Cranial Nerves Flashcards
CN I
- Name, number, function, sensory/motor/mixed, central connection(s)
Olfactory Sensory Olfaction Information collected in olfactory epithelium Fibers of olfactory neurons Central connection: olfactory bulb
CN II
optic
*Sensory
*Transmits information from retina
*Central connection: lateral geniculate nucleus, pretectal nucleus
Vision, pupillary light reflex
The other cranial nerve that does not join up with the brainstem
CN of diencephalon
**Extracranial vs intracranial
Compression to the optic chiasm particularly affects the fibers that are crossing over from the nasal half of each retina.
This produces visual defect affecting the peripheral vision in both eyes, known as abitemporal hemianopia
III
Name, number, function, sensory/motor/mixed, central connection(s)
Oculomotor
*MOTOR
*through innervation to different areas, plays a role in- raises/depresses/adducts the eyeball, elevates, abducts and laterally rotates the eyeball, raise upper eyelid
- Central connection: oculomotor nucleus
- Movement of eyeball, elevation of upper lid
(parasympathetic role- the central connection is the Edinger-Westphal nucleus (accessory oculomotor nucleus))
The _____ nerve leaves the cranial cavity via the superior orbital fissure.
divisions
III: Oculomotor
-Divides intoSUPERIORandINFERIOR BRANCHES.
Once within the orbital cavity, both branches innervate accessory structures of the eye:
Superior branch Motor innervation to the superior rectus and levator palpabrae superioris.
Inferior branch Motor innervation to the inferior rectus, medial rectus and inferior oblique.
Parasympathetic fibers to the ciliary ganglion, which ultimately innervates the sphincter pupillae and ciliary muscles.
*Parasympathetic
Your sad pupils make my Edinger-Westphal nucleus make my pupils look sad, too.
Parasympathetic & Oculomotor
Innervates sphincter pupillae and ciliary muscle of the eyeball via ciliary ganglion
*Central connection: Edinger-Westphal nucleus (accessory oculomotor nucleus)
Pupillary constriction and accommodation
The anatomical organization of the general somatic efferent (GSE) cell columns of the oculomotor nerve (CN III) complex
The Edinger-Westphal nucleus, whose axons (general visceral efferent) serve as preganglionic parasympathetic neurons, innervate the ciliary ganglia. The postganglionic parasympathetic neurons from the ciliary ganglia (not shown in figure) innervate the constrictor muscles of the pupil and the ciliary muscle.
IV
- Trochlear
- Motor
*Central connection: trochlear nucleus
Movement of eyeball
Fewest axons, but longest intracranial axon path
Only CN to cross the midline
Arises from thetrochlear nucleusof the brain, emerging from the posterior aspect of the midbrain
Only cranial nerve to exit from the posterior midbrain
It runs anteriorly and inferiorly within thesubarachnoidspacebefore piercing the dura mater adjacent to theposterior clinoid processof the sphenoid bone.
The nerve then moves along the lateral wall of thecavernous sinus(along with the oculomotor nerve, the abducens nerve, the ophthalmic and maxillary branches of the trigeminal nerve and the internal carotid artery) before entering the orbit of the eye viathesuperior orbital fissure.
Origin and distribution of the trochlear nerve (cranial nerve IV) to the superior oblique muscle.
As indicated in the cross section of the brainstem, note that this nerve exits the brain from the dorsal aspect, and it is the only nerve that is crossed.
Arrow indicates direction of movement of the bulb downward and inward.
Only CN to emerge from dorsal aspect of midbrain/brainstem
IV: Trochlear
Only CN to cross the midline
Examination of the Trochlear Nerve
Examination of the Trochlear Nerve
Examined in conjunction with the oculomotor and abducens nerves by testing the movements of the eye.
Patient is asked to follow a point with their eyes without moving their head.
The target is moved in an ‘H-shape’ and the patient is asked to report any blurring of vision ordiplopia(double vision).
Damage to the Trochlear Nerve
The most common cause iscongenital fourth nerve palsy, a condition of abnormal development. This may be curable with surgery.
