Chapter 14: The Brain and Cranial Nerves

Comprehensive vocabulary flashcards covering Chapter 14: The Brain and Cranial Nerves, including embryology, ventricular system, meninges, cerebrospinal fluid circulation, major brain divisions, cortical functional areas, white matter tracts, deep nuclei, brainstem structures, and all twelve cranial nerves.

Encephalization Quotient

A measurement of brain size relative to body size; in humans, who have the largest primate brain averaging $\sim 1{,}400\text{ g}$ and approximately $16\text{ billion}$ cortical neurons, this ratio doubles the neuron count found in great apes.

4 Major Brain Regions

1. The cerebrum

2. The Diencephalon

3. The Cerebellum

4. The Brainstem

▪ Midbrain

▪ Pons

▪ Medulla oblongata

Cerebral Cortex

A superficial layer of gray matter covering the cerebral hemispheres that contains billions of neurons arranged in six distinct layers, represents approximately $40\%$ of total brain mass, and serves as the executive suite for conscious mind and intellectual functions.

Cortex contains

Gyri- (rounded elevations) that increase surface area

Sulci- shallow grooves

Fissures- Deep Grooves- separate

gyri; fissures divide major brain regions.

Diencephalon

links the brainstem to the cerebral hemispheres.

Thalamus

relay and processing center for sensory information

Hypothalamus

forms the floor of the diencephalon; regulates emotions, autonomic functions, and hormone production

Infundibulum

connects the hypothalamus to the pituitary gland, integrating the nervous and endocrine systems

Hypophyseal portal system

connects to anterior pituitary

Hypothalamo-Hypophyseal tract

connects to posterior pituitary

Primary Brain Vesicles

The three initial cephalic expansions of the embryonic neural tube at 3 weeks of development: the prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

Secondary Brain Vesicles

The five subdivisions of the embryonic brain formed by 6 weeks: the telencephalon and diencephalon (derived from the prosencephalon), the undivided mesencephalon, and the metencephalon and myelencephalon (derived from the rhombencephalon).

Septum Pellucidum

A thin medial partition of brain tissue that separates the two lateral ventricles within the cerebral hemispheres.

Interventricular Foramen

The opening (also known as the foramen of Monro) that connects each lateral ventricle to the third ventricle in the diencephalon.

Cerebral Aqueduct

A slender passageway (also known as the aqueduct of Sylvius) running through the midbrain that connects the third ventricle to the fourth ventricle; it contains no choroid plexus and does not produce cerebrospinal fluid.

Dural Folds

Inward extensions of the inner meningeal layer of the dura mater that provide stabilization and support for the brain and contain the dural venous sinuses; major examples include the falx cerebri, tentorium cerebelli, and falx cerebelli.

Falx Cerebri

A sickle-shaped dural fold projecting between the cerebral hemispheres in the longitudinal fissure, attaching anteriorly to the crista galli and posteriorly to the internal occipital crest, and enclosing the superior and inferior sagittal sinuses.

Tentorium Cerebelli

A dural fold extending at right angles to the falx cerebri that separates and protects the cerebellum from the occipital lobes of the cerebrum; it houses the transverse sinus.

Falx Cerebelli

A midsagittal dural fold located inferior to the tentorium cerebelli that divides the two cerebellar hemispheres and contains the occipital sinus along its posterior margin.

Choroid Plexus

Vascular complexes in the brain ventricles consisting of specialized ependymal cells with microvilli and tight junctions that filter blood from capillaries to produce and maintain cerebrospinal fluid at a rate of approximately $500\text{ mL/day}$.

Arachnoid Granulations

Large clusters of finger-like arachnoid villi that project through the meningeal dura mater into the superior sagittal sinus in adults to reabsorb cerebrospinal fluid into the venous circulation.

Hydrocephalus

A pathological accumulation of cerebrospinal fluid resulting from an obstruction in circulation or drainage, causing increased intracranial pressure, compression of brain tissues, and enlargement of the infant head due to unfused skull bones.

Blood Brain Barrier

A protective, selectively permeable barrier isolating CNS neural tissue from general circulation, primarily formed by exceptionally impermeable tight junctions between capillary endothelial cells and regulated by astrocyte perivascular processes.

Primary Motor Cortex

The somatic motor control area situated within the precentral gyrus of the frontal lobe whose large pyramidal cells give rise to the descending pyramidal (corticospinal) tracts for voluntary skeletal muscle contractions.

Somatotopy

The precise spatial point-for-point mapping of body structures to specific regions of the central nervous system, illustrated graphically as motor and sensory homunculi.

Premotor Cortex

The motor planning region located immediately anterior to the precentral gyrus that organizes complex, learned, repetitive, and patterned motor sequences by transmitting activating signals to the primary motor cortex.

