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Cranial nerves: I, III, IV, VI and V: Objectives

Describe the origin and course of the  olfactory nerve , the central olfactory pathway and its function. Describe the origin and course of the  oculomotor  nerve and its function. Describe the origin and course of the  trochlear  nerve and its function. Describe the origin and course of the  trigeminal  nerve and its function. Describe the origin and course of the  abducens  nerve and its function.   Reading guide for this lecture:   A. R. Crossman, D.  Neary ,  Neuroanatomy  3rd Ed., chapter 16, p. 168, chapter 10, p. 103-107

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Cranial nerves: 12 pairs Supply of head and neck  Except  vagus  ( also thorax + abdomen)  Pass through foramina/fissures in skull

CN —G tic
Trigeminal
CNV
Facial
CN —&estBubcoeHear
CN X
Accessor•y
CNM Cranial root
Spinal root
CN XII —ßypgbssal
CNI
CNU
OJ 111
crux
Cribriform plate
Of ethmoid
Optic
Sup orbital
fissure
F ommen rotundum
F oramen
Intem ac oustic
J foramen
Hypoglossal canal

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Sensory Olfactory Optic Vestibulocochlear Motor Oculomotor Trochlear Abducent Accessory Hypoglossal Mix ed Trigeminal Facial Glossopharyngeal Vagus

Additional Parasympathetic component :  Oculomotor , Facial, Glossopharyngeal &  Vagus For supply of: Head, face : intraocular eye muscles  and  glands  Viscera  &  systems :  --smooth muscle, glands , cardiac muscle

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Olfactory and Optic nerves  enter brain  directly Cranial nerves  III-XII  enter/exit from  ventral  aspect of brain stem   EXCEPT  IV –Trochlear nerve ( dorsal aspect)

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General principles All  sensory  cranial nerves and  sensory roots of  mixed   nerves have a  sensory ganglion  along their course: similar to DRG of spinal nerves—( pseudounipolar  neurons) Sensory nuclei of cranial nerves in brain stem are  second order  neurons Where are the first order neurons? All sensations are carried from nuclei to  thalamus  by  “lemnisci”  / bundles of various names All  motor  nuclei of cranial nerves receive bilateral  corticonuclear   fibres  from cortex :central control (exceptions: part of facial and hypoglossal nuclei)

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Sensory Nuclei: General sensations :  trigeminal sensory nucleus Special sensations : Balance, Hearing, :  vestibular, cochlear   resply .   Vision: separate pathway(not in BS) Olfaction: separate pathway(not in BS) Special visceral afferent:  taste :  nucleus of  tractus    solitarius

Motor Nuclei :   Somatic  efferent:  Somatic striated muscle:  III,IV,VI,XII  ( yellow) Parasympathetic  General visceral efferent: Glands and smooth muscle:    Edinger   Westphal  ( pupillary reflexes), superior & inferior  salivatory  nuclei, dorsal  nucleus of  vagus Branchiomotor  nuclei  :Striated muscles of  Pharyngeal arches :  motor nuclei of V, VII, nucleus  ambiguus  (IX,X,XI)

Cranial nerve Nuclei of cranial nerves III-XII located in Brain Stem

Nuclei of cranial nerves  are long columns/groups of neurons in brainstem

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— sensory fibres
— rnotor fibres
optic (II)
eye
Trochlear (IV)
motor: superior
Oblique muscle
Abducent (VI)
motor: external
rectus muscle
Trigentinal (V)
sensory: face
sinuses, teeth, etc.
motor: muscles
Of mastication
2007
Olfactory (I)
ænsory: nose
Facial (VII)
motor:
muscles
Of the
face
motor:
submaxillary and
sublingual gland
anterior part Ot tongue
and sott palate
intermediate
(VIII)
sensory :
inner ear
•aestibular
cochlear
Oculomotor (III)
motor: all eye
muscles except
those supplied by
IV and VI
Ill
Hypoglossal
motor: muscles
Of the tongue
Glossopharyngeal OX)
motor:
pharyngeal
musculature
sensory:
posterior part
Of tongue,
tonsil, pharynx
Vagus (x)
motor:
heart, lungs,
bronchi,
gastrointestinal
tract
sensory:
heart, lungs,
bronchi, trachea,
larynx, pharynx,
gastrointestinal
tract, external ear
Accessory
motor: sterno-
cleidomastoid and
trapezius muscles

Cranial nerves: Nuclei of origin/termination( in brainstem) Course (intra +  extracranial ) Distribution   Function Testing Clinical Anatomy

