Nerve Supply of Head & Neck
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A brief presentation covering the following topics: 1. Nervous System 2. Nuclei 3. Olfactory Nerve 4. Optic Nerve 5. Oculomotor Nerve 6. Trochlear Nerve 7. Trigeminal Nerve 8. Abducent Nerve 9. Facial Nerve 10. Vestibulocochlear Nerve 11. Glossopharyngeal Nerve 12. Vagus Nerve 13. Accessory Nerve 14. Hypoglossal Nerve Note: Not a substitute for Textbook
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Nerve Supply of Head & Neck
- 1. Nerve Supply of Head & Neck Dr. Aneetinder Kaur PG 1st Year Department of Conservative Dentistry & Endodontics
- 2. Contents ā¢ Introduction to Nervous System ā¢ Nuclei ā¢ Olfactory Nerve ā¢ Optic Nerve ā¢ Oculomotor Nerve ā¢ Trochlear Nerve ā¢ Trigeminal Nerve ā¢ Abducent Nerve ā¢ Facial Nerve ā¢ Vestibulocochlear Nerve ā¢ Glossopharyngeal Nerve ā¢ Vagus Nerve ā¢ Accessory Nerve ā¢ Hypoglossal Nerve
- 4. NERVOUS SYSTEM ā¢ It is the chief controlling & coordinating system of the body ā¢ There are about 200 billion neurons in an adult brain ā¢ The sensory part collects information from surroundings & helps in gaining knowledge & experience. ā¢ The motor part is responsible for responses of the body. NERVOUS SYSTEM Central nervous system Brain Spinal cord Peripheral nervous system 1.Motor division ā¢Somatic nervous system 1.Autonomous nervous system Sensory division Inderbir Singh's Textbook of Human Neuroanatomy
- 5. Inderbir Singh's Textbook of Human Neuroanatomy
- 6. STRUCTURE OF NEURON ā CELL BODY ā Form grey matter & nuclei in CNS, ganglia in PNS ā CELL PROCESSES ā Dendrites- multiple, short, richly branched ā Axons Inderbir Singh's Textbook of Human Neuroanatomy
- 7. CLASSIFICATION OF NEURONS A/c to number of processes UNIPOLAR NEURONS Mesencephalic nucleus of fifth nerve BIPOLAR NEURONS First neuron of retina, ganglia of eighth nerve and olfactory mucosa PSEUDOUNIPOLAR NEURONS Dorsal nerve root ganglia and sensory ganglia of cranial nerves MULTIPOLAR NEURONS All motor and internuncial neurons Inderbir Singh's Textbook of Human Neuroanatomy
- 8. Inderbir Singh's Textbook of Human Neuroanatomy FUNCTIONAL CLASSIFICATION OF NEURONS Sensory neurons Primary neurons Secondary neurons Tertiary neurons Motor neurons Somatic motor neurons Autonomic neurons
- 9. PERIPHERAL NERVOUS SYSTEM CRANIAL NERVES 1) Olfactory Nerve 2) Optic Nerve 3) Oculomotor Nerve 4) Trochlear Nerve 5) Trigeminal Nerve 6) Abducent Nerve 7) Facial Nerve 8) Vestibulocochlear Nerve 9) Glossopharyngeal Nerve 10) Vagus Nerve 11) Accessory Nerve 12) Hypoglossal Nerve ā Spinal nerves 31 pairs ā¢ Cervical ā 8 ā¢ Thoracic -12 ā¢ Lumbar -5 ā¢ Sacral -5 ā¢ Coccygeal -1 Inderbir Singh's Textbook of Human Neuroanatomy
- 10. ATTACHMENT OF NERVES TO BRAIN ORIGIN ā¢ 1,2 : forebrain ā¢ 3,4: midbrain ā¢ 5 : pons ā¢ 6,7,8 : jun.between pons and medulla ā¢ 9,10,11,12 : medulla Inderbir Singh's Textbook of Human Neuroanatomy
- 11. NUCLEI
- 12. Inderbir Singh's Textbook of Human Neuroanatomy
- 13. Inderbir Singh's Textbook of Human Neuroanatomy
- 14. Inderbir Singh's Textbook of Human Neuroanatomy
- 15. OLFACTORY NERVE First cranial nerve concerned with smell pathway
- 16. Inderbir Singh's Textbook of Human Neuroanatomy
- 18. BD Chaurasias human anatomy volume ā ANOSMIA-loss of olfaction ā with ageing ā occurs in severe injuries which results in separation of olfactory bulb from the olfactory nerves & the nerve gets torn. ā Temporary in allergic rhinitis ā Frontal lobe abscess presses on the olfactory bulb ā UNCINATE FITS- Lesions of lateral olfactory area may cause temporal lobe epilepsy or uncinate fits which are characterized by imaginary disagreeable odors with involvement of tongue & lips.
