presentation shows what is meant by neurons?, how many cranial nerves are there? and what bis their importance?

1. CRANIAL NERVES
X - VAGUS
1
X - VAGUS
XI -SPINAL ACCESSORY
XII -HYPOGLOSSAL
PRESENTED BY :
DR. MEENAL ATHARKAR
MDS
DEPT OF ENDODONTICS AND CONSERVATIVE DENTISTRY

2. 2
 INTRODUCTION OF NERVOUS SYSTEM
- HISTORY
-NEURON
-CLASSIFICATION OF NERVE FIBERS
- NEUROGLIA
 EMBRYONIC DEVELOPMENT OF
CRANIAL NERVES
CRANIAL NERVES ( X to XII )
CONCLUSION
REFERENCES

3. HISTORY -
By means of nerves, the pathways of the senses are
distributed like the roots and fibers of a
tree."--Alessandro Benedetti, 1497
3
-In the fourth century B.C.,the Greek philosopher Aristotle believed
firmly that the nerves were controlled by and originated in the heart
because it was, in his interpretation, the first organ of the body and
the seat of all motion and sensation.

4. Galen saw the spinal cord as an extension of the brain which
carried sensation to the limbs. He believed that the nerves
controlled the actions of muscles in the limbs, and that the two
principal functions of the nervous system, sensation and motion,
were governed by two different types of nerves: respectively
Soft and Hard.
4
Soft and Hard.

5. 5
 Slightly more than a century later, Master Nicolaus offered a
more precise vocabulary to express the new complexity of the
nervous system, discarding the terms "soft" and "hard" for the
more familiar idea of Sensory and Motor nerves.

6. Harvey wrote in his Lectures on the Whole of Anatomy: "For the
nerves only carry down, they do not act, move, nor are they sentient
by a faculty, but are organs."
Descartes The essence of motor control is, then, the direction of animal
6
Descartes The essence of motor control is, then, the direction of animal
spirits into the proper inter-filamentous channels for transmission to the
proper nerve."

7. The enumerations of the modern 12 pairs of cranial nerves by
a number of anatomists are reviewed in a continuous
historical perspective using original texts and modern
translations. The history of the numeration of the nerves is
traced from Galen's classification into seven pairs (second
century A.D.), through to Willis' nine pairs (1664) and
Soemmerring's 12 pairs (1778).
7
Soemmerring's 12 pairs (1778).

8. One of the regulatory systems, made of millions of
neurons in precise pathways to transmit
electrochemical impulses, and of neuroglial cells
that have several functions, including formation of
myelin sheaths of neurons.
NERVOUS SYSTEM
myelin sheaths of neurons.
8

9. 9NERVOUS SYSTEM
CENTRAL NERVOUS PERIPHERAL NERVOUS
SYSTEM SYSTEM
Brain
Spinal Cord
Neurons
Their Process
- Formed by neurons n neuroglia. - Cranial nerves and spinal
nerves.
Spinal Cord Their Process

10. .
10
PERIPHERAL NERVOUS SYSTEM
SOMATIC NERVOUS SYSTEM
(Includes nerves supplying the
AUTONOMIC NERVOUS SYSTEM
(regulation of visceral or(Includes nerves supplying the
skeletal muscles ) Vegetative functions )
Sympathetic
Parasympatheti
c

11. NEURON :
A nerve cell, the structural and functional unit of the
nervous system.
Neurons function in initiation and conduction
11
Neurons function in initiation and conduction
of impulses.

12. Neuron is made up of 3 parts :
1. Nerve cell body
2.Dendrite
3. Axon
1.NERVE CELL BODY :
- Irregular in shape
- Neuroplasm contains large nucleus , nissle
bodies , neurofibrils, mitochondria and golgi
apparatus.
12
apparatus.
2. Dendrites :
- Branched process .
- Conductive nature .
- Transmits the impulse towards the nerve cell
body.
.

13. 3. AXON : the length of longest axon is about one meter .
- Axons are arranged in different bundles called fasciculi.
-Tubular sheath covering around whole
nerve formed by areolar membrane.
13
nerve formed by areolar membrane.

