Human Anatomy & Physiology: ANS, Special Senses, and Endocrine System

Comprehensive vocabulary flashcards covering Chapter 14 (Autonomic Nervous System), Chapter 15 (Special Senses), and Chapter 16 (Endocrine System).

Autonomic Nervous System (ANS)

A complex system of nerves that governs involuntary body actions, working continuously with the somatic nervous system to regulate visceral organs and maintain homeostasis.

Somatic Nervous System (SNS)

The division of the nervous system that operates under conscious control, employing a single lower motor neuron extending uninterrupted from the central nervous system to skeletal muscle fibers.

Preganglionic Neuron

The first neuron in the two-neuron autonomic motor pathway, whose cell body resides in the brainstem or spinal cord and whose preganglionic axon extends to an autonomic ganglion in the peripheral nervous system.

Ganglionic Neuron

The second neuron in the autonomic motor pathway, whose cell body is housed within an autonomic ganglion and whose postganglionic axon extends to target effector cells.

Parasympathetic Division

The craniosacral division of the ANS that conserves energy, promotes nutrient replenishment, and dominates during resting conditions to maintain 'rest-and-digest' functions.

Sympathetic Division

The thoracolumbar division of the ANS that prepares the body for physical activity, emergencies, and 'fight-or-flight' responses by increasing alertness, heart rate, and metabolic activity.

Sympathetic Tone

The continuous state of partial vasoconstriction of blood vessels maintained by baseline sympathetic vasomotor nerve activity to regulate systemic blood pressure.

Autonomic Neuropathy

Damage to autonomic nerves that occurs as a common complication of diabetes mellitus, leading to cardiovascular instability, sluggish pupil reactions, urinary incontinence, and impaired sweating.

Raynaud's Disease

A peripheral vascular disorder characterized by painful, exaggerated vasoconstriction in digits (fingers and toes), causing them to turn pale and cyanotic.

Autonomic Dysreflexia

A life-threatening, uncontrolled activation of autonomic neurons occurring in quadriplegics or individuals with spinal cord injuries above $T_6$, causing extreme, acute spikes in blood pressure.

Sensation

The conscious awareness of incoming sensory stimuli detected by internal or external sensory receptors.

Conjunctiva

A protective mucous membrane lining the anterior surface of the eye (excluding the cornea) and the inner surface of the eyelids that contains goblet cells to lubricate and moisten the eye.

Lacrimal Apparatus

The structural system that produces, collects, and drains lacrimal fluid (tears) across the eye surface to clean, moisten, and protect the eyeball.

Extrinsic Eye Muscles

Six straplike voluntary muscles (superior, inferior, lateral, and medial rectus, plus superior and inferior oblique) originating from the bony orbit and inserting on the eyeball to control eye movement.

Cornea

The transparent, avascular anterior region of the eye's fibrous tunic that allows light to enter and provides major light refraction.

Sclera

The tough, opaque fibrous tunic component forming the posterior majority of the eyeball wall, commonly called the 'white' of the eye.

Choroid

The highly vascularized, pigmented middle layer region of the eyeball that absorbs excess light and supplies oxygen and nutrients to the retina.

Iris

The colored, pigmented portion of the vascular tunic containing the sphincter pupillae and dilator pupillae smooth muscles that regulate pupil diameter.

Retina

The innermost layer of the eye wall composed of an outer pigmented layer attached to the choroid and an inner neural layer housing photoreceptors and associated neurons.

Optic Disc

The circular region on the posterior retina where ganglion cell axons converge to form the optic nerve (CN II), lacking photoreceptors and creating a blind spot.

Fovea Centralis

A small depressed area within the macula lutea of the retina containing the highest concentration of cones and virtually no rods, serving as the area of sharpest visual acuity.

Refraction

The bending of light rays as they pass at an oblique angle from one transparent medium to another of different density.

Nyctalopia

Night blindness resulting from severely hampered rod function or rod degeneration, most commonly caused by a prolonged vitamin A deficiency.

Taste Buds

Specialized sensory organs housing gustatory epithelial cells and supporting cells, located within tongue papillae (fungiform, foliate, and vallate) to detect tastants.

Auditory Ossicles

The three smallest bones in the body (malleus, incus, and stapes) situated within the middle ear cavity that mechanically transmit and amplify sound vibrations to the oval window.

Bony Labyrinth

A system of tortuous cavity spaces within the petrous portion of the temporal bone, comprising the vestibule, semicircular canals, and cochlea.

Perilymph

An extracellular fluid structurally similar to cerebrospinal fluid that fills the space between the bony labyrinth and membranous labyrinth in the inner ear.

Endolymph

The intracellular-like fluid contained within the membranous labyrinth of the inner ear that stimulates mechanoreceptive hair cells during hearing and balance movements.

Spiral Organ

The functional organ of hearing situated within the cochlear duct (scala media), consisting of sensory hair cells and supporting cells that detect fluid pressure waves.

Otitis Media

Middle ear inflammation or infection, particularly frequent in young children whose pharyngotympanic (auditory) tubes are shorter and horizontally oriented.

Presbycusis

An age-related form of sensorineural deafness resulting from progressive hair cell loss in the spiral organ, initially impairing perception of high-pitched sounds.