- 20. OPTIC NERVE ā¢ Second cranial nerve ā¢ Associated with sight
- 21. Inderbir Singh's Textbook of Human Neuroanatomy
- 22. Inderbir Singh's Textbook of Human Neuroanatomy OPTIC PATHWAY STRUCTURES IN VISUAL PATHWAY ā¢ Retina ā¢ Optic Nerve ā¢ Optic Chiasma ā¢ Optic Tract ā¢ Lateral Geniculate Body ā¢ Optic Radiation ā¢ Visual Area In Cortex
- 24. ā * SCOTOMA- Lesion in the retina forms blind spots ā OPTIC NERVE DAMAGE- Complete blindness of eye ā PAPILLOEDEMA- Results due to increased intracranial pressure & leads to swelling of optic disc ā OPTIC NEURITIS- Lesion of optic nerve resulting in visual acuity Inderbir Singh's Textbook of Human Neuroanatomy
- 25. Indian Jouranl of Opthamology
- 26. Dovepress Journal of eye and brain
- 27. OCULOMOTOR NERVE Third cranial nerve supplies extraocular as well as intraocular muscles
- 28. Inderbir Singh's Textbook of Human Neuroanatomy
- 29. Inderbir Singh's Textbook of Human Neuroanatomy
- 30. Inderbir Singh's Textbook of Human Neuroanatomy COURSE INTRANEURAL COURSE Fibres arise from nucleus & pass ventrally BASE OF BRAIN Attached to oculomotor sulcus CAVERNOUS SINUS IN THE ORBIT through middle part of superior orbital fissure UPPER DIVISION supplies superior rectus & part of levator palpebrae superioris. LOWER DIVISION Medial rectus, inferior rectus, inferior oblique
- 31. Inderbir Singh's Textbook of Human Neuroanatomy
- 33. Inderbir Singh's Textbook of Human Neuroanatomy ā Paralysis of third nerve results in- ā Ptosis (dropping of upper eyelid- LPS affected) ā lateral squint, ā dilatation of pupil (fixed pupil ) ā loss of accommodation ā , diplopia, ā slight proptosis ā Superior divisonal occulomotor nerve palsy can also be caused by fronto-ethmoidal sinusitis ā COMPRESSION OF OCCULOMOTOR NERVE- It can be due to extradural haematoma which leads to dilatation of pupil.
- 35. TROCHLEAR NERVE ļ§ Fourth cranial nerve ļ§Supplies only the superior oblique muscle of the eyeball
- 36. Inderbir Singh's Textbook of Human Neuroanatomy
- 37. Inderbir Singh's Textbook of Human Neuroanatomy COURSE & DISTRIBUTION
- 38. Inderbir Singh's Textbook of Human Neuroanatomy
- 39. TRIGEMINAL NERVE ā¢ Dentists nerve ā¢ Largest cranial nerve ā¢ Nerve of first brachial arch
- 40. Inderbir Singh's Textbook of Human Neuroanatomy
- 41. Inderbir Singh's Textbook of Human Neuroanatomy
- 42. DIVISIONS OF TRIGEMINAL NERVE TRIGEMINAL NERVE Ophthalmic nerve Carries sensory fibres from structures derived from frontonasal process Maxillary nerve Conveys afferent fibres from structures derived from maxillary process Mandibular nerve Carries sensory fibres derived from mandibular process Inderbir Singh's Textbook of Human Neuroanatomy
- 43. Inderbir Singh's Textbook of Human Neuroanatomy
- 44. Inderbir Singh's Textbook of Human Neuroanatomy
- 45. Inderbir Singh's Textbook of Human Neuroanatomy
- 46. x
- 47. Inderbir Singh's Textbook of Human Neuroanatomy
- 48. Cunninghamās Manual of Practical Anatomy
- 49. Inderbir Singh's Textbook of Human Neuroanatomy
- 50. Cunninghamās Manual of Practical Anatomy
- 52. (Ref- Christian Nordqvist-Trigeminal neuralgia- Symptoms, causes & treatment-Medical news today- 23 August 2017) ļ TRIGEMINAL NEURALGIA ā Trigeminal neuralgia (TN) is a relatively rare neuropathic disorder, characterized by extremely painful episodic facial pain involving one or more trigeminal nerve branches. ā Based on the International Classification of Headache Disorders- 3rd Edition (ICHD-3) TN is classified into three: Classical TN, Secondary TN, and Idiopathic TN, based on the presence or absence of an apparent disease process that could explain the neuralgia ā Flaccid paralysis of muscles of mastication ļ Hypoacusis- Partial deafness to low pitched sounds due to paralysis of tensor tympani muscle ļ ATYPICAL TRIGEMINAL NEURALGIA- It is a variation of typical TN. Pain may be burning, aching, cramping rather than sharp & stabbing. It occurs on one side of face & extends into upper neck or back of scalp. ā Quality of pain related to TN is described as electric shock-like, sharp, stabbing, or shooting, often triggered by immaterial sensory input such as washing face, brushing, wind blow, and talking
- 53. National Journal of Maxillofacial Surgery
- 54. BMC Oral Health , Clinical characterstics and associated factors of
- 55. Aurstralian Endodontic Journal , Trigeminal nerve injuries infiltration dentistry provides significantly better for pulpal anaesthesia in the anterior mandible compared with inferior dental block (IDBs), is suitable for exodontia in adults and children , is ideal for implant surgery is suitable for periodontal surgery ,improved patient comfort. Patients will undoubtedly prefer having full lingual sensation and shorter duration LA anaesthesia after dental treatment
- 56. ABDUCENT NERVE Sixth cranial nerve which supplies the lateral rectus muscle of the eyeball.