Other causes of trochlear nerve damage includediabetic neuropathy,thrombophlebitis of the cavernous sinusandraised intracranial pressure
V
Trigeminal
- Sensory and Motor
- General sensation and Opening and closing mouth (chew), tension on tympanic membrane
-plays a role in corneal reflex
Central connection (for the sensory portion) of the Trigeminal CN:
trigeminal sensory nuclei
Three sensory nuclei(mesencephalic, principal sensory, spinal nuclei of trigeminal nerve)
At the level of thepons, the sensory nuclei merge to form a sensory root
Take up more CNS real estate than any other cranial nerve cell group
(V2)
Maxillary Nerve (V2) (of CN 5)
- Maxillary nerve gives rise to 14 terminal branches, which innervate the skin, mucous membranes and sinuses of derivatives of theMAXILLARY PROMINENCE of the 1st pharyngeal arch:
- Lower eyelid and its conjunctiva
- Cheeks and maxillary sinus
- Nasal cavity and lateral nose
- Upper lip
- Upper molar, incisor and canine teeth and the associated gingiva
- Superior palate
Abduction def
“Abductionis movement away from the mid-line of the body. … abductor - amuscle that can act to cause anabductionmovement at a joint is called an abductor. For example, the abductor pollicis longusmuscle. toabduct(verb) - e.g. “heabducted his right arm up to shoulder height”.
VI
Abducens
Motor
Innervates lateral rectus muscle
*Central connection: abducens nucleus in the pons
Movement of eyeball
Sensory Portion of the VII
(: Facial)
Innervates anterior 2/3 of tongue
Central connection: nucleus solitarius (solitary nucleus)
Taste
Motor Portion of the VII: Facial
Motor Portion
Innervates muscles of facial expression, stapedius muscle
Central connection: facial nucleus
Facial movement, tension on bones of middle ear
Parasympathetic Portion of the VII: Facial
Parasympathetic Portion
Technically falls under motor
Innervates salivary and lacrimal glands via submandibular and pterygopalatine ganglia
Central connection: superior salivatory nucleus
Salivation and lacrimation
Helps with this as a parasympathetic resposne
Production of tears and saliva
Intracranial of the Facial
Intracranial
The nerve arises in thePONS
It begins as two roots; a largemotor root, and a smallsensory root.
The two roots travel through the internal acoustic meatus, a 1cm long opening in the petrous part of thetemporal bone. Here, they are in very close proximity to the inner ear.
Still within the temporal bone, the roots leave the internal acoustic meatus, and enter into theFACIAL CANAL
Within the facial canal, three important events occur:
Firstly the two rootsfuseto form the facial nerve.
Next, the nerve forms thegeniculate ganglion, L-shaped collection of fibers and sensory neurons of the facial nerve.
Lastly, the nerve gives rise to thegreater petrosal nerve(parasympathetic fibers to glands), the nerve tostapedius(motor fibers to stapedius muscle), and thechorda tympani(special sensory fibers to the anterior 2/3 tongue).
The facial nerve then exits the facial canal (and the cranium) via thestylomastoid foramen.This is an exit located just posterior to the styloid process of the temporal bone.
Facial: Intracranial Damage/Lesions
Intracranial Damage/Lesions
The muscles of facial expression will be paralysed or severely weakened.The other symptoms produced depend on the location of the lesion, and the branches that are affected:
Chorda tympani– reduced salivation and loss of taste on the ipsilateral 2/3 of the tongue.
Nerve to stapedius– ipsilateral hyperacusis (hypersensitive to sound).
Greater petrosal nerve– ipsilateral reduced lacrimal fluid production.
The most common cause of an intracranial lesion of the facial nerve is middle ear pathology – such as a tumor or infection.
If no definitive cause can be found, the disease is termed Bell’s palsy.
Nerve to stapedius damage
VII: Facial
Nerve to stapedius– ipsilateral hyperacusis (hypersensitive to sound).
VIII:
Vestibulocochlear
Sensory
Innervates vestibular apparatus, cochlea
Central connection: vestibular nuclei, cochlear nuclei
Vestibular sensation (position and movement of head), hearing
VIII: Vestibulocochlear damage
Vestibular neuritis: inflammation of thevestibular branchof the vestibulocochlear nerve.
Some cases are thought to be due to reactivation of the herpes simplex virus.
It presents with symptoms of vestibular nerve damage:
Vertigo– a false sensation thatoneself or the surroundings are spinning or moving.
