401. Consider the thoracic skeletal framework formed by the \(12\) thoracic vertebrae, \(12\) pairs of ribs and the single sternum. How many individual bones or adult vertebral units are represented in this framework?
ⓐ. \(25\)
ⓑ. \(36\)
ⓒ. \(37\)
ⓓ. \(49\)
Correct Answer: \(37\)
Explanation: The thoracic vertebral region contributes \(12\) adult vertebral units. The rib count is given in pairs, so it must first be converted to individual ribs: \[ 12\ \text{pairs}\times2=24\ \text{ribs} \] The sternum contributes one additional bone. The complete subtotal is: \[ 12+24+1=37 \] A result of \(25\) would incorrectly treat the \(12\) rib pairs as \(12\) individual ribs. The calculation integrates the dorsal vertebral component, the paired lateral ribs and the ventral sternum of the rib cage. It does not represent the entire axial skeleton, since the skull, hyoid, ear ossicles and nonthoracic vertebral regions are not included. The thoracic count uses \(12\) vertebral units, \(12\times2=24\) individual ribs and \(1\) sternum. Their sum is \(12+24+1=37\). Treating rib pairs as single bones would incorrectly produce \(25\), so the counting unit is decisive. The relation can be followed by noting that humans possess \(12\) pairs of ribs, giving \(24\) individual ribs in the complete thoracic cage.
402. Humans possess \(12\) thoracic vertebrae and \(12\) pairs of ribs. Which interpretation correctly avoids confusion between pairs and individual bones?
ⓐ. Twelve thoracic vertebrae imply only twelve individual ribs
ⓑ. The \(12\) rib pairs match the thoracic count, but represent \(24\) individual ribs
ⓒ. Each rib pair is counted as one bone because both ribs share a vertebral level
ⓓ. The \(12\) rib pairs contribute only \(12\) individual bones to the axial skeleton
Correct Answer: The \(12\) rib pairs match the thoracic count, but represent \(24\) individual ribs
Explanation: There are \(12\) thoracic vertebrae and \(12\) rib pairs, so the numerical values are equal only when ribs are counted as pairs. Each pair contains two individual ribs: \[ 12\times2=24 \] The axial-skeleton total must include \(24\) ribs, not \(12\). Thoracic vertebrae provide the dorsal articulations of the ribs, but a vertebra is not formed by fusion with a rib pair. The comparison illustrates why anatomical counting requires attention to the unit being reported. A value may represent individual bones, paired structures or fused adult units, and exchanging these units creates incorrect skeletal totals even when the digits appear familiar. The numerical relation is \[ 12\ ext{pairs} imes2=24\ ext{ribs} \] The equal number of thoracic vertebrae and rib pairs does not mean there are only \(12\) rib bones. The counting unit must be converted before individual-bone totals are compared.
403. The skull, hyoid and ear ossicles together contribute \(29\) axial bones. If the complete axial skeleton contains \(80\) bones, how many axial bones remain in the vertebral column, ribs and sternum combined?
ⓐ. \(49\)
ⓑ. \(50\)
ⓒ. \(51\)
ⓓ. \(52\)
Correct Answer: \(51\)
Explanation: The head-associated subtotal is: \[ 22\ \text{skull bones}+1\ \text{hyoid}+6\ \text{ear ossicles}=29 \] Subtracting this subtotal from the complete axial count gives: \[ 80-29=51 \] The remaining axial components independently verify the result: \[ 26\ \text{vertebral units}+24\ \text{ribs}+1\ \text{sternum}=51 \] The calculation performs a two-way reconciliation. It first derives the remainder from the full axial total and then confirms that remainder using the named non-head components. This approach detects omitted or double-counted structures and preserves the distinction between the \(22\)-bone skull and nearby axial bones that are counted separately. Subtraction gives \(80-29=51\). The same result can be verified independently as \(26\) vertebral units \(+24\) ribs \(+1\) sternum \(=51\). Agreement between the subtraction and component sum confirms that no axial category has been omitted or counted twice. The effect can be localised by noting that the axial skeleton includes the skull, vertebral column, sternum and ribs, whereas limbs and girdles form the appendicular skeleton.