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Origin: Olfactory receptors  : type of neurons?  Bipolar Central processes form olfactory  nerve  fibres bundles of these pass through cribriform plate of  ethmoid enter  olfactory bulb   synapse with cells of olfactory bulb-mitral cells-  olfactory tract

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Olfactory tract   narrow band of nerve cell processes or white matter Runs on inferior surface of frontal lobe divides into 2 into  Lateral & Medial Olfactory  striae Lateral olfactory stria  -axons  enter  olfactory area of  cerebral cortex : temporal  &  frontal lobe  cortex-same side Medial olfactory  stria   -sends axons to  opposite  olfactory bulb through  anterior commissure

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Unique feature of Olfactory pathway  only 2 neuronal sensory pathway Bypass thalamus

Identify Olfactory bulb, Tract and  Stria  in the figure

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Olfactory pathway: termination: Olfactory Cortex: temporal and frontal Lobes

Primary olfactory area:  Pyriform  cortex  in  uncus  ( temporal lobe) Secondary olfactory area ( 28)- entorrhinal  cortex These areas are connected to other cortical areas e.g.  frontal lobe for emotional and autonomic responses to olfactory sensations

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Testing - 1)Determine nasal passages are clear 2) Apply  recognisable  aromatic substances like oil of cloves, oil of peppermint, camphor, tobacco etc.  to each nostril Ask the patient the perception of smell & to identify the smell ( close each nostril while other is being tested) Note : Food flavors depend on sense of smell & not on taste!

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Bilateral anosmia   -loss of sense of smell-can be caused by disease of olfactory mucus membrane-e.g. common cold, allergic rhinitis Unilateral anosmia   -disease affecting olfactory nerves, bulb, or tract. Lesion of  one   olfactory cortex  will  not   cause complete anosmia as  fibres  from each olfactory tract travel to both cerebral hemispheres  throughmedial  olfactory striae Injury to olfactory nerves  -Fractures of cribriform plate of  ethmoid Pressure on olfactory bulbs or tracts   -frontal lobe  tumours ,  meningiomas  of anterior cranial  fosa - anosmia Congenital anosmia

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III,IV,VI Cranial nerves supply  Extraocular  muscles of eyeball-Hence MOTOR

Nerve supply of EO Muscles Recall formula SO4, LR6, ALL the rest-III Including LPS)

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Motor  to majority All EO Muscles  except  superior oblique and lateral rectus (SO4 and LR6) Parasympathetic  component: Innervates  smooth muscles  of eye Sphincter  pupillae  and  Ciliaris  muscles  Controls  light  and  accommodation  reflexes

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Nuclei of Origin Course (intra +  extracranial ) Distribution Function Testing Clinical Anatomy

Olfactory bulb
Optic nerve
Mammillary body
Oculomotor nerve
Figure 10.4 Ventral aspect of the brain showing the points of
attachment of cranial nerves l, II and III.

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Motor nucleus :  Location :  Midbrain : Periaqueductal grey matter at level of  superior  colliculus Motor part of III N . supplies all  extraocular  muscles except SO and LR

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Parasympathetic :  Edinger   Westphal   nucleus: Gives rise to  preganglionic parasympathetic  fibres -- Travel through  Oculomotor  nerves—synapse in  Ciliary  ganglion- postganglionic  fibres  short  ciliary  nerves- -- ciliaris   and  sphincter   pupillae  muscles (intrinsic smooth muscles of eye) For  accommodation  and  light  reflexes of eye

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Emerges in  interpeduncular  fossa medial to cerebral peduncles of MB Runs anteriorly –travels through lateral wall of cavernous sinus    Clinical implication ? Enters orbit through Superior orbital fissure

Piuitæy
seUae
snjs
Ophth*nic divisk» O' triwninal (V, I
Maxo-y ot trod" i nal nerve
@ Elsevier Drake at:
Grays Anatomy for Students - www.studentconsult.com

http://3.bp.blogspot.com/_plbJ03T5zBk/TD8NawBKuzI/AAAAAAAAAAM/t_tRFOrFiy4/s1600/cavernoussinusthumb2.jpg

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Recall that before entering the orbit III,IV,V1,V2  are in the  lateral wall  of cavernous sinus VI  cranial nerve runs  through  the sinus along with ICA

Clinical significance ? Nerves can be compressed due to a cavernous sinus thrombosis  Abducent  can be compressed  within  the sinus or due to an aneurysm ( abnormal dilatation) of the ICA within the cavernous sinus

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Pretectal area
Fibres from
optic tract
Pupillary constrictor
muscle of iris
Edinger-Westphal
nucleus
Red nucleus
Crus cerebri
Oculomotor nerve
Ciliary ganglion
Figure 10.6 Schematic representation of a transverse section through the most rostral part of the midbrain. The diagram shows the
pathways involved in the pupillary light reflex.

