9 & 10. Nervous System and Sensory Organs

Comprehensive vocabulary flashcards covering the nervous system and sensory organs, including neuron physiology, action potentials, synapses, brain structures, ear anatomy, and eye anatomy.

Dendrite

Branched extensions of a neuron that bring neural stimuli to the cell body.

Axon

A long cellular extension that carries neural stimuli away from the cell body.

Cell Body (Soma)

The core region of a neuron containing the nucleus and other essential organelles.

Schwann Cell

Specialized supporting cells that wrap around an axon, leaving space between each other, providing a medium for neural impulses.

Myelin Sheath

An insulating layer that encases each Schwann cell, insulating sections of the axon and facilitating the rapid movement of impulses across it.

Node of Ranvier

Portions of the axon exposed to the extracellular space that are rich in ion channels needed to keep the neural impulse moving.

Central Nervous System (CNS)

The anatomical division of the nervous system composed exclusively of the brain and spinal cord.

Peripheral Nervous System (PNS)

The anatomical division composed of all components of the nervous system that branch out from the central nervous system.

Afferent Nerves

Sensory nerves that conduct neural impulses toward the central nervous system.

Efferent Nerves

Motor nerves that conduct neural impulses away from the central nervous system toward peripheral effectors like skeletal muscles.

Somatic Nervous System

The functional system responsible for voluntary control over the nervous system, such as a canine wagging its tail.

Autonomic Nervous System

The functional system responsible for involuntary control over the nervous system, such as the heart beating.

Resting State (Neuron)

The polarized state where the inside of the cell is negative and the outside is positive, with sodium cations ($\text{Na}^+$) mostly extracellular and potassium cations ($\text{K}^+$) mostly intracellular.

Depolarization

The phase where sodium channels open, allowing $\text{Na}^+$ to rush into the cell via diffusion, making the inside positive and the outside negative.

Repolarization

The phase where potassium channels open, allowing $\text{K}^+$ to exit the cell via diffusion, restoring polarity so the inside becomes negative and the outside positive.

Refractory Period

The period where the sodium-potassium pump uses active transport to pump $\text{Na}^+$ out of the cell and $\text{K}^+$ into the cell to reset the resting ion distribution.

Sodium-Potassium Pump

A specialized membrane protein that actively pumps sodium cations out of the cell and potassium cations into the cell to restore resting ionic balance.

All-or-Nothing Principle

The principle stating that if a stimulus is too weak to reach the threshold, depolarization will not occur and the action potential will fail to fire completely.

Lidocaine

A local anesthetic and sodium channel blocker that prevents sodium channels from opening, blocking depolarization and stopping pain impulses from traveling to the brain.

Telodendron

Branched terminal structures at the distal end of an axon that terminate in synaptic bulbs.

Synaptic Bulb

The expanded terminal ending of a telodendron that contains synaptic vesicles packed with neurotransmitters.

Synaptic Cleft

The physical space or fluid-filled gap separating the synaptic bulb of a presynaptic neuron from the dendrite of a postsynaptic neuron.

Excitatory Neurotransmitter

A chemical messenger that triggers the postsynaptic neuron to depolarize, continuing the propagation of the nerve impulse (e.g., Epinephrine, Norepinephrine, Dopamine).

Inhibitory Neurotransmitter

A chemical messenger that induces hyperpolarization, making the interior of the neuron more negative and resistant to depolarization (e.g., GABA, Glycine).

Acetylcholine

A unique neurotransmitter capable of acting as both an excitatory and an inhibitory neurotransmitter depending on the site.

Vagus Nerve (Cranial Nerve X)

A cranial nerve extending to the heart and gastrointestinal tract that can trigger syncope (fainting) if excessively stimulated.

Sympathetic Nervous System

The fight-or-flight division of the autonomic nervous system that increases heart rate, dilates bronchioles and pupils, and shunts blood to skeletal muscles.

Parasympathetic Nervous System

The rest-and-restore division of the autonomic nervous system that decreases heart rate, constricts bronchioles and pupils, and stimulates digestive activity.

Tetany

Involuntary muscle spasms and tremors caused by hypocalcemia, which lowers the threshold and increases synaptic and muscular sensitivity.

Thermoception

The sensory perception of internal body temperature levels.

Normal Canine Body Temperature

A normal temperature range of $101.5 - 102.5^\circ\text{F}$.

Normal Feline Body Temperature

A normal temperature range of $100.5 - 102.5^\circ\text{F}$.

