CRANIAL NERVES PRE- SUMMARIZED NOTES, Study notes of Nursing

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ANATOMY, PHYSIOLOGY & PATHOLOGY

NOTES OF THE

NERVOUS SYSTEM

AND SPECIAL SENSES

FOURTH EDITION

CRANIAL NERVES PRE- SUMMARIZED NOTES

CRANIAL NERVES

Similarities Between Spinal Nerves & Cranial Nerves:

Cranial Nerves develop similar to Spinal Nerves, & hence have a similar

structural Organisation:

 Sensory Cranial Nerves:

Similar to Afferent Spinal Nerves – Sensory Cranial Nerves’

Dendrites are associated with peripheral sensory receptors &

their Cell Bodies are located in a Sensory Ganglia (Similar to

the Dorsal Root Ganglion in the spinal cord). Their axons

then terminate in the Sensory Nuclei of the Brainstem

(Similar to Dorsal Horn of Spinal Cord), and synapse with

one of the Ascending Pathways (Depending on the type of

stimulus):

• Touch → Posterior Pathway
• Pain → Spinothalamic
• Proprioception → Spinocerebellar

 Somatic Motor Cranial Nerves:

Similar to Efferent Spinal Nerves – Motor Cranial Nerves

(Both Somatic & Branchial) have their Cell Bodies in grey-

matter Motor Nuclei in the Brainstem (Similar to Ventral

Horn of Spinal Cord). Their axons leave the brainstem &

directly innervate the Skeletal Muscles.

 Visceral Motor Cranial Nerves:

 Note: There are 6 pharyngeal arches, but the 5th only exists

transiently during embryonic growth

 (No structures result from the 5th arch)

 Appear ≈4-5 weeks of development

Pharyngeal Arch Nerve Muscular Contributions 1 st^ – “Mandibular” Trigeminal (V) Muscles of Mastication:

• Ant. Digastric
• Mylohyoid
• Tensor Tympani
• Tensor Veli Palatini 2 nd^ – “Hyoid Arch” Facial (VII) - Muscles of Facial Expression
• Post. Digastric
• Stylohyoid
• Buccinator 3 rd (^) Glossopharyngeal (IX) - Stylopharyngeus 4 th^ Vagus^ (X)^ -^ Cricothyroid^ Muscle
• Soft Palate Muscles 6 th^ Vagus^ (X)^ -^ Intrinsic^ Laryngeal^ Muscles

THE 12 CRANIAL NERVES – Basic Overview:

 Olfactory -Smell

 Optic-Vision (Visual Acuity)

 Oculomotor (‘eye-mover’)-Controls 4 of the 6 eye muscles

 Trochlear (‘pulley’)-Controls 1 of the extrinsic eye muscles –

pulley shaped

 Trigeminal-3-branched (Ophthalmic, Maxillary, Mandibular)

sensory fibers to the face & cornea + Mastication

 Abducens (‘abduct’)-Controls the extrinsic eye muscle that abducts

the eyeball (lateral rotation)

 Facial-Facial expression (Furrow Brow, Shut Eyes, Smile)

 Vestibulocochlear-Hearing and balance (formerly the auditory

nerve)

 Glossopharyngeal (‘tongue & pharynx’)-Sensory Tongue and

pharynx (Gag reflex)

 Vagus (‘the wanderer’)-Mouth motor + parasympathetic effects in

the thorax & abdomen.

 Accessory-Neck and shoulder muscles

Tongue, External Neck Muscles – Sternocleidomastoid &

Trapezius)

Branchial Motor: “Special Visceral Efferents” (SVE)

 Innervate striated skeletal muscle derived from embryonic

pharyngeal arches. (Incl. Muscles of the Face, Palate,

Pharynx, Larynx & Mastication)

(Oculomotor, Trochlear, Trigeminal, Abducens, Facial, Glossopharyngeal, Vagus,

Accessory & Hypoglossal)

2. Involuntary (Visceral) Motor: “General Visceral Efferents” (GVE)

 Innervate Smooth Muscle in vessels/glands/etc. Via a 2-neuron

approach; (Presynaptic fibres emerge from the brain as cranial

nerves, which then synapse in a parasympathetic ganglion. The

postsynaptic neurons then innervate the smooth muscles & glands

etc.)

 Constitute the Cranial Outflow of the Parasympathetic Nervous

System.

(Oculomotor, Facial, Glossopharyngeal, Vagus)

3.Somatic Sensation: “General Somatic Afferents” (GSA)

 (Touch, Pressure, Heat, Cold, etc)

(Trigeminal, Facial, Glossopharyngeal & Vagus)

4.Visceral Sensation: “General Visceral Afferents” (GVA)

 (Blood Pressure & Blood-O2/CO2 from Carotid Sinus & Body,

plus Visceral Sensation from Pharynx, Larynx Trachea, Bronchi,

Lungs, Heart & GI Tract.)

