Nervous System, Special Senses, and Neural Integration

Comprehensive vocabulary flashcards covering the anatomical and physiological principles of the nervous system, neurophysiology, central and peripheral divisions, autonomic integration, and the special senses (vision, hearing, equilibrium, olfaction, and gustation).

Astrocyte

The most abundant type of neuroglia in the central nervous system, functioning to anchor neurons to blood vessels and form a living barrier between neurons and blood capillaries.

Microglial Cell

A defensive neuroglial cell of the central nervous system that acts as a specialized macrophage and is part of the immune system.

Ependymal Cell

A squamous to columnar ciliated neuroglial cell that lines the central fluid-filled cavities of the brain and spinal cord, forming a barrier and helping produce and circulate cerebrospinal fluid.

Oligodendrocyte

A central nervous system neuroglia with cellular processes that wrap around nerve fibers to form insulating myelin sheaths.

Satellite Cell

A peripheral nervous system neuroglial cell that surrounds neuron cell bodies in ganglia to control and support their chemical environment.

Schwann Cell

A peripheral nervous system neuroglia that forms segmented myelin sheaths around peripheral nerve fibers to insulate axons and speed impulse transmission.

Multiple Sclerosis

An autoimmune disorder in which the immune system attacks and destroys myelin sheaths around axons in the central nervous system, converting myelin into hardened, non-functioning scleroses and short-circuiting impulse propagation.

Nissl Bodies

Dense regions of well-developed rough endoplasmic reticulum and free ribosomes located within the perikaryon (soma) of a neuron that carry out high levels of protein synthesis.

Axon Hillock

The cone-shaped region of the neuron cell body from which the axon arises and where incoming graded potentials are summated to trigger an action potential.

Bipolar Neuron

A structural class of neuron characterized by exactly two processes extending from the soma (one dendrite and one axon); rare in the body and found primarily in special sensory organs such as the retina and olfactory epithelium.

Unipolar Neuron

A structural class of neuron possessing a single short process that emerges from the cell body and divides into a peripheral process and a central process; predominantly found in the dorsal root ganglia and cranial sensory ganglia.

Multipolar Neuron

The most common structural classification of neurons in the body, possessing three or more processes (one axon and multiple dendrites); functions primarily as motor neurons and interneurons in the central nervous system.

Resting Membrane Potential

The polarized electrical voltage across the plasma membrane of an unstimulated neuron, typically $-70\,\text{mV}$, maintained by ion concentration gradients, selective permeability, and the active $Na^+/K^+$ pump.

Graded Potential

A short-distance, localized variation in membrane potential that can be depolarizing or hyperpolarizing, varies in magnitude according to stimulus strength, and decrements as it spreads along the membrane.

Action Potential

A rapid, all-or-none reversal of membrane electrical potential lasting only a few milliseconds that travels along the entire length of an axon once threshold depolarization ($-55\,\text{mV}$ to $-50\,\text{mV}$) is reached.

Absolute Refractory Period

The period from the opening of voltage-gated $Na^+$ channels until they begin resetting to their resting closed state, during which the axon membrane is completely incapable of initiating another action potential regardless of stimulus strength.

Relative Refractory Period

The interval during repolarization and hyperpolarization when voltage-gated $K^+$ channels are open and $Na^+$ channels are closed, during which an action potential can only be generated by an exceptionally strong suprathreshold stimulus.

Continuous Conduction

A slow mode of action potential propagation occurring in unmyelinated axons, wherein voltage-gated channels regenerate the action potential at each adjacent point along the axon membrane at approximately $1\,\text{m/s}$.

Saltatory Conduction

A rapid mechanism of impulse transmission occurring in myelinated axons, in which local electrical current flows through the axoplasm to depolarize subsequent myelin sheath gaps (Nodes of Ranvier), allowing the action potential to jump between nodes $5$ to $7$ times faster than continuous conduction.

