D312 ANATOMY AND PHYSIOLOGY I - Set 2 - Part 2

Correct Answer: Depolarization of the postsynaptic muscle membrane

Option d is correct because if acetylcholine cannot bind postsynaptic receptors, sodium influx is blocked, preventing the depolarization of the muscle fiber membrane that normally triggers contraction. Option a is incorrect because calcium release from the sarcoplasmic reticulum occurs later in the excitation-contraction coupling sequence, after membrane depolarization has already been initiated by acetylcholine. Option b is incorrect because synaptic vesicle fusion with the presynaptic membrane occurs before acetylcholine is released and would not be affected by a drug blocking postsynaptic receptor binding. Option c is incorrect because the arrival of the action potential at the axon terminal happens before acetylcholine release and is an event in the motor neuron, unaffected by postsynaptic receptor blockade.

Correct Answer: Sustained stimulation from persistent acetylcholine

Option a is correct because without acetylcholinesterase to break down acetylcholine, the neurotransmitter would remain bound to receptors, causing continuous stimulation and preventing the muscle from relaxing. Option b is incorrect because acetylcholinesterase inhibition does not block calcium release directly, and the persistent acetylcholine would cause overstimulation rather than paralysis from absent signals. Option c is incorrect because while prolonged stimulation may eventually cause fatigue, the primary and most immediate effect would be sustained contraction from continuous acetylcholine receptor activation. Option d is incorrect because the nerve signals and acetylcholine are still present and active, meaning the muscle would be continuously stimulated rather than relaxed when the breakdown enzyme is inhibited.

Correct Answer: The sarcoplasmic reticulum within the fiber

Option c is correct because the sarcoplasmic reticulum is the specialized organelle in muscle fibers that stores calcium ions and releases them upon stimulation to initiate the contraction mechanism. Option a is incorrect because mitochondria are responsible for producing adenosine triphosphate for energy and do not serve as the primary calcium storage and release site for muscle contraction. Option b is incorrect because the Golgi apparatus is involved in processing and packaging proteins for secretion and does not function as a calcium reservoir in the muscle contraction sequence. Option d is incorrect because synaptic vesicles are located in the motor neuron's axon terminal and contain acetylcholine, not the calcium that is released inside the muscle fiber itself.

Correct Answer: Myosin remains bound to actin preventing relaxation

Option d is correct because if calcium is not returned to the sarcoplasmic reticulum, troponin remains activated and tropomyosin stays displaced, leaving myosin-binding sites exposed and cross-bridges locked. Option a is incorrect because acetylcholine release is controlled by motor neuron action potentials arriving at the axon terminal and is not triggered by calcium remaining in the muscle fiber cytoplasm. Option b is incorrect because spontaneous motor neuron firing is a separate event controlled by the nervous system and is not caused by calcium accumulation within the muscle fiber after contraction. Option c is incorrect because the periosteum is a membrane covering bone surfaces and has no connection to the intracellular calcium cycling or cross-bridge mechanics within a muscle fiber.

Correct Answer: Myosin-binding sites on actin are exposed

Option a is correct because after calcium is released from the sarcoplasmic reticulum, it binds troponin causing tropomyosin to shift, which exposes myosin-binding sites on actin as the next step. Option b is incorrect because the motor neuron stimulus is the very first stage of excitation-contraction coupling and occurs before calcium release, not after it in the sequence of events. Option c is incorrect because calcium being pumped back into the sarcoplasmic reticulum is the final stage that occurs after contraction is complete, not immediately following calcium release. Option d is incorrect because acetylcholine crossing the synaptic cleft is part of the neuromuscular junction events that occur before the excitation-contraction coupling sequence even begins inside the fiber.

Correct Answer: Hematopoiesis occurring in red bone marrow

Option b is correct because hematopoiesis is the process of blood cell production and it takes place primarily within red bone marrow found in spongy bone regions such as the epiphyses of long bones. Option a is incorrect because ossification refers to the process of new bone formation and does not describe blood cell manufacturing, which is a completely separate physiological function of the skeleton. Option c is incorrect because calcification is the deposition of calcium salts into bone matrix to harden it, and the periosteum is a membrane on the bone surface unrelated to blood cell production. Option d is incorrect because resorption is the breakdown of bone tissue by osteoclasts, and the medullary cavity in adults contains yellow marrow that stores fat rather than producing blood cells.

