The fibers of cranial nerve connect centrally to cranial nerve nuclei----group of neuron in which sensory or afferent fibers terminate and from which motor or efferent fibers originate

Motor fiber Sensory fiber Five main functional components of cranial nerve Motor fibers to voluntary (striated) muscle Motor fibers involved in innervating involuntary (smooth) muscles or glands. Motor fiber Fibers transmitting general sensation Fibers conveying sensation from the viscera Fibers transmitting unique sensations Sensory fiber

SENSORY & MOTORIC NERVES summary CN I (Olfactory) CN II (Optic) CN VIII (Vestibulocochlear) SENSORY NERVES CN IV (Trochlear) CN VI (Abduscent) CN XI(Spinal accessory) CN XII (Hypoglossal) MOTORIC NERVES CN V (Trigeminal) CN VII (Facial) CN IX (Glossopharyngeal) CN X (Vagus) SENSORY & MOTORIC NERVES

CRANIAL NERVE I The olfactory nerves arise from the olfactory receptor nerve cells in the olfactory mucous membrane located in the upper part of the nasal cavity above the level of the superior concha .

The olfactory receptor cells are scattered among supporting cells. Each receptor cell consists of a small bipolar nerve cell with a coarse peripheral process that passes to the surface of the membrane (apical surface) and a fine central process (basal srface)

From the coarse peripheral process, a number of short cilia arise, the olfactory hairs, which project into the mucus covering the surface of the mucous membrane. These projecting hairs react to odors in the air and stimulate the olfactory cells.

The fine central processes form the olfactory nerve fibers . Bundles of these nerve fibers pass through the openings of the cribriform plate of the ethmoid bone to enter the olfactory bulb. The olfactory nerve fibers are unmyelinated and are covered with Schwann cells.

Olfactory Bulb This ovoid structure in anterior cranial fossa, possesses several types of nerve cells, the largest of which is the mitral cell . The incoming olfactory nerve fibers synapse with the dendrites of the mitral cells and form rounded areas known as synaptic glomeruli. Smaller nerve cells, called tufted cells and granular cells, also synapse with the mitral cells.

Olfactory Tract This narrow band of white matter runs from the posterior end of the olfactory bulb beneath the inferior surface of the frontal lobe of the brain. It consists of the central axons of the mitral and tufted cells of the bulb and some centrifugal fibers from the opposite olfactory bulb. As the olfactory tract reaches the anterior perforated substance, it divides into medial and lateral olfactory striae. The lateral stria carries the axons to the olfactory area of the cerebral cortex, namely, the periamygdaloid and prepiriform areas. The medial olfactory stria carries the fibers that cross the median plane in the anterior commissure to pass to the olfactory bulb of the opposite side.

The periamygdaloid and prepiriform areas of the cerebral cortex are often known as the primary olfactory cortex. The entorhinal area (area 28) of the parahippocampal gyrus, which receives numerous connections from the primary olfactory cortex, is called the secondary olfactory cortex. These areas of the cortex are responsible for the appreciation of olfactory sensations . Note that in contrast to all other sensory pathways, the olfactory afferent pathway has only two neurons and reaches the cerebral cortex without synapsing in one of the thalamic nuclei.

CRANIAL NERVE II The fibers of the optic nerve are the axons of the cells in the ganglionic layer of the retina. They converge on the optic disc and exit from the eye, about 3 or 4 mm to the nasal side of its center, as the optic nerve. The optic nerve leaves the orbital cavity through the optic canal and unites with the optic nerve of the opposite side to form the optic chiasma in middle cranial fossa.

In optic chiasm fibers from the nasal (medial) half of each retina decussate in the chiasm and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract.

The optic tract emerges from the optic chiasma and passes posterolaterally around the cerebral peduncle. Most of the fibers now terminate by synapsing with nerve cells in the lateral geniculate body. A few of the fibers pass to the pretectal nucleus and the superior colliculus of the midbrain and are concerned with light reflexes. The axons of the nerve cells within the geniculate body leave it to form the optic radiation The tract passes posteriorly through the retrolenticular part of the internal capsule and terminates in the visual cortex (area 17)

CRANIAL NERVE III The oculomotor nerve has two motor nuclei: (1) the main motor nucleus and (2) the accessory parasympathetic nucleus. The main oculomotor nucleus is situated in the anterior part of the gray matter that surrounds the cerebral aqueduct of the midbrain . It lies at the level of the superior colliculus The accessory parasympathetic nucleus (Edinger-Westphal nucleus) is situated posterior to the main oculomotor nucleus

