Anatomy Lec.11 Cranial Nerves PDF

Neuroanatomy Lectures Lecture 11 Cranial Nerves ‫ ليث ثامر خزعل‬.‫د‬.‫م‬.‫ا‬ Cranial Nerves There are 12 pairs of cranial nerves, which leave the brain and pass through foramina and fissures in the skull. All the nerves are distributed in the head and neck, except cranial nerve X, wh...

Neuroanatomy Lectures Lecture 11 Cranial Nerves ‫ ليث ثامر خزعل‬.‫د‬.‫م‬.‫ا‬ Cranial Nerves There are 12 pairs of cranial nerves, which leave the brain and pass through foramina and fissures in the skull. All the nerves are distributed in the head and neck, except cranial nerve X, which also supplies structures in the thorax and abdomen. The cranial nerves are named as follows: 1. Olfactory 2. Optic 3. Oculomotor 4. Trochlear 5. Trigeminal 6. Abducent 7. Facial 8. Vestibulocochlear 9. Glossopharyngeal 10. Vagus 11. Accessory 12. Hypoglossal Organization of the Cranial Nerves The olfactory, optic, and vestibulocochlear nerves are entirely sensory. The oculomotor, trochlear, abducent, accessory, and hypoglossal nerves are entirely motor. The trigeminal, facial, glossopharyngeal, and vagus nerves are both sensory and motor nerves. Olfactory 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 Each receptor cell consists of a small bipolar nerve cell. olfactory hairs: a number of short cilia arise from the coarse peripheral process of the bipolar cell 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 possesses several types of nerve cells, the largest of which is the mitral cell, Smaller nerve cells, called tufted cells and granular cells, The olfactory bulb, in addition, receives axons from the contralateral olfactory bulb through the olfactory tract. Olfactory Tract 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 often known as the (primary olfactory cortex) 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 entorhinal area (area 28) of the parahippocampal gyrus, which receives numerous connections from the primary olfactory cortex, is called the (secondary olfactory cortex) The primary olfactory cortex sends nerve fibers to many other centers within the brain to establish connections for emotional and autonomic responses to olfactory sensations. A: Distribution of olfactory nerves on the lateral wall of the nose. B: Connections between the olfactory cells and the neurons of the olfactory bulb. C: Connections between the olfactory cell and the rest of the olfactory system. Optic Nerve (Cranial Nerve II) Origin of the Optic Nerve 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 fibers of the optic nerve are myelinated, but the sheaths are formed from oligodendrocytes rather than Schwann cells, since the optic nerve is comparable to a tract within the central nervous system. 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 Optic Chiasma In the chiasma, the fibers from the nasal (medial) half of each retina, including the nasal half of the macula, cross the midline and enter the optic tract of the opposite side, while the fibers from the temporal (lateral) half of each retina, including the temporal half of the macula, pass posteriorly in the optic tract of the same side 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, which is a small projection from the posterior part of the thalamus. A few of the fibers pass to the pretectal nucleus and the superior colliculus of the midbrain and are concerned with light reflexes Lateral Geniculate Body The lateral geniculate body is a small, oval swelling projecting from the pulvinar of the thalamus. It consists of six layers of cells, on which synapse the axons of the optic tract. The axons of the nerve cells within the geniculate body leave it to form the optic radiation Optic Radiation The fibers of the optic radiation are the axons of the nerve cells of the lateral geniculate body. The tract passes posteriorly through the retrolenticular part of the internal capsule and terminates in the visual cortex (area 17) Optic Pathway Visual field defects associated with lesions of the optic pathways. 1. Right-sided circumferential blindness due to retrobulbar neuritis. 2. Total blindness of the right eye due to division of the right optic nerve. 3. Right nasal hemianopia due to a partial lesion of the right side of the optic chiasma. 4. Bitemporal hemianopia due to a complete lesion of the optic chiasma. 5. Left temporal hemianopia and right nasal hemianopia due to a lesion of the right optic tract. 6. Left temporal and right nasal hemianopia due to a lesion of the right optic radiation. 7. Left temporal and right nasal hemianopia due to a lesion of the right visual cortex. Neurons of the Visual Pathway Four neurons conduct visual impulses to the visual cortex: (1) rods and cones, which are specialized receptor neurons in the retina; (2) bipolar neurons, which connect the rods and cones to the ganglion cells; (3) ganglion cells, whose axons pass to the lateral geniculate body; and (4) neurons of the lateral geniculate body, whose axons pass to the cerebral cortex Visual Reflexes Direct and Consensual Light Reflexes If a light is shone into one eye, the pupils of both eyes normally constrict. The constriction of the pupil on which the light is shone is called the direct light reflex; the constriction of the opposite pupil, even though no light fell on that eye, is called the consensual light reflex Accommodation Reflex When the eyes are directed from a distant to a near object, contraction of the medial recti brings about convergence of the ocular axes; the lens thickens to increase its refractive power by contraction of the ciliary muscle; and the pupils Corneal