Functional+Components+of+Cranial+Nerves

=**Objectives**=


 * 1. Review the components of a typical spinal nerve. How do those components compare and contrast to those of a cranial nerve.**

The 31 pairs of spinal nerves are attached to the spinal cord and use intervertebral foramen to go to their targets. Functionally, they are made up of somatic components (somatic afferents and efferents) and visceral components (autonomic efferents and afferents). Neuronal cell bodies of somatic afferents are located in the dorsal root ganglion. Neuronal cell bodies of somatic efferents are located in the ventral horn of the spinal cord. The ventral root and dorsal root meet to form the spinal nerve; this means that the spinal nerve is a mixed nerve with both somatic efferent (motor) and somatic afferent (sensory) fibers.
 * __Spinal Nerves__**

The 12 pairs of cranial nerves are attached to the brain and use named foramena in the skull to go to their targets. Cranial nerves are mostly //not// mixed nerves, though they can be: they may be somatic afferent only (sensory), somatic efferent only (motor), or both.
 * __Cranial Nerves__**

Cranial nerves may contain somatic afferent components (general sensation pain, touch, and temperature), special afferent components (smell, vision, hearing, taste), or visceral afferent components (sensory information from viscera).
 * __Cranial Nerve Sensory (Afferent) Components__**

__Cranial Nerves Containing Somatic Afferent Components__
 * Cranial Nerve || Name || Sensory Source ||
 * CN V1 || Ophthalmic Branch || Sensory from forehead, eyeball ||
 * CN V2 || Maxillary Branch || Sensory from cheek, nasal cavity, palate ||
 * CN V3 || Mandibular Branch || Sensory from chin, anterior 2/3 of tongue ||
 * CN VII || Facial Nerve || Sensory from external auditory meatus ||
 * CN IX || Glossopharyngeal Nerve || Sensory from posterior ½ of tongue, middle ear ||
 * CN X || Vagus Nerve || Sensory from posterior ear, external auditory meats ||

__Cranial Nerves Containing Special Afferent Components__
 * Cranial Nerve || Name || Special Sense ||
 * CN I || Olfactory Nerve || Smell ||
 * CN II || Optic Nerve || Vision ||
 * CN VII || Facial Nerve || Taste – anterior 2/3 of tongue ||
 * CN VIII || Vestibulocholear Nerve || Hearing ||
 * CN IX || Glossopharyngeal Nerve || Taste – posterior 2/3 of tongue ||
 * CN X || Vagus Nerve || Taste – epiglottis ||

__Cranial Nerves Containing Visceral Afferent Components__
 * Cranial Nerve || Name || Sensory Source ||
 * CN IX || Glossopharyngeal || Sensory from pharynx, carotid body, and carotid sinus ||
 * CN X || Vagus Nerve || Sensory from larynx, carotid body, carotid sinus, and viscera ||

The afferent cell bodies of cranial nerves are located in named ganglia or are specialized in some way; three cranial nerves (facial, glossopharyngeal, and vagus) have more than one type of sensory component but are housed in the same ganglia.
 * __Cranial Nerve Sensory Ganglia__**

__Cranial Nerves and Associated Named Sensory Ganglia__
 * Cranial Nerve || Name || Sensory Ganglia ||
 * CN I || Olfactory Nerve || Specialized cells in the olfactory epithelium (Anterior Olfactory Nuclei) ||
 * CN II || Optic Nerve || Specialized cells in the retina (Lateral Geniculate Nucleus) ||
 * CN V || Trigeminal Nerve || Trigeminal Ganglia ||
 * CN VII || Facial Nerve || Geniculate Ganglia ||
 * CN VIII || Vestibulocochlear Nerve || Specialized cells in the cochlea (Spiral Vestibular Ganglia) ||
 * CN IX || Glossopharyngeal Nerve || Superior and Inferior Glossopharyngeal Ganglia ||
 * CN X || Vagus Nerve || Superior and Inferior Jugular Ganglia ||

Cranial nerves may contain somatic efferent fibers (to skeletal muscle) or visceral efferent fibers (to smooth muscle and glands). Efferent fibers that go to skeletal muscle derived from the pharyngeal arches are called Special Visceral Efferents (SVE) but are similar in organization to other somatic efferents of the head.
 * __Cranial Nerve Motor (Efferent) Components__**

__Cranial Nerves Containing Somatic Efferent Components__
 * Cranial Nerve || Name || Efferent Target ||
 * CN III || Oculomotor Nerve || To extrinsic muscles of the eye and levator palpebral superioris, except LR6 and SO4 ||
 * CN IV || Trochlear Nerve || To Superior Oblique Muscle ||
 * CN VI || Abducens Nerve || To Lateral Rectus Muscle ||
 * CN XI || Accessory Nerve || To Sternocleidomastoid, trapezius ||
 * CN XII || Hypoglossal Nerve || To intrinsic and extrinsic muscles of the tongue ||