Prefrontal Cortex

Also called the anterior association area, this frontal lobe region manages intellect, complex learning abilities (cognition), recall, personality, working memory, judgment, and abstract reasoning.

Broca's Area

A specialized motor speech region situated anterior to the inferior premotor cortex (typically in the left hemisphere) that coordinates the respiratory, laryngeal, pharyngeal, and oral muscles necessary for speech vocalization.

Frontal Eye Field

A cortical region situated partially in and anterior to the premotor cortex and superior to Broca's area that regulates voluntary scanning and tracking movements of the eyes.

Primary Somatosensory Cortex

Cortical area located in the postcentral gyrus of the parietal lobe that receives general sensory input (touch, pressure, pain, vibration, temperature) and proprioceptive input to achieve spatial discrimination.

Somatosensory Association Cortex

A parietal lobe region located posterior to the primary somatosensory cortex that integrates sensory inputs to determine the size, texture, and spatial relationships of felt objects.

Primary Visual Cortex

Also called the striate cortex, this sensory area is located on the extreme posterior tip and within the calcarine sulcus of the occipital lobe to receive raw visual data from the retina.

Wernicke's Area

A language association region situated in the posterior portion of the superior temporal gyrus responsible for the comprehension of spoken and written language; lesions cause fluent, receptive aphasia.

Primary Olfactory Cortex

The sensory cortex located on the medial aspect of the temporal lobe within the piriform lobe and uncus that receives afferent smell signals directly via olfactory tracts for conscious perception of odors.

Gustatory Cortex

The region responsible for conscious perception and processing of taste stimuli, located in the insula deep to the lateral sulcus.

Association Fibers

White matter tracts that interconnect different cortical regions within the same cerebral hemisphere, comprising short arcuate fibers between adjacent gyri and long longitudinal fasciculi linking distinct lobes.

Corpus Callosum

The largest commissure of the brain, containing roughly $100\text{ million}$ axons lying superior to the lateral ventricles deep within the longitudinal fissure, facilitating communication between the two cerebral hemispheres.

Projection Fibers

White matter tracts that run vertically to link the cerebral cortex with the diencephalon, brainstem, cerebellum, and spinal cord; they condense into the internal capsule and flare out into the corona radiata.

Basal Nuclei

Subcortical gray matter masses embedded deep within the white matter of each cerebral hemisphere (consisting of the caudate nucleus, putamen, and globus pallidus) that subconsciously adjust muscle tone and coordinate learned movement patterns.

Claustrum

A slender sheet of gray matter situated lateral to the putamen deep within each hemisphere, proposed by Crick and Koch as a broad integrative hub or conductor of conscious sensory experience.

Thalamus

A bilateral egg-shaped sensory relay center making up approximately $80\%$ of the diencephalon, which filters and relays all ascending sensory information (except smell) to the cerebral cortex.

Lateral Geniculate Body

A specialized thalamic nucleus that receives visual input from the optic tract and projects visual impulses to the primary visual cortex.

Medial Geniculate Body

A thalamic nucleus that receives auditory signals from the inferior colliculi and relays them to the primary auditory cortex.

Hypothalamus

The primary visceral control center of the diencephalon situated below the thalamus, regulating body temperature, autonomic centers, hunger, thirst, circadian rhythms, and endocrine hormone secretion.

Supra-optic Nucleus

A hypothalamic nucleus that synthesizes antidiuretic hormone (ADH) to restrict renal water excretion, transporting it via axons to the posterior pituitary.

Paraventricular Nucleus

A hypothalamic nucleus that produces oxytocin to stimulate contractions of smooth muscle in the uterus and mammary glands.

Suprachiasmatic Nucleus

The master circadian pacemaker in the hypothalamus that receives retinal inputs to synchronize daily physiological cycles with the 24-hour light-dark cycle.

Cingulate Gyrus

The superior cortical arch of the limbic lobe lying immediately superior to the corpus callosum, functioning in emotion and cognitive processing.

Hippocampus

A crucial limbic nucleus situated deep to the parahippocampal gyrus along the floor of the lateral ventricle that is essential for learning and the formation, storage, and retrieval of long-term memories.

Amygdaloid Body

An almond-shaped limbic nucleus located at the tip of the inferior horn of the lateral ventricle that processes fear, governs the fight-or-flight response, and links emotions to specific memories.

Fornix

A C-shaped white matter tract that connects the hippocampus to the mammillary bodies of the hypothalamus, serving as a key communication link of the limbic system.

Corpora Quadrigemina

Four domelike nuclei located on the dorsal tectum of the midbrain, comprising two superior colliculi (visual reflex centers) and two inferior colliculi (auditory reflex and startle centers).

Substantia Nigra

A darkly pigmented midbrain nucleus containing dopamine-producing neurons whose degeneration is the underlying cause of Parkinson's disease.