Disseminated Intravascular Coagulation (DIC)

A fatal condition resulting from severe hyperthermia characterized by thromboembolisms, thrombocytopenia, hypoproteinemia, and systemic organ failure.

Nociception

The physiological perception of pain, consisting of four ordered steps: transduction, transmission, modulation, and perception.

Transduction (Pain)

The conversion of a physical noxious stimulus (such as a thorn puncture) into an electrical neural signal by sensory nerve endings.

Transmission (Pain)

The propagation of the transduced neural signal up the sensory nerve and spinal cord toward the brain.

Modulation (Pain)

The modification or amplification of the neural pain signal within the spinal cord before it arrives at higher brain centers.

Perception (Pain)

The final stage where higher brain structures recognize and interpret the sensory signal as a conscious painful experience.

Anesthesia

The complete loss of sensory perception and consciousness, commonly utilized for major surgical procedures like an ovariohysterectomy (OHE).

Analgesia

The selective decrease or suppression of the sensory perception of painful stimuli without loss of consciousness.

Corpus Callosum

A prominent white matter structure that connects and relays neural communication between the left and right cerebral hemispheres.

Gyrus

A raised fold or ridge on the cerebral cortex of the brain.

Sulcus

A shallow groove on the cerebral surface separating individual gyri.

Longitudinal Fissure

The deep, prominent midline groove that separates the left and right cerebral hemispheres.

Cerebellum

The brain region located ventrocaudal to the cerebrum that coordinates and facilitates motor functions.

Diencephalon

The central brain area comprising the thalamus (sensory relay), hypothalamus (endocrine regulation), and pituitary gland (hormone secretion).

Brainstem

The structure consisting of the midbrain, pons, and medulla oblongata that governs basic vegetative life functions such as heart rate regulation.

Meninges

A three-layered connective tissue covering consisting of the dura mater, arachnoid, and pia mater that envelopes the CNS and circulates cerebrospinal fluid ($\text{CSF}$).

Vomeronasal Organ (Jacobson's Organ)

An accessory olfactory structure located in the nasal cavity specialized for detecting pheromones.

Cerumen

Earwax produced by apocrine and sebaceous glands in the external ear to protect the tympanic membrane against pathogens, debris, and moisture.

Auditory Ossicles

The chain of three middle ear bones—malleus (hammer), incus (anvil), and stapes (stirrup)—that transfer sound vibrations from the eardrum to the oval window.

Eustachian Tube (Auditory Tube)

A conduit connecting the middle ear to the nasopharynx to equalize air pressure across the tympanic membrane.

Organ of Corti

The sensory receptor organ located inside the cochlear duct lined with hair cells that amplifies and converts sound vibrations into electrical nerve impulses.

Vestibule

The inner ear section containing the utricle and saccule, which senses linear acceleration and head tilt relative to gravity.

Otoconia (Otoliths)

Small calcium carbonate stones that weight the gelatinous cupula in the vestibule to bend stereocilia during head tilts.

Semicircular Ducts

Three fluid-filled canals oriented at $90^\circ$ to each other that maintain balance by detecting rotational movement of the head.

Otitis Interna (Otitis Labyrinthitis)

Inflammation of the inner ear causing hearing loss and vestibular signs including head tilt, ataxia, and nystagmus.

Cornea

The transparent, curved rostral section of the fibrous tunic that admits light into the eye.

Sclera

The opaque, fibrous, protective white outer coat of the eye.

Limbus

The anatomical border or junction where the cornea meets the sclera.

Tapetum Lucidum

A reflective surface lining the deep aspect of the choroid that reflects light back through the retina to optimize night vision.

Ciliary Body

Muscular ring-shaped structure in the vascular layer that suspends the lens via suspensory ligaments and controls lens accommodation.

Fovea Centralis

A small depression in the posterior retina densely packed with photoreceptor cells providing high visual acuity.

Optic Disc

The blind spot of the retina where nerve fibers converge to form the optic nerve (cranial nerve II), completely devoid of photoreceptors.

Nictitating Membrane

The third eyelid originating from the medial canthus that sweeps across to protect the ocular surface from debris.

Nystagmus

Involuntary, rhythmic, rapid oscillatory eye movements resulting from vestibular dysfunction, brain tumors, toxins, or ear infections.

Glaucoma

Pathological elevation of intraocular pressure within the eye resulting in compression of the optic nerve and retinal damage.

Cataract

Opacification of the crystalline lens caused by protein aggregation that obstructs the transmission of light to the retina.

Ocular Proptosis

Anterior displacement or bulging of the eyeball beyond the orbital rim, usually caused by severe head trauma.