Comprehensive Anatomy and Physiology: Nervous and Endocrine Systems

Comprehensive practice vocabulary flashcards covering the nervous system (electrophysiology, anatomy, spinal cord, reflexes, brain, sense organs, autonomic divisions) and the endocrine system (hypothalamus, pituitary, peripheral glands, and hormone mechanisms).

Auditory (Eustachian) Tube

An air duct connecting the middle ear to the nasopharynx that equalizes atmospheric pressure across the tympanic membrane; it is normally closed but opens during swallowing or yawning.

Auditory Ossicles

A trio of tiny middle-ear bones consisting of the malleus (attached to the tympanic membrane), incus (middle bridge), and stapes (whose footplate rests on the oval window) that mechanically transmit sound vibrations to the inner ear.

Spiral Organ (Organ of Corti)

The acoustic receptor structure located within the cochlear duct (scala media) containing roughly $3,500$ inner hair cells for hearing transduction and $20,000$ outer hair cells for frequency tuning.

Glaucoma

An ocular condition marked by pathologically elevated intraocular pressure caused by obstruction and buildup of aqueous humor, which can compress and damage the optic nerve and retina, potentially causing blindness.

Ciliary Body

A thickened anterior extension of the choroid that forms a muscular ring around the lens, suspends the lens via suspensory ligaments to alter its optical curvature, and secretes aqueous humor.

Optic Disc

The posterior region of the retina where ganglion cell axons converge and exit as the optic nerve; it lacks photoreceptors, creating a physiological blind spot compensated for by visual filling.

Emmetropia

The naturally relaxed state of normal vision where parallel light rays emitted from objects situated greater than $20\,\text{ft}$ away are precisely focused directly on the retina without muscular accommodation.

Hyperopia

Farsightedness resulting from an eyeball that is too short or a lens that is too thin, causing the focal point of near objects to fall behind the retina; corrected using a convex lens.

Rhodopsin

The visual photopigment embedded in the membranous discs of rod outer segments, formed by the binding of retinal (derived from vitamin A) to opsin, that mediates night (scotopic) vision.

Autonomic Nervous System (ANS)

A visceral motor division of the nervous system that unconsciously regulates cardiac muscle, smooth muscle, and glands to maintain homeostatic adjustments throughout the body.

Denervation Hypersensitivity

An exaggerated, hyperactive physiological response observed in cardiac or smooth muscle target tissues when their supplying autonomic postganglionic nerve fibers are severed.

Autonomic Tone

The continuous, baseline background firing rate of the sympathetic and parasympathetic divisions that balances visceral organ activity according to shifting systemic demands.

Sympathetic Chain Ganglia

A longitudinal series of interconnected paravertebral ganglia running adjacent to both sides of the vertebral column from cervical to coccygeal levels, receiving preganglionic fibers from spinal nerves $T1\text{ to }L2$.

White Communicating Ramus

The lateral branch containing small myelinated preganglionic sympathetic fibers that conducts nerve impulses from the spinal nerve into the adjacent paravertebral chain ganglion.

Gray Communicating Ramus

The medial bridge containing unmyelinated postganglionic sympathetic fibers that exit a chain ganglion to re-enter a spinal nerve and distribute to peripheral target effectors.

Adrenal Medulla

The modified sympathetic ganglion core of the adrenal gland composed of postganglionic chromaffin cells lacking axons that, upon direct preganglionic stimulation, releases $85\%$ epinephrine and $15\%$ norepinephrine into circulation.

Nicotinic Receptors

A class of cholinergic receptors located at neuromuscular junctions, on all autonomic postganglionic neurons, and in the adrenal medulla that invariably elicit excitatory responses upon binding acetylcholine.

Muscarinic Receptors

Cholinergic receptors found on all cardiac muscle cells, smooth muscle cells, and gland effectors that exhibit either excitatory or inhibitory effects depending on the receptor subclass.

Falx Cerebri

A crescent-shaped vertical fold of the inner meningeal dura mater that descends into the longitudinal fissure to partition the left and right cerebral hemispheres.

Arachnoid Granulations

Cauliflower-shaped extensions of the arachnoid villi that penetrate through the cranial dura mater into the superior sagittal sinus to reabsorb cerebrospinal fluid into systemic venous circulation.

Choroid Plexus

Spongy vascular networks of fenestrated capillaries located on the floors and walls of brain ventricles, covered by simple cuboidal ependymal cells with tight junctions that continuously filter blood plasma into cerebrospinal fluid.

Blood-Brain Barrier (BBB)

A selective physiological barrier comprised of capillary endothelial cells joined by tight junctions, a thick continuous basement membrane, and perivascular feet of astrocytes that restricts passage of blood-borne substances into neural tissue.

