W5 | Spinal Cord and Cranial Nerves

Vocabulary flashcards covering the gross anatomy, blood supply, meninges, and tracts of the spinal cord, as well as the structure, pathways, and functions of the 12 cranial nerves.

Conus Medullaris

The conical, tapered distal termination of the spinal cord located at approximately the $L1-L2$ vertebral level.

Cauda Equina

A bundle of spinal nerve roots that descend distal to the conus medullaris within the vertebral canal before exiting at their respective intervertebral foramina.

Filum Terminale

A strand of connective tissue continuous with the pia mater extending from the conus medullaris to anchor the spinal cord to the coccyx.

Cervical Enlargement

An expanded region of the spinal cord spanning from $C4$ to $T1$ that gives rise to the nerves innervating the upper limbs.

Lumbar Enlargement

An expanded region of the spinal cord spanning from $T11$ to $S1$ that gives rise to the nerves innervating the lower limbs.

Spinal Cord Length

The continuous caudal extension of the medulla oblongata measuring approximately $42-45\,\text{cm}$ in length and terminating at the $L1-L2$ vertebral level.

Spinal Segments

The $31$ functional divisions of the spinal cord corresponding to $31$ pairs of spinal nerves, categorized as $8$ cervical ($C1-C8$), $12$ thoracic ($T1-T12$), $5$ lumbar ($L1-L5$), $5$ sacral ($S1-S5$), and $1$ coccygeal ($CO1$).

Epidural Space

The real anatomical space situated between the dura mater and the periosteum of the vertebral canal, containing fat and the internal vertebral venous plexus.

Lumbar Puncture

A clinical procedure performed between the spinous processes of $L3$ and $L4$ to extract cerebrospinal fluid from the lumbar cistern in the absence of the spinal cord.

Dorsal Root

The sensory (afferent) nerve root that conducts incoming sensory impulses from peripheral receptors into the dorsal horn of the spinal cord.

Dorsal Root Ganglion

A nodular enlargement on the dorsal root containing the cell bodies of somatic and visceral sensory (afferent) neurons.

Ventral Root

The motor (efferent) nerve root that transmits motor commands from somatic and visceral motor neurons in the spinal cord out to effector organs.

Artery of Adamkiewicz

The largest segmental medullary artery, entering typically in the lumbar region to provide major blood supply to the lumbar enlargement of the spinal cord.

Anterior Spinal Artery

A single longitudinal artery arising from the vertebral arteries that runs along the anterior (ventral) median fissure to supply the anterior two-thirds of the spinal cord.

Posterior Spinal Arteries

Two longitudinal arteries originating from either the posterior inferior cerebellar arteries or vertebral arteries, running along the posterolateral sulci of the spinal cord.

Fasciculus Gracilis

An ascending sensory tract in the posterior funiculus carrying fine touch, vibration, pressure, and proprioception signals from the lower body ($T7$ and below).

Fasciculus Cuneatus

An ascending sensory tract in the posterior funiculus carrying fine touch, vibration, pressure, and proprioception signals from the upper body (above $T6$).

Lateral Spinothalamic Tract

An ascending sensory tract in the anterolateral system responsible for conveying pain and temperature sensations from the contralateral side of the body to the thalamus.

Ventral Spinothalamic Tract

An ascending sensory tract in the anterolateral system carrying crude touch and pressure sensations to the thalamus.

Corticospinal Tracts

Descending motor pathways originating in the primary motor cortex that mediate voluntary skeletal muscle movements, divided into anterior and lateral tracts.

Reticulospinal Tract

A descending motor pathway involved in maintaining posture and muscle tone in response to movement.

Vestibulospinal Tract

A descending motor pathway responsible for maintaining posture and equilibrium in response to vestibular sensory input.

Tectospinal Tract

A descending motor tract mediating postural reflexes of the head and neck in response to visual and auditory stimuli.

Rubrospinal Tract

A descending motor pathway involved in regulating and coordinating motor commands for arm and wrist movements.

Corticobulbar Tracts

Descending motor pathways extending from the primary motor cortex to lower motor neuron nuclei in the brainstem.

General Somatic Afferent (GSA)

A functional classification for cranial nerve fibers conveying general sensory inputs such as touch, pressure, pain, and temperature from the head and face.

General Visceral Afferent (GVA)

A functional classification for cranial nerve fibers carrying sensory information from internal visceral organs, blood vessels, and glands.

Special Sensory Afferent (SSA)

A functional classification for cranial nerve fibers dedicated to transmitting special senses including smell, vision, hearing, balance, and taste.

General Somatic Efferent (GSE)

A functional classification for cranial nerve fibers providing motor commands to somite-derived skeletal muscles.

General Visceral Efferent (GVE)

A functional classification for cranial nerve fibers delivering autonomic parasympathetic motor output to smooth muscle, cardiac muscle, and glands.

Cranial Nerve I (Olfactory Nerve)

A special sensory nerve ($SSA$) originating from olfactory receptors in the olfactory epithelium, passing through the cribriform plate to the olfactory bulb; damage results in anosmia.

