Cranial nerves

Cranial nerves

1. Classification of the cranial nerves.

2. Characteristics of the cranial nerves.

3. Conductive pathways of the cranial nerves.

4. Involvement of cranial nerves in autonomic distribution.

5. Rules for cortical control on cranial nerves.

6. Connections of the cranial nerves.

In accordance to direction of fibersSensory=ascending; motor=descending; mixed.

Cranial nerves

N Cranial nerve Nuclei Outlet /inlet/ from the brain

Outlet /inlet/ from the skull

Sensory ganglions

Vegetative ganglia

Region of supply

I Olfactorius Olfactory

----------- ---------- it connects to the olfactory bulb

Enters the skull through the lamina cribrosa /cribriform plate/

------------ ----------- Mucous membrane of sup. nasal meatus

II Opticus Optic

----------- ------------it is continued by the optic tract

Enters through the canalis opticus /optic canal/

----------- ------------ Retina

III Oculomotorius Oculomotor

n.motoriusn.Iacubovichn.Perl/colliculi sup. of the midbrain/

Fossa interpeduncularis

Fissura orbitalis superior

----------- g.ciliare/in the orbit, near to the optic canal/

Mm. of eyeball: rectus med., sup., inf., oblique inf., M. levator palpebrae superiorSphincter pupillae & ciliary mm.

N Cranial nerve Nuclei Outlet /inlet/ from the

brain

Outlet /inlet/ from the skull

Sensory ganglions

Vegetative ganglia

Region of supply

IV Trochlearis Trochlear

n.motorius/colliculi inf. of the midbrain/

Laterally from the pedunculi cerebri

Fissura orbitalis superior

------------- ------------ Sup. oblique m.

V Trigeminus Trigeminal n.ophthalmicusn.maxillarisn.mandibularis

n.motoriusn.pontinusn.mesencephalicusn.spinalis/rhomboid fossa/

Between the pons and middle cerebellar peduncles

Fissura orbitalis superiorFor.rotundumFor.ovale

g.trigeminale Gasser’s/near to the apex of the temporal pyramid/

------------ Face skin, mucous membrane of the nose, mouth, sinuses, teethMm. of mastication, mylohioid m.-ant.belli of digastric m., tensor velli palatini, tensor tympani

VI Abducens Abducent

n.motorius/rhomboid fossa/

Sul.bulbopontinus

Fissura orbitalis superior

----------- ----------- Lateral rectus m.

VII Facialis Facial

n.motoriusn.solitarius /+IX+X/n.salivatorius superior/rhomboid fossa/

Sul.bulbopontinus

For.stylomastoideus

g.geniculi /inside of the pyramid of the temporal bone/

g,pterygopalatinum/fossa pterygopalatina/g.submandibulare /near the homonymous gland/

Ant. part of the tongueMm. of facial expression, post. belli of digastric m.,Lacrimal, submandibular, sublingual glands, mucous glands of face region

VIII Vestibulocochlearis Vestibulocochlear

2 nn.cochleares4 nn.vestibulares/rhomboid fossa/

Sul.bulbopontinus

Meatus acusticus internus

g.spirale Corti’s /in the cochlea, canalis spiralis/g.vestibulare/in the internal auditory meatus/

----------------- Semicircular canals, membranous vestibulum of the internal ear.

Cochlea

IX Glossopharyngeus Glossopharyngeal

n.ambiguus /+X/n.solitarius /+VII+X/n.salivatorius inferior/rhomboid fossa/

Sul.retroolivarius

For.jugulare g.superius/in the jugular foramen/g.inferius /petrosum//in the petrosal fossa near to the jugular foramen/

g.oticum /exobase of the skull near to oval foramen/

Post.part body of the tongue, tonsils, pharynx, middle ear, sinocarotid glomulusStylopharyngeal m., pharyngeal mm.Parotid gland

X Vagus Vagus

n.ambiguus /+IX/n.solitarius /+VII+IX/n.dorsalis/rhomboid fossa/

Sul.retroolivarius

For.jugulare g.superius/in the jugular fossa/g.inferius/just below the jugular foramen/

gg.intraorganici or located near to organs

Post.part of the root of the tongue, epiglota, external earM.stylopharyngeus, pharyngeal mm.Pharynx, larynx, trachea, heart, lungs, GI tract

XI Accessorius Accessory

n.motorius/rhomboid fossa/

Sul.retroolivarius

For.jugulare ----------- --------------- Sternocleidomastoid, trapezius mm.