Medulla Oblongata

The most caudal portion of the brainstem, continuous inferiorly with the spinal cord, housing vital autonomic reflex nuclei including the cardiac center, vasomotor center, and respiratory center.

Pons

The brainstem region positioned superior to the medulla and anterior to the cerebellum that functions as an axonal bridge between brain regions and contains the pontine respiratory group.

Reticular Formation

A vertically organized loose web of gray matter cores extending throughout the brainstem that governs somatic motor control, gaze centering, cardiovascular function, pain modulation, consciousness, and habituation.

Cerebellum

A large posterior-inferior brain structure consisting of two hemispheres united by a central vermis that coordinates complex somatic movements by comparing intended motor commands with sensory feedback via thalamic circuits.

Thalamus

An egg-shaped diencephalic mass composed of at least $23$ nuclei that serves as the sensory gateway to the cerebral cortex, filtering and relaying nearly all afferent inputs (except olfaction).

Hypothalamus

The ventral diencephalic structure forming the floor and walls of the third ventricle that serves as the master integrating regulator for both the autonomic nervous system and endocrine system.

Basal Nuclei

Subcortical clusters of cerebral gray matter buried deep within the white matter—comprising the caudate nucleus, putamen, and globus pallidus—that receive midbrain and cortical inputs to regulate voluntary motor control.

Limbic System

A ring of interconnected cortical and subcortical structures, prominently featuring the hippocampus and amygdala, that mediates long-term memory formation, emotional behavior, gratification, and aversion.

Vagus (X) Nerve

The tenth cranial nerve, exhibiting the most extensive anatomical distribution, which provides mixed sensory and major parasympathetic motor innervation to thoracic and abdominal viscera as far as the proximal colon.

Spinal Meninges

Three protective connective tissue sheaths—outer fibrous dura mater, middle avascular web-like arachnoid mater, and inner vascular pia mater—that envelop the spinal cord and form the fluid-filled subarachnoid space.

Conus Medullaris

The tapering, cone-shaped inferior termination of the spinal cord proper, situated anatomically near lumbar vertebrae $L1\text{ to }L2$.

Cauda Equina

A bundle of nerve roots occupying the vertebral canal from $L2$ to $S5$ resembling a horse's tail that supplies motor and sensory innervation to the pelvic organs and lower limbs.

Epidural Space

An adipose- and blood vessel-filled space situated between the outer surface of the spinal dura mater and the surrounding bony walls of the vertebral canal, absent within the cranium.

Spinothalamic Tract

An ascending somatic sensory pathway within the anterolateral system formed by the axons of second-order neurons that transmits signals for pain, temperature, pressure, light touch, tickle, and itch to the thalamus.

Stretch (Myotatic) Reflex

A monosynaptic somatic reflex in which sudden physical stretching of a muscle spindle initiates an afferent volley that directly excites alpha motor neurons, eliciting protective muscle contraction.

Reciprocal Inhibition

A neural wiring phenomenon that prevents agonist and antagonist muscles from contracting simultaneously by using inhibitory interneurons to suppress motor output to antagonists during agonist excitation.

Tendon Reflex

A polysynaptic protective reflex mediated by Golgi tendon organs that excites inhibitory interneurons in the spinal cord, causing muscle relaxation in response to excessive tension to prevent tendon tearing.

Crossed Extensor Reflex

A contralateral somatic reflex arc in which the withdrawal of a stimulated limb via flexor muscles is accompanied by contraction of extensor muscles in the opposite limb to maintain physical balance.

Resting Membrane Potential (RMP)

The electrical charge difference across an unstimulated plasma membrane—typically $-70\,mV$ in neurons—maintained by $K^+$ outward diffusion through leak channels, trapped intracellular anions, and the $Na^+-K^+$ pump.

Sodium-Potassium ($Na^+-K^+$) Pump

A primary active transport membrane protein that utilizes ATP hydrolysis to translocate $3\,Na^+$ outward and $2\,K^+$ inward against their chemical concentration gradients, maintaining resting ionic equilibrium.

Local Potential

A short-range, graded, decremental, and reversible electrical fluctuation occurring on a neuron's dendrites or soma caused by ligand binding to gated ion channels, which can be excitatory (depolarizing) or inhibitory (hyperpolarizing).

Action Potential

A rapid, all-or-none, nondecremental, and irreversible reversal of membrane electrical polarity initiated at the axon trigger zone when a graded depolarization achieves the threshold value of $-55\,mV$.

Absolute Refractory Period

The operational phase of an excitable membrane lasting from threshold onset to early repolarization during which voltage-gated $Na^+$ channels are already open or inactivated, rendering the generation of another action potential completely impossible.

Relative Refractory Period

The period following the absolute refractory phase, coinciding with hyperpolarization, during which voltage-gated $K^+$ channels remain open; an action potential can only be generated by a suprathreshold stimulus.