Nystagmus– a repetitive, involuntary to-and-fro oscillation of the eyes.
Loss of equilibrium(especially in low light).
Nauseaandvomiting.
The condition is usually self-resolving. Treatment is symptomatic, usually in the form of anti-emetics or vestibular suppressants
inflammation of the_____ of the vestibulocochlear nerve leads to Vestibular neuritis:
vestibular branch
Tinnitus
The perception of chronic tinnitus has also been associated with hyperactivity in the central auditory system, especially in the auditory cortex.
In such cases, the tinnitus is thought to be triggered by damage to the cochlea (the peripheral hearing structure) or the vestibulocochlear nerve.
IX: Glossopharyngeal
One of the smallest cranial nerves
Has many functional components:
Taste
Sensation from 1/3 of tongue
Sensation from pharyngeal wall
Sensation from carotid sinus (baroceptors/blood pressure)
Sensation from external ear
Branchiomotor innervation of the stylopharyngeus muscle (swallowing)
Parasympathetic innervation to parotid gland (major salivary gland)
Functional parts of the IX: Glossopharyngeal
Functional parts
SVA (special visceral afferent)- taste
Inferior glossopharyngeal ganglion (or solitary nucleus)
GVA (general visceral afferent)- sensation from posterior tongue, pharyngeal wall, carotid sinus
Inferior glossopharyngeal ganglion
GSA (general somatic afferent)- sensation from external ear
Superior glossopharyngeal ganglion
*SVE (special visceral efferent)- branchiomotor to stylopharyngeus muscle
-Nucleus ambiguus
GVE (general visceral efferent)- parasympathetic to parotid (salivary gland)
Inferior salivatory nucleus
IX: Glossopharyngeal very important to help with
swallowing
IX: Glossopharyngeal
Supplies sensory innervation to the oropharynx, and thus carries the AFFERENTinformation for the gag reflex.
When a foreign object touches the back of the mouth, this stimulates CNIX, beginning the reflex.
The efferent nerve in this process is thevagus nerve.
An absent gag reflex signifies damage to the glossopharyngeal nerve.
X: Vagus
Large nerve
Largest !!! Cranial nerve
Has the most extensive distribution in the body of all cranial nerves
Innervates all the way down into the abdomen
Also has 5 functional components like the glossopharyngeal nerve (SVA, GVA, GSA, SVE, GVE)
2 rootlets that originate from the brain and join together
X: Vagus (In the Head)
In the Head
Originates from the medulla of the brainstem.
Exits the cranium via thejugular foramen,with the glossopharyngeal and accessory nerves (CN IX and XI respectively).
Within the cranium, theauricular brancharises.
Thissupplies sensation to the posterior part of the external auditory and canal external ear.
X: Vagus = In the Neck
In the Neck
Passes into the carotid sheath, travelling inferiorly with the internal jugular vein and common carotid artery.
At the base of the neck, the right and left nerves have differing pathways:
Theright vagus nervepasses anterior to the subclavian artery and posterior to the sternoclavicular joint, entering the thorax.
Theleft vagus nervepasses inferiorly between the left common carotid and left subclavian arteries, posterior to the sternoclavicular joint, entering the thorax.
X: Vagus - Several branches arise in the neck:
Several branches arise in the neck:
Pharyngeal branches– Provides motor innervation to the majority of the muscles of the pharynx and soft palate.
Superior laryngeal nerve– Splits into internal and external branches. The external laryngeal nerve innervates the cricothyroid muscle of the larynx. The internal laryngeal provides sensory innervation to the laryngopharynx and superior part of the larynx.
Recurrent laryngeal nerve(right side only) – Hooks underneath the right subclavian artery, then ascends towards to the larynx. It innervates the majority of the intrinsic muscles of the larynx.
X: Vagus - In the Thorax
In the Thorax
The right vagus nerve forms the posterior vagal trunk, the left forms theanterior vagal trunk.
Branches from the vagal trunks contribute to the formation of the oesophageal plexus, which innervates the smooth muscle of the oesophagus.
Two other branches arise in the thorax:
Left recurrent laryngeal nerve– hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx.
Cardiac branches– these innervate regulate heart rate and provide visceral sensation to the organ.
This leads to ? Referred pain ?
