EXS 217 Exam 3 (Chapters 15 & 16): Special Senses and the Endocrine System

Comprehensive vocabulary flashcards covering anatomical, physiological, and biochemical concepts of the special senses (vision, hearing, equilibrium, olfaction, gustation) and the endocrine system from EXS 217 Exam 3.

Superior oblique

The extrinsic muscle of the eye that is controlled via cranial nerve IV.

Lacrimal sac

The structure from which tears drain directly into the nasolacrimal duct.

Optic disc

The area where the optic nerve and blood vessels exit the eye; lacks rods and cones, creating a physiological blind spot.

Presbyopia

The inability of the lens of the eye to accommodate for near vision.

Chemoreceptors

Sensory receptors stimulated by chemical properties that mediate the special senses of taste (gustation) and smell (olfaction).

Umami

A savory taste perception associated with amino acids.

Spiral organ of Corti

The receptor organ for hearing located inside the cochlea.

Auditory ossicles

The three small bones of the middle ear—malleus, incus, and stapes (ordered from external to internal)—that transmit sound vibrations from the tympanic membrane to the internal ear.

Vestibulocochlear nerve

Cranial nerve VIII, associated with transmitting sensory impulses for hearing and equilibrium.

Sensorineural deafness

A form of hearing impairment caused by the loss of hair cells, damage to the cochlear nerve, or damage to the auditory cortex.

Fibrous layer

The outermost layer of the eyeball that provides structure, protection, and muscle attachment sites; composed of the cornea and sclera.

Vascular layer (uvea)

The middle layer of the eyeball that controls light entry and provides blood supply; composed of the iris, ciliary body, and choroid.

Cornea

The transparent, avascular anterior segment of the fibrous tunic that protects the eye, allows light to enter, and is richly innervated with pain receptors.

Sclera

The 'whites of the eye' covering roughly $80\%$ of the eyeball surface; provides shape, anchors muscles, contains blood vessels, and is continuous with the dura mater.

Choroid

A highly vascular, pigmented membrane that absorbs light to prevent internal reflections in the eye.

Ciliary body

An ocular structure that suspends the lens and produces aqueous humor.

Aqueous humor

Clear fluid produced by the ciliary body that fills the anterior portion of the eye and nourishes the cornea and lens.

Vitreous humor

A gel-like substance formed during fetal development that fills the posterior portion of the eye and maintains eyeball shape.

Phototransduction

The process of converting light energy into an electrochemical neuronal response.

Rods

Photoreceptors with high sensitivity suited for low light and grayscale vision; characterized by low visual acuity due to many-to-one ganglion cell convergence, concentrated in the peripheral retina (~$130\text{ million}$ per retina).

Cones

Photoreceptors with low sensitivity requiring bright light for color vision; characterized by high acuity via 1:1 ganglion cell convergence, concentrated in the central retina (~$6.5\text{ million}$ per retina).

Fovea centralis

The central depression of the macula lutea containing exclusively cones, providing the highest visual acuity.

Lens accommodation

The process where ciliary muscles contract to relieve tension on the lens, causing it to become more convex to focus on near objects.

Autocrine

Short-distance chemical signaling where the secreted chemical messenger binds to a receptor on the exact same cell.

Paracrine

Short-distance chemical signaling where the secreted messenger acts on receptor-bearing target cells within the same local tissue.

Endocrine signaling

Long-distance signaling involving the secretion of hormones into the bloodstream to act across the entire body.

Amino acid-based hormones

Water-soluble hormones that circulate freely in the blood and bind to membrane-bound receptors because they cannot cross the lipid cell membrane.

Steroid hormones

Lipid-soluble hormones synthesized from cholesterol that travel bound to carrier proteins in blood, cross cell membranes, and bind to intracellular receptors.

G protein-coupled receptors (GPCR)

A class of cell membrane-bound receptors that initiate intracellular signaling cascades upon binding a hormone.

Infundibulum

The funnel-like stalk structure that connects the hypothalamus to the pituitary gland.

Hypothalamic-hypophyseal tract

The neural pathway running down axons through the infundibulum connecting the hypothalamus to the posterior pituitary.

Hypothalamic-hypophyseal portal system

A vascular network of capillaries-veins-capillaries that carries releasing and inhibiting hormones from the hypothalamus to the anterior pituitary.