- 57. Inderbir Singh's Textbook of Human Neuroanatomy
- 58. Inderbir Singh's Textbook of Human Neuroanatomy
- 59. Journal of Ophthalmic & Vision Research, 8(2), 160ā171. 3. Bagheri, A., Babsharif, B., Abrishami, M., Salour, H., & Aletaha, ā Failure of abduction of the affected eye ā Commonest false localising sign with raised intracranial pressure ā Diplopia due to paralysis of right lateral rectus muscle
- 60. FACIAL NERVE Seventh cranial nerve Nerve of second branchial arch
- 61. Inderbir Singh's Textbook of Human Neuroanatomy
- 62. Inderbir Singh's Textbook of Human Neuroanatom
- 63. Inderbir Singh's Textbook of Human Neuroanatomy
- 64. Inderbir Singh's Textbook of Human Neuroanatomy
- 66. https://www.health.harvard.edu/pain/bells-palsy-overview ā¢ BELLS PALSY- Sudden paralysis of facial nerve at stylomastoid foramen causes inability to close mouth, asymmetry at corner of mouth, loss of wrinkling on forehead. ā¢ Lesion at chorda tympani nerve- bells palsy+ loss of taste sensation from ant two-third of tongue ā¢ UPPER MOTOR NEURON PALSY- Paralysis of contralateral lower quadrant of face ā¢ LOWER MOTOR NEURON PALSY- Paralysis of ipsilateral half of face ā¢ CROCODILE TEARS SYNDROME- Lacrimation occurs during eating due to abberant regeneration after trauma
- 68. VESTIBULO- COCHLEAR NERVE ļ§ It is the eighth cranial nerve ļ§Comprises of hearing & vestibular parts.
- 69. Inderbir Singh's Textbook of Human Neuroanatomy
- 70. Inderbir Singh's Textbook of Human Neuroanatomy
- 72. BD Chaurasias Human Anatomy Volume 3 ā VERTIGO- Illusion of rotatory movement due to disturbed orientation of body ā TINNITIS- Sensation of buzzing, ringing, hissing or singing quality ā MENIEREāS SYNDROME- Recurrent attacks of tinnitus, vertigo & hearing loss & sensitivity to noises ā ACOUSTIC NEUROMA- Benign tumor that affects nerves running from inner ear to brain Treatment includes- Stereostatic radiosurgery & Microsurgical removal ā DEAFNESS ā CONDUCTIVE DEAFNESS- Failure of sound waves to reach to the cochlea ā SENSORINEURAL DEAFNESS- Failure of production of action potential due to cochlear disease ā CORTICAL DEAFNESS- Bilateral or dominant posterior temporal lobe lesion
- 73. GLOSSOPHARYNGEAL NERVE Ninth cranial nerve Nerve of third branchial nerve
- 74. Inderbir Singh's Textbook of Human Neuroanatomy
- 75. Inderbir Singh's Textbook of Human Neuroanatomy
- 77. BD chaurasias Human Anatomy volume 3 ļ§ GLOSSOPHARYNGEAL NEURALGIA- Short, sharp severe attacks of pain affecting posterior part of pharynx ļ§ Pharyngitis causes referred pain to ear ļ§ Lesions cause ā Absence of parotid secreations , post 1/3rd tongue taste loss ā Loss of pain sensations from tongue , tonsils ,pharynx , soft palate ā Absent gag reflex
- 78. VAGUS NERVE Tenth cranial nerve with extensive course through head, neck, thorax & abdomen
- 79. Inderbir Singh's Textbook of Human Neuroanatomy
- 80. Inderbir Singh's Textbook of Human Neuroanatomy
- 81. Inderbir Singh's Textbook of Human Neuroanatomy Superior ganglionbranches ā¢ Meningeal branch ā¢ Auricular branch Inferior ganglion branches ā¢ Pharyngeal branches ā¢ Superior laryngeal nerve -external laryngeal nerve -internal laryngeal nerve ā¢ Recurrent laryngeal nerve ā¢ Cervical carotid branches ā¢ Anterior oesophageal plexus ā¢ Gastric , celiac ,hepatic branches
- 82. BD Chaurasias Human Anatomy Volume 3 ā¢ Irritation of auricular branch of vagus in external ear causes ā¢ Persistent cough ā¢ Vomiting ā¢ Sudden cardiac inhibition ā¢ Sensory ganglion may have viral infection of herpes zoster & vesicles appear. ā¢ Recurrent laryngeal nerve paralysis causes hoarseness & dysphonia ā¢ Tested clinically by comparing palatal arches on both sides. On paralyzed side, no arching is present & uvula is pulled to normal side. ā¢ Nasal regurgitation of liquids ā¢ Nasal twang & hoarseness of voice ā¢ Flattening of palatal arch ā¢ Vocal cords in cadaveric position ā¢ Dysphagia
- 83. ACCESSORY NERVE ā¢ Eleventh cranial nerve ā¢ Has a cranial & a spinal root
- 84. Inderbir Singh's Textbook of Human Neuroanatomy
- 86. https://www.physio-pedia.com/Adult-onset_Idiopathic_Torticollis ā Drooped shoulder and inability to turn chin to opposite side in lesions of spinal root ā Torticollis / wry neck due to irritation while lymphnode biopsy
- 87. HYPOGLOSSAL NERVE ā¢ Twelfth cranial nerve that supplies the muscles of tongue
- 88. Inderbir Singh's Textbook of Human Neuroanatomy
- 90. BD Chaurasias Human Anatomy Volume 3 Clinically tested by asking patient to protrude his tongue. If the nerve is paralyzed the tongue deviates to paralyzed side ā SUPRANUCLEAR LESION ā Paralysis without wasting ā Tongue moves sluggishly ā Defective speech ā Tongue deviates to opposite side on protrusion ā INFRANUCLEAR LESION ā Paralysis of tongue on that side ā Gradual atrophy of paralyzed half of tongue ā Tongue looks shrunken
- 91. Snellās Clinical Anatomy by Region NERVE SUPPLY OF FACE
- 92. REFERNCES ā¢ Inderbir Singh's Textbook of Human Neuroanatomy ā¢ BD Chaurasia Human Anatomy volume 3 ā¢ Snellās Clinical Anatomy by Region ā¢ Cunninghamās Manual of Practical Anatomy ā¢ https://hms.harvard.edu/news/how-covid-19-causes-loss-smell ā¢ Dovepress Journal of eye and brain ā¢ Indian Jouranl of Opthamology ā¢ Christian Nordqvist-Trigeminal neuralgia- Symptoms, causes & treatment-Medical news today- 23 August 2017 ā¢ Journal of Ophthalmic & Vision Research, 8(2), 160ā171. 3. Bagheri, A., Babsharif, B., Abrishami, M., Salour, H., & Aletaha, ā¢ Aurstralian Endodontic Journal , Trigeminal nerve injuries ā¢ BMC Oral Health , Clinical characterstics and associated factors of trigeminal neuralgia ā¢ https://www.health.harvard.edu/pain/bells-palsy-overview ā¢ https://www.physio-pedia.com/Adult-onset_Idiopathic_Torticollis
Editor's Notes
- Autonomous nervous system - involuntary Sympathetic nervous system Parasympathetic nervous system Enteric nervous system Somatic nervous system - voluntary Sympathetic nervous system Origin ā thoracolumbar outflow : T2 āL2-L3 Widely distributed Adrenergic system Parasympathetic nervous system Origin ā craniosacral outflow : 3,7,9,10 , S2-S4 In head ,neck and trunk Cholinergic system It innervates viscera ENTERIC NERVOUS SYSTEM * GIT *Pancreas *Gall bladder
