11 topics with brief reviews: definitions, key facts, and class questions.
Sensory organs are the peripheral parts of analyzers that connect the nervous system with the outside world. In this section, we examine the microscopic structure and embryonic development of the visual and olfactory systems, starting with a basic classification of receptor organs.
The bulk of the materials is devoted to the eye. You will study the histology of the fibrous and vascular tunics, refracting media (lens), and accessory apparatus. A special focus is on the retina. We will analyze in detail its neuronal composition, the architectonics of all ten layers, and the ultrastructural features of photoreceptors. The section concludes with the histology of the olfactory organ and the specific structural features of the olfactory epithelium.
During practical classes and exams, instructors are most strict in assessing knowledge of the sources of eye development, the exact sequence of retinal layers, and the synaptic connections between its neurons. Pay special attention to these topics during your preparation!
What is the main difference between primary and secondary sensory organs?
In primary sensory organs, the irritation is perceived by the neuron itself (neurosensory cell). In secondary sensory organs, the signal is first received by an epithelial cell (sensoepithelial), which then transmits it to a neuron via a synapse.
What do the accessory structures of the eye consist of?
It includes structures that ensure the movement and protection of the eyeball: extraocular muscles, eyelids, and the lacrimal apparatus.
What is the optic nerve formed from?
The optic nerve is formed by the axons of retinal ganglion neurons that grow through the optic stalk, which connects the optic vesicle to the brain.
What is the structural difference between the cornea and the sclera?
Unlike the sclera, which consists solely of dense connective tissue, the cornea has 4 additional layers: an anterior stratified epithelium, a posterior simple epithelium, and two limiting basement membranes (Bowman's and Descemet's).
Why do albinos have red-tinted eyes?
In the iris of albinos, pigment cells are absent. Because of this, numerous blood vessels of the vascular tunic show through the tissues, giving the eyes a red color.
Why is the basement membrane of the lens located on the outside?
The lens capsule is a derivative of the basement membrane of the embryonic lens vesicle. Since the vesicle is lined with epithelium from the inside, its basement membrane naturally lies on the outer surface.
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