The vagal trunks enter the abdomen via the oesophageal hiatus, (opening in the diaphragm)
X: Vagus -In the Abdomen
In the Abdomen
In the abdomen, the vagal trunks terminate by dividing into branches that supply the oesophagus, stomach and the small and large bowel (up to the splenic flexure).
X: Vagus
Sensory
Innervates pharynx, larynx, trachea, esophagus, external ear
Central connection: trigeminal sensory nucleus
General sensation
Sensory (special sensory)
Innervates thoracic and abdominal viscera, aortic bodies, aortic arch
Central connection: solitary nucleus
Visceral sensation, chemoreception, baroreception
Motor
Innervates soft palate, pharynx, larynx, upper esophagus
Central connection: nucleus amibiguus
Speech, swallowing
Parasympathetic
Innervates thoracic and abdominal viscera
Central connection: dorsal motor nucleus of vagus
Innervation of cardiac muscle, smooth muscle, and glands of cardiovascular system, respiratory, and gastrointestinal tracts
For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production.
X: Vagus - Sensory
Sensory
Innervates pharynx, larynx, trachea, esophagus, external ear
Central connection: trigeminal sensory nucleus
General sensation
XI: (Spinal) Accessory
Motor
Innervates sternomastoid and trapezius muscle
Central connection: spinal cord
Movement of head and shoulder
Examined by asking the patient to rotate their head and shrug their shoulders, both normally and against resistance.
XI: Accessory - why should not call cranial
Originally believed to have two roots- cranial and spinal
Turns out, the cranial root is actually mostly made of vagal nerve fibers
The spinal root gets fibers from the spinal accessory nucleus of the ventral cervical spinal cord
So, XI is not the most cranial Cranial nerve
XI: Accessory
slide 27ish through 31
XII: Hypoglossal
Motor
Innervates intrinsic and extrinsic muscles of tongue
Central connection: hypoglossal nucleus (medulla oblongata)
Found in the medulla
Movement of tongue
Not just talking or chewing
Varies in size among animals: in cats/dogs it will be smaller because they do not make elaborate vowels/speech. In a whale it will be even smaller
Passes laterally across the posterior cranial fossa, within thesubarachnoid space.
Exits the cranium via thehypoglossal canal.
Now extracranial, the nerve receives a branch of thecervical plexusthat conducts fibersfrom C1/C2 spinal nerve roots.
They do not combine with the hypoglossal nerve – they merely travel within its sheath.
It then passes inferiorly to the angle of themandible, crossing the internal and external carotid arteries, and moving in an anterior direction to enter the tongue.
XII: Hypoglossal (Role of the C1/C2 Roots)
Role of the C1/C2 Roots
The C1/C2 roots that travel with the hypoglossal nerve also have a motor function.
Branch off to innervate thegeniohyoid(elevates the hyoid bone) andthryohyoid(depresses the hyoid bone) muscles.
Another branch containing C1/C2 fibers descends to supply theansa cervicalis– a loop of nerves that is part of the cervical plexus. From the ansa cervicalis, nerves arise to innervate the omohyoid, sternohyoid and sternthyroid muscles.
These muscles all act to depress thehyoid bone.
XII: Hypoglossal
The hypoglossal nerve is examined by asking the patient to protrude their tongue.
Other movements such as asking the patient to push their tongue against their cheek and feeling for the pressure on the opposite side of the cheek may also be used if damage is suspected.
Patients will present with deviation of the tongue towards the damaged sideon protrusion, as well as possible muscle wasting and fasciculations (twitching of isolated groups of muscle fibers) on the affected side.
Cranial Nerves
attach directly to forebrain_____(while the rest attach to the midbrain/brainstem
Remember that sensory nerves are afferents and motor nerves are efferents
Pons: nuclei for CN V, VI, VII
Major part contains neurons that send axons to cerebellum
Motor control, especially of upper limb
Midbrain: nuclei for CN III and IV
I and II attach directly to forebrain, while the rest attach to the midbrain/brainstem
Remember that sensory nerves are afferents and motor nerves are efferents
Pons: nuclei for CN V, VI, VII
Major part contains neurons that send axons to cerebellum
Motor control, especially of upper limb
Midbrain: nuclei for CN III and IV
why is the image on slide 2 a lie
Nearly Impossible to See the Olfactory Nerve (see slide 6)
olfactory tract
Thelateral striasends carries the axons to the primary olfactory cortex.