Cranial Nerve II (Optic Nerve)

A special sensory nerve ($SSA$) arising from retinal photoreceptors, exiting via the optic canal to relay visual information through the optic chiasm and tract to the lateral geniculate nucleus.

Optic Chiasm

The anatomical structure where nerve fibers originating from the nasal retinas cross over to the contralateral side of the brain.

Extraocular Muscle Innervation Formula ($LR_6SO_4R_3$)

A mnemonic denoting that Lateral Rectus is innervated by $CN\,VI$, Superior Oblique by $CN\,IV$, and the Remaining extraocular muscles by $CN\,III$.

Cranial Nerve III (Oculomotor Nerve)

A motor ($GSE$) and visceral motor ($GVE$) nerve exiting via the superior orbital fissure; innervates levator palpebrae superioris, superior/inferior/medial recti, inferior oblique, pupillary sphincter, and ciliary muscles.

Edinger-Westphal Nucleus

The visceral motor ($GVE$) nucleus in the midbrain that sends preganglionic parasympathetic fibers via $CN\,III$ to the ciliary ganglion.

Ciliary Ganglion

The parasympathetic ganglion of $CN\,III$ that relays postganglionic fibers through short ciliary nerves to control pupillary constriction and lens accommodation.

Cranial Nerve IV (Trochlear Nerve)

A somatic motor nerve ($GSE$) and the only cranial nerve arising from the dorsal surface of the brainstem; passes through the superior orbital fissure to innervate the superior oblique muscle.

Cranial Nerve VI (Abducens Nerve)

A somatic motor nerve ($GSE$) originating from the pontine abducens nucleus, exiting via the superior orbital fissure to innervate the lateral rectus muscle.

Cranial Nerve V (Trigeminal Nerve)

The largest cranial nerve, serving as the primary general sensory nerve ($GSA$) for the head and face, and motor nerve ($GSE$) for muscles of mastication via its three main branches ($V_1$, $V_2$, $V_3$).

Ophthalmic Nerve ($V_1$)

The first division of $CN\,V$ ($GSA$) exiting through the superior orbital fissure; conveys sensory signals from the eye, upper eyelid, forehead, dorsum of the nose, and nasal cavity.

Maxillary Nerve ($V_2$)

The second division of $CN\,V$ ($GSA$) exiting through the foramen rotundum; supplies sensory input to the mid-face, palate, nasal cavity, maxillary sinus, and upper teeth.

Mandibular Nerve ($V_3$)

The third division of $CN\,V$ ($GSA$ and $GSE$) exiting through the foramen ovale; provides sensory innervation to the lower jaw, cheek, and anterior two-thirds of the tongue, and motor control to muscles of mastication.

Trigeminal Neuralgia

A condition causing sudden, severe, short-duration paroxysmal facial pain triggered by light sensory stimulation within the distribution of $CN\,V$.

Cranial Nerve VII (Facial Nerve)

A mixed nerve containing $GSE$, $GVE$, $GSA$, and $SSA$ modalities that exits via the internal acoustic meatus and stylomastoid foramen; innervates muscles of facial expression, taste on the anterior two-thirds of the tongue, and secretomotor glands.

Bell's Palsy

Unilateral facial nerve ($CN\,VII$) paralysis presenting with loss of function in muscles of facial expression, reduced lacrimation/salivation, and impaired taste on the anterior two-thirds of the tongue.

Cranial Nerve VIII (Vestibulocochlear Nerve)

A special sensory nerve ($SSA$) exiting the cranial cavity via the internal acoustic meatus; conveys equilibrium information from vestibular apparatus and auditory signals from the cochlea.

Cranial Nerve IX (Glossopharyngeal Nerve)

A mixed cranial nerve carrying $GVA$, $SSA$, $GVE$, and $GSE$ fibers through the jugular foramen; innervates stylopharyngeus muscle, parotid gland via the otic ganglion, and posterior one-third of the tongue.

Otic Ganglion

The parasympathetic ganglion linked with $CN\,IX$ that provides postganglionic secretomotor innervation to the parotid salivary gland.

Cranial Nerve X (Vagus Nerve)

A broad cranial nerve carrying $GSA$, $GVA$, $SSA$, $GVE$, and $GSE$ modalities through the jugular foramen; supplies parasympathetic motor control to thoracic and abdominal organs and motor output to pharyngeal/laryngeal muscles.

Nucleus Ambiguus

A brainstem motor nucleus giving origin to somatic motor fibers ($GSE$) carried by $CN\,IX$, $CN\,X$, and cranial roots of $CN\,XI$ to muscles of the pharynx and larynx.

Cranial Nerve XI (Accessory Nerve)

A somatic motor nerve ($GSE$) arising from spinal segments $C1-C5$, entering via the foramen magnum and exiting through the jugular foramen to innervate the sternocleidomastoid and trapezius muscles.

Cranial Nerve XII (Hypoglossal Nerve)

A somatic motor nerve ($GSE$) exiting through the hypoglossal canal to supply motor control to all intrinsic and extrinsic tongue muscles except the palatoglossus muscle.