Test: Embryology and Anatomy of Ear - 1 - NEET PG MCQ

The fusion failure of the 1st and 2nd arches results in the development of the “PRE-AURICULAR SINUS”. This condition is typically located between the tragus (derived from the 1st arch) and the ascending limb of the helix (originating from the 2nd arch). It is most often found either above the tragus or at the base of the helix (refer to the clinical image in the question).

• Children aged 5 to 7 years old are in a crucial stage of development.
• During this period, they exhibit rapid growth and notable changes in their physical, cognitive, and emotional abilities.
• Social interactions become more significant as they begin to form friendships and understand group dynamics.
• Education plays a vital role, with a focus on foundational skills such as reading, writing, and basic mathematics.
• Encouraging exploration and creativity is essential for fostering their curiosity.

1st pharyngeal pouch, 2nd pharyngeal pouch

The pharyngotympanic tube, also known as the Eustachian tube, plays a crucial role in maintaining equilibrium between the pressure in the middle ear and the external environment. It is essential for proper auditory function and is responsible for:

• Equalising air pressure in the middle ear
• Draining fluid from the middle ear to the nasopharynx
• Protecting the middle ear from potential pathogens

When this tube becomes blocked or dysfunctional, it can lead to various issues, including hearing problems, ear infections, and discomfort during changes in altitude.

The first cleft expands and meets the first pouch medially to create the tympanic membrane. Thus, the tympanic membrane consists of all three layers:

• The outer epithelial layer originating from ectoderm
• The inner endothelial layer from endoderm
• The fibrous layer situated between, derived from mesoderm

The retina forms from neuro-ectoderm. Dura mater originates from mesoderm, while pia and arachnoid are derived from the neural crest.

Petrosquamous suture

The mastoid is not fully developed at birth and continues to mature until the age of 18.

The largest air cell within the mastoid, known as the mastoid antrum, is already present at birth and resembles its adult form.

• The bony section of the external auditory canal (EAC) and the mastoid tip are absent at birth.
• The structures of the middle and inner ear reach adult size well before birth.
• The tympanic membrane (TM) is also of adult size; however, due to the lack of a bony part of the EAC, it is positioned horizontally.

The tympanic membrane, middle ear, and inner ear components are completely formed and are of adult dimensions at the time of birth. The structures of the orbit, however, keep developing following birth.

The maxilla and parietal bone keep growing even after birth.

Cartilaginous bones undergo ossification from a cartilage template (endochondral bone formation); for instance, the bony labyrinth, also referred to as the otic capsule. In contrast to cartilaginous bone, membranous bone, known as dermal bone, does not originate from cartilage that subsequently calcifies. Dermal bone develops within the dermis and grows solely through accretion—osteoblasts deposit the outer layer of the bone.

• Examples of membranous or dermal bones include the clavicle and patella.
• The inner ear's bony labyrinth is located in the petrous portion of the temporal bone.

This region is termed petrous (meaning rock-like) because it is among the densest bones in the body, although it is not the strongest. The strongest bone in the body is the femur.

Pneumatic bones are those that feature an air-filled cavity, contributing to their lightweight nature. In humans, these bones are associated with the nasal cavity and encompass the paranasal sinuses. In addition to reducing the weight of the skull, they also assist in sound resonance and function as air conditioning chambers for inhaled air.

• The pneumatic bones include the maxilla, frontal bone, sphenoid, and ethmoid.
• The mastoid is also commonly a pneumatic bone, containing numerous air cell spaces that give it a honeycomb-like structure.
• However, in some individuals, the mastoid may be diploic (filled with marrow) or sclerotic (solid bone without air).

The posterior and superior semicircular canals merge to create a common crus referred to as “crus commune”, which connects to the utricle. Consequently, the three semicircular canals have five openings into the utricle rather than six.

The Organ of Corti is a component of the membranous labyrinth.

The Organ of Corti is a crucial structure located within the cochlea of the inner ear. It plays a significant role in the process of hearing by converting sound vibrations into neural signals.

• Composed of hair cells, which are sensory receptors essential for auditory perception.
• The hair cells are supported by various types of supporting cells, providing structural integrity.
• When sound waves enter the cochlea, they create fluid movements that stimulate the hair cells.
• This stimulation generates electrical impulses that are transmitted to the brain via the auditory nerve.

Damage to the Organ of Corti can lead to hearing loss or impairment, highlighting its importance in auditory function.

Semicircular canals encompass cristae that detect angular or rotational acceleration.

• Gravitational shifts, head tilting, and linear acceleration are perceived by the maculae within the utricle and saccule.
• Sound is detected by the organ of Corti, located in the scala media, which rests on the basilar membrane.