COURSE OF OCULOMOTOR NERVE emerges from the midbrain in the middle cranial fossa it divides into a superior and inferior ramus, which enter the orbital cavity through superior orbital fissure

The occulomotor nerve supplies : The levator palpebra superior muscle Superior rectus muscle Medial rectus muscle Inferior rectus muscle Inferior oblique muscle Cilliary ganglion

CRANIAL NERVE IV The trochlear nerve, the most slender of the cranial nerves and the only one to leave the posterior surface of the brainstem, emerges from the midbrain and immediately decussates with the nerve of the opposite side. The trochlear nerve passes forward through the middle cranial fossa in the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure. The nerve supplies the superior oblique muscle of the eyeball. The trochlear nerve is entirely motor and assists in turning the eye downward and laterally.

CRANIAL NERVE V Trigeminal nerve nuclei : 1. The main sensory nucleus Lies in the posterior part of the pons,lateral to motor nucleus 2. The spinal nucleus continuous superiorly with the main sensory nucleus in the pons and extends inferiorly through the whole length of the medulla oblongata and into the upper part of the spinal cord as far as the second cervical segment 3. The mesencephalic nucleus situated in the lateral part of the gray matter around the cerebral aqueduct. It extends inferiorly into the pons as far as the main sensory nucleus 4. The motor nucleus The motor nucleus is situated in the pons medial to the main sensory nucleus

1. Ophthalmic nerve (CN V1) 2. Maxillary nerve (CN V2) The ganglion form three nerves / division : 1. Ophthalmic nerve (CN V1) 2. Maxillary nerve (CN V2) 3. Mandibular nerve (CN V3)

Pathway The trigeminal nerve leaves the anterior aspect of the pons as a small motor root and a large sensory root. The large sensory root now expands to form trigeminal ganglion, which lies within a pouch of dura mater called the trigeminal or Meckel cave. The ophthalmic, maxillary, and mandibular nerves arise from the anterior border of the ganglion.

The ophthalmic nerve (V1) contains only sensory fibers and leaves the skull through the superior orbital fissure to enter the orbital cavity. The maxillary nerve (V2) also contains only sensory fibers and leaves the skull through the foramen rotundum. The mandibular nerve (V3) contains both sensory and motor fibers and leaves the skull through the foramen ovale.

Branch of CN V1 : Tentorial nerve (a meningeal branch) Lacrimal nerve Frontal nerve - Supraorbital nerve - Supratrochlear nerve Nasocilliarry nerve - Sensory root of cilliary ganglion - Short cilliary nerves - Long cilliary nerves - Infratrochlear nerves - Anterior & posterior ethmoidal nerves

Branch of CN V2 : Meningeal branch zygomatic nerve -Zygomaticofacial branch -Zygomaticotemporal branch -Communicating branch to lacrimal nerve Ganglionic branches to (sensory root of) pterygopalatine ganglion Posterior superior alveolar branches -Infraorbital nerve -Anterior superior alveolar branches -Middle superior alveolar branches -Superior labial branches -Inferior palpebra branches -External nasal branches

Branch of CN V2 (con’t...): Greater palatine nerves Posterior inferior lateral nasal nerves Lesser palatine nerves Posterior superior lateral nasal branches Nasopalatine nerve Pharyngeal nerve

Branch of CN V3 : General sensory branches -Meningeal branches -Buccal nerve -Auriculotemporal nerve -Lingual nerve -Inferior alveolar nerve *Nerve to mylohyoid *Inferior dental plexus *Mental nerve Branchiomotor branches -Masseter -Temporal -Medial & lateral pterygoid -Mylohyoid -Anterior belly of digastric -Tensor tympani

CRANIAL NERVE VI Course of the Abducent Nerve The fibers of the abducent nerve pass anteriorly through the pons and emerge in the groove between the lower border of the pons and the medulla oblongata. The nerve then enters the orbit through the superior orbital fissure. The abducent nerve is entirely a motor nerve and supplies the lateral rectus muscle and, therefore, is responsible for turning the eye laterally.

CRANIAL NERVE VII The motor nucleus of the facial nerve is a branchiomotor nucleus in the ventrolateral part of the pons The cell bodies of the primary sensory neurons are in the geniculate ganglion

While traversing the temporal bone within the facial canal, CN VII gives rise to the: Greater petrosal nerve. Nerve to the stapedius. Chorda tympani nerve. Then, after running the longest intraosseous course of any cranial nerve, CN VII gives off the posterior auricular branch; enters the parotid gland; and forms the parotid plexus, which gives rise to the following five terminal motor branches: temporal, zygomatic, buccal, marginal mandibular, and cervical.

