Cranial Nerve Overview Flashcards
General Afferent Fibers
Sensory fibers which have their cells of origin in the craniospinal ganglia (Dorsal root ganglia; nuclei/ ganglia of specific cranial nerves)
a. General Somatic Afferent (GSA):
1. Exteroceptive impulses (pain, temperature, touch) from epithelium of ectodermal origin: all skin, lining of the external ear and tympanic membrane, conjunctiva covering the palpebral surface of the eye, lining of the external nares, nasal cavity and paranasal sinuses, lining of the mouth, the anterior 2/3 of the tongue, and lining of the cranium (dura mater)
- Proprioceptive impulses from sensory endings in the body wall, tendons, joints
b. General Visceral Afferent (GVA):
Fibers carrying sensory impulses (generally pain) from the visceral structures within the body lined by epithelium of endodermal origin: posterior third of the tongue, ducts of the parotid gland, carotid sinus, pharynx, pharyngotympanic tube & middle ear, larynx, bronchial tree, esophagus, gut, pancreaticohepatic ducts, and linings of the genitourinary ducts.
Note: although blood vessels are derived from mesoderm, they are still supplied with visceral afferent
Special Afferent Fibers
Found ONLY IN CRANIAL NERVES
a. special somatic afferent (SSA)
ear and eye (vision, hearing and equilibrium)
b. special visceral afferent (SVA)
specialized fibers for olfactory (smell) and gustatory (taste) receptors. Named visceral because of the functional association of the sensation with the digestive tract.
General efferent fibers
motor fibers which innervate the musculature of the body (except the ranchiomeric muscles)
a. General Somatic Efferent (GSE)
fibers conveying motor impulses to the somatic (skeletal) muscles
b. General Visceral Efferent (GVE)
AUTONOMIC FIBERS which innervate smooth muscle of the gut tube, blood vessels, arrector pili hair organs, and cardiac muscle, and fibers which regulate glandular secretion.
Subdivided into sympathetic and parasympathetic and found in spinal nerves and some cranial nerves
Special efferent fibers
Cranial nerves which innervate a specialized area of the skeletal musculature.
a. Special Visceral Efferent (SVE)
Nerves which innervate the skeletal muscles derived from the visceral (branchiomeric/ pharyngeal) arch mesoderm which includes muscles of mastication, facial expression, pharynx, palate, and larynx.
The visceral designation has nothing whatsoever to do with the autonomic nervous system.
SPECIAL SOMATIC EFFERENT (SSE)
Nerve fibers which can reflexively influence sensory input to the ear.
CN I
Olfactory (SVA)
- sense of smell
- because it assists the body in preparing for eating by causing reflex salivation and an increase in gastric motility, it is designated as a visceral afferent nerve.
CN II
Optic (SSA)
- afferent fibers of the retina; primary receptor for the sense of sight
CN III
Oculomotor (GSE, GVE-P)
- GSE: motor component innervates extra-ocular muscles of the eye which assist in rotational movement of the globe (eye)
- GVE-P: parasympathetic innervation of intra-ocular muscles of the eye responsible for changing the shape of the lens for accommodation (ability to focus on objects both near and far) and for narrowing the pupil (pupillary constriction); via inferior division of CN III and the ciliary ganglion.
CN IV
Trochlear (GSE)
Innervation of one extraocular eye muscle: superior oblique
Because this muscle utilizes a pulley to carry out its action, the nerve carries the name of the pulley: trochlea.
CN V
Trigeminal (GSA, SVE)
- GSA: The major sensory nerve of the head, it innervates a portion of the scalp
- SVE: motor innervation to skeletal muscles of pharyngeal arch origin, specifically the first arch: muscles of mastication (4), mylohyoid, anterior belly of the digastric muscle, tensor veli palatini and tensor tympani muscles.