404. An adult weighs \(72\,\mathrm{kg}\) and has an estimated muscle mass of \(40\,\mathrm{kg}\). Given that muscle normally contributes approximately \(40\text{–}50\%\) of adult body weight, which interpretation is correct?
ⓐ. Muscle contributes \(28.8\%\), which is below the expected range
ⓑ. Muscle contributes \(40.0\%\), which is at the lower boundary
ⓒ. Muscle contributes about \(55.6\%\), which is above the expected range
ⓓ. Muscle contributes \(50.0\%\), which is at the upper boundary
Correct Answer: Muscle contributes about \(55.6\%\), which is above the expected range
Explanation: The percentage contribution is calculated from the estimated muscle mass divided by total body mass: \[ \frac{40}{72}\times100\approx55.6\% \] The expected range for a \(72\,\mathrm{kg}\) adult would correspond to \(28.8\text{–}36.0\,\mathrm{kg}\) of muscle. An estimate of \(40\,\mathrm{kg}\) lies above that interval, and its calculated percentage exceeds the approximate \(50\%\) upper boundary. The result does not prove that the measurement is impossible, since the stated values describe an approximate population range, but it does show that this estimate is not within the expected interval. The biological interpretation must follow the calculated proportion rather than merely compare the number \(40\) with the lower percentage \(40\%\). The denominator must be the total body mass, so \(40\) is compared with \(72\), not with either endpoint of the percentage range. Reporting the result as about \(55.6\%\) preserves the approximate nature of the biological estimate.
405. A muscle sample is subjected to three stages. During Stage P, stimulation produces tension while its length is fixed. During Stage Q, an external force increases its length. During Stage R, removal of that force allows it to regain its original length. Which property sequence is demonstrated most directly?
ⓐ. \(Excitability and contractility \rightarrow extensibility \rightarrow elasticity\)
ⓑ. \(Elasticity and extensibility \rightarrow contractility \rightarrow excitability\)
ⓒ. \(Contractility and elasticity \rightarrow excitability \rightarrow extensibility\)
ⓓ. \(Excitability and extensibility \rightarrow elasticity \rightarrow contractility\)
Correct Answer: \(Excitability and contractility \rightarrow extensibility \rightarrow elasticity\)
Explanation: In Stage P, the muscle responds to stimulation, demonstrating excitability, and develops tension even though shortening is prevented, demonstrating contractility. Contractility includes the ability to shorten or generate tension. Stage Q tests extensibility, since the sample can be stretched beyond its resting length without immediately losing structural continuity. Stage R demonstrates elasticity, the tendency to return toward the original form after the stretching force is removed. These properties describe different aspects of muscle behaviour and should not be treated as interchangeable. Excitability concerns response to a stimulus, contractility concerns force production, extensibility concerns lengthening under an applied force, and elasticity concerns restoration after that force is withdrawn. Stage P demonstrates response and tension production, Stage Q tests the capacity to lengthen, and Stage R tests restoration after deformation. The order separates four properties through distinct observations.
406. The sarcolemma of one skeletal muscle fibre is ruptured, but the surrounding fascia and neighbouring fibres remain intact. Which outcome is most directly expected?
ⓐ. The whole fascicle loses bundling because one fibre membrane is ruptured
ⓑ. Neighbouring fibres lose excitation because they share a common sarcolemma
ⓒ. Collagenous fascia seals the ruptured membrane and preserves normal fibre excitation
ⓓ. The damaged fibre leaks sarcoplasm and loses excitation; fascicle bundling persists
Correct Answer: The damaged fibre leaks sarcoplasm and loses excitation; fascicle bundling persists
Explanation: The sarcolemma is the plasma membrane enclosing an individual muscle fibre and separating its sarcoplasm from the extracellular environment. Rupture of this membrane can permit leakage of sarcoplasmic contents and interfere with normal propagation of excitation along that fibre. Fascia operates at a higher organisational level by holding muscle fascicles together; its preservation can maintain the gross bundle arrangement even when one cellular membrane is damaged. Neighbouring fibres retain their own sarcolemmas and do not merge with the injured cell. The condition distinguishes damage to an individual multinucleate muscle fibre from disruption of the collagenous connective tissue organising the complete muscle. Fascia organises the bundle externally and can remain intact around neighbouring fibres. Rupture of one fibre’s plasma membrane instead compromises its intracellular contents and electrical continuity. This localisation preserves bundle structure while disabling the affected cell.
