Nervous System, Senses & Heart Lecture Flashcards

Comprehensive vocabulary flashcards covering the Nervous System, Special Senses, and the Heart.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord, serving as the integration and control center.

Peripheral Nervous System (PNS)

The division of the nervous system consisting of cranial and spinal nerves located outside the central nervous system.

Sensory (Afferent) Division

Functional division of the PNS that conveys nerve impulses from sensory receptors to the CNS.

Motor (Efferent) Division

Functional division of the PNS that transmits impulses from the CNS to effector organs, divided into somatic and autonomic branches.

Somatic Nervous System

The voluntary motor division of the PNS that conducts impulses from the CNS to skeletal muscle.

Autonomic Nervous System (ANS)

The involuntary motor division of the PNS that conducts impulses to smooth muscle, cardiac muscle, and glands.

Neurons

Excitable cells of nervous tissue specialized to conduct and transmit electrical signals.

Neuroglia

Non-excitable supporting cells of nervous tissue that can divide and make up about half of nervous tissue volume, comprising 4 CNS types and 2 PNS types.

Astrocytes

The most abundant and highly branched CNS neuroglia that support and brace neurons, mediate capillary-neuron exchanges, and control the chemical environment around neurons.

Microglial Cells

Small CNS glial cells with thorny processes that monitor neuron health, migrate to injured neurons, and phagocytize microorganisms and debris.

Ependymal Cells

Ciliated CNS neuroglial cells that line brain cavities and the central canal of the spinal cord to circulate cerebrospinal fluid.

Oligodendrocytes

CNS glial cells that form insulating myelin sheaths around central nerve fibers, with a single cell capable of wrapping up to $60$ axons.

Satellite Cells

PNS neuroglial cells that surround neuron cell bodies, acting as the functional counterpart to CNS astrocytes.

Schwann Cells

PNS neuroglial cells that wrap peripheral nerve fibers to form myelin sheaths, acting as the functional counterpart to CNS oligodendrocytes.

Dendrites

Short, branched neuronal processes serving as the receptive or input region that conduct graded potentials toward the cell body.

Axon

A single neuronal process arising from the axon hillock that acts as the conducting region, generating and propagating nerve impulses to axon terminals that release neurotransmitters.

Nuclei

Clusters of neuron cell bodies located within the central nervous system.

Ganglia

Clusters of neuron cell bodies located within the peripheral nervous system.

Tracts

Bundles of nerve fibers situated within the central nervous system.

Nerves

Bundles of nerve fibers situated within the peripheral nervous system.

Anterograde Axonal Transport

Movement of substances away from the neuron cell body along the axon, transporting mitochondria, enzymes, and membrane components.

Retrograde Axonal Transport

Movement of substances toward the cell body for degradation or signaling, a pathway exploited by polio, rabies, herpes simplex, and tetanus toxin.

Myelin

A protein-lipid substance that insulates and protects axons and increases the speed of nerve impulse conduction.

Myelin Sheath Gaps

Gaps along myelinated axons between neighboring Schwann cells (formerly called nodes of Ranvier) where axon collaterals can emerge.

White Matter

Regions of the brain and spinal cord consisting of dense collections of myelinated fibers, typically organized into tracts.

Gray Matter

Regions of the brain and spinal cord containing mostly neuron cell bodies and nonmyelinated fibers.

Resting Membrane Potential

The electrical potential difference across the resting neuronal membrane of approximately $-70\,\text{mV}$, maintained by higher extracellular $\text{Na}^+$ ($150\,\text{mM}$ vs. $15\,\text{mM}$) and higher intracellular $\text{K}^+$ ($150\,\text{mM}$ vs. $5\,\text{mM}$).

Depolarization

A shift in the membrane potential where the inside of the cell becomes less negative relative to the resting state, exerting an excitatory effect.

Hyperpolarization

An increase in membrane potential where the cell interior becomes more negative than the resting potential, exerting an inhibitory effect.

Graded Potentials

Short-lived, localized changes in membrane potential that dissipate across distance, initiated in dendrites or cell bodies via ligand- or mechanically-gated channels.

Threshold

The critical membrane potential level of $-55\,\text{mV}$ at the axon hillock required to trigger the opening of voltage-gated $\text{Na}^+$ channels and fire an action potential.

All-or-None Principle

The principle stating that an action potential fires at full magnitude ($\sim 100\,\text{mV}$, $0.5\text{--}2\,\text{msec}$) or not at all, without diminishing along the axon, with stimulus strength coded by frequency.

Absolute Refractory Period

The period following stimulation during which voltage-gated $\text{Na}^+$ gates are open or resetting, rendering the generation of another action potential impossible and enforcing unidirectional propagation.

Relative Refractory Period

The interval following the absolute refractory period where $\text{Na}^+$ gates have reset while $\text{K}^+$ channels remain open, permitting an action potential only in response to an exceptionally strong stimulus.

Saltatory Conduction

The rapid mode of nerve impulse transmission in myelinated axons, where the impulse jumps from one myelin sheath gap to the next.

Electrical Synapses

Synaptic junctions featuring gap junctions that allow direct ionic current flow to synchronize clusters of neurons.

Chemical Synapses

Specialized junctions that facilitate unidirectional communication via neurotransmitters released across the synaptic cleft from presynaptic to postsynaptic neurons.

Excitatory Postsynaptic Potential (EPSP)

A local graded depolarization produced by the opening of chemically gated $\text{Na}^+$ channels, bringing the postsynaptic membrane closer to threshold.

Inhibitory Postsynaptic Potential (IPSP)

A local graded hyperpolarization driven by $\text{K}^+$ efflux or $\text{Cl}^-$ influx, shifting the membrane potential farther away from threshold.