Visceral (Parasympathetic) Motor CN VII provides presynaptic parasympathetic fibers to the pterygopalatine ganglion for innervation of the lacrimal glands and to the submandibular ganglion for innervation of the sublingual and submandibular salivary glands.

Somatic (General) Sensory Some fibers from the geniculate ganglion supply a small area of the skin of the concha of the auricle, close to external acoustic meatus. Special Sensory (Taste) Fibers carried by the chorda tympani join the lingual nerve to convey taste sensation from the anterior two thirds of the tongue and soft palate.

CRANIAL NERVE VIII The vestibulocochlear nerve (CN VIII) emerges from the junction of the pons and medulla and enters the internal acoustic meatus . Here it separates into the vestibular and cochlear nerves

The vestibular nerve is composed of : The central processes of bipolar neurons in the vestibular ganglion. The peripheral processes of the neurons extend to the maculae of the utricle and saccule (sensitive to the line of linear acceleration relative to the position of the head) and to the cristae of the ampullae of the semicircular ducts (sensitive to rotational acceleration). The cochlear nerve is composed of : The central processes of bipolar neurons in the spinal ganglion The peripheral processes of the neurons extend to the spiral organ for the sense of hearing.

CRANIAL NERVE IX Somatic (Branchial) Motor Motor fibers pass to one muscle, the stylopharyngeus. Visceral (Parasympathetic) Motor presynaptic parasympathetic fibers are provided to the otic ganglion for innervation of the parotid gland. The otic ganglion is associated with the mandibular nerve (CN V3), branches of which convey the postsynaptic parasympathetic fibers to the parotid glaND

CRANIAL NERVE IX Somatic (General) Sensory The general sensory branches of CN IX are as follows : The tympanic nerve. The carotid sinus nerve to the carotid sinus, a baro-(presso-) receptor sensitive to changes in blood pressure, and the carotid body, a chemoreceptor sensitive to blood gas (oxygen and carbon dioxide levels). Special Sensory (Taste) Taste fibers are conveyed from the posterior third of the tongue to the sensory ganglia, the superior and inferior ganglia of CN IX.

CRANIAL NERVE X DIVISION BRANCHES Cranial -Meningeal branch -Auricular branch Cervical -Pharyngeal branch -cervical cardiac branches -Superior laryngeal nerve -Right reccurent laryngeal nerve Thoracic -Left reccurent laryngeal nerve -Thoracic cardiac branches -Pulmonary branches -Esophageal branches Abdominal -Gastric branches -Hepatic branches -Celiac branches -Pyloric branches -Renal branches -Intestinal branches

Distribution of cranial nerve XI The cranial root (part) is formed from the axons of nerve cells of the nucleus ambiguus Course of the Cranial Root The nerve runs laterally in the posterior cranial fossa and joins the spinal root. The two roots unite and leave the skull through the jugular foramen. The roots then separate, and the cranial root joins the vagus nerve to the muscles of the soft palate, pharynx, and larynx.

Distribution of cranial nerve XI The spinal root (part) is formed from axons of nerve cells in the spinal nucleus, which is situated in the anterior gray column of the spinal cord Course of the Spinal Root The nerve fibers emerge from the spinal cord midway between the anterior and posterior nerve roots of the cervical spinal nerves (C2-C4) ascends into the skull through the foramen magnum. joins the cranial root as they pass through the jugular foramenseparates from the cranial root and runs downward and laterally and enters the deep surface of the sternocleidomastoid muscle, The nerve then crosses the posterior triangle of the neck and passes beneath the trapezius muscle, which it supplies.

CRANIAL NERVE XII The hypoglossal nerve (CN XII) arises as a purely motor nerve by several rootlets from the medulla and leaves the cranium through the hypoglossal canal.  After exiting the cranial cavity, CN XII is joined by a branch or branches of the cervical plexus conveying general somatic motor fibers from C1 and C2 spinal nerves and somatic (general) sensory fibers from the spinal ganglion of C2  CN XII passes inferiorly medial to the angle of the mandible and then curves anteriorly to the intrinsic and extrinsic muscles of the tongue---styloglossus, hyoglossus, and genioglossus.

alhamdulillah….