XII HypoglossusHypoglossal

n.motorius/rhomboid fossa/

Sul.preolivarius

Can.nervi hypoglossi

----------- --------------- Mm. of the tongue

VIII

V, VII, IX, X

III, IV, VI, XI, XII

Classification of the cranial nervesIn according to their development all cranial nerves

are divided into 4 groups;●Derivatives of the brain (I,II);●Nerves developed in connection with the cranial miotoms

(III,IV,VI);●Derivatives of the visceral arches (V,VII,VIII,IX,X,XI);●Nerves developed through combining of the spinal nerves

(XII).

In according to their

components cranial

nerves can be classified

into:

2) sensory nerves

(I,II,VIII);

1) motor nerves

(IV,VI,XI.XII);

3) mixed nerves

(III,V,VII,IX,X)

The cranial nerves exit the

brain in an orderly fashion.

Two, olfactory and optic, are

located in the telencephalon.

Two, occulomotor and

trochlear,

are located in the midbrain.

Four, trigeminal, abducens,

facial

and acoustovestibular, are

located

in the pons.

The remaining four,

glossopharyngeal,

vagus, accessory and

hypoglossal

are located in the medulla.

It is most useful however to discuss them, not

related to location, but rather as to function.

There are 3 cranial nerves with primarily

sensory function.

Cranial nerve I, Olfactory, modulates smell,

cranial nerve II, Optic, modulates vision.

Cranial nerve VIII, Vestibulocochlear,

modulates hearing and balance.

There are 4 cranial nerves with primarily

motor function.

CN IV, Trochlear, innervates the superior oblique

muscle of the eyeball.

CN VI, Abducens, innervates the lateral rectus

muscle of the eyeball and abducts the eye.

CN XI, Accessory, innervates the trapezius

muscle in the back and shoulders.

CN XII, Hypoglossal, innervates the muscles of the

throat and enables us to swallow.

5 cranial nerves have mixed sensory, motor and

parasympathetic function.

The mixed cranial nerves are CN III Occulomotor,

CN V Trigeminal, CN VII Facial, CN IX

Glossopharyngeal and CN X Vagus.

The occulomotor nerve of the six eyeball muscles.

It also carries Parasympathetic input to the ciliary

ganglion to constrict pupil.

The trigeminal is a large important nerve which carries sensory input

from the face, cornea, mouth, nose and temporomandibular joint.

The trigeminal nerve also supplies motor innervation to the muscles of

mastication.

The facial nerve carries taste

sensation from the anterior 2/3 tongue.

It also supplies Motor function to

the muscles of facial expression.

Finally it carries Parasympathetic input

to the salivary and lacrimal glands.

The glossopharyngeal nerve

carries taste sensation from

the posterior 1/3 tongue.

It also carries general sensation

from the auditory tube and

pharynx.

It supplies stylopharyngeal

muscle.

It also supplies parasympathetic

input to the parotid gland.

Last, but certainly not least, is the vagus.

It supplies general sensory and motor

function to the larynx and pharynx.

Perhaps most importantly it supplies

Parasympathetic input to the heart

and lungs and gastro intestinal

tract to the level of the splenic

flexure of the colon.

Lamina cribrosa – I

Optic canal – II

Fissura orbitalis

superior –

III, IV, VI, V1

Foramen rotundum

– V2

Foramen ovale – V3

Meatus acusticus

internus – VII, VIII

Foramen jugulare –

IX, X, XI

Canalis hypoglossalis -

XII

Exit /entrance/ of the

cranial nerves

from the skull

Involvement of the cranial nerves in nerve-

supply to the organs

The cranial nerves may be grouped as follows:

● Oculomotor, trochlear, abducent, and hypoglossal nerves (III, IV, VI, XII and XI) supply skeletal muscle of specific regions of the head (eyeballs in the case of III, IV, and VI; tongue in the case of XII). Nerve III also contains parasympathetic fibers to the smooth muscle of the sphincter pupillae and the ciliary muscle (general visceral efferent). The spinal part of nerve XI supplies the sternomastoid and trapezius.

