Pupillary reflex pathway - All of the following are a part except?
What is the average axial length of the human eyeball?
Lens is attached to ciliary body via?
The zonules suspending the lens are attached to the?
Which area in the spleen is considered *primarily* thymus-dependent?
Ceruminous glands present in the ear are:
The narrowest part of the nasal cavity is?
When does the rudimentary cochlea develop in the fetus?
External auditory canal is formed by:
What is the significance of the term 'Corona mortis' in human anatomy?
NEET-PG 2015 - Anatomy NEET-PG Practice Questions and MCQs
Question 141: Pupillary reflex pathway - All of the following are a part except?
- A. Edinger Westphal nucleus
- B. Medial geniculate body (Correct Answer)
- C. Pretectal nuclei
- D. Retinal ganglion cell
Explanation: ***Medial geniculate body*** - The **medial geniculate body** is part of the **auditory pathway**, involved in processing sound information [2]. - It does not play a role in the **afferent** or **efferent** limbs of the pupillary light reflex. *Edinger Westphal nucleus* - The **Edinger-Westphal nucleus** is the **parasympathetic nucleus** of cranial nerve III (**oculomotor nerve**) [1]. - It provides preganglionic parasympathetic fibers that lead to pupillary constriction via the **ciliary ganglion** [1]. *Pretectal nuclei* - The **pretectal nuclei** receive input from the **retina** and are critical for the **afferent limb** of the pupillary light reflex [1], [3]. - They send fibers to the **Edinger-Westphal nuclei** bilaterally, mediating the direct and consensual light reflexes [1]. *Retinal ganglion cell* - **Retinal ganglion cells** are responsible for transmitting visual information from the **retina** to the brain [4]. - A subset of these cells, containing **melanopsin**, are photosensitive and specifically mediate the input for the **pupillary light reflex** [3].
Question 142: What is the average axial length of the human eyeball?
- A. 16 mm
- B. 20 mm
- C. 24 mm (Correct Answer)
- D. 28 mm
Explanation: ***24 mm*** - The **average axial length** of the human eyeball is approximately **24 mm**. - This length is crucial for **emmetropia**, where parallel light rays focus precisely on the retina. *16 mm* - An axial length of **16 mm** would indicate extreme **hyperopia** (farsightedness), as the eyeball would be significantly too short [1]. - This would result in light focusing behind the retina, leading to blurry vision. *20 mm* - An axial length of **20 mm** is still considerably shorter than average, suggesting **significant hyperopia**. - This deviation from the norm would impair visual acuity without corrective lenses. *28 mm* - An axial length of **28 mm** would classify the eye as significantly **myopic** (nearsighted), as the eyeball would be too long [1]. - In this case, light would focus in front of the retina, causing distant objects to appear blurry [1].
Question 143: Lens is attached to ciliary body via?
- A. Limbus
- B. Vitreous Humour
- C. Root of iris
- D. Zonular fibers (Correct Answer)
Explanation: ***Zonular fibers*** - The **suspensory ligaments** of the lens, known as zonular fibers (or **Zonules of Zinn**), connect the lens capsule to the ciliary body. - These fibers play a crucial role in **accommodation** by transmitting the tension from the ciliary muscle to the lens, causing it to change shape [2]. *Limbus* - The **limbus** is the junction between the cornea and the sclera, serving as a transitional zone [3]. - It does not directly attach the lens to the ciliary body but is an important anatomical landmark for eye surgery. *Vitreous Humour* - The **vitreous humor** is the clear, gel-like substance that fills the space between the lens and the retina [4]. - It maintains the shape of the eye and holds the retina in place, but it does not provide structural attachment for the lens. *Root of iris* - The **root of the iris** is the outermost part of the iris where it attaches to the ciliary body. - While it is adjacent to the ciliary body, it is the iris structure itself and does not serve to attach the lens [1].
Question 144: The zonules suspending the lens are attached to the?