Group A Fibers

Large-diameter, heavily myelinated nerve fibers comprising mostly somatic sensory and motor axons, capable of high conduction velocities exceeding $150\,\text{m/s}$.

Group C Fibers

Small-diameter, nonmyelinated nerve fibers that conduct electrical impulses at a slow velocity of approximately $1\,\text{m/s}$.

Dura Mater

The tough, fibrous outermost layer of the cranial and spinal meninges that protects the underlying central nervous system tissue.

Arachnoid Mater

The middle meninx featuring a web-like network of trabeculae that is separated from the pia mater by the subarachnoid space containing cerebrospinal fluid.

Pia Mater

The delicate, highly vascularized innermost connective tissue layer of the meninges that adheres tightly to the surface contours of the brain and spinal cord.

Choroid Plexus

Frond-shaped clusters of capillaries enclosed by ependymal cells located within brain ventricles that filter blood plasma to produce cerebrospinal fluid.

Hydrocephalus

A medical condition resulting from the obstruction of cerebrospinal fluid circulation or drainage, causing fluid buildup, enlarged ventricles, and increased intracranial pressure.

Commissural Fibers

Myelinated axon tracts within cerebral white matter (such as the corpus callosum and anterior commissure) that interconnect corresponding cortical areas between the left and right cerebral hemispheres.

Basal Nuclei

Subcortical clusters of gray matter cell bodies situated deep within the cerebral white matter (including the caudate and lentiform nuclei) that help control and refine skeletal muscle movements ordered by the cortex.

Thalamus

A large, egg-shaped bilateral mass of gray matter in the diencephalon that edits, sorts, and relays incoming sensory signals heading to the primary cerebral sensory cortex.

Hypothalamus

The inferior region of the diencephalon that serves as the main visceral integration center, regulating the autonomic nervous system, body temperature, thirst, appetite, hormone production, and emotional responses.

Corpora Quadrigemina

Four colliculi protruding from the dorsal midbrain (mesencephalon) that process visual and auditory sensory information and coordinate visual and auditory reflex head movements.

Purkinje Cells

Large, intricately branched neurons located within the cerebellar cortex whose axons project into the deep white matter to provide the entire output of the cerebellum.

Reticular Formation

A widespread network of neurons spanning the brain stem that filters repetitive sensory inputs, modulates skeletal and visceral muscle tone, and maintains alertness in the cerebral cortex.

Epineurium

The tough, fibrous outer connective tissue sheath that encases groups of fascicles and blood vessels to form a peripheral nerve.

Reflex Arc

The neural pathway mediating an automatic, involuntary motor response to a stimulus, composed of five elements: receptor, sensory neuron, integration center, motor neuron, and effector.

Crossed Extensor Reflex

A contralateral polysynaptic reflex consisting of an ipsilateral withdrawal reflex (flexor stimulation and extensor inhibition) coupled with a contralateral extensor reflex to maintain body balance.

Vagus Nerve (CN X)

Cranial nerve X, a mixed nerve carrying sensory fibers for taste and general visceral sensations, somatic motor fibers, and extensive parasympathetic motor fibers to organs in the thorax and abdomen.

Diverging Circuit

A neural circuit arrangement in which a single presynaptic neuron synapses with multiple postsynaptic neurons, amplifying an initial input into many divergent pathways.

Converging Circuit

A neural circuit in which multiple presynaptic inputs converge to synapse on a single postsynaptic output neuron, exerting a concentrating effect.

Reverberating Circuit

An oscillating neural circuit where signals travel along a chain of neurons with feedback collaterals returning to upstream neurons, producing rhythmic activities such as breathing or sleep-wake cycles.

Parallel After-Discharge Circuit

A neural circuit where an incoming signal stimulates parallel chains of neurons that reach a common output cell at varying times, creating a prolonged burst of impulses for complex mental processes.

Broca's Area

A specialized motor speech region situated in the frontal lobe of the dominant cerebral hemisphere that coordinates the muscular activities required for speech.

Wernicke's Area

A region within the posterior cerebral cortex association area (temporal and parietal lobes) responsible for the comprehension and processing of written and spoken language.

