Systemic Anatomy — MCQs

Systemic Anatomy Indian Medical PG Practice Questions and MCQs

Question 161: Sclera is weakest at the level of:

A. Ora serrata
B. Equator
C. Macula
D. Insertion of extraocular muscles (Correct Answer)

Explanation: ***Insertion of extraocular muscles*** - The sclera is thinnest (0.3-0.4 mm) and therefore weakest where the **tendons of the extraocular muscles insert**, as these points are subject to constant tugging and tension. - This anatomical feature is clinically relevant in cases of **globe rupture** (the sclera is most vulnerable here during trauma) and during **strabismus surgery**. - The four rectus muscles insert approximately 5-7 mm from the limbus, and these insertion sites represent the thinnest portions of the sclera. *Ora serrata* - This is the junction between the retina and the ciliary body, located approximately 6-7 mm behind the limbus. - The sclera at this location is relatively thick and robust to provide structural support. - Not a site of particular weakness. *Equator* - The equator is the imaginary circumferential line around the middle of the eyeball. - At this level, the sclera has a uniform thickness of approximately 0.6 mm, which is thicker than at muscle insertion sites. - Provides structural integrity and is not a point of weakness. *Macula* - The macula is a specialized area of the retina responsible for central high-acuity vision. - The sclera overlying the posterior pole (including the macular area) is approximately 1.0 mm thick, making it the **thickest portion** of the sclera. - Not a site of weakness; its significance lies in visual function, not mechanical strength.

Question 162: Which muscle originates from tendon of other muscle?

A. FCR
B. Lumbricals (Correct Answer)
C. Adductor pollicis
D. Palmaris longus

Explanation: Lumbricals - The lumbrical muscles are unique in the hand because they originate from the tendons of the flexor digitorum profundus (FDP), not from bone [1]. - This attachment allows them to flex the metacarpophalangeal (MCP) joints while extending the interphalangeal (IP) joints [1]. FCR - The flexor carpi radialis (FCR) muscle originates from the medial epicondyle of the humerus, a bony origin. - Its primary function is flexion and radial deviation of the wrist. Adductor pollicis - The adductor pollicis muscle has two heads, the oblique and transverse heads, both originating from various carpal bones and the third metacarpal. - It plays a crucial role in adducting the thumb. Palmaris longus - The palmaris longus muscle originates from the medial epicondyle of the humerus, similar to the FCR. - It contributes to wrist flexion and is absent in a significant portion of the population.

Question 163: Smallest muscle in the body is:

A. Interarytenoid
B. Stapedius (Correct Answer)
C. Superior oblique
D. Corrugator supercilli

Explanation: ***Stapedius*** - The **stapedius muscle** is located in the middle ear and is the **smallest skeletal muscle** in the human body. - It plays a crucial role in hearing by **stabilizing the stapes bone** [1] and protecting the inner ear from excessively loud sounds via the **acoustic reflex**. *Interarytenoid* - The **interarytenoid muscle** is a laryngeal muscle that adducts the vocal folds. - While small and essential for phonation, it is not the smallest muscle in the body. *Superior oblique* - The **superior oblique muscle** is one of the extrinsic ocular muscles responsible for eye movement [2]. - It is significantly larger than the stapedius muscle. *Corrugator supercilli* - The **corrugator supercilli** is a small muscle of facial expression responsible for drawing the eyebrows together. - Although small, it is larger than the stapedius muscle.

Question 164: Nodes of Rouviere -

A. Adenoids
B. Parapharyngeal node
C. Retropharyngeal node (Correct Answer)
D. None of the options

Explanation: ***Retropharyngeal node*** - The **Node of Rouviere** is specifically the uppermost lymph node in the **retropharyngeal chain**. - It is clinically important as it serves as the primary drainage site for the **nasopharynx**. *Adenoids* - **Adenoids** (pharyngeal tonsils) are lymphoid tissue located in the **nasopharynx**, but they are a diffuse collection of tissue, not a specific single lymph node. - While they are part of Waldeyer's ring and involved in immune function, they are distinct from the individual retropharyngeal lymph nodes. *Parapharyngeal node* - **Parapharyngeal nodes** are located in the **parapharyngeal space**, distinct from the more posterior retropharyngeal space. - They drain structures such as the oral cavity, oropharynx, and parotid gland, but are not synonymous with the Node of Rouviere. *None of the options* - This option is incorrect because **"Retropharyngeal node"** correctly identifies the Node of Rouviere.

Question 165: Normal volume of adult testis

A. 15-20 ml (Correct Answer)
B. 25-30 ml
C. 5-10 ml
D. 10-15 ml

Explanation: 15-20 ml - The **most commonly cited normal adult testicular volume** is **15-20 ml**, which represents the **typical average range** for healthy adult males. - This measurement is assessed clinically using a **Prader orchidometer** or more precisely with **ultrasound**. - While the broader normal range extends to 25 ml, **15-20 ml is considered the standard reference range** in most medical textbooks and clinical practice. *25-30 ml* - A volume of **25-30 ml** is at the **upper limit or above** the normal range. - While **up to 25 ml** may be within normal limits, **25-30 ml** exceeds the typical accepted range and is **not the most representative** of normal adult testicular volume. *5-10 ml* - A testicular volume of **5-10 ml** in an adult is **significantly below normal** and indicates **testicular hypotrophy or atrophy**. - This could suggest conditions such as **hypogonadism**, **Klinefelter syndrome**, or other testicular pathology. *10-15 ml* - While **10-15 ml** may be observed in some adults, it is at the **lower end of the acceptable range** and may warrant further evaluation. - The **standard normal range begins at 15 ml**, making this option **below the typical normal volume** cited in most medical references.