- A. Root of iris
- B. Ciliary body (Correct Answer)
- C. Anterior vitreous
- D. Limbus
Explanation: ***Ciliary body*** - The **suspensory ligaments of the lens**, also known as zonules of Zinn, connect the **lens capsule** to the **ciliary body**. - These zonules play a crucial role in **accommodation** by transmitting forces from the ciliary muscle to alter the shape of the lens. *Root of iris* - The **root of the iris** attaches the iris to the ciliary body but does not directly connect to the lens zonules. - The iris primarily controls the **pupil size** and light entry, while the zonules are involved in lens suspension and focusing. *Anterior vitreous* - The **anterior vitreous** is the part of the vitreous humor located in front of the lens. - While it is in close proximity to the lens, the zonules do not directly attach to the vitreous but rather to the ciliary body. *Limbus* - The **limbus** is the transitional zone between the cornea and the sclera, the white outer layer of the eye. - It is an important anatomical landmark for eye surgery and drainage of aqueous humor, but it has no direct role in suspending the lens.
Question 145: Which area in the spleen is considered *primarily* thymus-dependent?
- A. Mantle layer
- B. Malpighian corpuscle
- C. Periarteriolar lymphoid sheath (PALS) (Correct Answer)
- D. None of the options
Explanation: ***Periarteriolar lymphoid sheath (PALS)*** - PALS is the **T-cell zone** of splenic white pulp, containing predominantly **T-lymphocytes** arranged around central arterioles. [2] - This area is **thymus-dependent** as it houses mature T cells that have undergone thymic selection and education, making it the primary thymus-dependent area of the spleen. [1] *Mantle layer* - The mantle layer consists of **naïve B lymphocytes** that surround the germinal center within splenic follicles. - This area is **thymus-independent** and primarily involved in **B-cell responses** to antigens. *Malpighian corpuscle* - Also known as **splenic follicles** or white pulp, this area primarily functions as **B-cell aggregation zones**. - While containing both B and T cell areas, it's predominantly **thymus-independent** with its main role being B-cell activation and antibody production. *None of the options* - This option is incorrect because PALS clearly represents the primary **thymus-dependent area** in the spleen. - The spleen definitively contains thymus-dependent zones where **T-cell activation** and proliferation occur, specifically the PALS. [1]
Question 146: Ceruminous glands present in the ear are:
- A. Modified eccrine glands
- B. Modified apocrine glands (Correct Answer)
- C. Mucous gland
- D. Modified holocrine glands
Explanation: ***Modified apocrine glands*** - **Ceruminous glands** in the ear canal are specialized **apocrine glands** responsible for producing cerumen (earwax). - Like other apocrine glands, they secrete their product via **apical budding** of the cell, releasing fragments of the cell along with the secretion [1]. *Modified eccrine glands* - **Eccrine sweat glands** are distributed throughout the skin and produce a watery sweat for thermoregulation [1]. - They secrete their product directly onto the skin surface via **exocytosis**, without loss of cellular material. *Mucous gland* - **Mucous glands** (e.g., salivary glands, respiratory tract glands) produce **mucus**, a viscous secretion primarily for lubrication and protection. - Their secretions are rich in **mucin glycoproteins**, which is distinct from the lipid-rich cerumen. *Modified holocrine glands* - **Holocrine glands** (e.g., sebaceous glands) release their entire cell contents, including lipids and cellular debris, upon cell lysis. - While sebaceous glands contribute to earwax, ceruminous glands themselves operate via an **apocrine mechanism**, not holocrine [1].
Question 147: The narrowest part of the nasal cavity is?
- A. Internal nasal valve (Correct Answer)
- B. Antrochoanal region
- C. 1st nasal turbinate
- D. External nasal valve
Explanation: ***Internal nasal valve*** - The **internal nasal valve** is considered the narrowest and most restrictive part of the **nasal airway**. - It is formed by the caudal border of the **upper lateral cartilage**, septum, and the head of the inferior turbinate. *Antrochoanal region* - The **antrochoanal region** is the posterior opening of the nasal cavity into the nasopharynx. - While it can be narrowed by polyps or mucosal swelling, it is not anatomically the **narrowest fixed point** of the nasal cavity. *1st nasal turbinate* - The **inferior turbinate** (often referred to as the 1st turbinate) can contribute to nasal resistance, especially when enlarged. - However, the turbinate itself is a structure that can vary in size and degree of congestion, but the **internal nasal valve** represents a consistently narrower anatomical choke point. *External nasal valve* - The **external nasal valve** is formed by the ala, columella, and nostril rim, and represents the entrance to the nasal cavity. - While it is a critical area for airflow, it is typically wider than the **internal nasal valve**.