Themedial striacarry the axons across the medial plane of the anterior commissure where they meet the olfactory bulb of the opposite side.
Most CN nerves are wrapped in by epi-, peri- and endoneurium… what CN are not?
- optic: Due to its unique anatomical relation to the brain, the optic nerve is surrounded bycranial meninges
- Olfactory nerve too
bitemporal hemianopia*
CN II
Compression to the optic chiasm particularly affects the fibers that are crossing over from the nasal half of each retina.
This produces visual defect affecting the peripheral vision in both eyes, known as abitemporal hemianopia
II: Optic: Extracranial
Extracranial
The optic nerve is formed by the convergence of axons fromtheRETINAL GANGLION CELLS
Receive impulses from the photoreceptors of the eye (the rods and cones).
The nerve leaves the bony orbit via theOPTIC CANAL,a passageway through the sphenoid bone.
It enters the cranial cavity, running along the surface of themiddle cranial fossa(in close proximity to the pituitary gland).
Intracranial (CN II)
CN II
Within the middle cranial fossa, the optic nerves from each eye unite to form theOPTIC CHIASM. At the chiasm, fibers from the nasal (medial) half of each retina cross over, forming the optic tracts
So, optic nerve is before crossing, optic tract is after crossing
CN III innervates what to affect what?
*Innervates superior/inferior/medial rectus muscles (raises/depresses/adducts the eyeball), inferior oblique muscle (elevates, abducts and laterally rotates the eyeball) , levator palpebrae superioris muscle (raise upper eyelid)
CN III innervates
- superior rectus muscles
- inferior rectus muscles
- medial rectus muscles
- inferior oblique muscle
- levator palpebrae superioris muscle
CN 4 innervates
Innervates a single muscle, the superior oblique muscle
A muscle of oculomotion.
As the fibers from the trochlear nucleus cross in the midbrain before they exit, the trochlear neurons innervate the CONTRALATERALsuperior oblique.
***Only cranial nerve to exit from the posterior midbrain
CN 4
diplopia
double vision
CN 4
Sensory Portion of CN V - innervates
Sensory Portion
Innervates face, scalp, cornea, nasal cavity, oral cavity, cranial dura mater
Motor Portion of CN V
*Innervates muscles of mastication, tensor tympani
*Central connection (for motor): trigeminal motor nucleus
At the level of thePONS, the motor nucleus continues to form a motor root.
The motor root passes inferiorly to the sensory root, along the floor of the trigeminal cave. Its fibers are only distributed to themandibular division.
Opening and closing mouth (chew), tension on tympanic membrane
CN V - divisions **
Inmiddle cranial fossa, the sensory root expands into the trigeminal ganglion.
The peripheral aspect of the trigeminal ganglion gives rise to 3 divisions:ophthalmic(V1),maxillary(V2) andmandibular(V3).
trigeminal ganglion
CV V
The trigeminal ganglion islocated lateral to the cavernous sinus, in a depression of the temporal bone (trigeminal cave)
(V1)
Ophthalmic Nerve (V1) Gives rise to 3 terminal branches:frontal,lacrimalandnasociliary, which innervate the skin and mucous membrane of derivatives of the frontonasal prominence derivatives: Forehead and scalp Frontal and ethmoidal sinus Upper eyelid and its conjunctiva Cornea (see clinical relevance) Dorsum of the nose
V3
CN V: Mandibular Nerve
Mandibular nerve gives rise to four terminal branches in the infra-temporal fossa:buccal nerve,inferior alveolarnerve,auricotemporal nerve andlingualnerve.
These branches innervate the skin, mucous membrane and striated muscle derivatives of the mandibular prominenceof the 1st pharyngeal arch.
Sensory supply:
Mucous membranes and floor of the oral cavity
External ear
Lower lip
Chin
Anterior 2/3 of the tongue (only general sensation; special taste sensation supplied by the chorda tympani, a branch of the facial nerve)
Lower molar, incisor and canine teeth and the associated gingiva
Motor Supply:
Muscles of mastication; medial pterygoid, lateral pterygoid, masseter, temporalis
Anterior belly of the digastric muscle and the mylohyoid muscle (these are suprahyoid muscles)
Tensor veli palatini
Tensor tympani
The corneal reflex
The corneal reflex is the involuntaryblinkingof the eyelids – stimulated by tactile, thermal or painful stimulation of the cornea.