14. Axoplasm contain mitochondria, neurofibrils, axoplasmic
vesicles.
-Neurotransmitter substances are carried by axonal flow.
-Axons might be insulated by myelin sheath and called
14INTERNAL STRUCTURE OF AXON
AXIS CYLINDER :
-Axons might be insulated by myelin sheath and called
Myelinated Nerve Fibers.
Axis cylinder of nerve fiber is covered by a membrane called
neurilemma ,also called sheath of Schwan (non myelinated
fibers).

15. - Does not form a continuous sheath and is absent in regular
interval .
- Node of Ranvier.
- Segment of nerve fiber between two node is called internode.
-Responsible for white colour of the nerve.
CHEMISTRY :
15
CHEMISTRY :
-Formed by concentric layers of proteins alternating with lipids.

16. A) DEPENDING UPON THE NUMBER OF POLES :
16
A) DEPENDING UPON THE NUMBER OF POLES :

17. 1. Depending upon structure :
Myelinated Non Myelinated
2 Depending upon the distribution :
17
Somatic Nerve Fibers Visceral or Autonomic Nerve
Fibers

18. 3. Depending upon the origin :
Cranial Nerves Spinal Nerves
4. Depending upon functions :
Sensory Nerve Fibers Motor Nerve Fibers
18
5. Depending upon secretion of neurotransmitter :
Adrenergic Nerve Fibers Cholinergic Nerve Fibers

19. 6. DEPENDING UPON THE DIAMETER AND CONDUCTION
( EARLANGER –GASSER CLASSIFICATION )
19
TYPE DIAMETER (µ) VELOCITY OF
CONDUCTION (m/ sec )
1. A alpha 12 TO 24 70 TO 120
2. A beta 6 TO 12 30 TO 70
- Except C fibers all the nerve fibers are myelinated.
2. A beta 6 TO 12 30 TO 70
3. A gamma 5 TO 6 15 TO 30
4. A delta 2 TO 5 12 TO 15
5. B 1 TO 2 3 TO 10
6. C < 1.5 0.5 TO 2

20. EMBRYONIC DEVELOPMENT
20

21. EMBRYONIC DEVELOPMENT
 Neural tube gives rise to brain and spinal cord .
 It is formed from the ectoderm overlying notochord (process is
known as neurulation).
 Cranial is enlarged part of neural tube form brain.
21
 Cranial is enlarged part of neural tube form brain.
 Caudal tubular part forms spinal cord.

22. Nervous Tissue :
 Neurons and many neuroglial cells are formed in neural tube.
 Neural tube is first lined by single layer.
 These cells proliferate to form several layers.
Matrix cell layer/Germinal layer
The cells of this layer give rise to nerve cells ,neuroglial cells .
Mental layer
22
Mental layer
Developing nerve cell -Neuroglial cells.
Marginal zone
It provides a frame work into which the
processes of nerve cells developing in
mantle layer can grow.

23. Stages :
 One of the germinal cell passes from
germinal layer to mantle layer and become
APOLAR NEUROBLAST .
 Two process develop and convert apolar
neuroblast to a bipolar neuroblat .
 One of the process of neuroblast disappear
and it can now be called a unipolar
neuroblast .
23
and it can now be called a unipolar
neuroblast .
Multipolar neuron are formed.
- And these neurons grow into the marginal
layer and becomes the axon of nerve cell.
Neurons may remain in CNS or May grow
out as efferent nerve Fibers of peripheral
nervous system.

24. Formation of Myelin Sheath : 24

25. Formation of Myelin Sheath :
Formation of myelin sheath around axon is called
Myelinogenesis
Starts at 4th month of intrauterine life.
Completed by 2nd year after the birth.
The schwann cells wrap up and rotate around the axis cylinder
in
many concentric layers.
25
many concentric layers.
 Concentric layers fuse to produce the myelin sheath but
cytoplasm.
Outermost membrane of schwann cells remains as neurilemma .
Nucleus of these cells remains in between myelin sheath and
neurilemma.

