Systemic Anatomy — MCQs
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All of the following muscles have dual nerve supply, EXCEPT?
All are fibrous joints except:
The strongest attachment of the vitreous body to the surrounding structures is at the level of
Sclera is weakest at all of the following sites except:
Which of the following is NOT a hybrid muscle?
Hardest bone of the body is?
The number of ciliary processes is about:
Avascular coat in eye is:
Maximum cones are seen in:
The largest organ of the body is:
Systemic Anatomy Indian Medical PG Practice Questions and MCQs
Question 131: All of the following muscles have dual nerve supply, EXCEPT?
- A. Flexor digitorum profundus
- B. Pectineus
- C. Brachialis
- D. Flexor digitorum superficialis (Correct Answer)
Explanation: No changes were made to the original explanation because none of the provided references met the relevance criteria for the specific muscles and nerves discussed. ***Flexor digitorum superficialis*** - This muscle is solely innervated by the **median nerve**. - It works to **flex the middle phalanges** of the medial four digits. *Flexor digitorum profundus* - The medial half of the muscle, which supplies the ring and little fingers, is innervated by the **ulnar nerve**. - The lateral half, which supplies the index and middle fingers, is innervated by the **anterior interosseous nerve** (a branch of the median nerve). *Pectineus* - This muscle typically receives innervation from both the **femoral nerve** and the **obturator nerve**. - Its primary action is **adduction and flexion of the hip**. *Brachialis* - While primarily innervated by the **musculocutaneous nerve**, a small component also receives innervation from the **radial nerve**. - It is a powerful **flexor of the elbow joint**.
Question 132: All are fibrous joints except:
- A. Suture
- B. Gomphosis
- C. Symphysis pubis (Correct Answer)
- D. Distal tibiofibular joint
Explanation: ***Symphysis pubis*** - The **symphysis pubis** is a **cartilaginous joint (symphysis)**, specifically a secondary cartilaginous joint, connected by a disc of **fibrocartilage**. - Unlike fibrous joints, cartilaginous joints allow for **limited movement** and lack a joint cavity [2]. *Suture* - **Sutures** are a type of **fibrous joint** found only in the skull, connecting adjacent cranial bones [1]. - They are characterized by short collagen fibers that tightly interlock the bones, providing **immobile (synarthrotic)** connections. *Gomphosis* - A **gomphosis** is a specialized fibrous joint that anchors a **tooth** into its bony socket in the jaw. - The tooth is held in place by the **periodontal ligament**, composed of dense fibrous connective tissue. *Distal tibiofibular joint* - The **distal tibiofibular joint** is a **fibrous joint (syndesmosis)** where the tibia and fibula are connected by a strong interosseous membrane and ligaments. - It allows minimal movement and provides stability to the ankle mortise.
Question 133: The strongest attachment of the vitreous body to the surrounding structures is at the level of
- A. Optic disc
- B. Foveal region
- C. Posterior surface of the lens
- D. Vitreous base (Correct Answer)
Explanation: Vitreous base - The vitreous base is the strongest area of attachment of the vitreous body, where it firmly adheres to the ora serrata and 2mm anterior and posterior to it. - This strong adhesion makes the vitreous base a critical structure in relation to retinal tears and detachments, as traction here can be significant [1]. Optic disc - The vitreous has a circular attachment around the optic disc, known as the Weiss ring, which is generally weaker than the vitreous base. - While an attachment exists, it is not considered the strongest and can easily detach during a posterior vitreous detachment (PVD). Foveal region - The vitreous body has a weak attachment to the fovea, primarily through the foveal adhesion. - This attachment is usually delicate and can contribute to conditions like vitreomacular traction when abnormal, but it is not the strongest overall attachment. Posterior surface of the lens - The vitreous is connected to the posterior capsule of the lens via the hyaloideocapsular ligament of Weiger, forming a circular adhesion that is relatively weak and can often detach without consequence. - This attachment is primarily present in younger individuals and tends to loosen with age, unlike the strong and permanent bond at the vitreous base.
