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Cranial Nerves: Name, Origin, Functions, and Clinical Applications, Study notes of Biology

An overview of the twelve cranial nerves, including their names, origins, functions, and clinical applications. Each nerve is described in detail, with a focus on its sensory and motor functions and the clinical conditions that can result from damage to the nerve.

What you will learn

  • What clinical conditions can result from damage to each cranial nerve?
  • What are the twelve cranial nerves and where do they originate?
  • What are the functions of each cranial nerve?

Typology: Study notes

2021/2022

Uploaded on 09/12/2022

barnard
barnard 🇺🇸

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Cranial'Nerves'(also'see'tables'and'figures'in'text'for'details)'
'
#'
Name'
Origin'&'Course'
Functions'
Clinical'Applications'
I"
Olfactory"
Sensory"fibers"in"olfactory"
epithelium"project"through"
olfactory"foramina"of"
ethmoid"bone"to"synapse"
in"olfactory"bulb;"olfactory"
tract"enters"cerebral"
hemispheres"and"
terminates"in"primary"
olfactory"cortex"on"medial"
temporal"lobe"
Purely"sensory;"afferent"impulses"for"sense"
of"smell"
Lesions"of"fibers"or"fracture"of"ethmoid"
can"lead"to"anosmia"(loss"of"sense"of"
smell)"
II"
Optic"
Fibers"from"retina"form"
optic"nerve,"through"optic"
canal;"partial"crossover"of"
fibers"at"optic"chiasma,"
continue"as"optic"tracts"to"
thalamus"where"they"
synapse"with"fibers"
heading"to"occipital"visual"
cortex"
Purely"sensory;"afferent"impulses"for"vision"
Damage"to"optic"nerve"results"in"
blindness"to"that"eye,"damage"past"optic"
chiasma"leads"to"partial"loss"of"vision"
III"
Oculomotor"
Ventral"midbrain"through"
superior"orbital"fissures"to"
eyes"
Primarily"motor"with"a"few"proprioceptive"
afferents;"somatic"motor"fibers"to"some"of"
the"extrinsic"eye"muscles"and"to"levator"
palpebrae"superioris;"parasympathetic"
fibers"to"smooth"muscle"of"iris"and"lens"
Oculomotor"nerve"paralysis"results"in"
drooping"lid"(ptosis),"double"vision,"
trouble"focusing"on"close"objects"due"to"
inability"to"move"eye"inward"
IV"
Trochlear"
Dorsal"midbrain"through"
superior"orbital"fissures"to"
eyes"
Primarily"motor"with"a"few"proprioceptive"
afferents;"somatic"motor"fibers"to"one"
extrinsic"eye"muscle"
Damage"leads"to"double"vision"and"
inability"to"rotate"eye"inferiorly"and"
laterally"
V"
Trigeminal"
Pons"to"face"(3"branches)"
Mixed;"sensory"impulses"for"face"(touch,"
temperature,"pain);"motor"and"
proprioceptive"fibers"for"chewing"muscles"
Local"anesthetic"to"alveolar"branches"of"
maxillary"and"mandibular"divisions"blocks"
pain"during"dental"work"
VI"
Abducens"
Inferior"pons"through"
superior"orbital"fissures"to"
eyes"
Primarily"motor"with"a"few"proprioceptive"
afferents;"somatic"motor"fibers"to"one"
extrinsic"eye"muscle"
Abducens"paralysis"results"in"inability"to"
move"eye"laterally"
pf2

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Cranial Nerves (also see tables and figures in text for details)

# Name Origin & Course Functions Clinical Applications I Olfactory Sensory fibers in olfactory epithelium project through olfactory foramina of ethmoid bone to synapse in olfactory bulb; olfactory tract enters cerebral hemispheres and terminates in primary olfactory cortex on medial temporal lobe Purely sensory; afferent impulses for sense of smell Lesions of fibers or fracture of ethmoid can lead to anosmia (loss of sense of smell) II Optic Fibers from retina form optic nerve, through optic canal; partial crossover of fibers at optic chiasma, continue as optic tracts to thalamus where they synapse with fibers heading to occipital visual cortex Purely sensory; afferent impulses for vision Damage to optic nerve results in blindness to that eye, damage past optic chiasma leads to partial loss of vision III Oculomotor Ventral midbrain through superior orbital fissures to eyes Primarily motor with a few proprioceptive afferents; somatic motor fibers to some of the extrinsic eye muscles and to levator palpebrae superioris; parasympathetic fibers to smooth muscle of iris and lens Oculomotor nerve paralysis results in drooping lid (ptosis), double vision, trouble focusing on close objects due to inability to move eye inward IV Trochlear Dorsal midbrain through superior orbital fissures to eyes Primarily motor with a few proprioceptive afferents; somatic motor fibers to one extrinsic eye muscle Damage leads to double vision and inability to rotate eye inferiorly and laterally V Trigeminal Pons to face (3 branches) Mixed; sensory impulses for face (touch, temperature, pain); motor and proprioceptive fibers for chewing muscles Local anesthetic to alveolar branches of maxillary and mandibular divisions blocks pain during dental work VI Abducens Inferior pons through superior orbital fissures to eyes Primarily motor with a few proprioceptive afferents; somatic motor fibers to one extrinsic eye muscle Abducens paralysis results in inability to move eye laterally

VII Facial Pons through internal acoustic meatus of temporal bone, through stylomastoid foramen to face Mixed; 5 major branches (temporal, zygomatic, buccal, mandibular, cervical), chief somatic motor nerves of face, parasympathetic fibers to glands (lacrimal, nasal, salivary); afferent fibers from anterior tongue Herpes simplex viral infection may cause inflammation of nerve and Bell’s palsy: paralysis of facial muscles on one side, partial loss of taste, lower eyelid droops, mouth sags VIII Vestibulocochlear Hearing and equilibrium apparatus within temporal bone through internal acoustic meatus to pons-­‐ medulla border Purely sensory; afferent impulses for equilibrium and hearing Damage to cochlear portion causes deafness, damage to vestibular portion causes dizziness, involuntary eye movements, loss of balance and nausea IX Glossopharyngeal Medulla to throat via jugular foramen Mixed; somatic motor fibers to pharynx, parasympathetic fibers to salivary glands; afferent fibers for taste (posterior tongue), touch (pharynx and tongue), from carotid bodies for regulation of respiration and blood pressure Damage to nerve leads to difficulty swallowing and loss of taste on affected portion of tongue X Vagus Medulla through jugular foramen and neck to thorax and abdomen Mixed; somatic motor fibers for swallowing muscles, parasympathetic fibers for heart, lungs and abdominal viscera; afferent fibers from viscera, carotid sinus/bodies aortic bodies for regulation of blood pressure and respiration Damage causes hoarseness or loss of voice, difficulty swallowing, decreased digestive system motility; with total loss of vagus nerve on both sides body cannot survive due to unopposed sympathetic activity XI Accessory Medulla and spinal cord through jugular foramen; cranial root fibers join vagus, spinal root to sternocleidomastoid and trapezius Strictly motor; cranial division carries fibers to larynx, pharynx and soft palate; spinal division carries fibers to muscles Damage to spinal root causes paralysis of affected muscles XII Hypoglossal Medulla through hypoglossal canal to tongue Strictly motor; somatic motor fibers to intrinsic and extrinsic muscles of tongue Damage causes problems with speech and swallowing