407. Two structures are examined.
| Feature | Structure P | Structure Q |
|---|
| Number of sarcolemmas | One | Many |
| Nuclei | Many within common sarcoplasm | Many within each of several separate cells |
| Internal organisation | Numerous parallel myofibrils | Several elongated fibres grouped together |
Which interpretation is correct?
ⓐ. P is a fascicle, whereas Q is one syncytial muscle fibre
ⓑ. P is one syncytial muscle fibre, whereas Q is a fascicle
ⓒ. P is one myofibril, whereas Q is one sarcomere
ⓓ. P is fascia, whereas Q is sarcoplasm
Correct Answer: P is one syncytial muscle fibre, whereas Q is a fascicle
Explanation: Structure P is enclosed by one sarcolemma and contains numerous nuclei within one continuous sarcoplasm. This is the syncytial organisation of a skeletal muscle fibre. Its parallel myofibrils lie inside the same multinucleate cell. Structure Q contains several separate elongated cells, each possessing its own sarcolemma and multinucleate sarcoplasm, so Q represents a fascicle. A fascicle is a bundle of muscle fibres rather than one enlarged cell. The table separates two kinds of multiplicity: many nuclei within one fibre and many fibres within one bundle. Confusing these levels would incorrectly treat a cellular feature as though it described the organisation of the complete muscle. The biological evidence indicates that a skeletal muscle fibre is multinucleate and contains many myofibrils arranged within a common sarcoplasm. The supplied observations indicate that collagenous fascia encloses bundles called fascicles, and each fascicle contains multiple elongated muscle fibres.
408. In an experimental muscle fibre, the total amounts of actin and myosin remain normal, but their regular alternating distribution within the myofibrils is disrupted. Which observation is most likely?
ⓐ. Disorganised filaments produce stronger striations because protein amount is unchanged
ⓑ. Regular banding remains normal because total actin and myosin amounts are unchanged
ⓒ. Regular striations become indistinct despite normal actin and myosin amounts
ⓓ. Only A-band width changes while the alternating pattern remains regular
Correct Answer: Regular striations become indistinct despite normal actin and myosin amounts
Explanation: Skeletal-muscle striation depends on the orderly and repeated distribution of thin actin and thick myosin filaments within successive sarcomeres. The visible light and dark bands arise from differences in filament composition and overlap, not merely from the total quantity of actin and myosin in the fibre. Disrupting their periodic arrangement can make the banding pattern indistinct even though both proteins remain present. The treatment does not convert myofibrils into fascicles, since those structures belong to different organisational levels. The result shows that striation is an emergent property of precise spatial organisation rather than a simple consequence of possessing contractile proteins. The decisive clue indicates that contraction increases filament overlap, bringing Z lines closer and narrowing the I band and H zone without shortening actin or myosin. The normal relation requires recognising that the M line lies centrally within the H zone and helps organise the thick filaments.
409. Meromyosin molecules are separated into two fractions.
| Test | Fraction P | Fraction Q |
|---|
| Globular head and short arm | Present | Absent |
| ATPase activity | Present | Absent |
| Actin- and ATP-binding sites | Present | Absent |
| Elongated tail region | Absent | Present |
Which identification is correct?
