status, critical for swallowing and speech, makes 'd' the correct answer.

Correct Answer: B

Rationale: Extension is straightening the knee, increasing the angle between the femur and tibia, as when standing, driven by quadriceps contraction. Flexion bends the knee, decreasing the angle. Adduction moves the leg toward the midline, abduction away neither straighten it. Extension's role in aligning the leg, a basic joint motion, makes 'b' the correct term in kinesiology.

Correct Answer: B

Rationale: Voluntary muscles, or skeletal muscles, are under conscious control, enabling deliberate movements like walking or lifting. The hind limb, encompassing muscles like the quadriceps and hamstrings, exemplifies this attached to bones via tendons, they contract via somatic nervous system signals, allowing precise actions. The heart contains cardiac muscle, involuntary and self-regulating via pacemaker cells, beating without conscious input. The liver, a glandular organ, lacks muscle tissue; it metabolizes nutrients but doesn't move voluntarily. The lungs rely on the diaphragm and intercostal muscles for breathing, but these are partly involuntary, driven by autonomic reflexes, and the lung tissue itself isn't muscle. Skeletal muscles, striated and multinucleated, differ from cardiac (striated, single-nucleus) and smooth (non-striated, involuntary) types in structure and control. Anatomy texts highlight the hind limb's role in locomotion, with muscles like the gastrocnemius enabling voluntary flexion, contrasting with organs where autonomic control dominates, making it the clear site of voluntary muscle presence.

Correct Answer: B

Rationale: Endocrine glands secrete hormones (e.g., thyroid's thyroxine) directly into the bloodstream, lacking ducts, for systemic effects like metabolism regulation. Exocrine glands use ducts (e.g., salivary glands). Sebaceous and sweat glands , both exocrine, secrete oil and sweat externally. Endocrine glands' ductless, blood-mediated delivery, per glandular classification, makes 'b' the correct type.