In the corneal reflex, the ophthalmic nerve (V1) acts as theafferent – detecting the stimuli. The facial nerve is the efferent limb, causing contraction of the orbicularis oculi muscle.
If the corneal reflex is absent, it is a sign ofdamageto the trigeminal/ophthalmic nerve, or the facial nerve.
VI central connections
Central connection: abducens nucleus in the pons
-Exits at border between pons and medulla
-Entersthesubarachnoid spaceand pierces thedura materto run in a space known asDorello’s canal.
Travels through thecavernous sinusat the tip of thepetrous temporal bone,before entering the orbit of the eye through theSUPERIOR ORBITAL FISSURE
VI
Any pathology which leads todownward pressure on the brainstem (e.g.brain tumor, extradural hematoma) can lead to the nerve becoming stretched along theclivusof the skull.
Wernicke-Korsakoffsyndrome (caused by thiamine deficiency and generally seen in alcoholics) is a rare cause of sixth nerve palsy.
Other causes of abducens nerve damage includediabetic neuropathy
Patients will present with diplopia and a medially rotated eye which cannot be abducted past the midline. The patient may attempt to compensate by rotating their head to allow the eye to look sideways.
VII
both sensory and motor
Extracranial Damage/Lesions VII: Facial
Extracranial Damage/Lesions
Only themotor functionof the facial nerve is affected, resulting in paralysis or severe weakness of the muscles of facial expression.
There are various causes of extracranial lesions of the facial nerve:
Parotid glandpathology – e.g a tumour, parotitis, surgery.
Infectionof the nerve– particularly by the herpes virus.
Compressionduring forceps delivery – the neonatal mastoid process is not fully developed, and does not provide complete protection of the nerve.
Idiopathic– If no definitive cause can be found, the disease is termed Bell’s palsy.
VIII: Vestibulocochlear divsions (does not seem that important to alex)
The vestibular and cochlear portions of the vestibulocochlear nerve are functionally discrete, and so they originate from different nuclei in the brain:
Vestibular component– arises fromthe vestibular nuclei complex in the pons and medulla.
Cochlear component– arises from the ventral and dorsal cochlear nuclei, situated in the inferior cerebellar peduncle.
Both sets offibers combine in the pons to form the vestibulocochlear nerve. The nerve emergesfrom the brain at thecerebellopontine angleandexitsthe cranium via theinternal acoustic meatusof the temporal bone
IX: Glossopharyngeal
**functional parts ***
SVA (special visceral afferent)- taste
Inferior glossopharyngeal ganglion (or solitary nucleus)
GVA (general visceral afferent)- sensation from posterior tongue, pharyngeal wall, carotid sinus
Inferior glossopharyngeal ganglion
GSA (general somatic afferent)- sensation from external ear
Superior glossopharyngeal ganglion
SVE (special visceral efferent)- branchiomotor to stylopharyngeus muscle
Nucleus ambiguus
GVE (general visceral efferent)- parasympathetic to parotid (salivary gland)
Inferior salivatory nucleus
IX: Glossopharyngeal
slide 8 helps
One of the smallest cranial nerves
Has many functional components:
Taste
Sensation from 1/3 of tongue
Sensation from pharyngeal wall
Sensation from carotid sinus (baroceptors/blood pressure)
Sensation from external ear
Branchiomotor innervation of the stylopharyngeus muscle (swallowing)
Parasympathetic innervation to parotid gland (major salivary gland)
The glossopharyngeal nerve originates in themedullaoblongata
It emerges from the anterior aspect of the medulla, moving laterally in the posterior cranial fossa.
The nerve leaves the cranium via thejugular foramen.
At this point, thetympanicnervearises.
Sensory from middle ear and
*The glossopharyngeal nerve terminates by splitting into several sensory branches:
Pharyngeal branch– combines with fibers of the vagus nerve to form the pharyngeal plexus. It innervates the mucosa of the oropharynx (middle part of throat behind mouth)
Lingual branch– provides the posterior 1/3 of the tongue with general and taste sensation
Tonsillar branch– forms a network of nerves, known as the tonsillar plexus, which innervates the palatine tonsils.
