Cranial nerve 1-4

Unilateral Anosmia:

Can result from diseases affecting olfactory nerves, bulb, or tract: e.g.: fractures of the cribriform plate of the ethmoid bone, frontal lobe tumors, and meningiomas of the anterior cranial fossa.

Lesions of the Optic pathway: Bitemporal hemianopias:

Caused by pituitary tumors.

2- Consensual light reflex:

Constriction of the opposite pupil even though no light fell on the eye (this is due to bilateral fibers from pretectal nucleus to the Edinger- Westphal nuclei.

1- direct light reflex:

Constriction of the pupil on which the light is shone. Some fibers from the optic tract synapse on pretectal nucleus and from there to bilateral Edinger- Westphal nuclei, which are Parasympathetic nuclei, and nerve fibers from here reach the eye through the short ciliary nerves to constrictor pupillae muscle

Complete oculomotor paralysis:

Eye can not be moved upward, downward, or inward. At rest, the eye looks laterally (external strabismus) due to the activity of the lateral rectus and downward due to the activity of the superior oblique.

Corneal reflex: Efferent:

Facial nerve supplying the orbicularis oculi muscle causes blinking Internuncial neurons connect with the motor nucleus of facial nerve on both sides through the medial longitudinal fasciculus (MLF).

Optic nerve (CN II): Optic radiation:

Fibers leave the lat geniculate body as optic radiation to reach visual cortex (area 17).

Oculomotor nerve Clinical notes:

Oculomotor nerve has a long course and is prone to damage in head injuries. It is also commonly affected in diabetes, aneurysm, tumors and vascular disease

Olfactory nerve (CN I): Olfactory bulb:

contains 1- miteral cells that synapse with incoming olfactory nerves. 2- Tufted cells and 3- granular cells

A- Main motor nucleus:

situated in the periaqueductal gray of the midbrain,the fibers pass through the red nucleus and interpeduncular fossa

Motor

(efferent) signals are carried away from the CNS, They innervate muscles and glands

12 cranial nerves list

1- Olfactory nerve (CN I) is sensory 2- Optic nerve (CN II) is sensory 3- Oculomotor nerve (CN III) is motor 4- Trochlear (CN IV) is motor 5- Trigeminal (CN V) is sensory and motor 6- Abducent nerve (CN VI) is motor 7- Facial nerve (CN VII) is sensory and motor 8- Vestibulocochlear nerve (CN VIII) is sensory 9- Glossopharyngeal nerve (CN IX) is sensory and motor 10- Vagus nerve (CN X) is sensory and motor 11- Accessory nerve (CN XI) is motor 12- Hypoglossal nerve (CNXII) is motor

Bilateral connections and Motor nuclei of the cranial nerves

Bilateral connections are present for all the cranial motor nuclei except for part of the facial nucleus that supplies the muscles of the lower part of the face and a part of the hypoglossal nucleus that supplies the genioglossus muscle

Oculomotor nerve (CN III):

Has 2 motor nuclei: A- main motor nucleus B- parasympathetic nucleus

Visual reflexes

If a light is shone into one eye, the pupils of both eyes normally constrict

Incomplete oculomotor paralysis:

If autonomic part injured, it is called internal ophthalmoplegia If extraocular muscles paralysis occur, it is called the external ophthalmoplegia

Injuries of the trochlear nerve:

In head injuries, diabetes, tumor... Patients have double vision when looking straight downward, because of the paralysis of the superior oblique which turns the eye medially and downward. The patient has difficulty in turning the eye downward and laterally.

B- Parasympathetic (Edinger- Westphal) nucleus:

Is situated posterior to the main nucleus. Sends preganglionic fibers to the ciliary ganglion in the orbit (close to optic nerve). From there, postganglionic fibers reach the ciliary muscle and the constrictor pupillae muscle through the short ciliary nerves.

Optic nerve (CN II): Pathway:

It unites with the optic nerve of the opposite side to form the optic chiasma. In the chiasma, fibers from the medial (nasal) half of the retina cross the mid- line and enter the optic tract of the opposite side. But fibers from the temporal half of retina pass into the optic tract of the same side.

Corneal reflex:

Light touching of the cornea or conjunctiva results in blinking of the eyelid.

Complete oculomotor paralysis: sx

Patient has diplopia, ptosis of the upper lid, pupil is dilated. Accommodation is impossible

four main subdivisions Inputs and outputs

Somatic sensory, Visceral sensory, Somatic motor, Visceral motor

corticonuclear fibers

The majority of the corticonuclear fibers to the motor cranial nerve nuclei cross the median plane before reaching the nuclei.

Trochlear nerve (CN IV):

The nucleus is situated in the midbrain, in the anterior part of the periaqueductal gray at the level of the inferior colliculus. Fibers pass posteriorly and immediately decussates with the nerve of the opposite side.

General visceral motor nuclei:

These are the outflow of the parasympathetic portion of the autonomic nervous system: 1- Edinger-Westphal nucleus of CN III 2- Superior Salivatory Nucleus of CN VII 3- Inferior Salivatory Nucleus of CN IX 4- Dorsal Motor Nucleus of Vagus from CN X

Accommodation reflex:

When eyes are directed from a distant to near object, contraction of the medial rectus causes convergence of the ocular axes lens thickens to increase its refractive power by contraction of the ciliary muscle, and the pupils constrict to restrict the light waves to the thickest central part of the lens.

Olfactory nerve (CN I): Olfactory tract:

a band of white matter leaving the olfactory bulb and contains medial and lateral olfactory striae. The lateral stria carries the axons to the olfactory area of cortex (the periamygdaloid and prepiriform areas)

Accommodation reflex: Pathway:

afferent impulses travel all the way to the visual cortex, from there to frontal eye field. From here, fibers pass to the CNIII to activate the medial rectus muscle and to the Edinger-Westphal (parasympathetic) nucleus for contraction of ciliary muscle and constriction of pupil.

Sensory

afferent) signals picked up by sensor receptors carried by nerve fibers of PNS to the CNS

Bilateral Anosmia:

can be caused by disease of the olfactory mucous membrane, such as the common cold or allergic rhinitis.

Optic nerve (CN II): Origin:

ganglion cell layer of the Retina. The nerve then leaves the orbit through optic canal.

nerves distribution

in the head and neck, except for the tenth cranial nerve which also supplies thoracic and abdominal structures.

Main motor nucleus: innervation

innervates the following eye muscles: 1- medial rectus, 2- superior rectus 3- inferior rectus 4- inferior oblique 5- levator palpebrae superioris

12 cranial nerves

leave the brain and pass through foraminae and fissures in the skull.

Optic nerve (CN II): Lateral geniculate body:

most of the optic tract fibers terminate in lateral geniculate body of thalamus (some fibers get into the pretectal nucleus and superior colliculus for light reflexes).

Olfactory nerve (CN I): Origin

olfactory receptor nerve cells in the olfactory mucous membrane located in the roof of the nasal cavity.

Motor nuclei of the cranial nerves

receive impulses from the cerebral cortex (area 4 and the postcentral gyrus, etc) through the corticonuclear fibers.

Trochlear nerve (CN IV): innervates

the superior oblique muscle of the eye.

Olfactory nerve (CN I): Pathway

these nerve bundles pass through the cribriform plate and enter the Olfactory bulb inside the skull.

Corneal reflex: Afferents:

trigeminal nerve (ophthalmic branch), from cornea or conjunctiva to sensory trigeminal nucleus.