Cranial Nerves Flashcards
Describe Cranial nerves:
12 pairs in number containing mixed nerves: Sensory, motor, and parasympathetic
Arises from brain stem except for first two pairs. They are extensions of the brain itself.
Leaves cranium by passing through foramina at base of cranial fossae.
Numbered in roman numerals (opposite of spinal nerves)
Where do CN III, and IV arise from?
Highest part of brain (mid Brain)
Where does CN V arise from?
Second part of the brain stem AKA pons
Where does CN VI, VII, and VIII arise from?
The pontomedullary sulcus
Where does CN IX, X, XI, and XII arise from?
Different parts of the medulla
Define Olfactory Nerve
Cranial Nerve 1:
Pure Sensory (Smell)
Starts as bipolar neurons at the level of cribriform plate of ethmoid bone.
These neurons end at the olfactory bulb which inturn gives rise to olfactory tract.
Olfactory tract ends to enthorhinal area (frontal Lobe)
Describe Foramen Cecum:
Small vein passes through. The vein connects veins from the outside of the skull to the veins inside the skull.
Also supplies triangle area around nose.
Infection (pimple pop) to this area could affect the meninges (Meningitis)
Cribriform Plate:
Provides access to Cranial nerve 1 (Olfactory)
Optic Canal:
Passage for Cranial Nerve 2 (Optic)
Sub Orbital Fissure:
Passage for Cranial Nerve 3, Cranial Nerve 4, one division of Cranial Nerve V (5) known as V1, or Ophthalmic nerve
Foramen Rotundum
Passage for V2 Maxillary Nerve of CN V (5)
Foramen Ovale
Passage for V3 mandibular nerve of CN V (5)
Foramen Spinosum
Passage for middle meningeal artery (supplies meninges)
Carotid Canal
Passage for internal Carotid Artery
Internal Auditory meatus
Passage for CN VII (7) and CN VIII (8)
Jugular Foramen
Internal Jugular Vein starts here: Passage for CN IX (9), X (10) and XI (11)
Hypoglossal canal:
Passage for CN XII (12)
Foramen Magnum
Passage for Medulla of brainstem and vertebral arteries
Accessory Nerve: CN XI (11)
Pure motor nerve
Arises from medulla (cranial Root) and upper four segments of spinal cord (spinal root)
Passes through jugular foramen, where cranial root joins CN X (10) and distributes to laryngeal muscles via vagus.
Spinal Roots supplies SCM and Trapezius muscles.
Passes deep to SCM and becomes s/f at junction between upper third and distal 2/3 of scm. Lev scap sits deep to accessory nerve.
Junction between proximal 2/3 and distal 1/3 of the ant. border of trapezius.
Optic Nerve CN II (2)
Pure Sensory Nerve (Vision)
Arise from retina (cone and rods to bipolar cells to ganglion cells to optic nerve)
Left and right optic nerves exchange some fibers at optic chiasm and turn into optic tract
Optic tract ends to lateral geniculate body (thalamus) and continues as optic radiation
Optic radiation ends to visual cortex (occipital Lobe)
Occulomotor N CN III (3)
Mixed (motor & Parasympathetic nerve)
Arise from midbrain and passes thru superior orbital fissure.
Motor fibers supply some of the extraocular muscles (sup, inf, med, recti, and inf. oblique plus levator palpebra superioris)
Parasympathetic fibers: reach iris of the eye (after synaps in ciliary ganglion) supplies sphincter muscle of pupil (constricts iris)
Trochlear N (CN IV) 4
Pure motor nerve
Only cranial nerve that shows up posterior to brainstem
Smallest of all cranial nerves
Arises from midbrain and passes through superior orbital fissure
Only supplies one of the extraocular muscles (sup. Oblique)
Trigeminal N CN. V (5)
Only CN that has dermatome
Arise from pons and enters semilunar ganglion and then divides into three divisions:
Opthalmic (V1) Pure (General) Sensory - Enters the orbital Cavity through the superior orbital fissure.