26. CRANIAL NERVES
Ⅰ Olfactory nerve
Ⅱ Optic nerve
Ⅲ Oculomotor nerve
Ⅳ Trochlear nerve
Ⅴ Trigeminal nerve
Ⅵ Abducent nerve
26
Ⅵ Abducent nerve
Ⅶ Facial nerve
Ⅷ Vestibulocochlear nerve
Ⅸ Glossopharyngeal nerve
Ⅹ Vagus nerve
Ⅺ Accessory nerve
Ⅻ Hypoglossal nerve

27. 27

28. Extensive course.
The fibers of cranial root of XI nerve is also
distributed through it.
28
Motor division of the vagus nerve – basal
plate of the embryonic medulla oblongata.
Sensory division originates- cranial neural
crests.

29. Two ganglia
Superior Inferior
-Round -Cylinderical
29
-Round -Cylinderical
-Juglar foramen -Near the base of skull

30. Functional components
30
a) Special visceral efferent fibers :
- Nucleus ambiguus
- Muscles of palate, pharynx ,larynx.
b) General visceral efferent fibers :
- Dorsal motor nucleus
- Thoracic and abdominal viscera .
c) General visceral afferent fibers :
- Inferior ganglion
- Bring sensation from pharynx ,larynx ,trachea , oesophagus
and from abdominal and thoracic viscera.

31. 31
- These are conveyed by central processes of ganglion cells to
nucleus of tactus solitarius.
- Terminate in dorsal nucleus of vagus.
d) Special visceral afferent fibers :
- Inferior ganglion
- Carry sensation of taste from posterior most part of tongue and
from epiglottis .from epiglottis .
- Terminate in Tractus Solitarius
e) General somatic afferent fibers :
- superior ganglion.
- Skin of external ear.
- Terminate in the relation to spinal nucleus of trigeminal nerve.

32. 32
The vagus nerve includes axons which emerge from or converge onto three nuclei of the medulla

33. NUCLEI
33
1. NUCLEUS AMBIGUUS : A part of cranial root of accessary nerve
: partly of vagus.
2. Dorsal nucleus of vagus (parasympathetic ) :
- Mixed nucleus
- Fibers from main bulk of nerve
3. Nucleus of tractus solitarius ( gustatory) :
- Distributed through internal laryngeal nerve to the taste buds of
epiglottis and vallecula.
4. Nucleus of spinal tract of trigeminal nerve

34. 34

35. 35

36. The vagus nerve descends vertically within the carotid sheath
posterolateral to the internal and common carotid arteries and medial to
the internal jugular vein (IJV) at the root of the neck.
36

37.  Anterior and posterior gastric fibers are mainly formed by
oesophageal complex.
 Anterior gastric fibers – left vagus
 Posterior gastric fibers – right vagus
 The gastric nerves supply all abdominal organs and the
gastrointestinal tract ending just before the left colonic (splenic)
37
gastrointestinal tract ending just before the left colonic (splenic)
plexure.

38. 38
Branches in Head And Neck
Branches in juglar foramen Branches in neck
- Meningeal - Pharyngeal
- Auricular - Carotid- Auricular - Carotid
- Communicating branches - Superior laryngeal
- Right recurrent
laryngeal
- Cardiac

39. 39
Behind IJV
Enters mastoid
canaliculus
It crosses facial
canal 4mm above
stylomastoid
i) Meningeal branch :
- Supply durameter of posterior cranial fossa .
ii) Auricular branch :
- Arise from superior ganglion.
stylomastoid
foramen
It emerges
through
tympanomastoid
fissure
Ends by supplying the choncha,root of
auricle , posterior half of EAM,tympanic
membrane

40. 40
iii) Pharyngeal branch :
- Inferior ganglion
- Chiefly fibers : cranial root of accessary nerve.
- Passes between ECA & ICA .
-Reaches the upper border of middle constrictor pharyngeal plexus .-Reaches the upper border of middle constrictor pharyngeal plexus .
- Supply muscle of pharynx and soft palate except tensor veli
palatine.

41. 41
iv) Carotid branch : carotid sinus and carotid body.
HUMAN ANATOMY , B.D. CHAURASIA 4TH
EDITION

42. 42

43. 43
v) Superior laryngeal nerve :
- Inferior ganglion
- at middle constrictor it divides into two branches
external laryngeal internal laryngeal
- thin - thick
- accomapanies Sup. Thyroid - above the Sup. Laryngeal- accomapanies Sup. Thyroid - above the Sup. Laryngeal
artery vessel
-branches to inf.constrictor - pierces thyrohyoid memb.
and phyrngeal plexus
- supply the mucous membrane
- supply cricothyroid muscles of larynx upto level of
vocal folds.
.