Reflex Light touching of the cornea or conjunctiva results in blinking of the eyelids Visual Body Reflexes The automatic scanning movements of the eyes and head that are made when reading, the automatic movement of the eyes, head, and neck toward the source of the visual stimulus, and the protective closing of the eyes and even the raising of the arm for protection Pupillary Skin Reflex The pupil will dilate if the skin is painfully stimulated by pinching Oculomotor Nerve (Cranial Nerve III) The oculomotor nerve has two motor nuclei: (1) the main motor nucleus (2) the accessory parasympathetic nucleus. Course of the Oculomotor Nerve The oculomotor nerve emerges on the anterior surface of the midbrain. It passes forward between the posterior cerebral and the superior cerebellar arteries. It then continues into the middle cranial fossa in. the lateral wall of the cavernous sinus Here, it divides into a superior and an inferior ramus, which enter the orbital cavity through the superior orbital fissure. The oculomotor nerve supplies the following extrinsic muscles of the eye: the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique. It also supplies, through its branch to the ciliary ganglion and the short ciliary nerves, parasympathetic nerve fibers to the following intrinsic muscles: the constrictor pupillae of the iris and ciliary muscles. Therefore, the oculomotor nerve is entirely motor and is responsible for lifting the upper eyelid; turning the eye upward, downward, and medially; constricting the pupil; and accommodating the eye. The distribution of the oculomotor nerve Trochlear Nerve (Cranial Nerve IV) The trochlear nucleus is situated in the anterior part of the gray matter that surrounds the cerebral aqueduct of the midbrain The nerve fibers, after leaving the nucleus, pass posteriorly around the central gray matter to reach the posterior surface of the midbrain 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. Distribution of the trochlear nerve Trigeminal Nerve (Cranial Nerve V) is the largest cranial nerve and contains both sensory and motor fibers. It is the sensory nerve to the greater part of the head and the motor nerve to several muscles, including the muscles of mastication Trigeminal Nerve Nuclei (1) the main sensory nucleus, (2) the spinal nucleus, (3) the mesencephalic nucleus (4) the motor nucleus Course of the Trigeminal Nerve The trigeminal nerve leaves the anterior aspect of the pons as a small motor root and a large sensory root The nerve passes forward out of the posterior cranial fossa and rests on the upper surface of the apex of the petrous part of the temporal bone in the middle cranial fossa. The large sensory root now expands to form the crescent-shaped trigeminal ganglion, which lies within a pouch of dura mater called the trigeminal or Meckel cave Branches arise from the anterior border or 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 Distribution of the trigeminal nerve.  The sensory fibers to the skin of the face from each division supply a distinct zone, there being little or no overlap of the dermatomes (compare with the overlap of the dermatomes of the spinal nerves). As noted previously, the motor fibers in the mandibular division are mainly distributed to muscles of mastication  Sensory nerve supply to the skin of the head and neck. Note that the skin over the angle of the jaw is supplied by the great auricular nerve (C2 and C3) and not by branches of the trigeminal nerve. Abducent Nerve (Cranial Nerve VI) The abducent nerve is a small motor nerve that supplies the lateral rectus muscle of the eyeball The small motor nucleus is situated beneath the floor of the upper part of the fourth ventricle, close to the midline and beneath the colliculus facialis Course: 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 It passes forward through the cavernous sinus, lying below and lateral to the internal carotid artery. 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. Distribution of the abducent nerve Facial Nerve (Cranial Nerve VII) The facial nerve has three nuclei: (1) the main motor nucleus (2) the parasympathetic nuclei (3) the sensory nucleus Facial nerve nuclei and their central connections 1- Main Motor Nucleus lies deep in the reticular formation of the lower part of the pons The part of the nucleus that supplies the muscles of the upper part of the face receives corticonuclear fibers from both cerebral hemispheres The part of the nucleus that supplies the muscles of the lower part of the face receives only corticonuclear fibers from the opposite cerebral hemisphere 2- Parasympathetic Nuclei lie posterolateral to the main motor nucleus They are the superior salivatory and lacrimal nuclei 3- Sensory Nucleus The sensory nucleus is the upper part of the nucleus of the tractus solitarius. Course of the Facial Nerve fibers of the motor root travel posteriorly around the medial side of the abducent nucleus pass around the nucleus beneath the colliculus facialis in the floor of the fourth ventricle then emerge from the brainstem The sensory root (nervus intermedius) is formed of the central processes of the unipolar cells of the geniculate ganglion. It also contains the efferent preganglionic parasympathetic fibers from the parasympathetic nuclei - Two roots (sensory and motor) form the facial nerve that emerge from the anterior surface of the brain between the pons and the medulla oblongata - enter the internal acoustic meatus in the petrous part of the temporal bone laterally with the vestibular nerve - nerve enters the facial canal and runs laterally through the inner ear - On