Temporal Summation

Summation occurring when a single presynaptic neuron discharges multiple excitatory signals in rapid succession to reach threshold.

Spatial Summation

Summation occurring when multiple presynaptic axon terminals stimulate a single postsynaptic neuron concurrently.

Acetylcholinesterase

The enzyme responsible for terminating acetylcholine activity in the synaptic cleft by degrading it into acetate and choline.

Dura Mater

The strongest and outermost meninx, consisting of a periosteal layer and a meningeal layer that separate to form dural venous sinuses.

Falx Cerebri

A sickle-shaped dural septum situated along the longitudinal fissure and attached to the crista galli.

Tentorium Cerebelli

A horizontal dural fold resting over the cerebellum within the transverse fissure.

Arachnoid Mater

The web-like middle meningeal layer enclosing the subarachnoid space that contains cerebrospinal fluid and major blood vessels.

Arachnoid Granulations

Knoblike projections of the arachnoid mater that reabsorb cerebrospinal fluid into the venous bloodstream of the superior sagittal sinus.

Pia Mater

A delicate, highly vascularized meninx adhering tightly to every convolution of the brain surface.

Choroid Plexus

A network of capillaries enclosed by ependymal cells in the brain ventricles that produces about $150\,\text{ml}$ of cerebrospinal fluid every $8\,\text{hours}$.

Hydrocephalus

An abnormal accumulation of cerebrospinal fluid resulting from obstructed circulation or drainage, causing increased intracranial pressure.

Blood-Brain Barrier

A selective barrier established by tight junctions between capillary endothelial cells, allowing passage to fat-soluble compounds, glucose, and select ions and amino acids.

Wallerian Degeneration

The process of degeneration of the axon and its myelin sheath distal to the site of peripheral nerve injury.

Cauda Equina

The collection of nerve roots extending inferiorly from the conus medullaris of the spinal cord resembling a horse's tail.

Dermatome

An area of skin innervated by cutaneous sensory branches derived from a single spinal nerve (with the exception of C1).

Preganglionic Neuron

The first neuron in a two-neuron autonomic chain, having a cell body in the CNS and a myelinated axon running to an autonomic ganglion.

Postganglionic Neuron

The second neuron in an autonomic pathway, having an unmyelinated axon extending from an autonomic ganglion to an effector organ.

Sympathetic Tone

The continuous baseline state of partial constriction maintained in vascular smooth muscle by the sympathetic division.

White Ramus Communicans

A structure carrying myelinated preganglionic sympathetic axons from the spinal nerve to the paravertebral ganglion.

Gray Ramus Communicans

A structure carrying unmyelinated postganglionic sympathetic axons from the paravertebral ganglion back to the spinal nerve.

Cholinergic Fibers

Nerve fibers that synthesize and release acetylcholine, including all ANS preganglionic axons, all parasympathetic postganglionics, and select sympathetic postganglionics.

Adrenergic Fibers

Nerve fibers that release norepinephrine, encompassing the vast majority of sympathetic postganglionic fibers.

Trigeminal Nerve (CN V)

A mixed cranial nerve mediating touch, pain, and temperature sensation from the face, scalp, and teeth, and motor control over mastication.

Vagus Nerve (CN X)

A mixed cranial nerve supplying approximately $90\%$ of all parasympathetic fibers, innervating thoracic and abdominal viscera and depressing heart rate.

Sclera

The tough, opaque fibrous coat of the eyeball that maintains eye shape, protects internal structures, and anchors extrinsic muscles.

Cornea

The transparent anterior window of the eye fibrous layer, densely supplied with pain receptors mediating the corneal reflex.

Optic Disc

The unpigmented region where the optic nerve exits the eyeball, lacking photoreceptors and creating the functional blind spot.

Fovea Centralis

A minute focal pit within the retinal macula lutea composed entirely of cone photoreceptors, providing maximal visual acuity.

Rods

Dim-light and peripheral vision photoreceptors that display high light sensitivity without mediating color or sharp vision.

Cones

Photoreceptor cells active in bright light that mediate sharp, high-resolution color vision.

Aqueous Humor

A watery fluid generated by ciliary processes in the anterior segment that drains through the scleral venous sinus (canal of Schlemm).

Vitreous Humor

A durable gelatinous humor filling the posterior segment of the eye that transmits light and presses the neural retina against the choroid.

Glaucoma

An ocular pathology characterized by increased intraocular pressure due to impaired aqueous humor drainage, leading to optic nerve compression.

Crista Ampullaris

The sensory organ located in the ampulla of each semicircular canal that detects rotational dynamic equilibrium.

Maculae

Sensory receptor organs located in the utricle and saccule of the vestibule that detect linear acceleration and gravity.

Spiral Organ (of Corti)

The receptor structure for audition situated in the cochlear duct (scala media), consisting of hair cells positioned on the basilar membrane.

Pericardium

The double-walled fibroserous sac surrounding the heart, divided into an external fibrous pericardium and a two-layered serous pericardium.

Cardiac Tamponade

A medical emergency where excess fluid accumulates within the pericardial cavity, compressing the heart and impeding filling.

Endocardium

The glistening white endothelial lining of the inner heart chambers and heart valves, continuous with the endothelium of great vessels.

Angina Pectoris

Thoracic chest pain stemming from transient deficiency in myocardial blood supply without permanent myocardial necrosis.

Myocardial Infarction (MI)

Irreversible ischemic necrosis of cardiac myocytes caused by prolonged coronary artery occlusion, resulting in noncontractile scar tissue.

Sinoatrial (SA) Node

The primary pacemaker of the heart intrinsic conduction system located in the superior right atrium, generating impulses at $60\text{--}100/\text{min}$.

Atrioventricular (AV) Node

A node of cardiac conduction tissue at the junction between atria and ventricles that delays electrical impulses to permit complete atrial emptying.