● Trigeminal nerve (V) contains motor fibers to the muscles of mastication (special visceral efferent) and sensory fibers from various parts of the head, e.g., face, nasal cavity, tongue, and teeth (general somatic afferent).

● Facial, glossopharyngeal and vagus nerves (VII, IX, X) contain several components:

● (a) Motor fibers to the muscles of facial expression (VII) and the muscles of the pharynx and larynx (IX and X) (special visceral efferent). Many of the fibers to the pharynx and larynx are derived from nerve XI (internal branch) and travel by way of nerve X (hence XI is "accessory" to the vagus).

● (b) Parasympathetic secretory fibers to the lacrimal and salivary glands (nervus intermedius of VII), the salivary glands (IX), and certain glands associated with the respiratory and digestive systems (X) (general visceral efferent). Nerve X also supplies most of the smooth muscle of the respiratory and digestive systems, as well as cardiac muscle.

● (c) Taste fibers (nervus intermedius of VII; also IX and X) (special visceral afferent).

● (d) Fibers from the mucous membrane of the tongue and pharynx (hence the name glossopharyngeal) and of much of the respiratory and digestive systems (general visceral afferent) are contained in nerves IX and X.

● Olfactory, optic, and vestibulocochlear nerves (I, II, and VIII) pertain to organs of special sense (special afferent).

Ascending wayI. receiving part – in the region of sensory nerve-

supply

II. transmitter part:

ascending /sensory pathway/: has 3 neurons

the first - inside of sensory ganglion

the second - inside of the sensory nucleus

the third – in the thalamus

III. cortical center:

sensory: of general sensitivity – gyrus

postcentralis,

of taste & smell sensitivity – uncus

Descending somatic pathwayI. motor cortical center:

gyrus precentralis, gyrus paracentralis

II. descending somatic motor way:

has 2 neurons: the first - inside of cortex

(gyrus precentralis),

the second - inside of the motor nucleus

III. organ effector (striated muscles)

Motor vegetative nerves have

descending way, which includes:

3 neurons:

1st - inside of superior vegetative

center.

2nd - inside of the vegetative nucle.

3rd - inside of vegetative ganglion

organ effector - smooth muscles,

glands.

Connections of the cranial nerves - 2 groups of the connexions:

1) intrasystemic /with the cranial nerves/

2) intersystemic /with the spinal nerves/

Intrasystemic connexions at the level of the nuclei● fascial nerve has common sensory nucleus with the IX-th and X-th cranial

nerves

n. solitarius;

- the IX-th, X and XI-th have common motor nucleus – n. ambiguous;

Intrasystemic connexions at the level of the branchesAll branches of the trigeminal nerve form connexions with other cranial nerves:- ophthalmic nerve forms conexion with the oculomotor nerve in the region of the ciliary ganglionmaxillary nerve connects with the facial nerve /parasympathetic fibers ofthe zygomatic nerve from the maxillary nerve and sensory fibers of the lacrimal nerve/mandibular nerve connects with: facial nerve in the region of the submandibular ganglion;glossopharyngeal nerve in the region of the otic ganglionaccessory nerve with the glossopharyngeal and vagus nerve;glossopharyngeal & vagus nerves form pharyngeal plexus.

Intrasystemic

connections

Intersystemic connections1) In the region of the head

Branches of the trigeminal have connexions

with the sympathetic fibers originated

from the superior cervical ganglion:

Ophthalmic nerve - with fibers of ophthalmic

plexus.

Mandibular nerve – with fibers of the facial

plexus and plexus of the middle cerebral artery.

In the region of the neck

Facial nerve forms the cervical loop with the transverse nerve from the cervical plexus /formed by the spinal nerves.

2) In the region of the neck

Hypoglossal nerve forms the cervical

loop with the motor branches

of the cervical spinal nerves.

4) In the region of the thorax

&abdomen

Nervus vagus forms multiple

connections

with branches of the sympathetic

trunk

/plexus cardiacus, esophageus,

bronchialis, celiac, upper & lower

mesenteric/.

END