Divides into following branches:
Lacrimal for Lacrimal Gland
Naso-ciliary: Supplies eyeball, nasal cavity mucous membrane
Supra-orbital for the skin of forehead (highest point of skull is called vertex)
nerve exits through supraorbital foramen
Maxillary CN (V2)
Pure general sensory nerve.
Passes through foramen rotundum and enters pterygo-palatine fossa
Divides into following branches:
- Pharyngeal (naso-pharynx)
- Nasal (Nasal Cavity Postero-lateral Wall)
- Superior Alveolar (upper Teeth)
- Palatine (palate)
- Infra-Orbital (Skin of the face between lower eyelid and upper lip)
Mandibular CN (V3)
A mixed (motor and general sensory) nerve. Passes through foramen ovale and enters the infra-temporal fossa
Divides into following branches:
- Inferior alveolar (lower teeth & skin of chin, mylohyoid and ant. belly of digastric)
- Motor Branches to muscles of mastication tensor lympani and tensor velli palatini
- Buccal (Sensory to skin and mucous of cheek)
- Lingual (sensory for tongue, parasympathetic fibers from CN VII for submandibular and sublingual glands)
- Auriculotemporal (a strip of skin in front of the ear and parasympathetic fibers from CN IX to parotid gland)
Abducent N CN. VI (6)
Name comes from muscle it supplies (Lat rectus) Abduction of eye.
Pure motor nerve
Arises from midbrain and passes through superior orbital fissure.
Only supplies one of the extraocular muscles (lat. rectus)
Facial N CN VII (7)
Mixed (Sensory, motor, Parasympathetic) passes through internal auditory meatus and enters geniculate ganglion. Different fibers choose different passages to leave the cranium
Motor fibers pass through stylo-mastoid foramen to supply muscles of expression, stylo-hyoid, and posterior belly of digastric
Damage to motor fiber causes bells palsy
Sensory and some parasympathetic fibers pass via petro-tympanic fissure (as chorda tympani nerve) to joint the lingual nerve (V3) will carry sense of taste from anterior 2/3 of the tongue (taste) and also supplies submandibular and sublingual glands
Other parasympathetic fibers form the greater petrosal nerve that passes through a synonymous groove to get into the pteryogo-palatine ganglion. Then it distributes to the lacrimal gland and mucosal glands of nasal cavity and palate
Vestibulo-Cochlear N CN VIII (8)
Pure (special) sensory Nerve
Arises between medulla and pons
Passes through internal auditory meatus and ends to vestibule and cochlea of the inner ear. Carries sense of hearing (cochlear ganglion) and equillibrium/balance (Vestibular ganglion)
Glosso-Pharyngeal N CN IX (9)
mixed sensory motor and parasympathetic nerve
Arises from medulla and passes thru jugular foramen
Joints two sensory ganglia
Sensory fibers either end to posterior 1/3 of tongue (general and taste) or to the oropharynx (general) , carotid body/sinus (has mechano sensors that senses the pressure of the carotid Artery)
Motor Fibers only supply stylo-pharyngeus
parasympathetic fibers will supply the parotid gland through auriculo-temporal nerve.
Vagus N CN X (10)
Only cranial nerve to extend to thoracic viscera and abdomen (kidneys, pancreas, liver, biliary system are all controlled by vagus)
Stops at left 1/2 of transverse colon.
Is a mixed (sensory, motor and P/S) nerve
Arises from medulla and passes through jugular foramen
Joins two sensory ganglia
General sensory ganglia distribute to laryngo-pharynx, larynx and external ear while the sense of taste is collected from the back of the oral cavity.
Motor Fibers supply muscles of soft palate, pharynx, and larynx (not true)
Parasympathetic fibers regulate function of smooth muscles and glands of GI tract down to left 1/3 of transverse colon and thoracic Viscera
Hypoglossal N CN XII (12)
pure motor nerve
Arises from medulla and passes through hypoglossal canal
Nerve enters the tongue and supplies all intrinsic and extrinsic muscles.