Question 134: Sclera is weakest at all of the following sites except:
- A. Anteriorly
- B. Posteriorly (Correct Answer)
- C. Limbus
- D. At sites of extraocular muscle insertions
Explanation: ***Posteriorly*** - The sclera is **thickest posteriorly** (~1.0 mm), especially around the optic nerve, where it is reinforced by collagen fibers forming the lamina cribrosa. - This region provides structural integrity for the optic nerve head and resists intraocular pressure, making it the **strongest part of the sclera**. *At sites of extraocular muscle insertions* - The sclera is relatively **thin at the insertions of the rectus muscles** (~0.3-0.6 mm). - These areas represent sites of structural weakness and are vulnerable to perforation during strabismus surgery. *Anteriorly* - The sclera is significantly **thinner anteriorly** (~0.3-0.4 mm), particularly near the limbus where it transitions into the cornea [1]. - This anatomical thinning makes it more susceptible to scleral ectasia and rupture from trauma or increased intraocular pressure [1]. *Limbus* - The limbus is the **thinnest part of the sclera** (~0.3 mm), marking the transition zone between the cornea and the sclera. - Its thinness and unique histological structure make it a common site for surgical incisions and vulnerable to trauma.
Question 135: Which of the following is NOT a hybrid muscle?
- A. Sternocleidomastoid
- B. Flexor pollicis brevis
- C. Brachialis
- D. Adductor pollicis (Correct Answer)
Explanation: ***Adductor pollicis*** - The adductor pollicis is solely innervated by the **deep branch of the ulnar nerve (C8, T1)**, making it a non-hybrid muscle. - Its primary actions are **adduction, opposition, and flexion of the thumb**. *Sternocleidomastoid* - This muscle is considered hybrid because it is innervated by two different nerves: the **spinal accessory nerve (CN XI)** and branches from the **cervical plexus (C2-C3)**. - The spinal accessory nerve innervates primarily the motor function, while the cervical plexus provides proprioceptive fibers. *Flexor pollicis brevis* - This muscle often has a dual innervation, with its superficial head supplied by the **median nerve** and its deep head by the **ulnar nerve** [1]. - This dual innervation pattern qualifies it as a hybrid muscle [1]. *Brachialis* - The brachialis muscle is typically innervated by the **musculocutaneous nerve (C5, C6)**, but it also receives a small contribution from the **radial nerve (C7)**. - This additional supply from the radial nerve makes it a hybrid muscle.
Question 136: Hardest bone of the body is?
- A. Calcaneum
- B. Osseous labyrinth (Correct Answer)
- C. Head of humerus
- D. Tibial condyle
Explanation: ***Osseous labyrinth*** - The **petrous part of the temporal bone**, which houses the osseous labyrinth, is the **hardest and densest bone in the human body**. - It has the highest mineral density of all bones, with extremely thick and compact cortical bone designed to protect the delicate structures of the inner ear (cochlea and vestibular apparatus). - This exceptional hardness makes it highly resistant to fractures and often the last bone to decompose post-mortem. *Calcaneum* - The **calcaneus** (heel bone) is the largest tarsal bone and is indeed very strong and dense to withstand weight-bearing forces. - However, it contains significant **trabecular (cancellous) bone** architecture internally, which while strong, does not match the extreme cortical density of the petrous temporal bone [1]. - Its primary role is weight transmission and shock absorption, not maximal hardness. *Head of humerus* - The **head of the humerus** is primarily composed of **cancellous bone** covered by articular cartilage to facilitate smooth shoulder joint movement [1]. - Its structure is optimized for articulation and flexibility, with less cortical bone density compared to the petrous temporal bone. - It is designed for range of motion rather than maximum hardness. *Tibial condyle* - The **tibial condyles** are load-bearing surfaces of the proximal tibia covered by **articular cartilage**. - While they must withstand significant compressive forces, they contain substantial cancellous bone to allow for shock absorption [1]. - Their structure balances strength with flexibility, not maximal hardness.