Tinnitus

A phantom auditory sensation characterized by ringing, buzzing, or clicking in the ears in the absence of external auditory stimuli.

Hormonal Stimulation

A mechanism of endocrine reflex release in which a gland cell secretes its hormone in direct response to binding another hormone (tropic hormone).

Humoral Stimulation

A mechanism of endocrine release in which gland cells secrete hormones in response to altered blood levels of specific nutrients or critical ions (e.g., $\text{Ca}^{2+}$).

Neural Stimulation

A mechanism of hormone release initiated directly by action potentials and neural input from the nervous system.

Steroid Hormones

Lipid-soluble, lipophilic signaling molecules synthesized from cholesterol, including adrenal cortex hormones and gonadal steroids.

Biogenic Amines

Water-soluble hormones derived from modified amino acids (e.g., tyrosine), including catecholamines and melatonin, with lipid-soluble thyroid hormone as an exception.

Eicosanoids

A class of local hormones synthesized from membrane phospholipid fatty acids, such as prostaglandins that stimulate pain and inflammatory responses.

Up-Regulation

The cellular process in which a target cell increases its total number of receptors for a hormone, elevating its sensitivity to that hormone.

Down-Regulation

The cellular process in which a target cell decreases its number of receptors in response to persistently elevated hormone concentrations, reducing sensitivity.

Infundibulum

The thin, funnel-like connecting stalk attaching the pituitary gland to the base of the hypothalamus.

Antidiuretic Hormone (ADH)

A hypothalamic peptide hormone stored in the posterior pituitary that acts on kidney tubule cells to reabsorb water, reduce urine output, stimulate thirst, and constrict blood vessels.

Oxytocin

A hypothalamic peptide hormone stored in the posterior pituitary that stimulates uterine smooth muscle contractions during labor, milk ejection from mammary glands, and emotional bonding.

Growth Hormone (GH)

An anterior pituitary protein hormone that exerts direct metabolic anti-insulin effects and indirect anabolic growth-promoting actions by triggering liver release of insulin-like growth factors (IGFs).

Pituitary Dwarfism vs. Gigantism

Growth hormone conditions caused by hyposecretion in children leading to short stature (dwarfism) versus hypersecretion in children causing excessive body growth (gigantism).

Acromegaly

A metabolic and structural disorder caused by excessive growth hormone secretion in adults, resulting in bone enlargement in the face, hands, and feet, along with hyperglycemia.

Thyroid Hormone (TH)

The body's primary metabolic hormone synthesized by thyroid follicular cells as tetraiodothyronine ($T_4$) and triiodothyronine ($T_3$), acting to increase cellular metabolic rate.

Calcitonin

A peptide hormone secreted by parafollicular cells of the thyroid gland in response to high blood calcium levels that lowers blood calcium by inhibiting osteoclasts and promoting urinary calcium loss.

Graves' Disease

An autoimmune hyperthyroid condition characterized by elevated metabolic rate, weight loss, hyperactivity, heat intolerance, and exophthalmos (protruding eyes).

Goiter

An enlargement of the thyroid gland resulting from a compensatory hypertrophy caused by an insufficient dietary intake of iodine required for thyroid hormone production.

Aldosterone

The principal mineralocorticoid produced in the zona glomerulosa of the adrenal cortex that maintains electrolyte balance by fostering $\text{Na}^+$ retention and $\text{K}^+$ excretion in the kidneys.

Cortisol

The primary glucocorticoid synthesized in the zona fasciculata of the adrenal cortex that increases blood glucose levels, mobilizes stored nutrients, and helps the body resist long-term stressors.

Cushing Syndrome

A condition caused by chronic exposure to excessive glucocorticoid levels, characterized by body fat redistribution forming a 'buffalo hump', muscle weakness, hypertension, and hyperglycemia.

Addison Disease

A form of primary adrenal insufficiency resulting in a chronic deficit of glucocorticoids and mineralocorticoids, causing hypotension, weight loss, fatigue, and dark skin pigmentation.

Pancreatic Islets

Clusters of endocrine cells scattered among exocrine acinar tissue in the pancreas, containing alpha cells (glucagon) and beta cells (insulin).

Insulin

A protein hormone secreted by pancreatic beta cells in response to elevated blood glucose levels, facilitating glucose uptake into target cells, glycogen formation, and lowering blood sugar.

Glucagon

A protein hormone secreted by pancreatic alpha cells in response to low blood glucose levels that stimulates glycogenolysis and gluconeogenesis in hepatocytes to raise blood glucose.

Diabetes Mellitus

A group of metabolic disorders characterized by impaired cellular glucose uptake and hyperglycemia, caused by absent or diminished insulin release (Type 1) or target cell insulin resistance (Type 2).

Melatonin

A amine hormone secreted by the pineal gland during dark hours that regulates circadian rhythm and influences sleep cycles and mood.

Parathyroid Hormone (PTH)

A protein hormone produced by chief cells of the parathyroid glands that raises blood calcium concentrations by stimulating osteoclast activity, decreasing renal calcium loss, and activating calcitriol.

Erythropoietin (EPO)

A hormone released by kidney endocrine cells in response to low blood oxygen tension that acts on red bone marrow to stimulate red blood cell production.