- According to Area of Innervation ā¢ Somatic afferent fibres: Carry impulses from skin, bones, muscles, and joints to the CNS ā¢ Somatic efferent fibres: Carry impulses from CNS to the skeletal muscles ā¢ Visceral afferent fibres: Carry impulses from visceral organs and blood vessels to the CNS ā¢ Visceral efferent fibres: Carry impulses from CNS to the cardiac muscle, glands, and smooth muscles According to Diameter and Velocity of Conduction ā¢ A (subdivided into Ī±, b, g, Ī“) ā¢ B ā¢ C (unmyelinated) Sensory nerve fibres are also classified into I, II, III and IV Details of diameter and conduction velocity in the peripheral nerves with examples are given in Table 1.4. Presence of myelin sheath ā¢ Myelinated ā¢ Unmyelinated
- 1,2,8 : pure sensory 3,4,6,11,12 : pure motor Rest : mixed
- Sensory nucleus of the trigeminal nerve The sensory nucleus of the trigeminal nerve is a large cell group that receives the primary afferents of the trigeminal nerve. It extends caudally into the cervical spinal cord and rostrally into the midbrain; its principal divisions are the spinal trigeminal, principal sensory and mesencephalic nuclei (see Figs 21.10ā21.12) (Nieuwenhuys et al 2008; Olszewski 1950). On entering the pons, the fibres of the sensory root of the trigeminal nerve run dorsomedially towards the principal sensory nucleus, which is situated at this level. Before reaching the nucleus, approximately 50% of the fibres divide into ascending and descending branches; the others ascend or descend without division. The descending fibres, of which 90% are less than 4 Āµm in diameter, form the spinal tract of the trigeminal nerve, which embraces the spinal nucleus of the trigeminal nerve and reaches the upper cervical spinal cord (see Figs 21.6ā21.8; Fig. 21.10). There is a precise somatotopic organization within the tract (see Fig. 21.1). Fibres from the ophthalmic division of the trigeminal nerve lie ventrally, those from the mandibular division lie dorsally, and those from the maxillary division lie between. The tract is completed on its dorsal rim by fibres from the sensory roots of the facial, glossopharyngeal and vagus nerves. All of these fibres synapse in the pars caudalis of the spinal nucleus of the trigeminal nerve. The detailed anatomy of the spinal tract of the trigeminal nerve excited early clinical interest because it was recognized that dissociated sensory loss could occur in the trigeminal area. For example, in Wallenbergās syndrome (lateral medullary syndrome), occlusion of the posterior inferior cerebellar artery (a branch of the vertebral artery) leads to loss of pain and thermal sense on the ipsilateral half of the face with retention of common sensation (Haines 2013). Neurosurgery in this region, as early as the 1890s, attempted to alleviate paroxysmal trigeminal neuralgia. The introduction of medullary tractotomy confirmed that dissociated thermoanalgesia of the face was associated with destruction of the tract. There are conflicting opinions on the pattern of termination of the fibres in the spinal nucleus. It has long been held that fibres are organized rostrocaudally within the tract. According to this view, ophthalmic fibres are ventral and descend to the lower limit of the first cervical spinal segment, and maxillary fibres are central and do not extend below the medulla oblongata, whilst mandibular fibres are dorsal and do not extend much below the mid-medullary level. The results of section of the spinal tract in cases of severe trigeminal neuralgia support this distribution. It was found that a section 4 mm below the obex rendered the ophthalmic and maxillary areas analgesic, but tactile sensibility, apart from the abolition of ātickleā, was much less affected. To include the mandibular area it was necessary to section at the level of the obex. More recently, it has been proposed that fibres are arranged dorsoventrally within the spinal tract. There appear to be sound anatomicophysiological and clinical reasons for believing that all divisions terminate throughout the whole nucleus, although the ophthalmic division may not project fibres as far caudally as the maxillary and mandibular divisions. Fibres from the posterior face (adjacent to C2) terminate in the lower (caudal) part, whilst those from the upper lip, mouth and nasal tip terminate at a higher level. This can give rise to a segmental (cross-divisional) sensory loss in syringobulbia. Tractotomy of the spinal tract, if carried out at a lower level, can spare the perioral region, a finding that would accord with the āonion-skinā pattern of loss of pain sensation. However, in clinical practice, the progression of anaesthesia on the face is commonly ādivisionalā rather than strictly āonion-skinā in distribution. Fibres of the glossopharyngeal, vagus and facial nerves subserving common sensation (general somatic afferent) enter the dorsal region of the spinal tract of the trigeminal nerve and synapse with cells in the caudal part of the spinal nucleus. Consequently, operative section of the dorsal part of the spinal tract results in analgesia that extends to the mucosa of the tonsillar sinus, the posterior third of the tongue and adjoining parts of the pharyngeal wall (supplied by the glossopharyngeal nerve), and the cutaneous areas of the ear. Other afferents that reach the spinal nucleus are from the dorsal roots of the upper cervical nerves and from the sensoryāmotor cortex. The spinal nucleus of the trigeminal nerve consists of three parts: the pars oralis (which adjoins the principal sensory nucleus); the pars interpolaris; and the pars caudalis (which is continuous with the dorsal horn of the spinal cord). The pars caudalis is different from the other parts because it has a structure analogous to that of the dorsal