CRANIAL NERVES COMPONENTS

1. CRANIAL NERVES COMPONENTS By: Dr. Mujahid Khan

2. Oculomotor Nerve Oculomotor nerve contains somatic motor neurons which innervate extraocular muscles and preganglionic parasympathetic neurons Control the smooth muscle within the eye The motor neurons serving the extraocular muscles have their cell bodies in the ocular nucleus Lie at the base of the periaqueductal grey of the midbrain at the level of superior colliculus

3. Oculomotor Nerve Preganglionic parasympathetic neurons arise from the nearby Edinger-Westphal nucleus Oculomotor nerve runs in the wall of the cavernous sinus Enters orbit through the superior orbital fissure It supplies all the extraocular muscles except superior oblique and lateral rectus

5. Oculomotor Nerve It also innervates the striated muscle of the levator palpebrae superioris Preganglionic parasympathetic neurons terminate in the ciliary ganglion Post ganglionic neurons run in the short ciliary nerves to innervate the sphincter pupillae muscle of the iris and the ciliary muscle contained in the ciliary body

6. Trochlear Nerve It contains only somatic motor neurons These arise in the trochlear nucleus, which lies in the midbrain periaqueductal grey at the level of inferior colliculus It emerges from the dorsal aspect of the brainstem Runs in the lateral wall of the cavernous sinus Enters the orbit through the superior orbital fissure to supply the superior oblique Moves the eyeball downward and medially

8. Abducens Nerve Contains only somatic motor neurons Cell bodies of origin are located in abducens nucleus, which lies beneath the floor of the fourth ventricle in caudal pons Emerge from the ventral surface of the brainstem at the junction between pons and pyramid of the medulla Enters the orbit through superior orbital fissure Supplies the lateral rectus muscle , which abducts the eye

9. Trigeminal Nerve It has both sensory and motor components It is the main sensory nerve for the head and the muscles of mastication It attaches to the brainstem as two adjacent roots (sensory & motor) on the ventrolateral aspect of the pons Its sensory fibers are primary sensory neurons whose peripheral processes are distributed via ophthalmic, maxillary and mandibular divisions

11. Trigeminal Nerve Sensations of touch, pressure, pain and temperature are relayed from the face and scalp, the cornea, the nasal and oral cavities, including teeth and gums and the cranial dura mater Proprioceptive fibers are carried from the muscles of mastication and the TMJ Cell bodies of afferent are located in trigeminal ganglion except those carrying proprioception

13. Trigeminal Nerve The central processes of these cells terminate in the trigeminal sensory nucleus This nucleus extends throughout the length of the brainstem and into the upper cervical cord It consists of three nuclei: chief or principal sensory nucleus, mesencephalic nucleus and the spinal nucleus

15. Trigeminal Nerve There is a segregated distribution of afferent fiber termination in the trigeminal nucleus Fibers conveying touch and pressure terminate in the principal nucleus Fibers carrying pain and temperature end in the spinal nucleus Proprioceptive afferents from the muscles of mastication and TMJ have their cell bodies in the trigeminal ganglion

16. Trigeminal Nerve The motor axons of the trigeminal nerve arise from cells in the trigeminal motor nucleus which lies in the pontine tegmentum Axons leave the pons in the motor root of the trigeminal and then join the mandibular division They innervate various muscles but most significant are the muscles of mastication masseter, temporalis, lateral and medial pterygoid

17. Facial Nerve Facial nerve contains sensory, motor and parasympathetic components It joins the brainstem at the ventrolateral aspect of the caudal pons, near the pontomedullary junction The nerve consists of two routes: more lateral is sensory and parasympathetic fibers and more medial is motor

18. Facial Nerve The sensory fibers of the facial nerve supply taste sensation from the anterior two-thirds of the tongue, the floor of the mouth, and palate The cell bodies of primary afferent neurons lie in the geniculate ganglion Motor fibers of facial nerve originate in the facial motor nucleus of the caudal pontine tegmentum

