The Brain and Cranial Nerves

Comprehensive vocabulary flashcards covering the structural divisions of the nervous system, brain stem, diencephalon, cerebellum, cerebrum, functional cortical areas, meninges, cerebrospinal fluid dynamics, and cranial nerves.

Central Nervous System (CNS)

Division of the nervous system consisting of the brain and spinal cord, serving as integrative and control centers.

Peripheral Nervous System (PNS)

Division of the nervous system consisting of cranial nerves and spinal nerves that serves as communication lines between the CNS and the rest of the body.

Autonomic Nervous System (ANS)

Involuntary visceral motor division of the PNS that conducts impulses from the CNS to cardiac muscle, smooth muscle, and glands; divided into sympathetic and parasympathetic divisions.

Neural Tube

The embryonic cylindrical structure formed from surface ectoderm that subsequently develops into the brain and spinal cord.

Medulla Oblongata

The most caudal portion of the brain stem (approximately $1.5\,\text{inches}$ long) continuous with the spinal cord, containing the cardiovascular center, respiratory rhythmicity center, autonomic reflex centers (vomiting, coughing, swallowing, sneezing), and nuclei for CN VIII–XII.

Decussation of Pyramids

The crossover of motor tract axons in the pyramids of the medulla oblongata, which results in the left cerebral hemisphere controlling skeletal muscles on the right side of the body and vice versa.

Pons

Brain stem region situated directly superior to the medulla oblongata and anterior to the cerebellum (approximately $1\,\text{inch}$ long) that acts as a bridge connecting parts of the brain and spinal cord, containing nuclei for CN V–VIII.

Pontine Respiratory Group

A collection of nuclei in the pons (formerly known as the pneumotaxic center) that acts as an 'off-switch' to terminate medullary inspiratory activity, thereby regulating respiratory rate.

Midbrain

The region of the brain stem connecting the pons to the diencephalon, traversed by the cerebral aqueduct and containing the cerebral peduncles, tectum, and substantia nigra.

Cerebral Peduncles

Paired ventral structures of the midbrain ('little feet') containing descending tracts that conduct motor nerve impulses from the cerebral cortex to the spinal cord, medulla, and pons.

Tectum

The posterior roof of the midbrain composed of four rounded elevations known as the superior and inferior colliculi, which serve as reflex centers for visual, auditory, and startle reflexes.

Substantia Nigra

A darkly pigmented midbrain nucleus containing dopamine-releasing neurons that help regulate subconscious muscle activities; degeneration of these neurons causes Parkinson disease.

Reticular Formation

A diffuse network of neurons spanning the brain stem that maintains consciousness, alertness, and orientation, filters repetitive sensory inputs via habituation, and results in coma if damaged.

Cerebellum

The second-largest part of the brain ('little brain') situated inferior to the cerebrum and posterior to the brain stem; coordinates voluntary muscle movements, regulates posture, equilibrium, and balance, and aids in motor memory.

Thalamus

A large diencephalic relay station that functions like a router, receiving all sensory impulses (vision, hearing, touch, temperature, pain, pressure) and routing them to the appropriate regions of the cerebral cortex.

Pineal Gland

An endocrine structure within the epithalamus that secretes melatonin in the dark to establish and regulate the circadian sleep-wake cycle.

Melatonin

A sleep-inducing hormone produced by the pineal gland during darkness whose secretion is suppressed by ambient light (particularly blue light).

Hypothalamus

An inferior diencephalic structure that maintains homeostasis through the '6H' functions (hot, hungry, hydrated, hourly, horny, hormonal) and regulates the endocrine system by controlling the pituitary gland.

Cerebrum

The largest portion of the human brain (constituting over $80\%$ of brain mass) consisting of outer cerebral cortex gray matter and inner white matter, responsible for conscious thought, reasoning, and voluntary actions.

Cerebral Cortex

The external superficial layer of gray matter covering the cerebrum, organized into six cellular layers containing pyramidal and stellate cells, which mediates higher cognitive processes.

Gyri and Sulci

The surface folds (gyri) and shallow grooves (sulci) of the cerebral cortex that allow its expanded area of more than $3\,\text{square feet}$ to fit into the cranial cavity.

Corpus Callosum

A prominent band of commissural axons that links corresponding functional areas of the left and right cerebral hemispheres.

Basal Nuclei

Subcortical clusters of gray matter located deep within the cerebrum that facilitate the subconscious control of skeletal muscle movements, such as swinging the arms while walking.