Tropic hormones

Hormones that stimulate other endocrine organs to secrete their respective hormones.

Antidiuretic hormone (ADH)

A posterior pituitary hormone synthesized in the hypothalamus that decreases urine production and increases water reabsorption into the blood.

Oxytocin

A posterior pituitary hormone produced in the hypothalamus that initiates uterine contractions during labor and triggers milk release.

Parathyroid hormone (PTH)

A hormone that increases osteoclast activity to raise $\text{Ca}^{2+}$ levels in the blood.

Calcitonin

A hormone produced by the thyroid gland that decreases calcium ion concentration in the blood.

Insulin

A pancreatic hormone that lowers blood glucose levels by promoting the uptake of glucose and its conversion to glycogen.

Glucagon

A pancreatic hormone that raises blood glucose levels by stimulating the breakdown of glycogen into glucose.

Melatonin

A hormone produced by the pineal gland that regulates sleep/wake cycles.

Eustachian tube

The canal connecting the middle ear to the throat that equalizes air pressure across the tympanic membrane.

Oval window

The membrane-covered opening connecting the stapes to the internal ear that conducts vibrations into fluid.

Macula lutea

The retinal area at the center of vision that contains mostly cones and surrounds the fovea centralis.

Bipolar cells

Retinal interneurons that receive signals from photoreceptors and transmit them to ganglion cells.

Ganglion cells

Retinal neurons whose axons generate action potentials and exit the eye to form the optic nerve.

Rhodopsin

The light-absorbing visual pigment protein found within the membrane discs of rod photoreceptors.

Iris

The colored, muscular portion of the vascular layer that alters pupil diameter to regulate light entry.

Cataracts

A condition characterized by the clouding or opacification of the lens of the eye.

Growth hormone (GH)

An anterior pituitary hormone targeting the epiphyseal plates that stimulates cell division and somatic growth.

Thyroid-stimulating hormone (TSH)

A tropic hormone from the anterior pituitary that triggers the secretion of thyroid hormones.

Adrenocorticotropic hormone (ACTH)

An anterior pituitary hormone that stimulates the adrenal cortex to synthesize and secrete glucocorticoids.

Prolactin

An anterior pituitary hormone that stimulates milk production by the mammary glands.

Cortisol

A glucocorticoid hormone secreted by the adrenal gland that raises blood glucose during the stress response.

Thyroxine and triiodothyronine ($\text{T}_4$ and $\text{T}_3$)

Major metabolic hormones produced by the thyroid gland that regulate basal metabolic rate throughout the body.

Pupillary constriction

The parasympathetic response where circular muscles of the iris contract to decrease pupil diameter during bright light exposure or near vision.

Pupillary dilation

The sympathetic response where radial muscles of the iris contract to increase pupil diameter in dim lighting or during emotional arousal.

Accommodation pupillary reflex

The narrowing of the pupil when focusing on a near object to block light rays from diverging through the peripheral edges of the lens.

Eyeball convergence

The medial movement of both eyes toward the midline to keep an approaching target focused simultaneously on each fovea centralis.

Retinal pigmented layer

The outer single-cell layer of the retina that absorbs stray light to prevent scattering and provides metabolic support to photoreceptors.

Horizontal and amacrine cells

Retinal interneurons that mediate lateral inhibition and neural cross-talk to sharpen visual contrast and facilitate visual processing.

Semicircular canals

Tubular structures in the internal ear containing sensory receptors stimulated by head rotation and angular acceleration to maintain dynamic equilibrium.

Signal amplification

A biochemical mechanism in second-messenger cascades where one bound hormone molecule sequentially activates multiple downstream intracellular molecules.

Follicle-stimulating hormone (FSH)

A tropic hormone secreted by the anterior pituitary that stimulates gamete production, promoting ovarian follicle development and spermatogenesis.

Luteinizing hormone (LH)

An anterior pituitary tropic hormone that triggers ovulation in females and stimulates the synthesis of sex hormones by the gonads.

Epinephrine and norepinephrine

Catecholamine hormones secreted by the adrenal medulla that rapidly prepare the body for physical action during the fight-or-flight response.

Hypothyroidism

An endocrine condition characterized by underactivity of the thyroid gland, resulting in a deficit of metabolic hormones.

Pupil

The central circular aperture in the iris that regulates the passage of light into the interior of the eye.

