Human Anatomy and Physiology: ANS, Eye, Ear, and Nervous System

Flashcards covering human anatomy and physiology concepts including the autonomic nervous system, pharmacology, eye and vision structures/pathways, and ear and hearing/equilibrium mechanisms.

Preganglionic sympathetic neurons

Neurons with cell bodies located in the intermediate lateral cell column (IMLCC) of the thoracic or lumbar regions ($T1-L2$) of the spinal cord.

Preganglionic parasympathetic neurons

Neurons with cell bodies located in the brainstem (cranial nerves III, VII, IX, X) or sacral lateral gray column ($S2-S4$) of the spinal cord.

Postganglionic sympathetic neurons

Autonomic neurons with cell bodies in sympathetic trunk ganglia (paravertebral) or prevertebral ganglia (celiac, superior mesenteric, inferior mesenteric) that target adrenergic receptors.

Postganglionic parasympathetic neurons

Autonomic neurons with cell bodies located in terminal or intramural ganglia found within or near the walls of effector organs.

Vagus nerve (CN X)

Cranial nerve X containing preganglionic parasympathetic fibers that innervate the heart, lungs, and abdominal organs; stimulation decreases heart rate.

Muscle spindle

A sensory receptor that responds to excessive stretching (passive tension) of a muscle, triggering a reflex arc that results in muscle contraction.

Golgi tendon organ

A sensory receptor that responds to excessive contraction (active tension) of a muscle, triggering a reflex arc that results in muscle relaxation.

Alpha 1 receptor

Adrenergic receptor located on blood vessels that causes vasoconstriction when stimulated by epinephrine or agonists such as phenylephrine.

Beta 2 receptor

Adrenergic receptor that preferentially binds low concentrations of circulating epinephrine, inducing vasodilation and bronchodilation.

Clonidine

An alpha-2 adrenergic agonist that inhibits norepinephrine release from presynaptic neurons, resulting in vasodilation and reduced blood pressure.

Albuterol

A selective beta-2 adrenergic agonist used as an anti-asthmatic drug to induce bronchodilation, which can also increase heart rate.

Atropine

An anticholinergic drug that blocks muscarinic cholinergic receptors, reducing gut motility and sweat production while increasing heart rate.

Propranolol

A non-selective beta-blocker that inhibits beta-1 and beta-2 adrenergic receptors; reduces heart rate but is contraindicated in patients with asthma.

Phenylephrine

An alpha-1 adrenergic agonist that causes vascular smooth muscle vasoconstriction and reduces nasal congestion.

Isoproterenol

A non-selective beta-adrenergic agonist that stimulates beta-1 and beta-2 receptors, leading to increased heart rate and bronchodilation.

Carbidopa-Levodopa

A medication given to patients with Parkinson's disease containing levodopa, which crosses the blood-brain barrier as a precursor to dopamine.

Muscarine

A toxin that acts as a muscarinic cholinergic receptor agonist, slowing heart rate and causing excessive sweating, gastrointestinal cramping, and diarrhea.

Fibrous tunic

The superficial outermost layer of the eyeball, comprising the posterior white sclera and anterior transparent cornea.

Sclera

The white, opaque posterior structure of the fibrous tunic that maintains eyeball shape and protects internal structures.

Cornea

The transparent, avascular anterior portion of the fibrous tunic through which light rays pass into the eye; can be transplanted with minimal risk of rejection.

Vascular tunic

The middle layer of the eyeball (uvea), consisting of the choroid, ciliary body, suspensory ligaments, pupil, and iris.

Choroid

The highly vascular, pigmented posterior layer of the vascular tunic that absorbs light to prevent scattering inside the eye.

Ciliary body

Structure of the vascular tunic containing ciliary muscles (which control lens shape) and ciliary processes (which secrete aqueous humor).

Iris

The colored muscular ring of the vascular tunic containing radial and circular smooth muscles that adjust pupil size to regulate light entry.