Question 166: What is the narrowest part of the infant's respiratory tract?

A. Subglottis (Correct Answer)
B. Glottis
C. Carina
D. Epiglottis

Explanation: ***Subglottis*** - In infants and young children, the **cricoid cartilage** (forming the subglottis) is the narrowest and least distensible portion of the airway. - This anatomical feature makes the subglottis particularly susceptible to **edema** and obstruction during inflammation or infection, leading to conditions like **croup**. *Glottis* - The glottis is the narrowest part of the adult airway, but not the infant airway. - It consists of the **vocal cords** and the space between them, playing a crucial role in phonation. *Carina* - The carina is the point where the trachea divides into the two main bronchi. - While a significant anatomical landmark, it is not the narrowest part of the respiratory tract in infants or adults. *Epiglottis* - The epiglottis is a cartilaginous flap that prevents food from entering the trachea during swallowing. - While important for airway protection, it is not the narrowest part of the infant's respiratory tract.

Question 167: Anteroposterior diameter of normal adult eyeball is:

A. 23 mm
B. 25 mm
C. 23.5 mm
D. 24 mm (Correct Answer)

Explanation: ***24 mm*** - The average **anteroposterior diameter** of a normal adult eyeball is approximately **24 mm**. - This measurement is crucial for **refractive power calculations** and understanding visual acuity. *23 mm* - While close, **23 mm is slightly smaller** than the typical average anteroposterior diameter [1]. - A shorter anteroposterior diameter can lead to **hyperopia (farsightedness)** if the refractive power of the lens and cornea is normal [1]. *25 mm* - This value is slightly larger than the average. A longer anteroposterior diameter (e.g., beyond **24 mm**) is often associated with **myopia (nearsightedness)** [1]. - In myopia, the focal point of light falls in front of the retina due to the increased length of the eyeball [1]. *23.5 mm* - Similar to 23 mm, this value is a bit less than the **established average**. - Small deviations like this, if consistent, can impact the eyes' **refractive capabilities**.

Question 168: Most common site of hydatid cyst in human body is:

A. Right antero-inferior lobe of liver
B. Spleen
C. Left lobe of liver
D. Right postero-superior lobe of liver (Correct Answer)

Explanation: ***Right postero-superior lobe of liver*** - The **liver** is the most common organ affected by hydatid cysts due to its role in filtering blood from the portal circulation, which carries ingested *Echinococcus* eggs [1]. - Within the liver, the **right lobe** is more frequently involved than the left, and specifically, the **postero-superior segments** are the most common sites [1]. *Right antero-inferior lobe of liver* - While the human **liver** is the most common organ for hydatid cysts, the **antero-inferior lobe** is less frequently affected than the postero-superior region [1]. - The distribution within the right lobe tends to favor the posterior segments for initial lodging of the parasites. *Spleen* - The **spleen** is a possible site for hydatid cysts, but it is considered a **rare** location compared to the liver and lungs. - This is because the spleen is a secondary site, usually affected when parasites bypass the liver or primary cysts rupture and spread. *Left lobe of liver* - Although the **left lobe of the liver** can be affected by hydatid cysts, it is significantly **less common** than involvement of the right lobe [1]. - The size and typical blood flow patterns favor the right lobe as the primary site of infection.

Question 169: Iris is thinnest at:

A. Base
B. Ciliary zone
C. Collarette
D. Pupil margin (Correct Answer)

Explanation: ***Pupil margin*** - The iris is **thinnest** at the pupil margin, making it a common site for tears or dehiscence during trauma or surgery. - This anatomical feature is related to the termination of the iris stroma and muscle layers as they define the pupillary opening. *Base* - The iris base is generally thicker and more robust, attaching to the **ciliary body** and forming the root of the iris. - It contains a rich vascular supply and muscular structures, contributing to its relative strength. *Ciliary zone* - The **ciliary zone** (or ciliary part) of the iris lies between the base and the collarette. - While it is not the thickest part, it is thicker than the pupil margin and houses the majority of the iris stroma and blood vessels. *Collarette* - The **collarette** is a circular ridge near the middle of the iris, marking the junction between the pupillary and ciliary zones. - It is a prominent anatomical landmark but is not considered the thinnest part of the iris.

Question 170: Wieger's ligament is seen at:

A. Attachment of vitreous to posterior surface of lens (Correct Answer)
B. Posterior chamber
C. Suspension of ciliary body
D. Junction of cornea and sclera

Explanation: ***Attachment of vitreous to posterior surface of lens*** - Wieger's ligament is a **strong circular adhesion** between the anterior hyaloid membrane of the **vitreous body** and the posterior capsule of the **lens**. - This attachment is crucial for maintaining the position of the vitreous and lens, forming the **retrolental space of Berger**. *Posterior chamber* - The posterior chamber is the space between the **iris** anteriorly and the **lens** and **ciliary body** posteriorly, filled with aqueous humor [1]. - It does not specifically refer to Wieger's ligament, which is an anatomical structure at the vitreolenticular interface. *Suspension of ciliary body* - The ciliary body is suspended by the **ciliary muscles** and connected to the lens by the **zonular fibers** (suspensory ligaments of the lens) [3]. - These structures are involved in **accommodation** and aqueous humor production, distinct from Wieger's ligament [1]. *Junction of cornea and sclera* - This junction is known as the **limbus**, a crucial anatomical landmark for **corneal surgery** and containing the trabecular meshwork for aqueous humor outflow [1], [2]. - Wieger's ligament is located deep within the eye, specifically linking the vitreous and the lens, not at the superficial anterior ocular surface.

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