Saltatory Conduction

The rapid, energy-efficient propagation of nerve impulses along myelinated axons wherein electrical excitation leaps from one unmyelinated node of Ranvier to the next.

Synaptic Cleft

A narrow fluid-filled extracellular gap measuring roughly $20\text{ to }40\,nm$ separating the presynaptic axonal terminal from the postsynaptic receptive membrane at a chemical synapse.

Glutamate

An acidic amino acid neurotransmitter that accounts for roughly $75\%$ of all excitatory synaptic transmission within the human brain, playing central roles in learning and memory.

GABA (Gamma-Aminobutyric Acid)

The principal inhibitory amino acid neurotransmitter of the brain that operates by hyperpolarizing postsynaptic membranes, heavily concentrated in the thalamus, hypothalamus, and cerebellum.

Multipolar Neuron

A structural category of neuron characterized by having one single axon and multiple branching dendrites extending from the soma; it represents the most abundant neuron architecture in the CNS.

Unipolar Neuron

A neuron with a single short process emerging from the cell body that bifurcates into a continuous dendritic and axonal fiber; typified by primary somatic sensory neurons.

Astrocytes

The most abundant glial cells in the CNS, possessing perivascular feet that form the blood-brain barrier, regulate extracellular fluid chemistry by absorbing excess $K^+$ and neurotransmitters, and form supportive frameworks.

Oligodendrocytes

Branching neuroglial cells of the central nervous system whose flattened cytoplasmic processes wrap around multiple adjacent nerve fibers to produce myelin sheaths.

Microglia

Small phagocytic glial cells of the CNS derived from blood monocytes that wander through brain parenchyma to engulf cellular debris, apoptotic tissue, and infectious pathogens.

Schwann Cell (Neurolemmocyte)

A peripheral nervous system glial cell that winds consecutively around a segment of a single axon to produce the PNS myelin sheath, outer neurilemma, and assist in peripheral axonal repair.

Regeneration Tube

A cylindrical guiding conduit formed by Schwann cells, the basal lamina, and the neurilemma during peripheral nerve repair that directs the regenerating axonal growth process back to its effector.

Endocrine Glands

Ductless organs that release their active chemical secretions (hormones) directly into dense, fenestrated capillary beds for systemic distribution via the bloodstream to alter distant target cell physiology.

Adenohypophysis (Anterior Pituitary)

The glandular anterior three-fourths of the pituitary gland linked to the hypothalamus via the hypophyseal portal system, synthesizing and secreting six primary peptide hormones: FSH, LH, TSH, ACTH, PRL, and GH.

Hypophyseal Portal System

A specialized vascular route composed of primary capillaries in the hypothalamus, portal venules, and secondary capillaries in the anterior lobe that transports hypothalamic releasing and inhibiting hormones.

Neurohypophysis (Posterior Pituitary)

The posterior one-fourth of the pituitary gland composed of nervous tissue and unmyelinated axons extending from hypothalamic nuclei that stores and releases antidiuretic hormone and oxytocin.

Antidiuretic Hormone (ADH)

A nonapeptide hormone synthesized in the hypothalamic supraoptic nucleus and released from the neurohypophysis that acts on renal tubules to promote water retention, reduce urine output, and cause vasoconstriction.

Oxytocin (OT)

A peptide hormone synthesized predominantly by the paraventricular nucleus of the hypothalamus that stimulates uterine myometrial contractions during labor and promotes milk ejection during lactation.

Thyroid Gland

A highly vascular butterfly-shaped endocrine organ located inferior to the larynx composed of two lateral lobes joined by a central isthmus that contains colloid-filled follicles secreting $T_3$ and $T_4$.

Calcitonin

A polypeptide hormone secreted by parafollicular (C) cells of the thyroid gland in response to elevated blood calcium levels that stimulates osteoblast activity and promotes bone formation.

Parathyroid Hormone (PTH)

A protein hormone secreted by the parathyroid glands in response to hypocalcemia that elevates blood $Ca^{2+}$ by stimulating bone resorption, promoting renal synthesis of calcitriol, and reducing urinary calcium excretion.

Aldosterone

The principal mineralocorticoid steroid hormone secreted by the adrenal cortex that stimulates renal sodium retention and potassium excretion, sustaining systemic blood volume and blood pressure.

Pancreatic Islets

Endocrine micro-clusters scattered throughout the exocrine pancreas containing alpha cells that secrete glucagon during hypoglycemia and beta cells that secrete insulin during nutrient abundance.

Synergistic Effects

An interactive hormonal phenomenon wherein two or more hormones act concurrently on target cells to produce an overall physiological effect that is greater than the sum of their individual actions (e.g., FSH and testosterone in spermatogenesis).