Retina

The innermost tunic (sensory tunic) consisting of an outer pigmented layer and an inner neural layer containing photoreceptors, bipolar cells, and ganglion cells.

Rods

Photoreceptors in the neural retina containing a single visual pigment, specialized for dim light vision and absent from both the optic disc and fovea centralis.

Cones

Photoreceptors in the neural retina existing in three populations, specialized for bright light and color vision, providing maximum visual acuity.

Fovea centralis

A small depression in the posterior retina containing only cones, surrounded by the macula lutea, providing the highest visual acuity.

Optic disc

The area on the posterior retina where ganglion cell axons exit as the optic nerve; contains no photoreceptors and produces a blind spot.

Aqueous humor

A watery fluid secreted by ciliary processes into the anterior segment that provides nutrition to the lens and cornea before draining via the canal of Schlemm.

Vitreous humor

A viscous, gel-like substance filling the posterior cavity that helps maintain intraocular pressure and holds the neural retina against the pigmented layer.

Accommodation for close vision

The physiological mechanism where ciliary muscles contract, decreasing tension on suspensory ligaments and causing the lens to bulge for greater refraction.

Accommodation for distance vision

The physiological mechanism where ciliary muscles relax, increasing tension on suspensory ligaments and flattening the lens for reduced refraction.

Conjunctivitis

Inflammation of the conjunctiva membrane, often viral or bacterial, commonly called pinkeye.

Glaucoma

Pathological condition where intraocular pressure increases due to impaired drainage of aqueous humor, leading to optic nerve compression and potential blindness.

Cataract

Development of opacities within the lens that give it a milky appearance and hinder light transmission.

Strabismus

Weakness of external eye muscles causing a lack of parallelism between the visual axes, commonly known as lazy eye.

Optic chiasm

X-shaped anatomical structure where medial fibers of the optic nerves decussate, forming optic tracts that carry visual signals from both eyes.

Tympanic membrane

The eardrum; a thin membrane separating the outer ear canal from the middle ear that vibrates at frequencies matching incoming sound waves.

Auditory ossicles

The three small bones of the middle ear—malleus, incus, and stapes—that amplify sound vibrations from the tympanic membrane to the oval window.

Eustachian tube

The pharyngotympanic tube connecting the middle ear cavity to the nasopharynx to equalize air pressure across the tympanic membrane.

Otitis media

Inflammation of the middle ear cavity accompanied by fluid buildup, frequently affecting children due to shorter, horizontal Eustachian tubes.

Organ of Corti

The spiral receptor organ for hearing located in the cochlear duct (scala media) on the basilar membrane, containing hair cells embedded in the tectorial membrane.

Perilymph

Fluid filling the outer bony labyrinth chambers of the inner ear, including the scala vestibuli and scala tympani of the cochlea.

Endolymph

Fluid contained within the inner membranous labyrinth structures, including the cochlear duct, semicircular ducts, utricle, and saccule.

Macula

Equilibrium receptor structure located within the utricle and saccule consisting of hair cells covered by an otolithic membrane with otoliths, detecting linear acceleration.

Crista ampullaris

Equilibrium receptor structure located within the ampulla of each semicircular duct, consisting of hair cells capped by a gelatinous cupula to detect angular/rotational acceleration.

Cupula

A gelatinous dome-shaped cap covering hair cells in the crista ampullaris that sways with endolymph fluid flow to detect head rotation.

Vestibulocochlear nerve (CN VIII)

Cranial nerve VIII carrying auditory signals from the cochlea and equilibrium signals from the vestibular complex to the brain.

Conus medullaris

The cone-shaped terminal tip of the spinal cord ending around the L1-L2 vertebral level.

Cauda equina

The collection of spinal nerve roots extending inferiorly from the conus medullaris through the lower vertebral canal, resembling a horse's tail.

Phrenic nerve

A motor and sensory nerve arising from spinal segments C3-C5 of the cervical plexus that innervates the diaphragm.

Radial nerve

Brachial plexus nerve innervating extensor muscles of the upper limb; injury to this nerve causes wrist drop.