Cranial nerves LN Flashcards
What are the 12 cranial nerves?
-cranial nerve I (1) –> olfactory.
-cranial nerve II (2) –> optic.
-cranial nerve III (3) –> oculomotor.
-cranial nerve IV (4) –> trochlear.
-cranial nerve V (5) –> trigeminal.
-cranial nerve VI (6) –> abducent.
-cranial nerve VII (7) –> Facial
-cranial nerve VIII (8) –> vestibulo-cochlear
-cranial nerve IX (9) –>glossopharyngeal
-cranial nerve X (10) –>vagus
-cranial nerve XI (11) –>accessory
-cranial nerve XII (12) –> hypoglossal
Describe cranial nerve I
-olfactory nerve
-Special sensory (smell)
-They originate at chemoreceptors of olfactory epithelium (in the nose) and they enter cranium through foramina of cribriform plate of the ethmoid bone
-They terminate in olfactory bulbs (base of the brain at frontal ventral part)
-They are the only cranial nerves to attach directly to cerebrum
Describe cranial nerve II (2)
-optic nerve
-They are evaginations of the
diencephalon
-The axons of retinal ganglion cells are actually CNS fibre tracts
- Oligodendrocytes, rather than Schwan cells, provide myelin
-Cranial meninges extend to the eyeball
- They contain about 1 million fibres
-They exit eyeball at optic disc and
through optic canal
-There is partial crossover at optic chiasm to give binocular vision (e.g. left visual field conveyed by right optic tract to the right primary visual cortex)
- The optic tracts terminate in lateral geniculate nucleus, LGN (thalamic)
Describe cranial nerve III (3)
-oculomotor nerve
-They have somatic and visceral motor fibres
-They are the chief motor nerve to ocular and extra-ocular muscles
-Origin:
–2 oculomotor nuclei in mesencephalon:
The: -Somatic motor nucleus–> Visceral (parasympathetic)
And: -Accessory nucleus (Edinger-Westphal)
-Somatic motor fibres supply
4 out of the 6 extraocular
muscles:
–superior rectus
–medial rectus
–inferior rectus
–inferior oblique
-levator palpebrae superioris
(superior eyelid)
-proprioceptive afferents from
these muscles
Visceral motor fibres supply:
-parasympathetic innervation of eye via ciliary ganglion
-smooth muscle of pupil
(sphincter pupillae) – constriction
-ciliary body –> accommodation (change in lens shape)
Describe cranial nerve IV (4):
-trochlear nerve
-Somatic motor + proprioception
Origin: dorsal mesencephalon. Trochlear nucleus within PAG
Path:
–emerges from the posterior (dorsal) brain surface and running longest intracranial course,
-entering dura mater at free edge of cerebellar tentorium
–and in lateral wall of cavernous sinus.
–Enters orbit through the superior orbital fissure.