ⓐ. P-LMM tail region and Q-G-actin monomer
ⓑ. P-tropomyosin strand and Q-HMM head region
ⓒ. P-F-actin polymer and Q-LMM tail region
ⓓ. P-HMM head region and Q-LMM tail region
Correct Answer: P-HMM head region and Q-LMM tail region
Explanation: Heavy meromyosin contains the globular myosin head and the short arm projecting from the thick filament. The head acts as an ATPase and possesses binding sites for both ATP and actin, so Fraction P represents HMM. Light meromyosin forms the elongated tail portion of the molecule and lacks the globular catalytic and binding features listed for P, identifying Fraction Q as LMM. The two regions cooperate within the complete meromyosin molecule: LMM contributes the tail arrangement, while HMM forms the projecting cross arms that participate directly in cross-bridge cycling. Actin and tropomyosin belong to the thin filament and cannot satisfy the combined structural and enzymatic observations. The altered condition reveals that each myosin head possesses ATPase activity together with binding sites for ATP and actin. The combined condition reveals that light meromyosin contributes mainly to the thick-filament backbone, whereas heavy meromyosin forms the projecting head and short arm.
410. Two myosin preparations are tested. In Preparation P, the ATP-binding site is blocked but the actin-binding site remains intact. In Preparation Q, the actin-binding site is blocked while ATP binding and ATPase activity remain intact. Which prediction is most accurate?
ⓐ. Both preparations contract normally because one intact binding site compensates for the blocked site
ⓑ. P contracts normally, whereas Q forms cross bridges without an actin-binding site
ⓒ. P loses actin binding despite an intact site, whereas Q loses ATP binding despite an intact site
ⓓ. P cannot complete ATP-dependent energisation or detachment; Q cannot form actin-myosin cross bridges
Correct Answer: P cannot complete ATP-dependent energisation or detachment; Q cannot form actin-myosin cross bridges
Explanation: The myosin head requires its ATP-binding and ATPase functions for energetic resetting and for ATP-dependent detachment from actin. Blocking the ATP-binding site in Preparation P disrupts these nucleotide-dependent stages even though the head can still recognise actin. In Preparation Q, energy-related functions remain available, but the head cannot attach to an exposed actin site, so a cross bridge cannot form. The two defects act at different points of the same molecular cycle. Troponin regulates exposure of sites on actin, and acetylcholine is released from a motor-neuron ending; neither function is performed by the myosin binding sites tested here. The functional consequence follows from the fact that each myosin head possesses ATPase activity together with binding sites for ATP and actin. The structural consequence follows from the fact that loss of a binding or ATPase site impairs a specific head function even when the rest of the thick filament remains present.
411. One motor neuron branches to \(18\) skeletal muscle fibres and forms one terminal contact with the sarcolemma of each fibre. How many motor units and neuromuscular junctions are represented?
ⓐ. \(18\) motor units and \(1\) neuromuscular junction
ⓑ. \(1\) motor unit and \(18\) neuromuscular junctions
ⓒ. \(18\) motor units and \(18\) neuromuscular junctions
ⓓ. \(1\) motor unit and \(1\) neuromuscular junction
Correct Answer: \(1\) motor unit and \(18\) neuromuscular junctions
Explanation: A motor unit consists of one motor neuron together with all the muscle fibres supplied by it. Since the same neuron supplies all \(18\) fibres, the entire arrangement constitutes one motor unit. A neuromuscular junction is the individual contact between a motor-neuron ending and the sarcolemma of one muscle fibre. The description specifies one terminal contact on each of the \(18\) fibres, producing \(18\) neuromuscular junctions. This distinction separates a functional neural group from its multiple cellular contact sites. The number of fibres or junctions can vary within a motor unit, but the defining feature remains their common supply by one motor neuron. Motor-unit count follows neurons, not fibres: one motor neuron together with all \(18\) supplied fibres forms one motor unit. Junction count follows contacts: one terminal contact on each fibre gives \(18\) neuromuscular junctions. The two totals represent different structural totals.
412. During repeated stimulation under limited oxygen availability, lactic-acid concentration in a muscle rises steadily while mechanical performance declines. Which inference is best supported?