Sympathetic Nervous System

The thoracolumbar division ($T_1-L_2$) of the autonomic nervous system that drives fight-or-flight responses, elevating heart rate, dilating bronchioles, increasing blood pressure, and mobilizing body systems during physical activity.

Parasympathetic Nervous System

The craniosacral division (cranial nerves III, VII, IX, X and $S_2-S_4$) of the autonomic nervous system that conserves energy and mediates rest-and-repose functions such as digestion and waste elimination.

Nicotinic Receptor

A chemically gated ion channel cholinergic receptor found on skeletal neuromuscular junctions and autonomic ganglion cells that always causes direct excitation by allowing $Na^+$ influx.

Muscarinic Receptor

A G-protein-coupled cholinergic receptor located on all parasympathetic target effectors and certain sympathetic target organs, mediating either excitatory or inhibitory metabolic changes.

Sensory Adaptation

A physiological reduction in receptor sensitivity and impulse generation in the prolonged presence of a constant, unchanging stimulus.

Lacrimal Apparatus

The physiological system consisting of the lacrimal gland, excretory ducts, lacrimal puncta, canaliculi, lacrimal sac, and nasolacrimal duct that produces, distributes, and drains tears.

Pupillary Dilator Muscles

Radial smooth muscle fibers of the iris innervated by the sympathetic nervous system that contract to enlarge the pupil under dim light conditions or heightened sympathetic tone.

Pupillary Constrictor Muscles

Circular concentric smooth muscle fibers of the iris innervated by parasympathetic motor fibers that contract to constrict the pupil in bright light or during close vision.

Canal of Schlemm

A circular venous vessel situated at the limbus (corneoscleral junction) that reabsorbs aqueous humor from the anterior chamber and returns it to venous blood.

Glaucoma

A pathology characterized by abnormally elevated intraocular pressure resulting from obstructed aqueous humor drainage, causing pressure against the vitreous body and optic nerve damage.

Myopia

A refractive eye disorder (nearsightedness) where parallel light rays converge in front of the retina because the eyeball is excessively elongated, requiring a diverging (concave) lens for optical correction.

Hyperopia

A refractive eye condition (farsightedness) where light rays focus behind the retina because the eyeball is too short, requiring a converging (convex) lens for correction.

Rhodopsin

The deep-purple visual photopigment located in the membrane discs of rod photoreceptor outer segments, formed by the binding of the opsin protein to 11-cis retinal.

Bleaching of Rhodopsin

The light-driven reaction in which light-absorbed photons cause 11-cis retinal to isomerize into 11-trans retinal, detaching from opsin and breaking down the pigment molecule.

Fovea Centralis

A distinct pit in the center of the macula lutea that contains the highest concentration of cones and provides the sharpest, highest-resolution visual acuity.

Auditory Ossicles

A trio of small synovial bones situated in the middle ear cavity—the malleus, incus, and stapes—that mechanically transfer and amplify vibrations from the tympanic membrane to the oval window.

Organ of Corti

The specialized sensory receptor structure for hearing located within the cochlear duct (scala media), consisting of auditory hair cells supported on the basilar membrane and stimulated against the tectorial membrane.

Static Equilibrium

The maintenance of body and head posture relative to the pull of gravity and linear acceleration when the body is motionless, detected by maculae in the utricle and saccule.

Statoconia

Small calcium carbonate crystals situated on the gelatinous layer of the macula in the inner ear vestibule that shift under gravitational pull, bending hair cell stereocilia.

Dynamic Equilibrium

The maintenance of head and body balance during rotational or angular movement, mediated by cristae ampullares within the ampullae of the semicircular canals.

Selective Serotonin Reuptake Inhibitor

A class of pharmaceutical agents (such as fluoxetine) that selectively blocks the reuptake proteins of presynaptic neurons, prolonging the duration and concentration of serotonin in the synaptic cleft to enhance postsynaptic transmission.