Oculomotor  nerve: Pathway for pupillary light and accommodation reflexes

Note   bilatera l connections of  pretectal   nucleus to EW nucleus Important in direct and consensual light reflexes

Parasympathetic part :  EW nucleus- -preganglionic  fibres - ciliary  ganglion  within orbitpostganglionic  fibres  in  short  ciliary  nerves  supply  sphincter  pupillae  and  ciliaris  muscle

Recall Motor part  :Supplies all EO muscles (except SO, LR) +  Levator   palpebrae   superioris  ( elevates upper eyelid)  Effects of paralysis/lesion of III nerve?  Ptosis  or drooping of upper eyelid

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Lesions of  Oculomotor  nerve or its nucleus would manifest as--?

Ptosis  or drooping of upper eyelid: muscle involved?  LPS Paralysis of EO muscles : SR, IR, MR,IO    Deviation  of eye to-?  Lateral side  ( LR working, and  downwards & laterally  (SO working)   Accommodation and light reflexes ? -- - Absent in affected eye Pupil ?  Dilated and non-reactive on affected side

Figure 10.12 Right oculomotor (Ill) nerve palsy. The upper part of
the diagram shows ptosis on the right. The lower part shows that, with
elevation of the eyelid, the eyeball can be seen to be abducted and the
pupil dilated.

http://www.beltina.org/pics/ptosis_eye.jpg

http://t3.gstatic.com/images?q=tbn:ANd9GcRbiIrlaQIGZvQzJ-PYy03EOUW3LlgGCWrm2g9gx99QzAIoJ5-aTg

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Lesions of Midbrain can involve  oculomotor  nerve or nucleus

Tumour : blockage of cerebral aqueduct and involvement of central grey matter Vascular lesions: Weber’s syndrome Benedikt’s  syndrome

o
00
o
o
o
00
o
o
Figure 5—26 Pathology of the midbrain. A. Tumor of the midbrain blocking the cerebral aqueduct.
B. Weber's syndrome, involving the oculomotor nerve and the crus cerebri following occlusion of
the blood supply to the midbrain. C. Benedikt's syndrome, involving the red nucleus and the
medial lemniscus following occlusion of the blood supply to the midbrain.

Which structures would be affected? Effects of lesion?

B,C: involvement of III nerve in different lesions

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Trochlear nerve :Motor to Superior oblique muscle of eye

Origin: Trochlear Nucleus : somatic motor neurons Location : central grey matter in midbrain at level of  inferior  colliculus Course : Nerve crosses to  opposite   side within midbrain Emerges  dorsally  ( only cranial nerve to do this) below inferior  colliculus Long intracranial course —winds around MB, travels forward— Enters  cavernous  sinus lateral wall Orbit  through superior orbital fissure

Ocubrnotor r•ve 0111
Piuitæy
seUae
snjs
Ophth*nic divisk» O' tri*minal (V, I
Maxo-y Wvisü» ot trod" i nal nerve

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Lesion of the trochlear nerve or its nucleus would manifest as?

Loss of action of  Superior oblique  muscle of eye—inability to look down & laterally Hence eye turns medially while looking down Diplopia  on  looking downwards —e.g. going down the stairs

Lesion is contralateral: Why? Nerves cross to opposite side inside midbrain

Inferior
colliculus
Trochlear
nerve
Cerebral
aqueduct
Trochlear
nucleus
Medial
longitudinal
fasciculus
Superior
cerebellar
'Xiuncle
Crus cerebri
Figure 10.7 Transverse section through the midbrain at the level
of the inferior colliculus. The diagram shows the location of the
trochlear nucleus and the course of trochlear nerve fibres.

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Abducent  (Motor) (VI): “ abducere ”= to go awaysupplies lateral  rectus muscle of eye: Abduction of eyeball

Motor nucleus : In floor of fourth ventricle:  Forms  facial  colliculus   ( facial nerve winds around it) Nerve emerges anteriorly from pons at  junction of pons and medulla  in the  anterolateral sulcus

Optic chiasma
Floor of
hypothalamus
Mammillary
body
Trochlear
nerve (IV)
Pons
Middle
cerebellar
peduncle
Hypoglossal
nerve (XII)
Pyramid
Decussation of
pyramids
Spinal
cord
(a) Ventral view
Optic nerve
Thalamus
Optic tract
Infundibulum
(pituitary removed)
Oculomotor nerve (Ill
Crus cerebri of
cerebral peduncles
(midbrain)
Infundibulum
Pituitary gland
Trigeminal nerve (V) -
Abducens nerve (VI)
Facial nerve (VII) —
Vestibulocochlear—
nerve (VIII)
Glossopharyngeal —
nerve OX)
Vagus nerve (X) —
Accessory
nerve (XI)
Ventral root
of first cervical
nerve

http://3.bp.blogspot.com/-n9x_6iUMxwI/UILuYSspsdI/AAAAAAAAB6I/l9OXXdlTDmU/s1600/brain+stem+anatomy.jpg

