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Questions and Answers
What is the primary function of the cornea in the eye?
Which type of senses provides sensory information about internal organs?
What is the outer layer of the eyeball called?
What is the diameter of the adult eyeball approximately?
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Which part of the eye is involved in the drainage of aqueous humor?
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Which layer of the eyeball provides shape and rigidity?
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What type of sensory input is provided by somatic senses?
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Where does perception primarily occur in the brain?
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What is the primary function of the pigmented layer of the retina?
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What is the role of the central retinal artery?
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What composes the refractive media of the lens?
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Which structure is essential for focusing images on the retina?
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What does the anterior cavity of the eyeball consist of?
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How often is aqueous humor replaced?
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What is the purpose of the central retinal vein?
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What primarily accounts for the refraction of light in the eye?
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Which part of the eye is lined by the retina?
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What happens to light rays from objects that are 6 m or closer to the eye?
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What is the term used for the increase in lens curvature when focusing on a close object?
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How far can a young adult typically focus an object with maximum accommodation?
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What occurs to the ciliary muscle when viewing distant objects?
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Which type of lens will refract light rays toward each other?
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What role do zonular fibers play when focusing on distant objects?
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What is the primary cause for the lens's focusing power increase?
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What is the primary function of the vitreous body within the vitreous chamber?
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Which substance primarily makes up the vitreous body?
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What is the normal range for intraocular pressure in the eye?
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What process involves the bending of light as it passes through different transparent substances?
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How does the brain ensure that we perceive images correctly, despite them being inverted on the retina?
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What role does phagocytic cells play in the vitreous chamber?
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Which of the following is NOT a process involved in forming clear images on the retina?
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What primarily maintains the shape of the eyeball?
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What is the role of axon collaterals of retinal ganglion cells in the visual processing pathway?
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Which system is responsible for processing information about movement and spatial organization in the visual cortex?
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What type of cells provide physical support and detoxification in the olfactory epithelium?
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What do basal cells in the olfactory system do?
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Which of the following best describes the function of the suprachiasmatic nucleus?
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The optic radiations consist of axons projected from which part of the brain?
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Which cells in the olfactory system are responsible for containing the olfactory cilia?
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What is the main purpose of Bowman's glands in the nasal cavity?
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Study Notes
Sense and Perception
- Sense is the ability to perceive stimuli, while sensation is the process initiated by stimulating sensory receptors.
- Perception is the conscious awareness of those stimuli.
- Stimulation of sensory receptors does not immediately result in perception.
- Perception occurs when action potentials reach the cerebral cortex.
- There are two basic groups of senses: general and special senses.
General Senses
- General senses have receptors distributed over a large part of the body.
- General senses are divided into somatic senses, which provide information about the body and the environment, and visceral senses, which provide information about various internal organs.
- Visceral senses primarily involve pain and pressure.
Special Senses
- Special senses are more specialized in structure and localized to specific parts of the body.
- Special senses are smell, taste, sight, hearing, and balance.
The Eyeball - Anatomy
- The adult eyeball measures approximately 2.5 cm in diameter.
- The wall of the eyeball consists of three layers: the fibrous tunic, the vascular tunic, and the retina.
Fibrous Tunic
- The fibrous tunic is the outermost layer of the eyeball, consisting of the anterior cornea and posterior sclera.
- The cornea is a transparent coat that covers the colored iris. It helps focus light onto the retina.
- The sclera, or “white” of the eye, covers the entire eyeball except the cornea.
- The sclera provides shape and rigidity to the eyeball, protects its inner parts, and serves as an attachment point for extrinsic eye muscles.
- The scleral venous sinus, also known as the canal of Schlemm, is located at the junction of the sclera and cornea. This sinus drains aqueous humor.
Retina
- The retina is the third and innermost layer of the eyeball, lining the posterior three-quarters of the eyeball.
- It is the beginning of the visual pathway.
- The optic disc is the site where the optic (II) nerve exits the eyeball.
- The central retinal artery, a branch of the ophthalmic artery, and the central retinal vein are bundled together with the optic nerve.
- Branches of the central retinal artery nourish the anterior surface of the retina, and the central retinal vein drains blood from the retina.
Pigmented Layer of Retina
- The pigmented layer is a sheet of melanin-containing epithelial cells located between the choroid and the neural part of the retina.
- Melanin in the pigmented layer helps absorb stray light rays.
Neural (Sensory) Layer of Retina
- The neural layer is a multilayered outgrowth of the brain that processes visual data extensively before sending nerve impulses into axons that form the optic nerve.
The Lens
- The lens is located behind the pupil and iris.
- Crystallins, proteins arranged like the layers of an onion, comprise the refractive media of the lens and make it transparent.
- The lens is enclosed by a clear connective tissue capsule and held in position by encircling zonular fibers, which attach to the ciliary processes.
- The lens helps focus images on the retina for clear vision.
Interior of The Eyeball
- The lens divides the interior of the eyeball into two cavities: the Anterior cavity and the Vitreous chamber.
Anterior Cavity
- The anterior cavity, located anterior to the lens, consists of two chambers: the anterior chamber and the posterior chamber.
- The anterior chamber lies between the cornea and the iris.
- The posterior chamber lies behind the iris, in front of the zonular fibers and the lens.