Question 137: The number of ciliary processes is about:
- A. 50-60
- B. 20-30
- C. 90-100
- D. 70-80 (Correct Answer)
Explanation: ***70-80*** - The ciliary body contains numerous ciliary processes, typically numbering between **70-80**. - These processes are responsible for producing **aqueous humor** and housing the **zonular fibers** that support the lens. *50-60* - This range is a slight underestimation of the actual number of **ciliary processes**. - While close, it does not represent the typical count found in most individuals. *20-30* - This number is significantly lower than the average count of **ciliary processes**. - Such a low number would likely impact the production of **aqueous humor** and lens support. *90-100* - This range is an overestimation of the typical number of **ciliary processes**. - While variability exists, this count is higher than what is generally observed.
Question 138: Avascular coat in eye is:
- A. Choroid
- B. Retina
- C. Sclera
- D. Cornea (Correct Answer)
Explanation: ***Cornea*** - The **cornea** is the transparent, avascular (lacking blood vessels) front part of the eye that covers the iris, pupil, and anterior chamber [1]. - Its avascular nature is crucial for maintaining its **transparency**, essential for light transmission to the retina [1]. *Choroid* - The **choroid** is a highly vascular layer of the eye, rich in blood vessels, located between the retina and the sclera [1]. - Its primary function is to provide **oxygen and nutrients** to the outer layers of the retina [1]. *Retina* - The **retina** is the light-sensitive layer at the back of the eye, which contains photoreceptor cells [1]. - While it has its own blood supply (retinal vessels), it is not considered an avascular coat; it actively consumes high amounts of **oxygen and nutrients** [1]. *Sclera* - The **sclera**, or the white outer layer of the eyeball, is relatively avascular compared to the choroid, but it does contain some blood vessels, particularly in its superficial layers [1]. - Its primary role is to provide **structural support** and protection to the inner components of the eye [1].
Question 139: Maximum cones are seen in:
- A. Limbus
- B. Macula lutea
- C. Blind spot
- D. Fovea centralis (Correct Answer)
Explanation: ***Fovea centralis*** - The **fovea centralis** is a small, central pit located within the macula lutea of the retina, and it is the area of **highest visual acuity** due to a very high concentration of cones [1]. - It contains almost exclusively **cones**, responsible for detailed color vision and bright light conditions [1]. *Limbus* - The **limbus** is the border between the cornea and the sclera, and it is not involved in photoreception [2]. - It plays a crucial role in maintaining corneal integrity and is a source of **corneal stem cells**. *Macula lutea* - The **macula lutea** is a yellow-pigmented oval area near the center of the retina that is responsible for sharp, detailed central vision [1]. - While it has a high concentration of **cones**, the very highest concentration is specifically found in its center, the **fovea centralis** [1]. *Blind spot* - The **blind spot**, also known as the optic disc, is the area where the **optic nerve** exits the eye [2]. - It contains **no photoreceptors** (neither rods nor cones) and therefore cannot detect light.
Question 140: The largest organ of the body is:
- A. Skin (Correct Answer)
- B. Liver
- C. Gluteus maximus
- D. Femur
Explanation: **Skin** - The skin, or **integumentary system**, is the **largest organ** in the human body by both surface area and weight. [1] - It serves crucial functions including **protection**, temperature regulation, **sensation**, and synthesis of vitamin D. [1] *Liver* - The liver is the **largest internal organ** of the body, playing vital roles in metabolism, detoxification, and protein synthesis. - While significant in weight, its overall surface area and comprehensive coverage of the body are less than that of the skin. *Gluteus maximus* - The **gluteus maximus** is the largest muscle in the human body, primarily responsible for hip extension. - It is a single muscle and not considered an organ, fitting under the broader category of the muscular system. *Femur* - The **femur**, or thigh bone, is the longest and strongest bone in the human body. - It is part of the skeletal system and, similar to the gluteus maximus, it is a single component rather than a comprehensive organ.
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