ⓐ. Increasing dependence on anaerobic glycogen breakdown contributes to fatigue
ⓑ. The rising lactic-acid level indicates increasingly efficient aerobic metabolism
ⓒ. The force decline reflects increased ATP production by anaerobic metabolism
ⓓ. Fatigue is unrelated to the metabolic shift because the filaments remain intact
Correct Answer: Increasing dependence on anaerobic glycogen breakdown contributes to fatigue
Explanation: Limited oxygen availability favours greater reliance on anaerobic breakdown of glycogen for energy production. Lactic acid accumulates under this condition, and its increasing concentration accompanies the observed reduction in muscular performance. The combined trends support the interpretation that anaerobic metabolism and lactic-acid accumulation contribute to fatigue during repeated activity. The data do not indicate improved aerobic metabolism, which would depend more strongly on oxygen-supported mitochondrial activity. Actin and myosin filaments slide without permanently shortening, and the sarcoplasmic reticulum is not expected to disappear. The inference connects a metabolic shift with declining performance rather than confusing fatigue with loss of the structural contractile proteins. Limited oxygen favours greater anaerobic use of glycogen, producing lactic acid while yielding less sustainable performance. The parallel rise in lactate and decline in force supports this metabolic contribution to fatigue.
413. A red muscle fibre is altered so that its myoglobin content falls markedly, but it retains abundant mitochondria and continues to depend mainly on aerobic metabolism. Which conclusion is most defensible?
ⓐ. Loss of myoglobin alone converts all red-fibre features to white-fibre features
ⓑ. Reduced myoglobin lowers oxygen storage and removes the contractile proteins
ⓒ. It loses much red colour and oxygen storage but retains other red-fibre features
ⓓ. Abundant mitochondria preserve both aerobic capacity and the original red colour
Correct Answer: It loses much red colour and oxygen storage but retains other red-fibre features
Explanation: Myoglobin contributes to the reddish appearance of red fibres and supports oxygen availability within the muscle cell. A marked decrease should reduce both colour intensity and oxygen-storage capacity. Fibre identity, however, reflects several coordinated traits, including mitochondrial abundance, sarcoplasmic-reticulum abundance and the dominant energy pathway. The altered fibre retains numerous mitochondria and mainly aerobic metabolism, so it does not acquire the complete profile of a typical white fibre. Myoglobin is not a contractile protein, and its loss does not directly eliminate actin-myosin cross bridges. The case demonstrates why classification should use a multidimensional profile rather than treating one changed characteristic as sufficient to transform the entire fibre type. Colour and oxygen-binding capacity depend strongly on myoglobin, whereas mitochondrial abundance and aerobic dependence describe additional traits. Altering one feature does not automatically convert the fibre into a complete white-fibre profile.
414. In a paired matrix experiment, calcium salts are selectively removed from bone Sample P, while chondroitin salts are selectively removed from cartilage Sample Q. Which result is most consistent with their normal matrix roles?
ⓐ. P gains hardness, whereas Q gains pliability after salt removal
ⓑ. P retains normal hardness, whereas Q develops bone-like rigidity
ⓒ. P loses pliability, whereas Q loses mineral hardness
ⓓ. P loses mineral hardness, whereas Q loses normal pliability
Correct Answer: P loses mineral hardness, whereas Q loses normal pliability
Explanation: Calcium salts are major contributors to the hard matrix of bone. Their removal should reduce the rigidity and hardness that allow bone to support the body and act as a firm skeletal element. Chondroitin salts contribute to the comparatively pliable matrix of cartilage. Removing them should impair that normal matrix property rather than converting the cartilage into mineralised bone. The experiment compares two chemically distinct skeletal matrices and links each salt with a characteristic material outcome. Bone and cartilage remain different tissues even after alteration; changing one matrix component does not automatically transform one tissue into the other. The relevant distinction emerges when calcium salts make bone matrix hard, whereas chondroitin salts contribute to the greater pliability of cartilage. The broader pattern remains consistent when a matrix defect changes the mechanical property linked to the affected material without automatically converting bone into cartilage or cartilage into bone.