Correct Answer: Calcium and phosphate

Option d is correct because bones serve as the body's primary storage site for calcium and phosphate, which can be deposited into or released from the skeleton to maintain mineral homeostasis. Option a is incorrect because sodium and potassium are primarily regulated through kidney function and fluid balance mechanisms, and bones are not the principal reservoir for these two electrolytes. Option b is incorrect because iron is mainly stored in the liver and in hemoglobin within red blood cells, while zinc is distributed throughout various tissues rather than concentrated in bone. Option c is incorrect because while small amounts of magnesium are found in bone, magnesium and manganese together are not the two minerals stored in the greatest quantities within bone tissue.

Correct Answer: Heart and lungs protected by the rib cage

Option a is correct because the rib cage, also called the thoracic cage, is an axial skeleton structure that encloses and protects the heart, lungs, and great vessels within the thoracic cavity. Option b is incorrect because the kidneys are located retroperitoneally in the posterior abdominal region and are partially protected by the lower ribs, not primarily by the pelvic girdle structure. Option c is incorrect because the pectoral girdle consists of the clavicles and scapulae connecting the upper limbs to the trunk and does not enclose or directly shield the liver from trauma. Option d is incorrect because the scapulae are flat bones of the shoulder girdle on the posterior trunk and do not form an enclosing protective cage around the intestines or abdominal organs.

Correct Answer: Yellow marrow storing adipose tissue

Option c is correct because in adults the medullary cavity of the diaphysis is filled with yellow marrow, which is primarily composed of adipose tissue that stores fat for energy reserves. Option a is incorrect because red marrow is found in the spongy bone of the epiphyses and other locations in adults, not filling the medullary cavity of the diaphysis where yellow marrow resides. Option b is incorrect because hyaline cartilage at the growth plate is located in the metaphysis region of growing bones and does not fill the hollow medullary cavity inside the diaphysis shaft. Option d is incorrect because spongy bone with trabeculae is found at the epiphyses and within flat and irregular bones, not occupying the open medullary cavity within the tubular diaphysis shaft.

Correct Answer: Bones serve as levers for muscle action

Option d is correct because bones function as rigid levers that muscles pull against during contraction, creating movement at joints where two or more bones articulate with each other. Option a is incorrect because bones do not store mechanical energy for muscles to release, as the energy for muscle contraction comes from cellular metabolic processes involving adenosine triphosphate. Option b is incorrect because bones do not produce neural signals for muscles, as the nervous system generates and transmits the electrical impulses that stimulate muscles to contract or relax. Option c is incorrect because muscles generate force by pulling their attachment points closer together through contraction, not by pushing bones apart to create space between skeletal structures.

Correct Answer: Projections are raised attachment points for soft tissue

Option a is correct because bone projections are areas where the surface extends outward, serving as attachment points for tendons, ligaments, and other soft tissue structures involved in movement. Option b is incorrect because holes or openings in bone that allow passage of blood vessels and nerves are classified as foramina or fissures, which are distinct from raised projection features. Option c is incorrect because smooth joint surface areas are articular features where bones meet at joints, and they serve a different function than the raised projections used for tissue attachment. Option d is incorrect because hollow cavities within bone are depressions or spaces such as sinuses or fossae, not projections, which by definition extend outward from the bone surface.

Correct Answer: Sternum and twelve pairs of ribs

Option c is correct because the thoracic cage consists of the sternum with its three parts and twelve pairs of ribs, together protecting the heart, lungs, and major vessels. Option a is incorrect because clavicles and scapulae form the pectoral girdle connecting the upper limbs to the trunk and are not components of the protective thoracic cage around chest organs. Option b is incorrect because while the vertebral column runs behind the thoracic cage, the vertebrae and sacrum alone do not constitute the thoracic cage that encloses the chest cavity anteriorly. Option d is incorrect because the coxal bones and sacroiliac joint are components of the pelvic girdle in the lower body and have no structural relationship to the thoracic cage in the chest.

Correct Answer: Manubrium, body, xiphoid process

Option b is correct because the sternum's three parts from superior to inferior are the manubrium at the top articulating with the clavicles, the body in the middle, and the xiphoid process at the bottom. Option a is incorrect because this sequence places the body first and the manubrium last, reversing the correct superior-to-inferior order of the sternum's three distinct anatomical sections. Option c is incorrect because the xiphoid process is the most inferior part of the sternum and should be listed last, not first, in a top-to-bottom ordering of the three sections. Option d is incorrect because while the manubrium is correctly placed first, the xiphoid process should be last and the body should be in the middle of the correct superior-to-inferior sequence.