• SVA
- SVA (special visceral afferent)- taste
* Inferior glossopharyngeal ganglion (or solitary nucleus)
IX: *
Glossopharyngeal
Sensory (special sensory)
Innervates posterior 1/3 of tongue, carotid body, carotid sinus
Central connection: solitary nucleus
Taste, chemoreception, baroreception
Motor
Innervates stylopharyngeus muscle (acts to shorten and widen the pharynx, and elevate the larynx during swallowing)
Central connection: nucleus ambiguus
Swallowing
*Parasympathetic
Innervates parotid salivary gland via otic ganglion
Central connection: inferior salivatory nucleus
Salivation
Supplies sensory innervation to the oropharynx, and thus carries the afferentinformation for the gag reflex.
When a foreign object touches the back of the mouth, this stimulates CNIX, beginning the reflex.
The efferent nerve in this process is thevagus nerve.
An absent gag reflex signifies damage to the glossopharyngeal nerve.
GVA
GVA (general visceral afferent)- sensation from posterior tongue, pharyngeal wall, carotid sinus
*SVE
- SVE (special visceral efferent)- branchiomotor to stylopharyngeus muscle
- Nucleus ambiguus
X: Vagus
Large nerve
Largest !!! Cranial nerve
Has the most extensive distribution in the body of all cranial nerves
Innervates all the way down into the abdomen
Also has 5 functional components like the glossopharyngeal nerve (SVA, GVA, GSA, SVE, GVE)
2 rootlets that originate from the brain and join together
In the Head
Originates from the medulla of the brainstem.
Exits the cranium via thejugular foramen,with the glossopharyngeal and accessory nerves (CN IX and XI respectively).
Within the cranium, theauricular brancharises.
Thissupplies sensation to the posterior part of the external auditory and canal external ear.
In the Neck
Passes into the carotid sheath, travelling inferiorly with the internal jugular vein and common carotid artery.
At the base of the neck, the right and left nerves have differing pathways:
Theright vagus nervepasses anterior to the subclavian artery and posterior to the sternoclavicular joint, entering the thorax.
Theleft vagus nervepasses inferiorly between the left common carotid and left subclavian arteries, posterior to the sternoclavicular joint, entering the thorax.
exits out the jugular foramen
glossopharyngeal and accessory nerves (CN IX and XI respectively).
Within the cranium, theauricular brancharises.
X: Vagus
XI
X: Vagus
Several branches arise in the neck:
Pharyngeal branches– Provides motor innervation to the majority of the muscles of the pharynx and soft palate.
Superior laryngeal nerve– Splits into internal and external branches. The external laryngeal nerve innervates the cricothyroid muscle of the larynx. The internal laryngeal provides sensory innervation to the laryngopharynx and superior part of the larynx.
Recurrent laryngeal nerve(right side only) – Hooks underneath the right subclavian artery, then ascends towards to the larynx. It innervates the majority of the intrinsic muscles of the larynx.
In the Thorax
The right vagus nerve forms the posterior vagal trunk, the left forms theanterior vagal trunk.
Branches from the vagal trunks contribute to the formation of the oesophageal plexus, which innervates the smooth muscle of the oesophagus.
Two other branches arise in the thorax:
Left recurrent laryngeal nerve– hooks under the arch of the aorta, ascending to innervate the majority of the intrinsic muscles of the larynx.
Cardiac branches– these innervate regulate heart rate and provide visceral sensation to the organ.
This leads to ? Referred pain ?
The vagal trunks enter the abdomen via the oesophageal hiatus, (opening in the diaphragm)
In the Abdomen
In the abdomen, the vagal trunks terminate by dividing into branches that supply the oesophagus, stomach and the small and large bowel (up to the splenic flexure).