horn of the spinal cord, with a similar arrangement of cell laminae (subnuclei zonalis, gelatinosus and magnocellularis), and is involved in trigeminal pain perception. Cutaneous nociceptive afferents and small-diameter muscle afferents terminate in layers I, II, V and VI of the pars caudalis (see Fig. 21.1). Low-threshold mechanosensitive afferents of AĪ² neurones terminate in layers III and IV of the pars caudalis and in the rostral (interpolaris, oralis, principal sensory) nuclei. Many of the neurones in the pars caudalis that respond to cutaneous or tooth-pulp stimulation are also excited by stimulation of jaw or tongue muscles. This indicates that convergence of superficial and deep afferent inputs via wide-dynamic-range or nociceptive-specific neurones occurs in this nucleus. Similar convergence of superficial and deep inputs occurs in the rostral nuclei and may account for the poor localization of trigeminal pain, and for the spread of pain, which often makes diagnosis difficult. There are distinct subtypes of cells in lamina II. Afferents from āhigher centresā arborize within it, as do axons from nociceptive and low-threshold afferents. Descending influences from these higher centres include fibres from the periaqueductal grey matter and from the nucleus raphe magnus and associated reticular formation. The nucleus raphe magnus projects directly to the pars caudalis, probably via enkephalin, noradrenaline (norepinephrine) and 5-HT (5-hydroxytryptamine, serotonin)-containing terminals. These fibres directly, or indirectly through local interneurones, influence pain perception. Stimulation of periaqueductal grey matter or nucleus raphe magnus inhibits the jaw-opening reflex to nociception, and may induce primary afferent depolarization in tooth-pulp afferents and other nociceptive facial afferents. Neurones in the pars caudalis can be suppressed by stimuli applied outside their receptive field, particularly by noxious stimuli. The pars caudalis is an important site for relay of nociceptive input and functions as part of the pain āgate controlā. However, rostral nuclei may also have a nociceptive role. Tooth-pulp afferents via widedynamic-range and nociceptive-specific neurones may terminate in rostral nuclei, which all project to the subnucleus caudalis. Most fibres arising in the trigeminal sensory nuclei cross the midline and ascend as trigeminothalamic fibres (trigeminal lemniscus). They end in the contralateral ventral posteromedial thalamic nucleus, from which third-order neurones project to the cortical postcentral gyrus (areas 3, 1, 2). However, some trigeminal nuclear efferents ascend to the ipsilateral ventral posteromedial nucleus. Fibres from the pars caudalis, especially from laminae I, V and VI, also project to the rostral trigeminal nuclei, cerebellum, periaqueductal grey of the midbrain, parabrachial area of the pons, the brainstem reticular formation and the spinal cord. Fibres from lamina I project to the subnucleus medius of the medial thalamus Vagal nucleus The vagal nucleus (the dorsal motor nucleus of the vagus) lies slightly dorsolateral to the hypoglossal nucleus, from which it is separated by the nucleus intercalatus. It extends caudally to the first cervical spinal segment and rostrally to the open part of the medulla under the vagal trigone in the floor of the fourth ventricle (see Fig. 21.8). The vagal nucleus is a general visceral efferent nucleus and is the largest parasympathetic nucleus in the brainstem. Most (80%) of its neurones give rise to the preganglionic parasympathetic fibres of the vagus nerve. The remainder are interneurones or project centrally. The vagal nucleus innervates the non-striated (smooth, cardiac) muscle of the viscera of the thorax (heart, bronchi, lungs and oesophagus) and abdomen (stomach, liver, pancreas, spleen, small intestine and proximal part of the colon), and glandular epithelium. Neurones within the nucleus are heterogeneous and can be classified into nine subnuclei, which are regionally grouped into rostral, intermediate and caudal divisions. Topographic maps of visceral representation in animals suggest that the heart and lungs are represented in the caudal and lateral part of the nucleus, the stomach and pancreas in intermediate regions, and the remaining abdominal organs in the rostral and medial part of the nucleus. There is a sparse sensory afferent supply, which arises in the nodose ganglion and projects directly to the nucleus and possibly beyond into the nucleus tractus solitarius. Hypoglossal nucleus The prominent hypoglossal nucleus lies near the midline in the dorsal medullary grey matter. It is approximately 2 cm long. Its rostral part lies beneath the hypoglossal trigone in the floor of the fourth ventricle (see Fig. 21.5) and its caudal part extends into the closed part of the medulla. The hypoglossal nucleus consists of large motor neurones interspersed with myelinated fibres. It is organized into dorsal and ventral nuclear tiers, each divisible into medial and lateral subnuclei. There is a musculotopic organization of motor neurones within the nuclei that corresponds to the structural and functional divisions of tongue musculature. Thus, motor neurones innervating tongue retrusor muscles are located in dorsal/dorsolateral subnuclei, whereas motor neurones innervating the main tongue protrusor muscle are located in ventral/ ventromedial regions of the nucleus. Although relatively little is known about the organization of motor neurones innervating the intrinsic muscles of the tongue, experimental evidence suggests that motor neurones of the medial division of the hypoglossal nucleus innervate tongue muscles that are orientated in planes transverse to the long axis of the tongue (transverse and vertical intrinsics and genioglossus), whereas motor neurones of the lateral division innervate tongue muscles that are orientated parallel to this axis (styloglossus, hyoglossus, superior and inferior longitudinal). Hypoglossal fibres