medial wall of the tympanic cavity, the nerve expands to form the sensory geniculate ganglion - the facial nerve turns downward on the medial side of the aditus of the mastoid antrum, descends behind the pyramid, and emerges from the stylomastoid foramen  Branches of the facial nerve within the petrous part of the temporal bone; the taste fibers are shown in black. The glossopharyngeal nerve is also shown Distribution of the facial nerve Distribution of the Facial Nerve The motor nucleus supplies the muscles of facial expression, the auricular muscles, the stapedius, the posterior belly of the digastric, and the stylohyoid muscles The superior salivatory nucleus supplies the submandibular and sublingual salivary glands and the nasal and palatine glands. The lacrimal nucleus supplies the lacrimal gland. The sensory nucleus receives taste fibers from the anterior two-thirds of the tongue, the floor of the mouth, and the palate. Vestibulocochlear Nerve (Cranial Nerve VIII) - the vestibular nerve - the cochlear nerve the vestibular nerve The vestibular nerve conducts nerve impulses from the utricle and saccule that provide information concerning the position of the head; the nerve also conducts impulses from the semicircular canals that provide information concerning movements of the head. They enter the anterior surface of the brainstem in a groove between the lower border of the pons and the upper part of the medulla oblongata The Vestibular Nuclear Complex (1) the lateral vestibular nucleus, (2) the superior vestibular nucleus (3) the medial vestibular nucleus, and (4) the inferior vestibular nucleus Vestibular nerve nuclei and their central connections Cochlear Nerve The cochlear nerve conducts nerve impulses concerned with sound from the organ of Corti in the cochlea. The fibers of the cochlear nerve are the central processes of nerve cells located in the spiral ganglion of the cochlea They enter the anterior surface of the brainstem at the lower border of the pons on the lateral side of the emerging facial nerve and are separated from it by the vestibular nerve Cochlear Nuclei Anterior and posterior cochlear nuclei Cochlear nerve nuclei and their central connections  Course of the Vestibulocochlear Nerve The vestibular and cochlear parts of the nerve leave the anterior surface of the brain between the lower border of the pons and the medulla oblongata They run laterally in the posterior cranial fossa and enter the internal acoustic meatus with the facial nerve. The fibers are then distributed to the different parts of the internal ear Distribution of the vestibulocochlear nerve Glossopharyngeal Nerve (Cranial Nerve IX) The glossopharyngeal nerve has three nuclei: (1) the main motor nucleus: supply the stylopharyngeus muscle (2) the parasympathetic nucleus (3) the sensory nucleus: is part of the nucleus of the tractus solitarius Course It leaves the anterolateral surface of the upper part of the medulla oblongata as a series of rootlets in a groove between the olive and the inferior cerebellar peduncle leaves the skull through the jugular foramen The nerve then descends through the upper part of the neck in company with the internal jugular vein and the internal carotid artery to reach the posterior border of the stylopharyngeus muscle, which it supplies. The nerve then passes forward between the superior and middle constrictor muscles of the pharynx to give sensory branches to the mucous membrane of the pharynx and the posterior third of the tongue Vagus Nerve (Cranial Nerve X) The vagus nerve has three nuclei: 1) the main motor nucleus: is formed by the nucleus ambiguus The efferent fibers supply the constrictor muscles of the pharynx and the intrinsic muscles of the larynx 2) the parasympathetic nucleus: efferent fibers are distributed to the involuntary muscle of the bronchi, heart, esophagus, stomach, small intestine, and large intestine as far as the distal one-third of the transverse colon afferent fibers from the hypothalamus and from the glossopharyngeal nerve (carotid sinus reflex). 3) the sensory nucleus Course of the Vagus Nerve Leave medulla oblongata as a series of rootlets in a groove between the olive and the inferior cerebellar peduncle leaves the skull through the jugular foramen two sensory ganglia, a rounded superior ganglion, and a cylindrical inferior ganglion the cranial root of the accessory nerve joins the vagus nerve and is distributed mainly in its pharyngeal and recurrent laryngeal branches The vagus nerve descends vertically in the neck within the carotid sheath with the internal jugular vein and the internal and common carotid arteries The right Vagus nerve The left Vagus nerve  Distribution of the Vagus nerve Accessory Nerve (Cranial Nerve XI) The accessory nerve is a motor nerve that is formed by the union of a cranial and a spinal root. The cranial root (part) is formed from the axons of nerve cells of the nucleus ambiguus The spinal root (part) is formed from axons of nerve cells in the spinal nucleus Distribution of the accessory nerve Hypoglossal Nerve (Cranial Nerve XII) The hypoglossal nerve is a motor nerve that supplies all the intrinsic muscles of the tongue as well as the styloglossus, the hyoglossus, and the genioglossus muscles. The hypoglossal nerve fibers emerge on the anterior surface of the medulla oblongata between the pyramid and the olive leaves the skull through the hypoglossal canal In the upper part of its course, the hypoglossal nerve is joined by C1 fibers to from the cervical plexus the hypoglossal nerve controls the movements and shape of the tongue Distribution of hypoglossal nerve