Peripheral Nervous System, Central Nervous System, and Cranial Nerves Flashcards

Vocabulary practice flashcards generated from lecture notes covering the Peripheral Nervous System, Autonomic Nervous System subdivisions, brain structure, and cranial nerves.

Somatic Nervous System

A division of the peripheral nervous system that includes sensory neurons related to touch, pain, temperature, proprioception, and special senses, as well as motor neurons that innervate skeletal muscles under voluntary control.

Autonomic Nervous System (ANS)

A division of the peripheral nervous system responsible for involuntary control of smooth muscles, cardiac muscles, and glands through sensory receptors in organs and a two-neuron motor pathway.

Preganglionic Neuron

The first motor neuron in an autonomic pathway, having its cell body located in the brainstem or spinal cord and a lightly myelinated axon extending to an autonomic ganglion or the adrenal medulla.

Postganglionic Neuron

The second motor neuron in an autonomic pathway, whose cell body is located in an autonomic ganglion and whose unmyelinated axon extends directly to an effector organ.

Sympathetic Nervous System

The "fight-or-flight" division of the autonomic nervous system that mobilizes the body during activity by increasing alertness, metabolism, heart rate, and blood pressure.

Parasympathetic Nervous System

The "rest-and-digest" division of the autonomic nervous system that conserves energy and maintains homeostasis by slowing down body activities and promoting digestive and urinary functions.

Push-Pull Phenomenon

The collective, opposing control exerted by both the sympathetic and parasympathetic divisions of the autonomic nervous system to sustain homeostatic balance.

Dual Innervation

The dynamic antagonism where visceral organs receive nerve fibers from both the sympathetic and parasympathetic divisions of the ANS to produce opposite physiological effects.

Thoracolumbar Division

Another term for the sympathetic nervous system, derived from the location of its preganglionic neuron cell bodies in the lateral horns of spinal cord segments $T1$ through $T12$ and $L1$ through $L2/3$.

White Ramus Communicans

A short segment containing myelinated preganglionic sympathetic axons that leave a spinal nerve to enter the nearest sympathetic trunk ganglion.

Gray Ramus Communicans

A short pathway containing unmyelinated postganglionic sympathetic axons that exit a sympathetic trunk ganglion to merge with a spinal nerve.

Sympathetic Trunk Ganglia

A chain of autonomic ganglia located anterior and lateral to the vertebral column, consisting of cervical, thoracic, lumbar, sacral, and coccygeal ganglia.

Paravertebral (Prevertebral) Ganglia

Autonomic ganglia situated anterior to the vertebral column near major abdominal arteries (celiac, superior mesenteric, inferior mesenteric, aorticorenal, and renal) responsible for sympathetic output below the diaphragm.

Chromaffin Cells

Modified sympathetic postganglionic cells located in the adrenal medulla that secrete norepinephrine and epinephrine into the bloodstream upon stimulation by preganglionic neurons.

Splanchnic Nerves

Nerves formed by sympathetic preganglionic axons that pass through the sympathetic trunk without synapsing, extending onward to synapse in paravertebral ganglia or the adrenal medulla.

Cephalic Periarterial Nerves

Nerves formed by postganglionic sympathetic axons ascending to the superior cervical ganglion that supply visceral effectors of the face and head.

Terminal Ganglia

Parasympathetic autonomic ganglia located very close to or within the walls of target visceral organs.

Pelvic Splanchnic Nerves

Nerves originating from sacral spinal cord segments $S2$ through $S4$ that carry parasympathetic preganglionic fibers to pelvic floor plexuses and pelvic organs.

Cholinergic Neurons

Neurons that produce and release the neurotransmitter acetylcholine (ACh) from their axon terminals, including all autonomic preganglionic neurons and parasympathetic postganglionic neurons.

Adrenergic Neurons

Neurons that release norepinephrine (NE) from their axon terminals, which includes most sympathetic postganglionic neurons.

Nicotinic Receptors

A class of cholinergic receptors found on postganglionic neurons that always induce an excitatory response when bound by acetylcholine (ACh).

Muscarinic Receptors

A class of cholinergic receptors found on target effectors that can cause either excitatory or inhibitory responses when bound by acetylcholine (ACh).

Adrenergic Receptors

Receptors located on visceral effectors that bind epinephrine or norepinephrine, divided into alpha ($\text{α}_1, \text{α}_2$) and beta ($\text{β}_1, \text{β}_2, \text{β}_3$) subclasses.

Autonomic Reflex Arc

A neural pathway regulating involuntary visceral activities, consisting in order of a receptor, sensory neuron, integrating center (hypothalamus, brainstem, or spinal cord), two motor neurons in series, and an effector.

Sympathomimetic Drugs

Pharmacological agents that mimic the action of norepinephrine or epinephrine at sympathetic synapses, such as phenylephrine.

Sympatholytic Drugs

Medications that inhibit sympathetic nervous system function by acting as antagonists to adrenergic receptors, such as $\text{β}$-blockers (metoprolol and propranolol).

Parasympathomimetic Drugs

Drugs that enhance or mimic cholinergic effects at postganglionic parasympathetic terminals, such as pilocarpine.

Anticholinergic Drugs

Medications that inhibit parasympathetic function by acting as muscarinic receptor antagonists, such as atropine and scopolamine.

Neural Tube

A hollow tube formed during early embryonic development from the folding of the outermost cell layer that gives rise to the central nervous system and brain ventricles.

Primary Brain Vesicles

The three initial embryonic brain expansions formed at two months of development: the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon).

Secondary Brain Vesicles

The five embryonic brain divisions arising from primary vesicles: telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon.