44. vi) Recurrent laryngeal nerve :
44

45. 45
vi) Recurrent laryngeal nerve :
-Winds backwards below the subclavian artery.
-Runs upward and medially behind subclavian and common
carotid arteries to reach the tracheo-oesophageal groove .
-It is relatd to inferior thyroid artery.
-It may be superficial or deep to artery.
-The nerve passes deep to lower border of inferior
constrictor
and enters the larynx behind cricothyroid joint .

46. 46
 It Supplies -
a) Supplies all intrinsic muscles of larynx.
b) Sensory nerves to larynx below vocal cords.
c) Cardiac branches
d) Branches to trachea, oesophagus.
e) Inferior constrictor

47. 47
vii) Left recurrent laryngeal nerve :
- Arise from vagus.
- Crosses the left side of aorta .
- Loops around the ligamentum arteriosum and reaches the tracheo-
esophageal groove.
- Does not have to pass behind the subclavian artery and carotid
arteries.
- Posterior to the inferior thyroid artery.

48. 48
vii) Cardiac branches :
- 4 in number.
SUPERIOR INFERIOR
- 4 in number.
- Left interior branch goes to superficial cardiac plexus.
- The other 3 cardiac nerves go to the deep cardiac plexus.

49. 49
APPLIED ANATOMY :
 Tested clinically by comparing the palatal arches on two sides.
On paralysed site –no arching and uvula is pulled to normal
side.
 Paralysis produces : Paralysis produces :
- Nasal regurgitation of swallowed liquids
-Nasal twang in voice
- Hoarseness of voice
-Flattening of palatal arch
-Dysphagia

50. 50
 Irritation of auricular branch of vagus in external ear may
cause persistent cough, vomiting or even death due to sudden
cardiac inhibition.
 Stimulation of auricular branch –increased appetite.
 Sensory ganglion may have viral infection called Herpes zoster. Sensory ganglion may have viral infection called Herpes zoster.
Vesicles over the skin of auricle.

51. Clinical anatomy
51
- Lesion of an entire vagus nerve is uncommon.
- A)Pharyngeal branches : dysphagia
- B)Superior laryngeal nerve :
 Anesthesia of Sup. part of larynx.
 Paralysis of cricothyroid muscle Paralysis of cricothyroid muscle
 Voice is weak and tires easily
 Lesion of LRN is more common (longer course)
 Proximal lesions of vagus nerve affect pharyngeal and superior
laryngeal nerves , causing difficulty in swallowing.

52. 52
 The two somatic sensory branches of the vagus nerve, the
auricular branch and the superior laryngeal nerve, can also
be the site of a rare pain syndrome that resembles that of
TN.
 It is thought that compression of the upper fibers of the
vagal nerve as they leave the brain stem and traverse the
subarachnoid space to the jugular foramen is the cause of
vagal neuralgia.

53.  Vagus nerve neuralgia is characterized by paroxysms of shock-like
pain in the side of the thyroid cartilage, pyriform sinus, angle of
the jaw.
 The trigger zone is usually in the larynx; attacks are precipitated
by talking, swallowing, yawning, or coughing.
53
by talking, swallowing, yawning, or coughing.
 When other portions of the vagus nerve are involved, the patient
might have hiccups, excessive salivation, or coughing. The pain is
similar to TN except for its location.

54. 54
 The diagnosis is established by the history and by identifying
the site of the trigger zone.
 Associated vagal nerve findings also pinpoint this nerve as the
site of the pain.
 Laryngeal topical anesthesia or blockade of the superior
laryngeal nerve stops the pain and is useful diagnostic and
prognostic procedure.

55. Ramsay-Hunt Syndrome
55
 Zoster infection of geniculate ganglion with involvement of
external ear & oral mucosa.
 Facial paralysis, pain of external auditory meatus & pinna of
ear.
 Vesicular eruptions in the oral cavity & oropharynx with Vesicular eruptions in the oral cavity & oropharynx with
hoarseness, tinnitus & vertigo.