__Cranial Nerves Containing Special Visceral Efferent Components__
 * Cranial Nerve || Name || Efferent Target ||
 * CN V3 || Mandibular Branch || To muscles of mastication ||
 * CN VII || Facial || To muscles of facial expression ||
 * CN IX || Glossopharyngeal || To stylopharyngeous muscle ||
 * CN X || Vagus nerve || To muscles of palate, pharynx, and larynx ||


 * 2. Review the general plan for the sympathetic division of the autonomic nervous system. Describe the pathways for sympathetic fibers to the head and neck.**

Sympathetics originate on the lateral horn of T1-L2 where they travel along the ventral root, go to a white ramus and ascend. Head and neck sympathetics typically come from the T1-T4 lateral horns. The fibers ascend to the cervical ganglion, typically the superior cervical ganglion where they synapse. The post ganglionic sympathetic then follows vasculature or named nerves until it reaches its target (sweat glands, papillary dilator muscle, etc).


 * 3. Review the general plan for the organization of the parasympathetic division of the autonomic nervous system. What cranial nerves are associated with the parasympathetic division of the autonomic nervous system.**

Cranial nerves may contain somatic efferent fibers (to skeletal muscle) or visceral efferent fibers (to smooth muscle and glands). Visceral efferent components are part of the parasympathetic division of the autonomic nervous system. Three of these ganglia are associated with branches of the trigeminal nerve (CN V) but do not arise from the trigeminal nerve. However, postganglionic fibers are distributed across branches of the maxillary and mandibular branches of the trigeminal nerve.

__Cranial Nerves with Visceral Efferent Components__
 * Cranial Nerve || Name || Efferent Target ||
 * CN III || Oculomotor Nerve || To sphincter pupillae and ciliary muscle ||
 * CN VII || Facial Nerve || To lacrimal gland, mucus membrane of the nose and palate, sublingual and submandibular glands ||
 * CN IX || Glossopharyngeal Nerve || To parotid gland ||
 * CN X || Vagus Nerve || To mucus membrane of the pharynx and larynx and muscles of thorax and upper GI tract ||

Visceral afferents use a two chain system where a preganglion neuron in the CNS synapses to a postganglionic neuron in an autonomic ganglia.
 * __Cranial Nerve Autonomic Ganglia__**

__ Cranial Nerves and Associated Autonomic Ganglia__
 * Cranial Nerve || Name || Autonomic Ganglia ||
 * CN III || Oculomotor Nerve || Ciliary ganglion ||
 * CN VII || Facial Nerve || Pterygopalatine ganglion and submandibular ganglion ||
 * CN IX || Glossopharyngeal Nerve || Otic ganglion ||
 * CN X || Vagus Nerve || Terminal ganglia in the wall of the organ ||


 * 4. Diagram all the cranial nerves with a parasympathetic component. Identify the course of the preglanglionic and postganglionic fibers, as well as the location and the name of the ganglion associated with each nerve.**

__CN III – Oculomotor Nerve__ Preganglionic parasympathic cell bodies residing in the CNS travel out along the oculomotor nerve through the superior orbital fissure and travel along the inferior division of the oculomotor nerve. It then gives off a parasympathetic root to the ciliary ganglion which travels to the ciliary ganglion located posterior to the eye. Preganglionic parasympathetic fibers synapse here and the postganglionic parasympathetic fibers travel out of the ciliary ganglion via short ciliary nerves to supply the papillary sphincter and ciliary muscles.

__CN VII – Facial Nerve__ The facial nerve has two associated parasympathetic ganglion.

//Pterygopalatine Ganglion// Preganglionic parasympathetic cell bodies in the brain stem travel along the facial nerve through the internal auditory meatus where it reaches the geniculate ganglion. It continues through the geniculate ganglion along the greater petrosal nerve, exiting at the hiatus of the facial canal. At this point, postganglionic sympathetic nerve fibers traveling up from the deep etrosal nerve join the preganglionic parasympathetic fibers and form the nerve of the pterygoid canal as they transverse the pterygoid canal. After passing through the canal, the preganglionic parasympathetic fibers reach the pterygopalatine ganglion where they synapse. Postganglionic parasympathetic and sympathetic fibers then distribute along the maxillary branch of the trigeminal nerve.