Red Nucleus

A highly vascularized midbrain nucleus containing iron pigment that provides subconscious motor control of upper limb position and maintains background muscle tone.

Pons

The bulging brainstem region positioned between the midbrain and medulla oblongata that contains ascending and descending tracts, respiratory centers (apneustic and pneumotaxic), and nuclei for cranial nerves V, VI, VII, and VIII.

Decussation of Pyramids

The morphological crossing of approximately $85\%$ of descending corticospinal motor fibers across the midline on the ventral aspect of the lower medulla oblongata.

Olives

Oval lateral protuberances on the medulla oblongata produced by the underlying inferior olivary nuclei, which relay muscle and joint stretch information to the cerebellum.

Solitary Nucleus

A visceral sensory nucleus in the medulla oblongata that receives afferent information from cranial nerves VII, IX, and X regarding visceral sensation and taste.

Purkinje Cells

Massive inhibitory neurons in the cerebellar cortex with elaborate dendritic arbors receiving up to $200{,}000$ synapses, constituting the sole output pathway from the cerebellar cortex to deep cerebellar nuclei.

Arbor Vitae

The branching, tree-like pattern of internal white matter visible in sagittal and sectional views of the cerebellum.

Cerebellar Peduncles

Three pairs of nerve fiber tracts (superior, middle, and inferior) that connect the cerebellum to the midbrain, pons, and medulla oblongata, respectively.

Olfactory Nerve (CN I)

A special sensory nerve originating in the olfactory epithelium that passes through the cribriform plate of the ethmoid to synapse in the olfactory bulb for the perception of smell.

Optic Nerve (CN II)

A special sensory nerve carrying visual impulses from retinal ganglion cells through the optic canal of the sphenoid bone to converge at the optic chiasm.

Oculomotor Nerve (CN III)

A motor nerve emerging from the ventral midbrain that innervates four extrinsic eye muscles (superior, inferior, and medial rectus; inferior oblique), the levator palpebrae superioris, and provides parasympathetic control to the ciliary muscle and pupillary sphincter via the ciliary ganglion.

Trochlear Nerve (CN IV)

The smallest cranial nerve, arising from the dorsal midbrain and passing through the superior orbital fissure to innervate the superior oblique muscle as it passes through a pulley-like sling.

Trigeminal Nerve (CN V)

The largest cranial nerve; a mixed nerve emerging from the pons that divides into ophthalmic ($\text{V}_1$), maxillary ($\text{V}_2$), and mandibular ($\text{V}_3$) branches to convey sensory input from the face and motor fibers to the muscles of mastication.

Tic Douloureux

Also called trigeminal neuralgia; a severe neuropathic condition caused by irritation or vascular compression of the trigeminal nerve that produces intense, stabbing facial pain along the maxillary and mandibular distributions.

Abducens Nerve (CN VI)

A somatic motor nerve emerging at the border between the pons and medulla that exits via the superior orbital fissure to innervate the lateral rectus muscle, causing eye abduction.

Facial Nerve (CN VII)

A mixed cranial nerve emerging from the pons that provides somatic motor control to the muscles of facial expression, special sensory taste to the anterior two-thirds of the tongue, and parasympathetic fibers to the lacrimal, submandibular, and sublingual glands.

Bell's Palsy

A temporary condition caused by inflammation or viral swelling of the facial nerve, leading to ipsilateral paralysis of facial muscles, eyelid drooping, corner-of-mouth sagging, and partial loss of taste.

Vestibulocochlear Nerve (CN VIII)

A sensory cranial nerve entering the brainstem at the pontomedullary junction, consisting of a vestibular branch for equilibrium and balance and a cochlear branch for hearing.

Glossopharyngeal Nerve (CN IX)

A mixed nerve emerging from the medulla that traverses the jugular foramen to convey taste and general sensation from the posterior third of the tongue, innervate the stylopharyngeus muscle, monitor carotid body and sinus receptors, and supply parasympathetic fibers to the parotid gland via the otic ganglion.

Vagus Nerve (CN X)

The only cranial nerve to extend beyond the head and neck into the thoracic and abdominopelvic cavities, providing extensive parasympathetic motor innervation to cardiovascular, respiratory, and digestive organs.

Accessory Nerve (CN XI)

A motor nerve formed from rootlets arising from the superior cervical spinal cord ($\text{C}_1\text{–}\text{C}_5$) that ascend through the foramen magnum and exit via the jugular foramen to innervate the sternocleidomastoid and trapezius muscles.

Hypoglossal Nerve (CN XII)

A motor nerve emerging from the medulla oblongata that exits through the hypoglossal canal to provide somatic motor innervation to the intrinsic and extrinsic muscles of the tongue for food manipulation, swallowing, and speech.