56. Vaso vagal syncope
56
 Transient loss of consciousness due to cerebral ischemia, caused by
reduction of blood supply to brain.
 Vasodilation
 Vagal stimulation dramatic fall in blood pressure
 Sign- nausea, weakness, sweating, hypotension
 Causes- pain/fear, postural changes, anoxia
 Dental consideration-
Surgery in morning
Minimize waiting
Avoid anxiety
Administer adequate pain control.

57. SPINAL ACCESSARY NERVE
57

58. FUNCTIONAL COMPONENTS :
1) Cranial Root :
- Special visceral (branchial) efferent.
- Nucleus Amiguus
- Distributed through the branches of vagus to muscles of palate,
pharynx, larynx, possibly the heart.
58
pharynx, larynx, possibly the heart.

59. 59
2. Spinal Root :
-Special visceral efferent
-Long Spinal Nucleus
-Supply to Sternocleidomastoid and Trapezius muscle .

60. 60
COURSE AND DISTRIBUTION OF CRANIAL ROOT
 Cranial root emerges in form of 4 to 5 rootlets which are attached to
posterolateral sulcus of medulla .
 Rootlets soon join together to form a single trunk .

61. COURSE AND DISTRIBUTION OF SPINAL ROOT
• C1- C5
• Foramen Magnum
• Jugular Tubercle
• Jugular Foramen
61
• Jugular Foramen
• Unites &Separates
• IJV & ICA
• Deep To Parotid & Styloid Process
• Angle Of Mandible & Mastoid Process
• SCM
EXTRACRANIAL

62. DEEP SCM
OCCIPITAL ARTERY
ANT. BORDER OF SCM
62
ANT. BORDER OF SCM
POSTERIOR OF NECK
LEVATOR SCAPULA
ANT. TRAPEZIUS 5CM ABOVE
CLAVICLE

63. 63
- Supplies :
a) Sternocleidomastoid
b) Trapezius
- Cervical nerves provide a proprioceptive supply to these
muscles .

64. APPLIED anatomy
64
- TEST :
i) Asking the patient to shrug his shoulders (trapezius) against
resistance and comparing the power on two sides.
ii) Asking the patient to turn the chin to opposite side againstii) Asking the patient to turn the chin to opposite side against
resistance and again comparing the power on two sides.

65. 65
- Lesions are accompanied by lesions of 9th ,10th nerve (close
inter-relationship in cranium) .
- Irritation of nerve by enlarge lymph nodes may produce
torticollis or wry neck.

66. Superficial passage through the
posterior triangle – spinal root is
susceptible to injury.66

67. HYPOGLOSSAL NERVE67

68. 68
FUNCTIONAL COMPONENTS/NUCLEAR COLUMNS :
A) General somatic efferent column
- Fibers arise from the hypoglossal nucleus which lies in
medulla,in floor of fourth ventricle deep to hypoglossal
triangle.
B) General somatic afferent column
- Nucleus is spinal nucleus of cranial nerve V where
proprioceptive fibers from tongue end.

69. 69

70. 70
NUCLEUS :
- 2 cm long , lies in floor of fourth ventricle beneath hypoglossal
triangle.
- Divides into parts for individual muscles innervated.
- Connection of nucleus with opposite pyramidal tract forms
supranuclear pathway of nerve.supranuclear pathway of nerve.
- It is also connected to cerebellum,reticular formation of
medulla , sensory nuclei of 5th nerve , and the nucleus of
tractus solitarius.

71. 71
COURSE AND RELATIONS :
INTRA NEURAL COURSE :
- the fibers pass forwards lateral to medial longitudinal bundle , medial
lemniscus and pyramidal tract , and medial to reticular formation and
olivary nucleus .
- Nerve is attached to anterolateral sulcus of medulla , between pyramid
and olive by 10 to 15 rootlest .and olive by 10 to 15 rootlest .
- Rootlets run laterally ( behind the vertebral artery and join to form two
bundles which pierce the durameter seperately near hypoglossal canal.
- The nerve leaves skull through the hypoglossal (anterior condylar )
canal.