Ciliary muscles

Smooth muscle rings within the vascular tunic that alter lens curvature to adjust optical focus for near or distant vision.

Ciliary zonule (suspensory ligaments)

A ring of fibrous strands extending from the vascular tunic to the lens capsule that transmits tension to adjust optical focal power.

Ciliary processes

Epithelial folds within the anterior vascular tunic containing capillaries that secrete aqueous humor.

Lens

A transparent, avascular, biconvex optical structure that focuses light onto the retina.

Lens epithelium

The anterior single layer of cuboidal cells that gives rise to crystalline-filled optical fibers.

Lens fibers

Densely packed, anucleated, elongated cells containing crystalline proteins that make up the transparent bulk of the focusing disc.

Visible light spectrum

The narrow band of electromagnetic radiation spanning wavelengths from $380\,\text{nm}$ to $700\,\text{nm}$ that stimulates retinal photoreceptors.

Opsin

The transmembrane protein component of visual pigments that binds retinal to absorb specific wavelengths of light.

Cone photoreceptor classes

The three retinal subtypes—short-wavelength (blue), medium-wavelength (green), and long-wavelength (red)—distinguished by their spectral sensitivities.

Color perception

The sensory interpretation generated in the cerebral cortex from the differential stimulation ratios across the three types of cones.

Perception of white

The visual sensation produced when short, medium, and long wavelength cones are stimulated simultaneously and equally.

Neural layer of the retina

The inner retinal sublayer composed of photoreceptors, bipolar cells, and ganglion cells that processes and transmits electrical impulses.

Visual acuity

The resolving power, clarity, and sharpness of sight, which reaches its maximum at the fovea centralis.

Light refraction

The deflection or bending of light rays as they pass obliquely from one optical medium to another of different optical density.

Convex lens

An optical element thicker at the center than at the edges that bends parallel light rays inward to focus them into an inverted image.

Inverted image

The upside-down and reversed visual projection formed on the retina when light passes through a convex focusing structure.

Thyrotropin-releasing hormone (TRH)

A hypothalamic neurohormone that travels through the portal system to stimulate the anterior pituitary to secrete TSH.

Thyroid gland

A butterfly-shaped endocrine organ located anterior to the trachea that secretes metabolic regulators and calcitonin.

Paraventricular and supraoptic nuclei

Hypothalamic neuronal clusters that synthesize oxytocin and antidiuretic hormone (ADH), respectively.

Pituitary gland (hypophysis)

A dual-lobed neuroendocrine organ seated in the sella turcica of the sphenoid bone that governs somatic growth, metabolic rate, and reproduction.

Adenohypophysis

The glandular anterior portion of the master endocrine gland regulated by hypothalamic releasing and inhibiting hormones delivered via a local portal system.

Neurohypophysis

The neural posterior portion of the master endocrine gland that stores and secretes hypothalamic hormones transported down unmyelinated axons.

Steroid hormone transport proteins

Plasma carrier proteins that reversibly bind lipid-soluble messengers, rendering them temporarily soluble in aqueous blood for circulatory transit.

Thyroid hormone signaling exception

An amino acid-derived messenger that, unlike other water-soluble hormones, travels bound to plasma carriers and binds to intracellular target receptors.

Cyclic AMP (cAMP) signaling cascade

A second-messenger pathway where hormone-receptor binding sequentially activates a G protein and adenylate cyclase, converting ATP to cyclic nucleotides that activate protein kinase A.

Diabetes mellitus

A chronic metabolic disease marked by persistent hyperglycemia resulting from impaired insulin secretion or target cell insulin insensitivity.

Estrogen and progesterone

Ovarian steroid hormones that regulate the female reproductive cycle, maintain pregnancy, and promote secondary sexual characteristics.

Testosterone

The primary androgenic steroid hormone secreted by testicular Leydig cells that stimulates spermatogenesis and promotes male secondary sexual characteristics.

Special senses vs. general senses

Sensory modalities confined to specialized anatomical organs in the head versus widespread somatic sensations distributed throughout bodily tissues.

Olfactory epithelium

A specialized patch of pseudostratified tissue in the superior nasal cavity housing primary chemoreceptive neurons for odor sensation.

Melanin in the eye

A dark cellular pigment within the vascular and retinal layers that absorbs extraneous light to reduce internal reflection and determines iris coloration.