Dural Folds

Inward extensions of the meningeal layer of the dura mater (falx cerebri, falx cerebelli, tentorium cerebelli) that provide structural support and anchor brain structures within the cranium.

Cerebrospinal Fluid (CSF)

A clear fluid containing water, glucose, electrolytes, proteins, and lymphocytes that cushions, protects, nourishes, and maintains buoyancy for the brain and spinal cord.

Choroid Plexuses

Networks of blood capillaries lined with ependymal cells located inside brain ventricles that filter blood plasma to continuously produce cerebrospinal fluid.

Blood-Brain Barrier

A dynamic physical barrier formed by capillary endothelial cells with tight junctions and astrocyte foot processes that selectively restricts chemical entry into brain extracellular fluid.

Gyri and Sulci

Gyri are raised ridges and sulci are shallow grooves on the surface of the cerebral cortex that function together to increase total cortical surface area.

Corpus Callosum

A large band of deep white matter tracts connecting the right and left cerebral hemispheres, facilitating interhemispheric communication.

Basal Nuclei

Clusters of gray matter situated deep within the cerebral hemispheres responsible for cognitive processing, movement planning, procedural learning, and memory.

Broca's Area

A motor speech region located in the left frontal lobe responsible for coordinating the complex muscle movements necessary for speech production.

Broca's Aphasia

A language disorder caused by damage to Broca's area resulting in broken, non-fluent speech articulate difficulty, despite intact language comprehension.

Primary Somatosensory Cortex

A functional cortical region in the postcentral gyrus of the parietal lobe that processes general somatic sensory inputs such as touch, temperature, pressure, pain, and proprioception.

Sensory Homunculus

A spatial map mapped onto the primary somatosensory cortex depicting the disproportionate representation of various body parts based on sensory receptor density.

Thalamus

A major diencephalic sensory relay station superior to the midbrain that processes and relays all incoming sensory information (except smell) to specific areas of the cerebral cortex.

Hypothalamus

The principal diencephalic homeostatic center regulating the autonomic nervous system, endocrine functions via the pituitary gland, body temperature, thirst, satiety, emotional patterns, and sleep-wake cycles.

Pineal Gland

An endocrine structure located within the epithalamus that secretes the hormone melatonin to regulate circadian rhythms and sleep cycles.

Medulla Oblongata

The most inferior segment of the brainstem containing medullary pyramids, vital autonomic centers (cardiovascular, respiratory, swallowing, vomiting), and nuclei for cranial nerves $VIII$ through $XII$.

Pons

A brainstem region superior to the medulla that bridges the cerebral cortex with the opposite cerebellar hemisphere and collaborates with the medulla to regulate breathing.

Midbrain

The superior brainstem section housing the corpora quadrigemina (superior and inferior colliculi for visual and auditory reflexes), cerebral peduncles, red nuclei, and substantia nigra.

Substantia Nigra

A midbrain nucleus containing dopamine-secreting neurons that control subconscious motor activity, the degeneration of which is associated with Parkinson's disease.

Arbor Vitae

The distinctive tree-like branching pattern of inner white matter within the cerebellum.

Hippocampus

A limbic system structure crucial for processing, consolidating, and storing long-term memories.

Amygdala (Amygdaloid body)

A limbic system structure primary involved in regulating emotional states, particularly fear, rage, and threat detection.

Olfactory Nerve (CN I)

A purely sensory cranial nerve originating in the olfactory epithelium of the nasal cavity that conducts impulses for the sense of smell through the cribriform plate to the olfactory bulb.

Optic Nerve (CN II)

A special sensory cranial nerve carrying visual impulses from retinal ganglion cells through the optic canal to the optic chiasm, thalamus (LGN), and primary visual cortex.

Oculomotor Nerve (CN III)

A motor cranial nerve supplying somatic motor fibers to extraocular eye muscles and autonomic parasympathetic fibers to the ciliary muscle and iris sphincter for lens accommodation and pupil constriction.

Trochlear Nerve (CN IV)

A somatic motor cranial nerve arising from the posterior midbrain that innervates the superior oblique muscle to depress and intort the eyeball.

Trigeminal Nerve (CN V)

The largest cranial nerve, featuring three branches (ophthalmic $\text{V}_1$, maxillary $\text{V}_2$, mandibular $\text{V}_3$) that supply general facial sensation and motor innervation to the muscles of mastication.

Abducens Nerve (CN VI)

A somatic motor cranial nerve originating in the pons that innervates the lateral rectus muscle, responsible for abducting the eye outward.

Facial Nerve (CN VII)

A mixed cranial nerve providing motor control for facial expression muscles, special taste sensation to the anterior two-thirds of the tongue, and parasympathetic innervation to tear and salivary glands.

Vestibulocochlear Nerve (CN VIII)

A purely sensory cranial nerve consisting of a vestibular branch for detecting balance and equilibrium and a cochlear branch for auditing hearing.

Glossopharyngeal Nerve (CN IX)

A mixed cranial nerve responsible for taste on the posterior one-third of the tongue, swallowing muscle control, parotid salivary gland secretion, and monitoring blood pressure via the carotid sinus.

Vagus Nerve (CN X)

The longest cranial nerve, providing extensive parasympathetic motor control to thoracic and abdominal visceral organs, regulating heart rate, digestive motility, secretion, and airway diameter.

Accessory Nerve (CN XI)

A somatic motor cranial nerve originating from the upper spinal cord and medulla that innervates the sternocleidomastoid and trapezius muscles to coordinate head turning and shoulder shrugging.

Hypoglossal Nerve (CN XII)

A motor cranial nerve arising from the medulla that innervates intrinsic and extrinsic tongue muscles to control speech, chewing, and swallowing.