-It innervate superior oblique extraocular muscle of eye. Uses pulley (trochlea) to redirect line of pull
Describe cranial nerve V (5)
-trigeminal nerve
-Has motor function
-It is the principal general sensory nerve to the head (face, teeth, mouth, nasal cavity, cranial dura)
-largest cranial nerve
-Originate/terminate in pons-medulla-spinal cord
-There are 4 trigeminal nuclei: 1 motor, 3 sensory
-Motor (small) and sensory (large) roots
-Sensory root: central branches of the sensory neurons located in the trigeminal ganglion (i.e., semilunar ganglion; equivalent to DRG (dorsal respiratory group))
-Cutaneous zones innervated by the 3 divisions
-each CN V division supplies skin and mucous membranes and innervates the dura
-CN V divides into 3 branches from the trigeminal ganglion
-Ophthalmic nerve (CN V1)-sensory only
-Maxillary nerve (CN V2)-sensory only
-Mandibular nerve (CN V3)-sensory and motor
-Sensory afferents from mucosa of anterior 2/3 tongue, floor of mouth, mandibular, teeth, skin of lower lip, lower face, cheek, external ear, dura in middle cranial fossa
-motor efferents to muscles of mastication (temporalis & masseter), medial and lateral pterygoids, tensor tympani, anterior belly of digastric and mylohyoid muscles
Describe cranial nerve VI (6):
-abducens nerve
-somatic motor + proprioception
-For eye movements –abduction
-Origin: pons
-Path:
-emerges between pons/medulla, runs intradurally through cavernous sinus to enter orbit via Superior orbital fissure
-It innervate lateral rectus extraocular muscle
Describe cranial nerve VII (7)
-facial nerve
-General and special sensory (taste from anterior 2/3 tongue)
-Somatic (muscles of facial expression) and visceral (parasympathetic) and motor
(proprioceptive)
- Motor nuclei in pons –is the origin to larger motor root (facial nerve proper)
-Travels with CNVIII through internal acoustic meatus in petrous part of temporal bone
- Cell bodies for sensory neurons are located in geniculate ganglion
- Taste sensation -nucleus of the solitary tract
-General sensory -spinal nucleus of the trigeminal nerve
- Intermediate (sensory) nerve carries taste, parasympathetic and somatic sensory fibres
The motor branches of CN VII
-Stapedius -protection of middle ear in response to loud noise
-Posterior belly of digastric
-Stylohyoid
-Muscles of facial expression and Scalp
Special sensory:
-balance -vestibular branch
- hearing -cochlear branch
-originate in vestibular apparatus and cochlea of inner ear
-CN VIII separates into vestibular and cochlear nerves when it enters
internal acoustic meatus
Describe CN VIII (8)
-vestibulocochlear nerve
-CN VIII terminates in vestibular and cochlear nuclei of pons and medulla oblongata
describe CN IX (9)
-vagus nerve
- General and special sensory (major),
-Motor (minor) to head & neck, and parasympathetic
-The nuclei in medulla send/receive CN IX (9) fibres (2 shared with CN X(10))
-Inferior salivatory nucleus supplies parasympathetic to otic ganglion/parotid gland
-Nucleus Ambiguous, supplies motor fibres to pharynx and larynx (shared with CN X(10)).
-Nucleus Tractus Solitarus, receives afferent fibres from carotid sinus and body. Shared with CN X (10)
Sensory component of CN IX:
-Lingual and pharyngeal branches:
general sensory information. From palatine tonsil, soft palate, posterior 1/3 tongue. Taste sensory fibres from posterior 1/3 tongue.
-Carotid branch: blood pressure and blood gases information
Motor component of CN IX
-CN IX supplies motor fibres to the:
-Stylopharyngeus (elevates larynx and shortens pharynx), and;
-Pharyngeal muscles
Describe CN X (10)
-vagus nerve
-Has sensory, motor and parasympathetic
-Arises as group of rootlets (8-10) from medulla oblongata
-Most extensive distribution of all CN
-4 divisions: cranial, cervical, thoracic, abdominal
-Nuclei in medulla
Sensory input from:
-aortic body chemo-and baroreceptors
-Mucous membranes throat, thoracic and abdominal viscera
-Taste receptors
describe CN XI (11)
-accessory nerve
-Motor input to neck and upper
back muscles (sternocleidomastoid and trapezius muscles)
-Origin: motor nuclei of spinal cord
-–Column of anterior (ventral) horn
motor neurons. C1-C6
-CN XI (11) enters cranium via
foramen magnum and exits via jugular foramen with IX (11) & X (10)
describe CN XII (12)
-Hypoglossal nerve
-Motor input to intrinsic and extrinsic muscles of tongue (styloglossus, hyoglossus, genioglossus)
-Voluntary control
-Clinically assessed with voluntary
tongue protrusion
-CN XII (12) exits via hypoglossal
canal
-Lingual branches supply all intrinsic and extrinsic tongue muscles (except palatoglossus)