Correct Answer: The incus positioned between malleus and stapes

Option d is correct because the incus, also known as the anvil, sits between the malleus and stapes in the ossicular chain, relaying vibrations from the malleus to the stapes. Option a is incorrect because the malleus is the first bone in the chain that connects directly to the tympanic membrane and receives vibrations before passing them to the incus in the middle. Option b is incorrect because the stapes is the last bone in the chain that connects to the oval window of the inner ear, receiving vibrations from the incus rather than occupying the middle position. Option c is incorrect because the hyoid bone is located in the anterior neck and is not part of the auditory ossicle chain, as it supports the tongue and is involved in swallowing and speech.

Correct Answer: Malleus, incus, stapes

Option a is correct because sound vibrations travel from the tympanic membrane to the malleus first, then to the incus in the middle, and finally to the stapes at the oval window. Option b is incorrect because the incus is the middle bone in the chain and does not connect directly to the tympanic membrane, so it cannot be the first ossicle to receive sound vibrations. Option c is incorrect because the stapes is the last ossicle in the chain and transmits vibrations to the oval window, not the first bone to receive them from the eardrum membrane. Option d is incorrect because this sequence places the malleus in the middle position rather than first, and the malleus is the bone that directly attaches to and receives vibrations from the eardrum.

Correct Answer: The trigeminal nerve controlling jaw muscles

Option c is correct because the trigeminal nerve, cranial nerve five, provides motor innervation to all four muscles of mastication: the temporalis, masseter, medial pterygoid, and lateral pterygoid. Option a is incorrect because the facial nerve, cranial nerve seven, controls the muscles of facial expression such as the orbicularis oculi and orbicularis oris, not the muscles of mastication. Option b is incorrect because the hypoglossal nerve, cranial nerve twelve, controls the intrinsic and extrinsic muscles of the tongue for speech and swallowing, not the jaw-closing chewing muscles. Option d is incorrect because the vagus nerve, cranial nerve ten, has widespread autonomic functions including regulation of heart rate and digestion but does not innervate the muscles of mastication.

Correct Answer: The facial nerve, cranial nerve seven

Option a is correct because the facial nerve, cranial nerve seven, innervates all muscles of facial expression including those around the eyes, mouth, forehead, and scalp regions of the face. Option b is incorrect because the trigeminal nerve controls the muscles of mastication for chewing and provides sensory input from the face, but does not control the muscles producing facial expressions. Option c is incorrect because the accessory nerve, cranial nerve eleven, controls the sternocleidomastoid and trapezius muscles for head turning and shoulder movement, not facial expression muscles. Option d is incorrect because the glossopharyngeal nerve, cranial nerve nine, is involved in taste sensation from the posterior tongue and swallowing reflexes, not in controlling facial expression muscles.

Correct Answer: Diaphragm and intercostal muscles

Option d is correct because the diaphragm is the dome-shaped muscle that flattens during inhalation to increase thoracic volume, and the intercostal muscles between ribs assist by adjusting rib cage position. Option a is incorrect because the rectus abdominis and quadratus lumborum are abdominal wall muscles involved in trunk flexion and lateral bending, not the primary muscles responsible for respiratory mechanics. Option b is incorrect because the erector spinae and transversospinalis groups are deep back muscles involved in extending, rotating, and stabilizing the vertebral column, not changing thoracic cavity volume. Option c is incorrect because the pectoralis major and latissimus dorsi are large muscles that move the upper limb at the shoulder joint and are not the primary muscles driving respiratory volume changes.

Correct Answer: Rectus abdominis, obliques, and transverse abdominis

Option b is correct because the rectus abdominis, external and internal obliques, and transverse abdominis form the abdominal wall and together flex the trunk, rotate it, and compress the cavity. Option a is incorrect because the erector spinae, multifidus, and semispinalis are deep back muscles that extend and stabilize the spine rather than forming the anterior and lateral abdominal wall. Option c is incorrect because iliocostalis, longissimus, and spinalis are the three columns of the erector spinae group in the back, and they extend the vertebral column rather than flex the trunk. Option d is incorrect because the levator ani, coccygeus, and sphincter urethrae are pelvic floor muscles that support pelvic organs and control urinary continence, not abdominal wall muscles.

Correct Answer: The erector spinae group for extension

Option c is correct because the erector spinae group consists of three columns called iliocostalis, longissimus, and spinalis, each with cervical, thoracic, and lumbar divisions that extend the spine. Option a is incorrect because the transversospinalis group, including the multifidus and semispinalis, primarily provides rotation and stabilization of the spine rather than serving as the main extensors. Option b is incorrect because the abdominal obliques are located on the lateral abdominal wall and perform trunk rotation and flexion, which is the opposite action of the spinal extension described. Option d is incorrect because the rotator cuff group stabilizes the glenohumeral joint at the shoulder and has no involvement in extending or supporting the vertebral column in the back.