415. An artificial skeletal framework supports body weight and encloses vulnerable organs but lacks surfaces to which muscles can attach. Which skeletal function is impaired most directly?
ⓐ. formation of a rigid enclosure that protects internal organs
ⓑ. transmission of muscular force to move skeletal elements
ⓒ. maintenance of a framework that supports body weight
ⓓ. retention of hard mineralised material in skeletal elements
Correct Answer: transmission of muscular force to move skeletal elements
Explanation: The framework still supports body weight and protects enclosed organs, so those skeletal functions remain present. The missing feature is attachment for muscles. Skeletal muscles generate force internally, but useful movement requires that this force be transmitted to bones or cartilages through secure attachment. Without appropriate attachment surfaces, contraction cannot move the skeletal elements effectively around joints. The defect removes the link between muscular force production and skeletal movement while preserving support and protection. This distinction shows that the skeleton is not merely a passive protective shell; it also provides the mechanical anchorage required for coordinated movement and locomotion. Support and protection remain possible in the artificial framework, but without anchorage the force of contraction cannot be transferred effectively to the skeletal levers.
416. Humans possess \(12\) pairs of ribs, and every rib has \(2\) articulation surfaces at its dorsal end. Which combined conclusion is correct?
ⓐ. The \(24\) ribs provide \(24\) dorsal surfaces, and only true ribs are bicephalic
ⓑ. The \(24\) ribs provide \(48\) dorsal surfaces, and only floating ribs are bicephalic
ⓒ. The \(24\) ribs provide \(48\) dorsal surfaces; ventral attachment defines their classes
ⓓ. The \(12\) pairs provide \(12\) dorsal surfaces, while rib thickness defines the three classes
Correct Answer: The \(24\) ribs provide \(48\) dorsal surfaces; ventral attachment defines their classes
Explanation: Twelve rib pairs correspond to \(24\) individual ribs. Each rib has two articulation surfaces at its dorsal end, so the complete set provides \[ 24\times2=48 \] dorsal articulation surfaces. This bicephalic arrangement is a shared rib feature and does not separate true, false and floating ribs. Their classes depend on the ventral relation: true ribs attach directly to the sternum through hyaline cartilage, false ribs \(8\text{–}10\) join the cartilage of the seventh rib, and floating ribs \(11\text{–}12\) lack ventral attachment. The numerical and classificatory parts of the question therefore use different evidence. Dorsal anatomy establishes the \(48\)-surface total, while the form of ventral attachment determines the category assigned to each rib pair. The multiplication uses individual ribs after converting pairs, whereas the classification uses attachment pattern. Keeping these two operations separate prevents the pair count from being confused with the number of articulation surfaces.
417. All carpals, metacarpals and phalanges of both upper limbs and all tarsals, metatarsals and phalanges of both lower limbs are removed from an otherwise complete appendicular skeleton. How many appendicular bones remain?
ⓐ. \(20\)
ⓑ. \(14\)
ⓒ. \(26\)
ⓓ. \(30\)
Correct Answer: \(20\)
Explanation: One upper limb has \(8+5+14=27\) distal hand bones, so both upper limbs contribute \(54\). One lower limb has \(7+5+14=26\) distal foot bones, so both lower limbs contribute \(52\). The total removed is \(54+52=106\). The complete appendicular skeleton contains \(126\) bones, leaving \(126-106=20\). These \(20\) bones consist of the \(14\) remaining proximal limb bones and the \(6\) girdle bones. The proximal subtotal is \(2\times3=6\) for humerus, radius and ulna of both upper limbs and \(2\times4=8\) for femur, patella, tibia and fibula of both lower limbs. Each upper limb loses \(8+5+14=27\) distal bones, so both lose \(54\). Each lower limb loses \(7+5+14=26\), so both lose \(52\). The total removed is \(106\), and \(126-106=20\) appendicular bones remain, including proximal limb bones and both girdles.
418. A classification report lists fibrous, cartilaginous, synovial, hinge, pivot, gliding, saddle and ball-and-socket as eight equivalent structural classes of joints. Which correction is biologically valid?
