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Anatomy & Physiology: Eye, Visual Pathway, Chemical Senses, and Ear

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  • Fibrous layer of the eyeball

    Consists of the sclera and cornea. The sclera shapes and protects the eye and anchors muscles. The cornea is transparent and refracts light.

  • Function of the sclera

    Shapes the eye, protects it, and anchors the eye muscles. It is opaque and covers 5/6 of the eyeball.

  • Function of the cornea

    Transparent layer that refracts light entering the eye. It has no blood vessels.

  • Vascular layer components

    Includes the choroid, ciliary body, and iris. Provides blood supply, holds the lens, and controls light entry.

  • Function of the choroid

    Supplies oxygen and nutrients to the outer retina and absorbs stray light with brown pigment.

  • Ciliary body functions

    Contains smooth muscle to hold the lens and secretes aqueous humor via capillaries.

  • Iris muscles and their functions

    Sphincter pupillae constricts the pupil; dilator pupillae dilates the pupil. Controls light entry.

  • Sensory layer of the eye

    Contains cells like bipolar, ganglion, amacrine, and horizontal cells that process visual signals.

  • Optic disc

    Blind spot where the optic nerve exits the eye; contains no photoreceptors.

  • Photoreceptors: rods vs cones

    Rods detect dim light and black/white vision; cones detect bright light and color.

  • Aqueous humor function

    Fills the anterior segment, helps shape the eye, and protects internal structures.

  • Glaucoma cause

    Excess aqueous humor increases intraocular pressure, potentially causing blindness.

  • Vitreous humor

    Gel-like fluid in the posterior segment that maintains eye shape and supports the retina.

  • Lens structure and function

    Transparent, avascular structure made of crystallin-filled fibers; focuses light precisely on the retina.

  • Cataracts

    Clouding of the lens due to aging; surgery is the only treatment.

  • Light adaptation

    When moving from dark to bright, pupils constrict and cones activate to reduce glare.

  • Dark adaptation

    When moving from bright to dark, pupils dilate and rods activate as cones stop working.

  • Pathway of light through the eye

    Light passes through cornea → aqueous humor → lens → vitreous humor → retina → photoreceptors.

  • Accommodation

    Process of increasing lens curvature to focus light on the retina for near objects.

  • Convergence

    Both eyes simultaneously point toward the same object to maintain single binocular vision.

  • Lens correction for myopia

    Use a concave lens to correct nearsightedness caused by an eyeball that is too long.

  • Lens correction for hyperopia

    Use a convex lens to correct farsightedness caused by an eyeball that is too short.

  • Astigmatism cause and correction

    Caused by unequal curvatures of cornea or lens; corrected with ground lenses, corneal implants, or laser surgery.

  • Visual pathway overview

    Retinal ganglion axons form optic nerve; fibers cross at optic chiasm; signals go to lateral geniculate nucleus and visual cortex.

  • Role of melanopsin-containing retinal ganglion cells

    Regulate wake/sleep signals, pupillary reflexes, and circadian rhythms via hypothalamic nuclei.

  • Olfactory receptor cells

    Bipolar neurons in the olfactory epithelium that detect odors and send signals to the brain.

  • Supporting and basal cells in olfaction

    Supporting cells protect receptors; basal cells regenerate olfactory receptor neurons.

  • Olfactory pathway

    Olfactory receptor cells → olfactory bulb → olfactory tract → olfactory cortex and limbic system.

  • Taste receptor organs

    Taste buds on fungiform, foliate, and circumvallate papillae detect chemicals dissolved in saliva.

  • Effect of smell on taste

    Taste is about 80% dependent on smell; both require aqueous solutions to activate receptors.

  • Ear parts and functions

    External and middle ear handle hearing; internal ear handles hearing and balance (equilibrium).

  • Balance function in the ear

    Uses fluid-filled canals in the inner ear to detect head movement and maintain equilibrium.