Question 148: When does the rudimentary cochlea develop in the fetus?
- A. First week
- B. 4th to 8th week (Correct Answer)
- C. 8th to 12th week
- D. 16 to 20th week
Explanation: 4th to 8th week - The **cochlea** begins its development from the **otic vesicle** around the **4th week** of gestation and undergoes extensive coiling. - By the **8th week**, the cochlea has achieved its characteristic snail-like shape, though further differentiation and maturation continue. *First week* - The first week of embryonic development involves **fertilization**, **cleavage**, and **implantation**, with no organogenesis occurring [1]. - At this stage, the embryo is a **blastocyst**, and specific organ structures like the cochlea have not yet begun to form [1]. *8th to 12th week* - While significant maturation of the inner ear structures occurs during this period, the **rudimentary cochlea** has already formed its basic shape by the 8th week. - This phase involves further differentiation of the **organ of Corti** and development of neural connections, rather than the initial formation of the cochlea itself. *16 to 20th week* - By the 16th to 20th week, the inner ear structures are largely developed and functional, including the **cochlea**, which is capable of responding to sound stimuli. - This period marks the onset of **fetal hearing** and continued fine-tuning of the auditory system, far beyond the rudimentary stage of cochlear development.
Question 149: External auditory canal is formed by:
- A. 1st branchial groove (Correct Answer)
- B. 1st visceral pouch
- C. 2nd branchial groove
- D. 2nd visceral pouch
Explanation: 1st branchial groove - The **external auditory canal** is primarily derived from the **first branchial (pharyngeal) groove** during embryonic development [1]. - This groove deepens to form the primitive external auditory meatus, which later develops into the adult external auditory canal [1]. *1st visceral pouch* - The **first pharyngeal (visceral) pouch** gives rise to structures like the **eustachian tube** (auditory tube) and the **middle ear cavity** (tympanic cavity) [1]. - It does not contribute to the formation of the external auditory canal. *2nd branchial groove* - The **second pharyngeal (branchial) groove** contributes to the formation of the **cervical sinus**, which normally obliterates. - Persistence of this groove can lead to **cervical cysts or fistulae**, but it is not involved in ear development. *2nd visceral pouch* - The **second pharyngeal (visceral) pouch** develops into the **palatine tonsils** and its fossa. - It plays no role in the formation of the external auditory canal or other ear structures.
Question 150: What is the significance of the term 'Corona mortis' in human anatomy?
- A. Anastomosis between superior and inferior gluteal arteries
- B. A ligament connecting the pubic symphysis
- C. A nerve crossing the pelvic brim
- D. Anastomosis between obturator and inferior epigastric vessels (Correct Answer)
Explanation: ***Anastomosis between obturator and inferior epigastric vessels*** - **Corona mortis**, meaning "crown of death" in Latin, refers to a clinically significant vascular anastomosis that passes over the superior pubic ramus. - This anastomosis usually occurs between the **obturator artery** (a branch of the internal iliac artery) and the **inferior epigastric artery** (a branch of the external iliac artery), posing a risk of severe hemorrhage during surgical procedures in the retropubic space [1]. *Anastomosis between superior and inferior gluteal arteries* - While gluteal arteries do anastomose, they form a crucial part of the **cruciate anastomosis of the thigh**, not the corona mortis. - This anastomosis is important for blood supply to the hip joint and thigh musculature, far removed from the retropubic space. *A ligament connecting the pubic symphysis* - The pubic symphysis is connected by ligaments such as the **superior and arcuate pubic ligaments**, which provide stability to the joint. - These are fibrous structures and do not represent a vascular anastomosis. *A nerve crossing the pelvic brim* - Several nerves cross the pelvic brim, such as the **obturator nerve** or the **femoral nerve**, but these are neural structures. - The term corona mortis specifically refers to a **vascular connection**, not a nerve.