ⓐ. Fibrous, hinge and pivot are structural classes of cartilaginous joints
ⓑ. Synovial joints form a structural subtype within the ball-and-socket class
ⓒ. Cartilaginous and fibrous joints are movement subtypes of hinge joints
ⓓ. Fibrous, cartilaginous and synovial are classes; the other five are synovial
Correct Answer: Fibrous, cartilaginous and synovial are classes; the other five are synovial
Explanation: Fibrous, cartilaginous and synovial joints form the broad structural classification based on connecting material, cavity and characteristic mobility. Ball-and-socket, hinge, pivot, gliding and saddle describe specialised arrangements within the synovial class. They differ in the shapes and relations of their articulating surfaces and in the movements those surfaces permit. Treating all eight terms as equivalent categories mixes two hierarchical levels. For example, the shoulder is structurally synovial and more specifically ball-and-socket, while the atlas-axis articulation is synovial and more specifically pivot. Accurate classification requires stating both the broad joint class and, where relevant, the synovial subtype. Hinge, pivot, gliding, saddle and ball-and-socket describe structural subtypes within the synovial class, not categories parallel to the three major joint classes.
419. Assertion: The pubic symphysis is classified as a cartilaginous joint even though its connecting material is described as fibrous cartilage.
Reason: The bones are joined by cartilage and permit limited movement, so the word “fibrous” within the cartilage name does not make the joint a fibrous suture.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not correctly explain Assertion
ⓒ. Assertion is true, but Reason is false
ⓓ. Assertion is false, but Reason is true
Correct Answer: Both Assertion and Reason are true, and Reason correctly explains Assertion
Explanation: The pubic symphysis joins the two pelvic halves ventrally through fibrous cartilage and permits limited movement. These features place it in the cartilaginous class. A fibrous joint, such as a cranial suture, is formed by dense fibrous connective tissue directly uniting bones and normally permits no movement. The adjective “fibrous” in fibrous cartilage describes the type of cartilage present; it does not place the joint in the fibrous-joint category. The reason identifies the structural and functional criteria that determine classification and directly explains why the assertion is correct. This distinction prevents terminology within a tissue name from being confused with the broader class of the joint. The supported inference is that the pubic symphysis is a cartilaginous joint with limited movement rather than a synovial hip articulation.
420. Two patients show the following findings.
| Feature | Patient P | Patient Q |
|---|
| Body-fluid \(\mathrm{Ca^{2+}}\) | Markedly reduced | Not reported as reduced |
| Muscle response | Rapid involuntary spasms | No characteristic spasms |
| Bone mass | Normal | Reduced |
| Additional finding | No estrogen-related change identified | Decreased estrogen and fractures |
Which diagnosis is most appropriate?
ⓐ. P-tetany and Q-osteoporosis
ⓑ. P-osteoporosis and Q-tetany
ⓒ. P-gout and Q-myasthenia gravis
ⓓ. P-arthritis and Q-muscular dystrophy
Correct Answer: P-tetany and Q-osteoporosis
Explanation: Patient P has the defining combination of reduced body-fluid \(\mathrm{Ca^{2+}}\) and rapid involuntary muscle spasms, identifying tetany. The normal bone mass prevents the low calcium finding from being treated automatically as osteoporosis. Patient Q shows reduced bone mass, decreased estrogen and increased fracture occurrence, which together support osteoporosis. The absence of characteristic spasms separates Q from tetany. The table distinguishes two conditions that may both be loosely associated with calcium-related ideas but affect different biological outcomes. Tetany is primarily expressed through abnormal muscular spasms under low body-fluid calcium, whereas osteoporosis is a skeletal loss-of-mass disorder associated with fracture susceptibility. The most informative relation is that osteoporosis involves reduced bone mass and increased fracture risk and may be associated with decreased estrogen. The decisive interpretation is that two independent sets of findings may support coexisting disorders instead of one diagnosis being forced to explain every sign.