NOTE: the nucleus of the trigeminal nerve does not contain GVE-P cell bodies/ fibers of its own. However, since it distributes to the majoriy of the structures of the head and face, it is utilized as a carrier for GVE-P fibers of CNS III, VII, IX and distributes their fibers to the smooth muscles of the eye (iris & ciliary muscles of the lens) and to the glands of the head: mucous, salivary and lacrimal (tear production)
CN VI
Abducens (GSE)
- .innervation of one extra-ocular eye muscle: lateral rectus
- Because this muscle is responsible for turning the eye laterally, it is named for its ability to abduct the eye
CN VII
Facial (SVE, GSA, SVA, GVA, GVE-P)
- SVE: motor innervation to skeletal muscles of pharyngeal arch origin, specifically the second arch: muscles of facial expression, stylohyoid, posterior belly digastric muscle, and stapedius (ear)
- GSA: sensory to a portion of the skin of the external ear and external auditory meatus
- SVA: taste to the anterior 2/3 of the tongue via chorda tympani
- GVA: sensory to the uppermost portion of the pharynx (pharyngeal vault)
- GVE-P: parasympathetic to the lacrimal gland, nasal, palatal, oral, and pharyngeal mucous glands via the greater petrosal nerve and the pterygopalatine ganglion; to the submandibular and sublingual salivary glands via chorda tympani and the submandibular ganglion.
Note: CN VII possesses a sensory ganglion (geniculate) which houses the cell bodies of its SVA and GVA fibers.
CN VIII
Vestibulocochlear (SSA, SSE)
- SSA: afferent fibers from the organ of corti related to the sense of hearing. Afferent fibers from the semicircular canals, utricle and saccule of the internal ear relative to the sense of equilibrium
- SSE: Motor fibers related to modifying auditory input
CN IX
Glossopharyngeal (SVE, GSA, SVA, GVA, GVE-P)
- SVE: motor innervatino to skeletal muscle of pharyngeal arch origin, specifically arch three: sylopharyngeus
- GSA: sensory to a portion of the skin of the external ear
- SVA: taste from the posterior third of the tongue
- GVA: sensory to epithelium of endodermal origin which lines the majority of the pharynx from the base of the skull to the laryngeal aditus, Eustacian tube, middle ear, internal surface of the tympanic membrane, mastoid air cells, tonsils, posterior third of the tongue, parotid gland and carotid sinus.
- GVE-P: secretory fibers to the parotid salivary gland via the lesser petrosal nerve and otic ganglion
Note: the main trunk of CN IX possesses superior and inferior ganglia which respectively coontain cell bodies of GSA (superior) and SVA/GVA (inferior) fibers
CN X
Vagus (SVE, GSA, SVA, GVA, GVE-P)
- SVE: motor innervation to skeletal muscles of pharyngeal arch origin, specifically arches four and six: muscles of the pharynx and palate (superior, middle and inferior pharyngeal constrictor muscles, salpingopharyngeus, levator veli palatini, palatoglossus, palatopharyngeus), larynx (posterior and lateral cricoarytenoid, transverse and oblique arytenoid, thyroarytenoid, cricothyroid) and upper portion of the esophagus
- GSA: cutaneous innervation to the skin of the external ear, external auditory meatus, external surface of the tympanic membrane, and dura mater of the posterior cranial fossa
- SVA: taste from the area of the epiglottic valleculae
- GVA: sensory innervation to epithelium of endodermal origin which lines the root of the tongue, larynx, lining of the respiratory system, heart, entire gut tube to the distal third of the transverse colon, to thecapsule of other visceral organs (liver, spleen, kidney) and to the gonads.
- GVE-P: Parasympathetic innervation to mucous glands in the larynx, smooth muscle and glands of hte gut tube to the distal third of the transverse colon, respiratory system, and to cardiac muscle
Note: the main trunk of CN X possesses superior and inferior ganglia which respectively contain cell bodies of GSA (superior) and SVA/ GVA (inferior) fibers.
CN XI
Spinal accessory (GSE)
GSE: motor innervation to the sternocleido mastoid and trapezius muscles
