D312 ANATOMY AND PHYSIOLOGY I - Set 3 - Part 1

Correct Answer: Iliacus and psoas major crossing the hip

Option d is correct because cardiac muscle is both involuntary and striated, meaning it contracts without conscious control while displaying a striped appearance under microscopic examination, fitting both clues provided. Option a is incorrect because skeletal muscle is indeed striated, but it is a voluntary muscle type requiring conscious effort to contract, which contradicts one of the stated characteristics. Option b is incorrect because smooth muscle is involuntary, matching one clue, but it is non-striated and does not display a striped pattern when examined under a microscope. Option c is incorrect because dense connective tissue is not classified as muscle tissue at all and does not possess the ability to contract rhythmically like muscle cells do.

Correct Answer: Perimysium

Option a is correct because perimysium is the connective tissue sheath that wraps around fascicles, which are the grouped bundles of individual skeletal muscle fibers within the larger muscle structure. Option b is incorrect because endomysium is the innermost connective tissue layer that surrounds each individual muscle fiber, not the bundle of fibers known as a fascicle. Option c is incorrect because epimysium is the outermost connective tissue covering that encases the entire muscle, not the intermediate bundles of fibers found within it. Option d is incorrect because endosteum is a membrane that lines the inner surface of bones and is not part of the connective tissue organization found in skeletal muscles.

Correct Answer: Troponin

Option c is correct because when calcium ions bind to troponin, this regulatory protein undergoes a conformational shape change that subsequently pulls tropomyosin away from the binding sites on actin. Option a is incorrect because tropomyosin does not directly bind calcium ions itself but instead is physically moved aside by troponin after troponin changes shape in response to calcium binding. Option b is incorrect because myosin is the thick filament protein that forms cross-bridges with actin and does not serve as a calcium-binding regulatory protein in this contraction process. Option d is incorrect because actin is the thin filament protein that contains the binding sites for myosin and does not change shape in response to calcium binding during contraction.

Correct Answer: Actin and myosin filaments

Option b is correct because myofibrils are composed of two types of myofilaments, with actin forming the thin filaments and myosin forming the thick filaments essential for muscle contraction. Option a is incorrect because troponin and tropomyosin are regulatory proteins that sit on the actin filaments and control the contraction process, but they are not the primary myofilaments themselves. Option c is incorrect because collagen and elastin are structural proteins found in connective tissues throughout the body, not the contractile myofilaments located inside skeletal muscle fibers. Option d is incorrect because keratin is a structural protein in skin and hair while fibrin is a clotting protein in blood, and neither is found as a myofilament in muscle.

Correct Answer: Epimysium then perimysium then endomysium

Option d is correct because the outermost layer covering the entire muscle is epimysium, the next layer wrapping each fascicle is perimysium, and the innermost layer surrounding individual fibers is endomysium. Option a is incorrect because this sequence incorrectly places perimysium as the outermost layer, when in reality epimysium covers the entire muscle and is encountered first during dissection. Option b is incorrect because this sequence is completely reversed, listing the innermost layer first and the outermost layer last, which is the opposite of the correct anatomical order. Option c is incorrect because while it correctly starts with epimysium, it then incorrectly places endomysium before perimysium, reversing the order of the middle and innermost connective tissue layers.

Correct Answer: Acetylcholine

Option a is correct because acetylcholine is the specific neurotransmitter released at the neuromuscular junction that crosses the synaptic cleft and binds to receptors on the muscle fiber membrane. Option b is incorrect because dopamine is a neurotransmitter primarily involved in brain pathways related to reward, motivation, and motor control centers, not at the neuromuscular junction with skeletal muscle. Option c is incorrect because serotonin is a neurotransmitter associated with mood regulation, sleep cycles, and digestive function in the body, not the signal used at the neuromuscular junction. Option d is incorrect because norepinephrine is a neurotransmitter and hormone associated with the sympathetic nervous system stress response, not the chemical messenger used at skeletal muscle junctions.

Correct Answer: Acetylcholinesterase

Option c is correct because acetylcholinesterase is the specific enzyme located in the synaptic cleft that rapidly breaks down acetylcholine, stopping the signal and preventing continuous unwanted stimulation of the muscle. Option a is incorrect because lipase is a digestive enzyme responsible for breaking down fats and lipids in the gastrointestinal system, not for degrading neurotransmitters at the neuromuscular junction. Option b is incorrect because amylase is a digestive enzyme that breaks down starches and carbohydrates into simpler sugars and has no role in neurotransmitter breakdown at synapses. Option d is incorrect because kinase is a broad category of enzymes that add phosphate groups to proteins during cellular signaling and does not specifically degrade acetylcholine in the synaptic cleft.