emerge ventrally from their nucleus, traverse the reticular formation lateral to the medial lemniscus, pass medial to the inferior olivary nuclei, and curve laterally to emerge as a linear series of 10ā15 rootlets in the ventrolateral sulcus between the pyramid and olivary eminence (see Fig. 21.8). The hypoglossal nucleus receives corticonuclear fibres from the precentral gyrus and adjacent areas of predominately the contralateral hemisphere. They synapse either on motor neurones of the nucleus directly or on interneurones. Evidence indicates that the most medial hypoglossal subnuclei may receive projections from both hemispheres. The nucleus may connect with the cerebellum via adjacent perihypoglossal nuclei, and perhaps also with the medullary reticular formation, the trigeminal sensory nuclei and the nucleus solitarius. Inferior olivary nucleus The olivary nuclear complex consists of a large principal olivary nucleus and smaller medial accessory and dorsal accessory olivary nuclei (see Figs 21.8, 21.10). They are also precerebellar nuclei, a group that includes the pontine, arcuate, vestibular, reticulocerebellar and spinocerebellar nuclei, all of which receive afferents from specific sources and project to the cerebellum. The inferior olivary nucleus contains small neurones, most of which form the olivocerebellar tract, which emerges primarily from the hilum to run medially and intersect the medial lemniscus (see Fig. 21.8). Its fibres cross the midline and sweep either dorsal to, or through, the opposite olivary nuclei. They intersect the lateral spinothalamic and rubrospinal tracts and the spinal nucleus of the trigeminal nerve, and enter the contralateral restiform body (and eventually the inferior cerebellar peduncle), where they constitute its major component. Fibres from the contralateral inferior olivary complex terminate on Purkinje cells in the cerebellum as climbing fibres; there is a one-to-one relationship between Purkinje cells and neurones in the complex (Nieuwenhuys et al 2008). Afferent connections to the inferior olivary nuclei are both ascending and descending. Ascending fibres, Nucleus solitarius The nucleus solitarius (solitary nucleus, nucleus of the solitary tract) lies lateral or ventrolateral to the vagal nucleus (see Fig. 21.8). A neuronal group ventrolateral to the nucleus solitarius has been termed the nucleus parasolitarius. The nucleus solitarius is intimately related to, and receives fibres from, the tractus solitarius, which carries afferent fibres from the facial, glossopharyngeal and vagus nerves (Ciriello 1983, Haines 2013, Hamilton and Norgren 1984). These fibres enter the tract in descending order and convey gustatory information from the lingual and palatal mucosa. They may also convey visceral impulses from the pharynx (glossopharyngeal and vagus) and from the oesophagus and abdominal alimentary canal (vagus). There is some overlap in this vertical representation. The nucleus solitarius is thought to project to the sensory thalamus and thence to the cerebral cortex (Hamilton and Norgren 1984). It may also project to the upper levels of the spinal cord through a solitariospinal tract. Secondary gustatory axons cross the midline. Many subsequently ascend the brainstem in association with the medial lemniscus and synapse on the most medial neurones of the ventral posteromedial thalamic nucleus (in a region sometimes termed the accessory arcuate nucleus). Axons from the ventral posteromedial nucleus radiate through the internal capsule to the anteroinferior area of the sensoryāmotor cortex and the insula. It is thought that other ascending paths end in a number of the hypothalamic nuclei, and so mediate the route by which gustatory information may reach the limbic system and allow appropriate autonomic reactions to be made. Nucleus ambiguus The nucleus ambiguus is a group of large motor neurones, situated deep in the medullary reticular formation (see Fig. 21.10). It extends rostrally as far as the upper end of the vagal nucleus, while caudally it is in line with, but is not continuous with, the nucleus of the accessory nerve. Fibres emerging from it pass dorsomedially, then curve laterally. Rostral fibres join the glossopharyngeal nerve. Caudal fibres join the vagus and are distributed to the pharyngeal constrictors, intrinsic laryngeal muscles and striated muscles of the palate and upper oesophagus. The nucleus ambiguus receives corticonuclear fibres bilaterally with a contralateral preponderance and is connected to many brainstem centres. At its upper end, a small retrofacial nucleus intervenes between it and the facial nucleus. Although the nucleus ambiguus is generally regarded as a special visceral efferent nucleus, it is also a reputed source of general visceral efferent fibres to the vagus. Swallowing and gag reflexes Swallowing is initiated when food or liquid stimulates sensory nerves in the oropharynx and is usually regarded as programmed motor behaviour rather than a reflex. The patterning and timing of striated muscle contraction that occur in the pharynx, larynx and oesophagus during swallowing are generated in the brainstem in a network of neural circuits. The afferent limb is the glossopharyngeal nerve: information is relayed via the nucleus solitarius to the nucleus ambiguus, which contains the motor neurones innervating the muscles of the palate, pharynx and larynx. If stimulation of the oropharynx occurs other than during swallowing, a gag reflex may be initiated. There is a reflex contraction of the muscles of the pharynx, soft palate and fauces that, if extreme, may result in retching and vomiting. Cough and sneeze reflexes The cough reflex is normally initiated by irritation of tracheal or laryngeal mucosae: there is evidence of both mechanosensing and chemosensing cough receptors (McGarvey 2014). Coughing involves a sequence of coordinated events that produce the profound change in breathing pattern needed to expel an irritant from the lower airway. Rapid