Histology of the eye and ear
The eyes are vital for visual perception, serving as the primary organ for detecting and interpreting light stimuli. Their intricate structure allows for the formation of clear images, enabling humans to navigate and comprehend the surrounding world.
The ears are essential for auditory perception, detecting sound waves and converting them into signals that the brain interprets. Additionally, the ears contribute to spatial awareness and balance through the vestibular system, crucial for coordination and orientation in the environment.
Cornea and ciliary body
The cornea is a transparent circular layer that covers the pupil, iris and anterior chamber of the eye. Histologically, it is composed of proteins and cells organized into 5 layers, ranging from superficial to deep: stratified squamous corneal epithelium, anterior limiting membrane (Bowman's membrane), proper substance (corneal stroma), posterior limiting membrane (Descemet's membrane) and corneal endothelium.
The ciliary body forms a complete ring around the iris. It is a ring of smooth muscle that holds the lens in place via the suspensory ligaments and controls the shape of the lens. In cross-section, the ciliary body is triangular. It is made up of 3 parts: ciliary epithelium, ciliary stroma and ciliary muscle.
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The retina constitutes the inner layer (internal tunic) of the eyeball. Its function is to convert visual stimuli from the outside environment into neural impulses that are transmitted to the cerebral cortex via the optic nerve for interpretation and analysis.
The retina is composed of epithelial, glial, and neural cells that are organized into 10 distinctive layers. Out of these, the first 9 layers belong to the inner neurosensory retina, one of which are the photoreceptors that are sensitive to light. The 10th layer constitutes the outer retinal pigmented epithelium (RPE), which serves to absorb light that passes through the retina and prevent it from reflecting back to the neurosensory layer.
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Eyelid and conjunctiva
The eyelids are thin mobile folds of soft tissue covering and protecting the anterior surface of the eyeball. The skin of the eyelids is loose and lacks fat with very small hair follicles that contain our eyelashes. These follicles are associated with the sebaceous glands and the modified apocrine sweat glands.
The conjunctiva is a transparent mucous membrane that lines the inner surface of the eyelids (palpebral conjunctiva) and the exposed anterior surface of the sclera (bulbar conjunctiva). It consists of a stratified columnar epithelium with numerous goblet cells. This is supported by a thick lamina propria of loose vascular connective tissue. The mucous secretions from the goblet cells are added to the tear film that coats the conjunctival epithelium and the cornea.
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The cochlea, which is found in the inner ear, has a distinct microanatomy. Cochlea is Greek for snail, and that’s exactly how this structure looks–a spiral and hollow bone chamber in which sound waves propagate from the base (near the oval window) to the apex. It houses the spiral organ, an elaborate configuration of membranous labyrinth and hair cells designed for auditory reception.
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