X: Vagus
Sensory
Innervates pharynx, larynx, trachea, esophagus, external ear
Central connection: trigeminal sensory nucleus
General sensation
Sensory (special sensory)
Innervates thoracic and abdominal viscera, aortic bodies, aortic arch
Central connection: solitary nucleus
Visceral sensation, chemoreception, baroreception
Motor
Innervates soft palate, pharynx, larynx, upper esophagus
Central connection: nucleus amibiguus
Speech, swallowing
Parasympathetic
Innervates thoracic and abdominal viscera
Central connection: dorsal motor nucleus of vagus
Innervation of cardiac muscle, smooth muscle, and glands of cardiovascular system, respiratory, and gastrointestinal tracts
For example, in the stomach, the vagus nerve increases the rate of gastric emptying, and stimulates acid production.
helps with swallowing
X: Vagus
and more!!
should not be called a cranial nerve
XI: (Spinal) Accessory
and really olfactory
Cranial Part
Immediately after leaving the skull, cranial part combines withthevagus nerve(CN X) at the inferior ganglion of vagus nerve (a ganglion is a collection of nerve cell bodies).
The fibers from the cranial part are then distributed through thevagus nerve.
For this reason, the cranial part of the accessory nerve is considered as part of the ________
vagus nerve.
XII: Hypoglossal
Motor
Innervates intrinsic and extrinsic muscles of tongue
Central connection: hypoglossal nucleus (medulla oblongata)
Found in the medulla
Movement of tongue
Not just talking or chewing
Varies in size among animals: in cats/dogs it will be smaller because they do not make elaborate vowels/speech. In a whale it will be even smaller
Passes laterally across the posterior cranial fossa, within thesubarachnoid space.
Exits the cranium via thehypoglossal canal.
Now extracranial, the nerve receives a branch of thecervical plexusthat conducts fibersfrom C1/C2 spinal nerve roots.
They do not combine with the hypoglossal nerve – they merely travel within its sheath.
It then passes inferiorly to the angle of themandible, crossing the internal and external carotid arteries, and moving in an anterior direction to enter the tongue.
Role of the C1/C2 Roots
The C1/C2 roots that travel with the hypoglossal nerve also have a motor function.
Branch off to innervate thegeniohyoid(elevates the hyoid bone) andthryohyoid(depresses the hyoid bone) muscles.
Another branch containing C1/C2 fibers descends to supply theansa cervicalis– a loop of nerves that is part of the cervical plexus. From the ansa cervicalis, nerves arise to innervate the omohyoid, sternohyoid and sternthyroid muscles.
These muscles all act to depress thehyoid bone
Role of the C1/C2 Roots
The C1/C2 roots that travel with the hypoglossal nerve also have a motor function.
Branch off to innervate thegeniohyoid(elevates the hyoid bone) andthryohyoid(depresses the hyoid bone) muscles.
Another branch containing C1/C2 fibers descends to supply theansa cervicalis– a loop of nerves that is part of the cervical plexus. From the ansa cervicalis, nerves arise to innervate the omohyoid, sternohyoid and sternthyroid muscles.
These muscles all act to depress thehyoid bone
sensory nerves are ____ and motor nerves are _____
sensory nerves are afferents and motor nerves are efferents
___ nerves are afferents and ___ nerves are efferents
sensory nerves are afferents and motor nerves are efferents
Shortest cranial nerve
CN1
Does not emanate from brainstem
CN of telencephalon
Olfactory receptor cells are bipolar nerve cells with a peripherally directed dendrite which terminates in a knob from which numerous cilia project.
The olfactory chemoreceptors are located on these cilia.
Synapse on mitral cells of olfactory bulb
*Olfactory tract:
Unmyelinated, covered by olfactory Schwann cells (olfactory ensheathing glia)
Nerve capable of regeneration
Information passed on to olfactory cortex and amygdala
Damage –> Inability to smell
Age: the older you get, the less you can smell
Possibly due to repeated damage and infections over time
Oculomotor: originates, path
- Originates from the anterior aspect of the midbrain.
- Moves anteriorly, passing below the posterior cerebral artery, and above the superior cerebellar artery.
- Pierces the dura mater and enters the lateral aspect of the cavernous sinus.
*The nerve leaves the cranial cavity via the superior orbital fissure.
CNII does not join up with the brainstem
-is it part of the CNS or PNS?
The other cranial nerve that does not join up with the brainstem
CN of diencephalon
Technically part of theCNS rather than thePNS because it is derived from an out-pouching of thediencephalon (optic stalks) during embryonic development.