Limbic System

A functional ring of cortical, diencephalic, and midbrain structures ('the emotional brain') that regulates emotions (pleasure, pain, fear, anger) and contributes to long-term memory formation.

Brodmann's Areas

A numbered histological map of the cerebral cortex that categorizes cortical regions based on their cytoarchitecture and maps them to specific functions.

Primary Motor Cortex

Cortical area located within the precentral gyrus of the frontal lobe (Brodmann area 4) that controls the execution of voluntary muscle contractions.

Motor Homunculus

A topographical mapping of the human body along the precentral gyrus where the anatomical size of each body region is proportional to the precision of fine motor control dedicated to it.

Broca's Area

The motor speech center located in the frontal lobe (Brodmann areas 44 and 45) that coordinates the muscular movements required to produce spoken language.

Primary Somatosensory Cortex

Cortical area situated in the postcentral gyrus of the parietal lobe (Brodmann areas 1, 2, and 3) that receives general somatic sensory inputs such as touch, proprioception, pain, and temperature.

Sensory Homunculus

A somatosensory map along the postcentral gyrus in which the representation of each body part is sized proportionally to the density of sensory receptors located there.

Primary Visual Cortex

The region located in the occipital lobe (Brodmann area 17) responsible for receiving and processing visual sensory input from the retinas.

Prefrontal Cortex

The anterior region of the frontal lobe responsible for higher-order reasoning, executive functions, judgment, morality, decision-making, and personality integration.

Wernicke's Area

A cortical association region in the temporal and parietal lobes responsible for understanding and comprehending spoken and written language.

Hemispheric Lateralization

The functional specialization of each cerebral hemisphere, where the left hemisphere typically governs logic, mathematics, and language, while the right hemisphere governs spatial, artistic, and musical abilities.

Electroencephalogram (EEG)

A non-invasive diagnostic record of brain electrical activity generated by millions of cortical neurons, recorded using scalp electrodes to diagnose brain trauma, sleep disorders, and brain death.

Alpha Waves

Rhythmic EEG waves with a frequency of $10\text{--}12\,\text{Hz}$ present in awake, resting individuals with their eyes closed, which disappear during sleep.

REM Sleep

Rapid eye movement sleep stage characterized by high cortical metabolic activity, dreaming, and profound relaxation/inhibition of voluntary skeletal muscles.

Falx Cerebri

A large, sickle-shaped vertical fold of the dura mater that descends into the longitudinal fissure to separate the right and left cerebral hemispheres.

Tentorium Cerebelli

A transverse crescent-shaped extension of dura mater that supports the occipital lobes of the cerebrum and separates them from the underlying cerebellum.

Cerebrospinal Fluid (CSF)

A clear, colorless protective fluid circulating through the brain ventricles, central canal, and subarachnoid space that provides buoyancy, mechanical cushioning, and chemical transport.

Choroid Plexus

Specialized capillary networks lined by ependymal cells situated in each brain ventricle that continuously secrete cerebrospinal fluid at a rate of approximately $20\,\text{mL/h}$.

Arachnoid Villi

Finger-like extensions of the arachnoid mater that project into the dural venous sinuses to reabsorb cerebrospinal fluid back into the venous bloodstream.

Hydrocephalus

An abnormal buildup of cerebrospinal fluid and intracranial pressure within the ventricles due to impaired drainage, obstruction, or overproduction.

Blood-Brain Barrier (BBB)

A selective physiological barrier composed of tight junctions between capillary endothelial cells and astrocyte perivascular feet, protecting neural tissue from harmful bloodborne substances.

Olfactory Nerve (CN I)

Sensory cranial nerve comprising axons that penetrate the cribriform plate of the ethmoid bone to convey the sense of smell to the olfactory bulbs.

Optic Nerve (CN II)

Sensory cranial nerve formed by ganglion cell axons from the retina that conveys visual sensory information to the optic chiasm and brain.

Oculomotor Nerve (CN III)

Cranial nerve providing somatic motor innervation to extraocular eye muscles and the levator palpebrae superioris, as well as parasympathetic motor control for pupillary constriction.

Trigeminal Nerve (CN V)

The principal sensory cranial nerve of the face with three major branches (ophthalmic, maxillary, mandibular) that also provides motor innervation to the muscles of mastication.

Facial Nerve (CN VII)

Mixed cranial nerve with five somatic branches innervating the muscles of facial expression, transmitting taste from the anterior two-thirds of the tongue, and innervating salivary glands.

Bell's Palsy

Acute peripheral paralysis of the facial nerve (CN VII) that results in unilateral facial drooping, inability to close the eyelid, and impaired salivation and taste.