Correct Answer: Sarcoplasmic reticulum

Option d is correct because the sarcoplasmic reticulum is the specialized internal storage compartment in muscle fibers that releases calcium ions, which are essential for exposing myosin-binding sites on actin. Option a is incorrect because mitochondria are organelles responsible for producing energy through cellular respiration and do not serve as the primary calcium storage site for muscle contraction signaling. Option b is incorrect because the Golgi apparatus processes and packages proteins for transport within or outside the cell and is not involved in calcium storage and release for muscle contraction. Option c is incorrect because the nucleus contains genetic material and controls cellular activities through gene expression, but it does not store or release calcium ions for muscle contraction.

Correct Answer: They are pumped back into the sarcoplasmic reticulum

Option b is correct because after contraction ends, calcium ions are actively pumped back into the sarcoplasmic reticulum for storage, which allows tropomyosin to re-cover the binding sites and muscle relaxation occurs. Option a is incorrect because the calcium ions used during excitation-contraction coupling are recycled internally back into the sarcoplasmic reticulum rather than being expelled outside the muscle cell membrane. Option c is incorrect because calcium binding to troponin is temporary during active contraction, and the ions are removed and returned to storage when the contraction signal stops. Option d is incorrect because mitochondria produce energy and do not serve as the destination for calcium ions during the relaxation phase of the muscle contraction and relaxation cycle.

Correct Answer: Synaptic vesicles

Option a is correct because synaptic vesicles are the specialized membrane-bound sacs located in the presynaptic terminal that store acetylcholine and release it into the synaptic cleft upon stimulation. Option b is incorrect because lysosomes are organelles containing digestive enzymes used for breaking down waste materials and cellular debris, not for storing and releasing neurotransmitters at nerve terminals. Option c is incorrect because ribosomes are cellular structures responsible for protein synthesis by translating messenger RNA and have no role in storing or releasing chemical neurotransmitters at synapses. Option d is incorrect because vacuoles are storage organelles commonly found in plant cells and some animal cells used for holding nutrients or waste, not for neurotransmitter release.

Correct Answer: Trigeminal nerve

Option c is correct because the trigeminal nerve, designated as cranial nerve five, provides motor innervation to all the muscles of mastication including the temporalis, masseter, and pterygoid muscles. Option a is incorrect because the facial nerve, cranial nerve seven, controls the muscles of facial expression such as those around the eyes and mouth, not the muscles responsible for chewing. Option b is incorrect because the vagus nerve, cranial nerve ten, handles sensory, motor, and autonomic functions related to visceral organs and does not innervate the muscles of mastication. Option d is incorrect because the hypoglossal nerve, cranial nerve twelve, specifically controls the muscles of the tongue for movement and speech, not the jaw muscles used for chewing.

Correct Answer: Infraspinatus

Option d is correct because the infraspinatus is one of the four rotator cuff muscles, along with supraspinatus, teres minor, and subscapularis, that collectively stabilize the glenohumeral shoulder joint. Option a is incorrect because the deltoid is a large superficial muscle responsible for abducting the arm and is not classified as one of the four rotator cuff stabilizing muscles. Option b is incorrect because the biceps brachii is an anterior arm muscle primarily responsible for elbow flexion and forearm supination, not part of the rotator cuff group. Option c is incorrect because the latissimus dorsi is a large back muscle that acts on the humerus for extension and adduction but is not one of the four rotator cuff muscles.

Correct Answer: Rectus abdominis

Option a is correct because the rectus abdominis is the vertical muscle running along the anterior abdominal wall that is primarily responsible for flexing the trunk when performing movements like crunches. Option b is incorrect because the external oblique is an abdominal muscle oriented diagonally that is more involved in lateral flexion and rotation of the trunk rather than straight forward trunk flexion. Option c is incorrect because the transverse abdominis is the deepest abdominal muscle layer that runs horizontally and primarily functions to compress the abdominal contents and stabilize the core. Option d is incorrect because the quadratus lumborum is a posterior abdominal wall muscle located in the lower back region that primarily assists with lateral flexion, not anterior trunk flexion.