inspiration is followed by an expiratory effort against a closed glottis, the rapid generation of intrapulmonary pressure and the sudden opening of the glottis and contraction of intercostal and abdominal wall muscles, collectively producing a high-velocity flow of expired air that sweeps irritant material up towards the pharynx in a forceful exhalation (cough). Laryngeal branches of the vagus nerve carrying general visceral afferent information (with cell bodies in the inferior vagal ganglion) terminate in the nucleus of the solitary tract. Second-order neurones project to medullary respiratory centres (including a putative cough centre) and to the nucleus ambiguus, recruiting motor neurones innervating pharyngeal, laryngeal, diaphragmatic, intercostal and abdominal muscles Stimulation of nasal mucosa by physical or chemical irritants initiates a sneezing reflex. Afferent impulses travel via the ethmoidal and maxillary nerves to the spinal nucleus of the trigeminal nerve. Interneurones project to the nucleus ambiguus and a putative āsneezing centreā in the rostral dorsolateral medulla (Seijo-MartĆnez et al 2006). Recruitment of a critical number of inspiratory and expiratory neurones initiates a sneeze, which involves eye closing and deep inspiration, followed by explosive exhalation as described above. If the oropharyngeal isthmus is closed by the action of palatoglossus, the air flow is diverted through the nasal cavity; otherwise the stream of expelled air flows through both oral and nasal cavities.
- : Functional classification of cranial nerve nuclei. The upper figure shows the arrangement of nuclear columns in the brainstem of the embryo. The lower figure shows the nuclei derived from each column. Numbers indicate the cranial nerves connected to the nuclei (Abbreviations: SVE, special visceral efferent; GVE, general visceral efferent; GVA, general visceral afferent; SVA, special visceral afferent; GSA, general somatic afferent; SSA, special somatic afferent; SE, somatic efferent)
- arises from the olfactory epithelium in the nasal cavity and terminates directly in cortical and subcortical areas of the frontal and temporal lobes;
- Transmits sense of smell Branches arise from sensory cells of nasal mucosa, enter cranial cavity as olfactory filament through openings of cribriform plate of ethmoid bone Enter olfactory bulb singly Bulb is vestigial of olfactory lobe of macrosmatic mammals.
- The axons of the optic nerve (II) pass into the optic chiasma, where medially positioned axons decussate; all of the axons emerge as the optic tract, which terminates in the lateral geniculate nucleus of the thalamus (
- Second pair of cranial nerve Nerve of visual sense Arise in ganglion cells of retina Enters cranial cavity through optic foramen
- 1 half hemianopia Same half of both eyes homonymous Different half heteronymous
- Contains somatic & parasympathetic visceral efferent fibres Somatic fibres responsible for most of the extrinsic muscles of the eye Parasympathetic fibres relay in ciliary ganglion Postganglionic fibres arising from ciliary ganglion, enter eyeball & supply ciliary muscles or muscles of accommodation & sphincter of pupil Enters orbit through superior orbital fissure
- Supplies : Levator palpebrae superioris Superior , medial ,inferior rectus Inferior oblique
- Fixed pupil ā loss of sympathetic fibres WEBERāS SYNDROME- A midbrain lesion causing contra lateral hemiplegia & ipsilateral paralysis of third nerve
- Carries somatic fibers , motor . supply superior oblique muscle of eyeball / SO 4 Passes through superior orbital fissure Only cranial nerve that emerges from dorsal aspect of brain stem
- Diplopia occurs on looking downwards It results in defective depression of adducted nerve Extorsion of the eyeball
- Diplopia on looking downwards but single vision above horizontal plane
- At meckelās cave ā apex of petrous temporal bone
- 1st branch of V th cranial nerve Purely sensory & smallest of 3 divisions Supplies eyeball, conjunctiva, lacrimal gland, parts of mucous membrane of nose & PNS & skin of forehead, eyelids & nose Divides into 3 main branches just before passing through superior orbital fissure ā Nasocilliary Frontal Lacrimal ā smallest branch
- Neuropathic pain as defined by International Association for the Study of Pain is a type of pain initiated or caused by a primary lesion or dysfunction in the nervous system [1]. It is caused by neural injury or painful states associated with either peripheral or central nerve injury.
- There are relatively few reports on endodontic nerve injuries which may not be limited to those teeth proximal to the IAN canal but may occur in maxillary teeth as well Neuropathic pain (NP) syndromes are chronic pain disorders that develop after a lesion of the peripheral or central nervous structures that are normally involved in signalling pain. The characteristics of NP differ substantially from those of other chronic pain states, that is, chronic nociceptive pain, which develops while the nervous system that is involved in pain processing is intact. As well as the existence of negative somatosensory signs (deficit in function) there other definitive features that are characteristic of neuropathic conditions (allodynia, hyperalgesiaPrevention of endodontic-related neuropathy: risk factors In this cohort, there appeared to be several prominent risk factors which were as follows: ā¢ GDP (80% of referrals) ā¢ Proximity of tooth to IAN canal ā 90% of the mandibular teeth in this series were close to the IAN canal or premolars adjacent to the mental foramen ā¢ Detectable overfill occurred in 60% of cases and over instrumentation during preparation in all cases resulting in one or a combination of ā mechanical injury ā haemorrhagic/ischaemic injury ā chemical injury (Figs 1,2 Why should it be any different in dentistry? We already have the evidence that demonstrates the fact that
- Mixed nerve Contains two nerves ā facial nerve proper and intermediate nerve .