- Both chambers are filled with aqueous humor, a clear, watery fluid that nourishes the lens and cornea.
- Aqueous humor continuously filters out of blood capillaries in the ciliary processes and enters the posterior chamber.
- It flows forward between the iris and the lens, through the pupil, and into the anterior chamber.
- Aqueous humor is completely replaced about every 90 minutes.
Vitreous Chamber
- The vitreous chamber is the larger posterior cavity of the eyeball, located between the lens and the retina.
- The vitreous body, a transparent jellylike substance, is found within the vitreous chamber.
- The vitreous body holds the retina flush against the choroid, providing an even surface for clear image reception.
- The vitreous body is formed during embryonic life and consists of mostly water, collagen fibers, and hyaluronic acid.
- Phagocytic cells within the vitreous body remove debris, keeping the eye clear for unobstructed vision.
Intraocular Pressure
- The intraocular pressure is mainly produced by the aqueous humor and partly by the vitreous body.
- Normal intraocular pressure is about 16 mmHg (millimeters of mercury).
- Intraocular pressure maintains the shape of the eyeball and prevents it from collapsing.
Image Production
- The eye resembles a camera in its function, focusing an image of an object onto a light-sensitive “film” – the retina.
- The eye uses three processes to form clear images on the retina: refraction, accommodation, and constriction.
Refraction of Light Rays
- When light rays traveling through a transparent substance pass into another transparent substance with a different density, they bend at the junction – this is known as refraction.
- Light rays are refracted at the anterior and posterior surfaces of the cornea as they enter the eye.
- The lens further refracts the light rays, focusing them on the retina.
- Images focused on the retina are inverted (upside down) and undergo right-to-left reversal.
- The brain interprets these images as correctly oriented in space.
- About 75% of the total refraction of light occurs at the cornea.
- The lens provides the remaining 25% of focusing power and undergoes changes to view near or distant objects.
Accommodation and the Near Point of Vision
- A convex lens, like the lens of the eye, refracts light rays toward each other.
- A concave lens refracts light rays away from each other.
- The lens of the eye is convex on both its anterior and posterior surfaces, and its focusing power increases as its curvature becomes greater.
- The lens becomes more curved when focusing on a close object, increasing refraction of light rays.
- This increase in curvature is called accommodation.
- The near point of vision refers to the minimum distance at which an object can be clearly focused with maximum accommodation. This distance is about 10 cm (4 in.) in a young adult.
Accommodation Mechanism
- When viewing distant objects, the ciliary muscle is relaxed, and the lens is flattened due to taut zonular fibers.
- When viewing a close object, the ciliary muscle contracts, pulling the ciliary process and choroid forward towards the lens.
- This action releases tension on the lens and zonular fibers, making it more curved for near vision.
Constriction of the Pupil
- The pupil, the opening in the center of the iris, regulates the amount of light entering the eye.
- Circular muscles within the iris constrict the pupil, reducing the amount of light entering.
- This process is triggered by bright light and is important for protecting the retina from damage by excessive light.
Brain Pathway for Vision
- Axons from retinal ganglion cells form the optic nerve that exits the eye medially.
- The optic nerves from both eyes converge at the optic chiasm.
- At the optic chiasm, axons from the medial half of each retina cross over to the opposite side.
- Axons from the lateral half of each retina remain uncrossed.
- Each optic tract consists of crossed and uncrossed axons that project from the optic chiasm to the thalamus on one side.
- Axon collaterals (branches) of the retinal ganglion cells project to the midbrain, participating in neural circuits that govern constriction of the pupils and coordination of head and eye movements.
- Collaterals also extend to the suprachiasmatic nucleus of the hypothalamus, which establishes patterns of sleep and other activities on a circadian schedule based on light and darkness intervals.
- The axons of thalamic neurons form the optic radiations as they project from the thalamus to the primary visual area of the cortex on the same side.
Visual Processing
- Visual signals are processed by at least three separate systems in the cerebral cortex.
- One system processes information related to the shape of objects.
- Another system processes information regarding the color of objects.
- A third system processes information about movement, location, and spatial organization.
The Olfactory System
- The sense of smell reacts to odorants, molecules in the air.
- Odorants enter the nasal cavity and are trapped in epithelial cells lining the nose, stimulating scent receptors.
- The nose is lined with three types of epithelial cells: olfactory receptor cells, supporting cells, and basal cells.
Olfactory Receptor Cells
- Olfactory receptor cells are bipolar neurons with one axon and one dendrite.
- They contain olfactory cilia, hair-like projections that have receptors stimulated by odorants.
Supporting Cells
- Supporting cells are columnar epithelial cells that provide physical support, nourishment, insulation, and protection to olfactory receptor cells.
- They detoxify chemicals that come in contact with the olfactory epithelium.
Basal Cells
- Basal cells are stem cells that constantly divide to produce new olfactory receptor cells.
Olfactory Gland or Bowman’s Gland
- The olfactory glands are epithelial cells lining the nasal cavity that produce mucus to keep the nasal cavity moist.
- They are important for odor determination but do not directly participate in it.
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Description
Explore the concepts of sense and perception, including the differences between general and special senses. This quiz delves into the anatomy of the eyeball and how sensory receptors function in the perception of stimuli. Test your knowledge on the fundamental principles of sensory processing.