Generally the parasympathetic fibers go to wherever there are mucus membranes while the sympathetic fibers go to the vasculature of the mucus glands, either travel with the parasympathetics or go along multiple different paths. Parasympathetics supply the glands of the nasal cavity, hard palate, and soft palate. It also gives off a communicating parasympathetic branch that joins the lacrimal nerve of the ophthalmic branch (CN V1) to supply the lacrimal gland.

//Submandibular Ganglion// Preganglionic parasympathetic cell bodies in the brain stem travel along the facial nerve and pass through the internal auditory meatus into the geniculate ganglion where they take a right turn and enter the facial canal. As it travels the facial canal, it jumps off onto the chorda tympani. It continues with chorda tympani as the lingual nerve from the mandibular branch of trigeminal nerve joins it. Then the preganglionic parasympathetic fibers jump off at the submandibular ganglion and synapse. Postganglionic parasympathetic fibers then go to supply the submandibular gland the sublingual glands.

__CN IX – Glossopharyngeal Nerve__ Preganglion parasympathetic cell bodies in the brain stem travel out on the glossopharyngeal nerve through the jugular foramen and through the superior and inferior glossopharyngeal ganglion. It jumps off onto the tympanic branch and then to the lesser petrosal nerve where it continues until ire aches the otic ganglion. There the preganglionic parasympathetic fibers synapse and the postganglionic parasympathetic fibers go on to innervate the parotid gland.

__CN X – Vagus Nerve__ Preganglionic parasympathetic fibers in the CNS travel on the vagus nerve through the jugular foramen and through the superior and inferior jugular ganglion where they branch off to supply the mucosa of the pharynx, larynx, viscera of the neck, thorax, and abdomen via pharyngeal branch, superior laryngeal branch (external and internal divisions), recurrent laryngeal branch, superior and inferior cardiac branches, etc.


 * 5. What role does the trigeminal nerve serve in the autonomic control of structures in the head and neck? Identify portions of the trigeminal nerve associated with the autonomic components of other cranial nerves.**

Three of the cranial nerves have postganglionic parasympathetic components are associated with branches of the trigeminal nerve (CN V). However, these postganglionic parasympathetic fibers are distributed across branches of the trigeminal nerve and do not arise from the trigeminal nerve. The trigeminal nerve is basically like a highway on which postganglionic parasympathetic fibers from the facial (CN VII) and glossopharyngeal (CN IX) can travel along to reach their targets.

__Lacrimal Gland__ (Maxillary Nerve, Lacrimal Nerve of Ophthalmic Nerve) To reach the lacrimal gland, parasympathetic fibers must travel from the brain stem through the auditory meatus, geniculate ganglion, greater petrosal nerve, pterygoid canal and synapse at the pterygopalatine ganglion. There postganglionic fibers travel along branches of the maxillary nerve (CN V2), going up to the zygomatic branch, zygomaticotemporal branch and to a communicating branch of the zygomaticotemporal branch that joins with the lacrimal branch of the ophthalmic nerve (CN V1). It then travels along the lacrimal branch to reach the lacrimal gland.

__Mucus Glands of the Nasal Cavity, Hard and Soft Palate__ (Maxillary Nerve) To reach the mucus glands of the nasal cavity and palate, parasympathetic fibers must travel from the brain stem through the auditory meatus, geniculate ganglion, greater petrosal nerve, pterygoid canal and synapse at the pterygopalatine ganglion. There postganglionic fibers travel along branches of the maxillary nerve (CN V2), traveling along any branches that supply a mucus membrane: pharyngeal, nasal, nasal septum, greater and lesser palatine, anterior and posterior superior alveolar, and infraorbital branches.

__Submandibular and Sublingual Glands__ (Lingual Nerve of Mandibular Nerve) To reach the mucus submandibular and sublingual glands, parasympathetic fibers must travel from the brain stem through the auditory meatus, geniculate ganglion, facial canal, and chorda tympani. The chorda tympani joins with the lingual branch of the mandibular branch of the trigeminal nerve (CN V3). The parasympathetics continue on the lingual branch and jump off to synapse at the submandibular ganglion. Postganglionic parasympathetic fibers then either go to innervate the submandibular gland or jump back on the lingual branch, traveling to innervate the sublingual gland.

__Parotid Gland__ (Auriculotemporal of Mandibular Nerve) To reach the parotid gland, parasympathetic fibers must travel from the brain stem through the jugular foramen, superior and inferior glossopharyngeal ganglion, tympanic branch, lesser petrosal nerve and synapse in the otic ganglion. Postganglionic parasympathetic fibers then travel along the auriculotemporal branch of the mandibular branch of the trigeminal nerve (CN V3) and jump off to innervate the parotid gland.