- Seventh cranial nerve of second branchial arch NUCLEI- There are 4 nuclei situated in the lower pons- Motor nucleus or branchiomotor Superior salivatory nucleus or parasympathetic Lacrimatory nucleus Nucleus of tractus solitarius
- Rmsay hunt syndrome ļ SCHIRMER TEST- decrease in lacrimation of 75% or more as compared to normal side. Or < 10mm for both sides at 5 min. ļ STAPEDIAL REFLEX TESTING - if absent , site of lesion between geniculate ganglion and stapedius muscle. If present then site of lesion is distal to stapedius muscle. ļ TASTE TESTING ā conc. Sweet, salt, sour and bitter solution tested along lateral margin of anterior 2/3 of tongue towards tip / electrogustometry ( EGM ) ļ SUBMANDIBULAR GLAND FLOW- compared by sialometry using 6% citric acid. ļ TESTING FACIAL MOVEMENT
- Sensory nerve Has two roots - vestibular and cochlear Vestibular root : impulse from vestibular apparatus /balance Cochlear root : transmit impulse from auditory apparatus /sound Function : transmit sound and equilibrium from internal ear to brain.
- Rinne- base of tuning fork on the mastoid process, ātell me when it stopsā, then bring it to the ear, āCan hear it? ā With nerve deafness the note is audible at the external meatus, as air and bone conduction are reduced equally, so that air conduction is better as is normal. This is termed Rinne-positive. With conduction [middle ear] deafness no note is audible at the external meatus. This is termed Rinne-negative A vibrating tuning fork is placed on the centre of the forehead. Normally the sound is heard in the centre of the forehead. With nerve deafness the sound is transmitted to the normal ear. With conduction deafness the sound is heard louder in the abnormal ear. Patients with defective hearing should be referred for audiometry. This measures the degree of hearing loss at different sound frequencies.
- innitus-the perception of sound in the absence of an actual external sound-represents a symptom of an underlying condition rather than a single diseaseTreatments for tinnitus include pharmacotherapy, cognitive and behavioral therapy, sound therapy, music therapy, tinnitus retraining therapy, massage and stretching,
- Intracranial course: The glossopharyngeal nerve emerges from medulla as a series of rootlets between the olive and inferior cerebellar peduncle. It traverses the posterior cranial fossa and exits through the jugular foramen. Extracranial course: The superior and inferior sensory ganglia are situated on the nerve at the exit. The glossopharyngeal nerve descends in the neck and supplies stylopharyngeus muscle. The nerve then passes between superior and middle constrictors of pharynx and supply the mucosa of the pharynx and posterior one-third of tongue.
- Emerges from lateral surface of medulla oblongata & passes in front of vagus nerve through jugular foramen Contains motor fibres Motor supply to stylopharyngeus muscle & participates with vagus in supplying constrictors of pharynx & palatopharyngeus muscle Sensory supply to parts of tonsil, adjacent pharyngeal mucosa , base of tongue Taste sensation from vallate and foliate papillae
- Intracranial course: The vagus nerve emerges as a series of rootlets in a groove between the olive and inferior cerebellar peduncle. It traverses the posterior cranial fossa and exits the skull through jugular foramen. The superior Figure 6.23: Vagus nerve: Origin, course and distribution (Abbreviations: SVE, special visceral efferent; GVE, general visceral efferent; SVA, special visceral afferent; GVA, general visceral afferent; GSA, general somatic afferent) sensory ganglion of the nerve is located in the jugular foramen. Extracranial course: The inferior ganglion of vagus lies just below the jugular foramen. Just below the inferior ganglion, the cranial root of accessory nerve joins the vagus nerve to be distributed along its pharyngeal and laryngeal branches. In the neck, the vagus lies in the carotid sheath along with the internal jugular vein and common carotid arteries. The right vagus passes posterior to the root of right lung, contributes to pulmonary plexus, and then runs on the posterior surface of oesophagus, contributing to the oesophageal plexus. It enters theabdomen by passing through the oesophageal opening in the diaphragm. It supplies stomach, duodenum, liver, kidneys, small and large intestine up to the junction of proximal two-thirds and distal third of transverse colon. It has a wide distribution in the abdomen via coeliac, superior mesenteric and renal plexuses. The left vagus enters thorax, contributes to pulmonary and oesophageal plexuses, then enters abdomen supplies stomach, liver, duodenum and head of pancreas. Cricothyroid Levator veli palatini Salpingopharyngeus Palatopharyngeus Palatoglossus Palatopharyngeus Superior, middle , inferior pharyngeal constrictor . Muscles of larynx
- Stimulation auricular branch of vagus causes increased appetite
- Cranial root : joins vagus nerve and innervates all laryngeal muscles except cricothyroid Spinal root : innervates trapezius , SCM
- This can be explained as follows. One of the genioglossus muscles, which pull the tongue forward, is paralyzed on the affected side. The other, normal genioglossus muscle pulls the unaffected side of the tongue forward, leaving the paralyzed side of the tongue stationary. The result is the tip of the tongueās deviation toward the paralyzed side. In patients with long-standing paralysis, the muscles on the affected side are wasted, and the tongue is wrinkled on that side