Correct Answer: Semimembranosus

Option c is correct because the semimembranosus is one of the three hamstring muscles in the posterior thigh compartment, along with the biceps femoris and semitendinosus, responsible for hip extension. Option a is incorrect because the rectus femoris is part of the quadriceps group located in the anterior thigh compartment, responsible for knee extension and hip flexion, not the posterior hamstrings. Option b is incorrect because the sartorius is the longest muscle in the body, crossing the anterior thigh diagonally, and it is not classified as part of the posterior hamstring muscle group. Option d is incorrect because the vastus lateralis is one of the four quadriceps muscles in the anterior thigh compartment involved in knee extension and is not a member of the hamstrings.

Correct Answer: Gastrocnemius and soleus

Option b is correct because the gastrocnemius and soleus are the two superficial posterior lower leg muscles primarily responsible for plantar flexion, which is the action of pointing the toes downward. Option a is incorrect because the tibialis anterior is located in the anterior compartment and performs dorsiflexion, which is the opposite motion of pointing the toes downward toward the ground. Option c is incorrect because the fibularis longus and brevis are located in the lateral lower leg compartment and primarily perform eversion, which is turning the sole of the foot outward. Option d is incorrect because the tibialis posterior and flexor hallucis longus are deep posterior compartment muscles that assist with plantar flexion but are not the superficial muscles asked about.

Correct Answer: Integration

Option d is correct because integration is the nervous system function involving the processing and interpretation of sensory information within the central nervous system before an appropriate response is generated. Option a is incorrect because sensation refers to the initial detection of stimuli by sensory receptors, which is the first step, not the processing and interpretation of the information received. Option b is incorrect because response refers to the final step where the nervous system activates effector organs like muscles and glands to produce an action after information has been processed. Option c is incorrect because conduction describes the transmission of electrical impulses along neurons and is not one of the three primary named functions of sensation, integration, and response.

Correct Answer: Sympathetic nervous system

Option a is correct because the sympathetic nervous system activates the fight-or-flight response, increasing heart rate, breathing rate, and blood pressure to prepare the body for physical action during stress. Option b is incorrect because the parasympathetic nervous system promotes the rest-and-digest response, slowing the heart rate and redirecting energy toward digestion, which is the opposite of the stress response. Option c is incorrect because the somatic nervous system controls voluntary skeletal muscle movements and receives sensory input from the body surface, not involuntary stress-related organ responses. Option d is incorrect because the enteric nervous system specifically manages the nerve plexuses of the gastrointestinal tract, controlling digestion and peristalsis rather than the whole-body stress response.

Correct Answer: Enteric nervous system

Option c is correct because the enteric nervous system creates nerve plexuses that innervate the gastrointestinal tract, using chemoreceptors and stretch receptors to independently control peristalsis and glandular secretions. Option a is incorrect because the somatic nervous system deals with voluntary control of skeletal muscles and sensory input from the body surfaces, limbs, and special sense organs, not gut motility. Option b is incorrect because the sympathetic division of the autonomic nervous system manages the fight-or-flight response across many organs and does not independently regulate gut peristalsis using local plexuses. Option d is incorrect because while the parasympathetic division promotes digestion as part of rest-and-digest, the enteric nervous system is the specific division with independent gut wall plexuses described here.

Correct Answer: Brain and spinal cord

Option b is correct because the central nervous system is composed exclusively of the brain and the spinal cord, which together serve as the main processing and integration centers of the nervous system. Option a is incorrect because cranial nerves and spinal nerves are components of the peripheral nervous system that carry sensory and motor signals between the central nervous system and the rest of the body. Option c is incorrect because sensory and motor neurons are functional classifications of nerve cells found throughout both the central and peripheral nervous systems, not the structural components defining the CNS. Option d is incorrect because the sympathetic and parasympathetic divisions are subdivisions of the autonomic nervous system within the peripheral nervous system, not parts of the central nervous system itself.

Correct Answer: Blood pressure, heart rate, and digestion

Option d is correct because blood pressure, heart rate, and digestion are all involuntary functions regulated by the autonomic nervous system, which controls smooth muscle, cardiac muscle, and glandular activity. Option a is incorrect because walking, jumping, and grasping are voluntary skeletal muscle movements controlled by the somatic nervous system, not the involuntary regulation provided by the autonomic nervous system. Option b is incorrect because reading, writing, and speaking are complex voluntary activities involving conscious control of skeletal muscles and higher brain functions, not autonomic nervous system regulation of organs. Option c is incorrect because throwing and lifting are voluntary physical actions requiring conscious skeletal muscle activation through the somatic nervous system, not the involuntary control of the autonomic division.