(Oculomotor, Trigeminal, Facial, Glossopharyngeal, Vagus)

5.Special Sensation: “Special Somatic/Visceral Afferents” (SSA/SVA)

 (Vision, Taste, Smell, Hearing & Balance)

(Olfactory, Optic, Facial, Vestibulocochlear, Vagus)

YOU NEED TO KNOW WHICH NERVES CARRY EACH TYPE OF INFORMATION

Nerve Functional Components Location of Nerve Cell Bodies Cranial Exit Point Functions (major) I Olfactory nerve Special Sensory Olfactory Epithelium Cribriform Plate of The Ethmoid Bone Smell II Optic nerve Special Sensory Retinal Ganglion Optic Canal Vision and associated reflexes III Oculomotor nerve Somatic Motor Midbrain Superior Orbital Fissure Movements of eyes (Superiorly, Inferiorly & Medially) Visceral Motor (parasympathetic) Presynaptic: Midbrain Postsynaptic: Ciliary Ganglion Pupillary constriction and lens accommodation (parasympathetic) IV Trochlear nerve Somatic Motor Midbrain Superior Orbital Fissure Movements of eyes (Inferolaterally) V Trigeminal nerve

• V Ophthalmic Division General Sensory Trigeminal Ganglion Superior Orbital Fissure Sensation from Cornea, & V 1 Dermatome
• V2 Maxillary Division Foramen Rotundum Sensation from Maxillary Teeth, Nasal Mucosa, Maxillary Sinuses, Palate, & V 2 Dermatome

Visceral Sensory Superior Ganglion Visceral Sensation from Base of Tongue, Pharynx, Larynx Trachea, Bronchi, Heart, Esophagus, Stomach & Intestine → L-Colic Flexure. Special Sensory Inferior Ganglion Taste (Epiglottis & Palate) General Sensory Superior Ganglion Sensation from the External Ear. XI Spinal Accessory Somatic Motor Spinal Cord Jugular Foramen Sternocleidomastoid & Trapezius Muscles XII Hypoglossal Somatic Motor Medulla Hypoglossal Canal Intrinsic & Extrinsic Muscles of the Tongue. Cranial Nerve Nuclei:

Location:

 CN I (Olfactory) & II (Optic) = Are both extensions of the

Forebrain.

 CN III – XII (All others) = They originate from Nuclei located in

the Brainstem.

Organisation:

 Nuclei of similar Functional Components (Ie: General

Somatic/Visceral Motor or General Somatic/Visceral Sensory) are

generally aligned into functional columns in the brainstem.

Cranial Nerve: Receptor Types: Sensory Ganglia: Olfactory Olfactory (Smell) Olfactory Epithelium Optic Retinal (Vision) Retina of the Eye Trigeminal Somatosensory Trigeminal Ganglion Facial Somatosensory Geniculate Ganglion Vestibulocochlear Equilibrium & Hearing Vestibular Ganglion & Spiral Ganglion Glossopharyngeal Somatosensory, Visceral & Taste Inferior Ganglion Vagus Somatosensory, Visceral & Taste Superior & Inferior Ganglion

Parasympathetic Ganglia of Cranial Nerves:

Cranial Nerve Ganglion Location Main Distribution Oculomotor Ciliary Between the Optic Nerve & the Lateral Rectus Muscle of Eye Ciliary Muscle & Pupillary Sphincter of Eyes Facial Pterygopalatine In Pterygopalatine Fossa; Just anterior to the opening of the Pterygopalatine Canal. Lacrimal (Tear) Gland Submandibular Just inferior to Submandibular Salivary Duct Sublingual & Submandibular Salivary Glands Glossopharyngeal Otic Between Tensor Veli Palatini & Mandibular Nerve (Just anterior to Foramen Ovale of Sphenoid Bone) Parotid Salivary Gland.

Note:Sympathetic Input is important for the Dual Innervation setup of the

Autonomic NS. The Sympathetic Fibres ascending from the Superior Cervical

Sympathetic Ganglion hitch a ride with the Parasympathetic Cranial Nerves and

follow them to their targets

II.Optic:

Function:

o Purely Special Sensory; Carry Afferent Impulses of Vision

Origin & Course:

 Fibres arise from the Retina and form the Optic Nerve

 The Optic Nerve passes through the Optic Canal of the

Orbit.

 The Optic Nerves converge to form the Optic Chiasma

where half of each nerve’s fibres cross over & continue on

as Optic Tracts

 The Optic Tracts synapse in the Thalamus, & Thalamic

fibres extend to the Visual Cortex

Origin & Course:

 Fibres arise from the Midbrain and pass through the Superior

Orbital Fissure to the Eye.

V.Trigeminal:

Note: Has 3 Divisions (Ophthalmic, Maxillary & Mandibular), each with

different specific functions & courses through the skull.

Function:

 Mostly Somatosensory (From Face)

 Some Branchial Motor

Origin & Course:

 Ophthalmic – Fibres run from Face → Through Superior Orbital

Fissure → Pons.

 Maxillary – Fibres run from face → Through the Foramen

Rotundum → Pons.

 Mandibular – Fibres pass through the Foramen Ovale

VIII.Vestibulocochlear:

Function:

 Special Sensory:

 Vestibular Branch – Sense of Equilibrium/Balance.

 Cochlear Branch – Sense of Hearing.

Origin & Course:

 Fibres arise from the Vestibule & the Cochlear of the Inner Ear of

the Temporal Bone & pass through the Internal Acoustic Meatus

and enter the brainstem @ the Pons-Medulla Border.