20. Facial Nerve The axons initially pass dorsally, looping over the abducens nucleus beneath the floor of the fourth ventricle Motor fibers are distributed to the muscles of facial expression, platysma, stylohyoid, the posterior belly of digastric muscle and stapedius Facial motor nucleus receives afferents from other brainstem areas for the mediation of certain reflexes

22. Facial Nerve Reflex connections are established, which mediate protective eye closure in response to visual stimuli or tactile stimulation of the cornea (corneal reflex) Corticobulbar fibers from motor cortical areas innervate the facial motor nucleus Those controlling motor neurons which supply the muscles of the upper face (frontalis, orbicularis oculi) are distributed bilaterally

23. Facial Nerve Those which control the motor neurons supplying the muscles of the lower face are entirely crossed Unilateral upper motor neuron therefore give rise to paralysis of the lower facial muscles Preganglionic parasympathetic fibers of facial nerve originate in the superior salivatory nucleus of the pons Post ganglionic fibers from the pterygopalatine ganglion innervate the lacrimal gland and the nasal and oral mucous membranes

25. Vestibulocochlear Nerve It is a sensory nerve Conveys impulses from the inner ear Has two components: Vestibular nerve carries information related to position and movement of the head Cochlear nerve carries auditory information

27. Vestibulocochlear Nerve Both divisions contain the axons of first order sensory neurons Both divisions pass together through the internal auditory meatus Attach to the brainstem at the junction of the medulla and pons, in the region known as the cerebellopontine angle

29. Glossopharyngeal Nerve It is principally a sensory nerve Its afferent fibers convey information from: Receptors for general sensation in the pharynx, posterior third of the tongue, eustachian tube and middle ear Taste buds of the pharynx and posterior third of the tongue Chemoreceptors in the carotid body and baroreceptors in the carotid sinus

31. Glossopharyngeal Nerve Motor component of the glossopharyngeal nerve is small and arises from cells in the rostral part of the nucleus ambiguus Preganglionic parasympathetic fibers in the glossopharyngeal nerve originate in the inferior salivatory nucleus of the rostral medulla

32. Vagus Nerve Its rootlets attach to the lateral aspect of the medulla immediately caudal to the glossopharyngeal nerve The afferent fibers convey: Receptors for general sensation in the pharynx, larynx, esophagus, tympanic membrane, external auditory meatus, concha and external ear

34. Vagus Nerve Chemoreceptors in the aortic bodies and baroreceptors in the aortic arch Receptors widely distributed throughout the thoracic and abdominal viscera Within the brain the receptors for general sensation end in the trigeminal sensory nucleus

35. Vagus Nerve Its motor fibers arise from the nucleus ambiguus of the medulla They innervate the muscles of the soft palate, pharynx, larynx and upper part of esophagus The parasympathetic fibers originate from the dorsal motor nucleus of vagus in the medulla They are distributed widely throughout the cardiovascular, respiratory and gastrointestinal systems

37. Accessory Nerve It is a pure motor nerve Consists of cranial and spinal parts Cranial part emerges from the caudal part of the nucleus ambiguus Spinal part arises from the cervical segments 1-5 Spinal part ascends upward through the foramen magnum

38. Accessory Nerve Then both the roots descend in jugular foramen In the jugular foramen cranial part joins the vagus and are distributed with it to larynx , pharynx and soft palate The spinal root fibers supply to the sternomastoid and trapezius muscles

40. Hypoglossal Nerve It is a pure motor nerve Arises from the hypoglossal nucleus in the floor of the fourth ventricle It innervates both intrinsic and extrinsic muscles of the tongue Hypoglossal nucleus receives afferent from the nucleus solitarius and trigeminal nucleus to control reflex movement of chewing, sucking and swallowing It also receives corticobulbar fibers from the opposite motor cortex