72. Internal Juglar Vein
Inclines Laterally
Crosses The Vagus ( Laterally )
EXTRA CRANIAL COURSE
72
Crosses The Vagus ( Laterally )
B/W IJV &ICA
Deep To Parotid Gland & Styloid Process, Post
Belly Of Diagstric & Stylohyoid, Occipital artery.
Hooks SCM branch of occipital artery

73. Crosses ICA & ECA
Loops lingual artery
Passes by digastric
73
Enters Submandibular region
Continues forward
Hyoglossus & Genioglossus, Mylohoid
Enter tongue & supply its muscle

74. 74
BRANCHES AND DISTRIBUTION :
-In addition to its own fibers , the nerve also carries some
fibers that reach it from spinal nerve C1 and are distributed
through it.
Containing
fibers of XII
nerve
Containing
fibers of
nerve C1

75. 75
A) FIBERS OF HYPOGLOSSAL NERVE PROPER
Supply extrinsic and intrinsic muscles of tongue except
palatoglossus which is supplied by fibers of cranial accessory
nerve through vagus and pharyngeal plexus.

76. 76
b) FIBERS OF NERVE C1
Meningeal
branch
• Enters skull
through
hypoglossal
canal
• Supplies
Descending
branch
• Continues
as
descendens
hypoglossai
or upper
Other
branches
• Thyrohyoid
• Geniohyoid
muscles
• Supplies
bone an
meninges
or upper
root of
ansa
cervicalis

77. APPLIED ANATOMY
77
- Hypoglossal nerve accompanies tonsillar artery on lateral wall
at pharynx.
- Because this wall is thin , CN XII is vulnerable to injury
during during tonsillectomy .
- Injury to CN XII paralyse the ipsilateral half of tongue .
After some time tongue atrophies , making it appear shrunken- After some time tongue atrophies , making it appear shrunken
and wrinkled .
- When tongue protruded , its tip deviates toward the paralyzed
side because of unopposed action of genioglossus in normal
side of tongue.

78. TEST – Protrusion and other movements
78
 The patient should be instructed to stick the tongue straight out.
 The tongue held in this position allows the clinician to visually
inspect for lateral deviation, abnormal muscular mass, and
aberrant movement.aberrant movement.
 An assessment should be made of lateral and vertical
movements of the tongue.

79. 79
a) Infranuclear lesion :
-Gradual atrophy of paralysed half of tongue.
b) Supranuclear lesion :b) Supranuclear lesion :
-Paralysis without wasting.
-Tongue moves sluggishly resulting in defective speech.
-On protrusion tongue deviates to opposite side.

80.  Disorders of cranial nerve XII (hypoglossal nerve) cause
weakness or wasting (atrophy) of the tongue on the affected
side. As a result, people have difficulty speaking, chewing, and
swallowing.
Disorders of the hypoglossal nerve may result from a tumor at
80
 Disorders of the hypoglossal nerve may result from a tumor at
the base of the skull, a stroke, infections of the brain stem, or an
injury to the neck, including that due to surgical removal of a
blockage from an artery in the neck.

81.  Damage due to amyotrophic lateral sclerosis produces a
distinctive wormlike movement of the tongue.
 Magnetic resonance imaging (MRI) is usually performed to
look for a tumor or evidence of a stroke.
81
look for a tumor or evidence of a stroke.
 Treatment depends on the elimination of the cause.

82. SUMMARY
There are 12 pairs of cranial nerves and move to cover
the needs of the cranium and face, rather than make their
way down through the spinal cord .These nerves are
important to consider ,as most are of critical importance to
sensory data, yet do not pass through the central cord and
82
sensory data, yet do not pass through the central cord and
so can not be intercepted at the same juncture.

83. REFERENCES
83
 1. BURKET’S ORALMEDICINE 10TH EDITION
 2.HUMAN ANATOMY, B.D. CHAURASIA , 4TH EDITION.
 3.GRAY’S ANATOMY 39TH EDITION.
 4.ESSENTIAL CLINICAL ANATOMY , SECOND EDITION ,KEITH N MOORE
 5.HUMAN EMBRYOLOGY, 8TH EDITION, INDERBEER SINGH
 6 . HUMAN PHYSIOLOGY, THIRD EDITION,A.K.JAIN
 7.http://www.bmc.med.utoronto.ca/cranialnerves/images/stories/Accessory/xi
-4_nolabels.jpg