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Course:  Travels  through   cavernous sinus   along with Internal carotid artery    Clinical implication ? Can be compressed in cavernous sinus thrombosis or any abnormal dilatation ( aneurysm) of ICA WITHIN the sinus Enters orbit through superior orbital fissure

Distribution : Motor to Lateral rectus muscle

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Lesion of the  abducent  nerve or its nucleus would manifest as-?

Figure I ().13 Left abducens (VI) nerve palsy. On looking in the
direction of the arrow, the left eye fails to alniuct,

http://www.arabmedmag.com/issue-28-02-2007/images/art-cou548723_004.gif

Failure to abduct the affected eye When patient is asked to look laterally “Squint” or strabismus Diplopia on looking?

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Trigeminal nerve  (V) Mixed                              Main sensory nerve for head, face                              Motor to muscles of mastication

Nuclei : Located in Medulla, Pons and Midbrain ( “Share the work” Motor and Main Sensory nuclei : Located in  Pons

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Trigeminothalamic fibres to the ventral
posterior nucleus of the thalamus
Mesencephalic nucleus
Chief sensory nucleus
Proprioception
Touch/pressure
Pain/temperature
Trigeminal ganglion
Nucleus of the spinal
tract Of the trigeminal
lure I O. 1 5 The brain stem indicating the location of the trigeminal sensory nucleus and its major connections.

Sensory nuclei in brain stem In pons:   Main sensory  :  receives  touch, pressure  sensations In medulla:  Nucleus of spinal tract of trigeminal : receives  pain, temperature  sensations In midbrain:  Mesencephalic  nucleus:  receives  proprioception

All sensory  fibres  ascend through brain stem as the  trigeminal  lemniscus   to the thalamus of  opposite side .

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Midbrain
Pons
Medulla
Mesencephalic nucleus
Principle sensory nucleus
Trigeminal
ganglion
Spinal
nucleus
o
teachmeanatomy

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Trigeminal nerve: Course and Distribution

Sensory distribution General Sensations  from face, scalp, cornea, nasal and oral cavities, teeth and gums,  paranasal  air sinuses, anterior 2/3 of tongue, cranial  dura  mater  Proprioception  from TM joint and muscles of mastication and face  Carried by Ophthalmic, Maxillary and Mandibular divisions of trigeminal as shown. Nerves are peripheral and central processes of  trigeminal  ganglion( similar to DRG)located on sensory part of V nerve in  trigeminal cave  in middle cranial fossa Central processes travel through trigeminal nerve to respective sensory nuclei in brain stem

Motor distribution : through  mandibular nerve :  Nerve of  Ist  arch Muscles of mastication Other muscles developed from  1 st  pharyngeal arch : tensor tympani, tensor  palati ,  mylohyoid , anterior belly of digastric

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Trigeminal nerve in Middle cranial fossa  (trigeminal cave)

Ophthalmic
division
Maxillary
division
Mandibular
division
Ophthalmic
nerve
Maxillary
nerve
Mandibular
nerve
Trigeminal
ganglion
Mesencephalic
nucleus
Main sensory
nucleus
Spinal nucleus

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Sensory function : test sensations with cotton wool or pin over areas of distribution of V nerve-e.g. anterior 2/3of tongue, face etc. Motor function : ask patient to clench his/her teeth and masseter& temporalis are palpated

Also afferent for corneal and  conjunctival  reflexes (sensory)

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Trigeminal neuralgia : unknown causes—pain in distribution of V nerve ( usually maxillary and- mandibular div. areas) Viral infection—Herpes zoster—pain and eruptions along distribution of its divisions Lesions of nerve  or its  nuclei :   ipsilateral Lesions of brain stem—damage to  trigeminal  lemniscus   —loss of  all  sensations on  opposite side of scalp and face Lesion in medulla ?  selective loss of pain and temperature sensations:  Lesion in pons :  involving Motor & sensory nuclei: paralysis of concerned muscles and ? Sensations( touch , pressure) Lesion in  midbrain ? –which nucleus?  Mesencephalic  N-loss of ? Proprioception

Cranial nerves: I, III, IV, VI and V: Objectives

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