The Cranial Nerves Flashcards
What are the segmental trunk nerves
Somatic nervous system under voluntary control
1 = Afferent (sensory)
2 = interneuron
3 = Pre ganglionic efferent
4 = Post ganglionic efferent (motor)
Primary afferent cell bodies in dorsal root ganglion
Dorsal and ventral roots fuse to form single spinal nerve carrying all 4 nerve types
What do segmental trunk nerves have additionally
Has additional ganglion where pre and post ganglionics synapse
What are different about segmental head nerves from segmental trunk nerves
Autonomic efferent neurons leave via dorsal root
Dorsal and ventral roots do not unite
Head has 5th neuronal component
Where does striated muscle arise from and how is it innervated
Striated muscle arising from somites (e.g. muscle of eyeball + tongue) supplied by somatic efferents as in trunk
Striated muscle arising from lateral plate mesoderm (e.g. muscles of facial expression, chewing, swallowing) supplied by special visceral efferents leaving via dorsal root
What does segment 1 not have
No pharyngeal arch so it borrows its dorsal root nerve from segment 2 = opthalmic division of V
What are the 2 major divisions of the dorsal root of segment 2
Maxillary
Mandibular divisions of V
What do segments 4,5 + 6 loose
4+5 loose their somites so they don’t have a ventral root nerve
6 looses its pharyngeal arch so doesn’t have a dorsal root nerve
What do segments 6 and 7 do
Somites unite to form tongue muscles so does their ventral root XII
What do segments 5 and 7 do
Share their dorsal root nerve (X/XI)
What are cranial nerves I, II and VIII
I = olfactory nerve - smell
II = optic nerve - sight
VIII = vestibulo-cochlear (auditory) - balance and hearing
What should each segment have
Dorsal and ventral root
Dorsal roots innervate all structures (principally pharyngeal arch) contain SA, AA, AE SVE neurons
Ventral roots innervate somites contain SE neuron’s only except CN III has a small AE component to ciliary muscles and SVE to levator palpebrae superioris
What does segment 1 ventral root contain
Ventral root nerve III (occulomotor) SE somites forming most orbital muscles, all rectus (except lateral) and ventral oblique.
AE parasympathetic to ciliary muscle. Constricts pupil
SVE to levator palpebrae superioris. Raises upper eyelid
What does segment 1 dorsal root contain
Dorsal root nerve = Opthalmic division of V (Trigeminal)
No pharyngeal arch so no dorsal root - borrows off 2
SE - ectoderm only, forms skin on top of head above eyes
SVE, AA, AE - none
What does segment 2 ventral root contain
Ventral root nerve = IV Trochlea
SE - so it’s forms dorsal oblique orbital muscle
What does segment 2 dorsal root contain
Dorsal root = V Trigeminal
Mouth splits this into 2 major divisions maxillary (SA) and mandibular (SA + SVE)
SA - ectoderm forms most of skin of face, rostral 2/3 tongue
SVE - pharyngeal arch 1 forms muscle or chewing
AA - none
AE - none
What does segment 3 ventral root contain
Ventral root nerve = IV abducent
SE - somite forms lateral rectus + retractor oculi/bulbi
What does segment 3 dorsal root contain
Dorsal root nerve = VII Facial
SA - ectoderm forms small area of skin in external ear cavity
SVE - pharyngeal arch 2 forms muscles of facial expression
AA - taste from rostral 2/3 of tongue, palate. Invades territory of V
AE - to mandibular / sublingual salivary glands, nasal cavity glands, lacrimal gland
What does segment 4 ventral root contain
Ventral root = none
Somite 4 = lost
What does segment 4 dorsal root contain
Dorsal root nerve = IX glosso-pharyngeal
SA - ectoderm forms very small area in ear canal
SVE - pharyngeal arch 3 forms stylopharyngeus muscle
AA - endoderm forms lining of pharynx / caudal 1/3 of tongue, aortic arch 3 forms internal carotid (carotid sinus and body)
AE - motor to parotid salivary gland. Most important to initiate swallowing reflex
What does segment 5 ventral root contain
Ventral root nerve = none
Somite 5 lost
What does segment 5 dorsal root contain
Dorsal root nerve = X/XI Vagal-accessory complex
SE - ectoderm forms very small area of ear canal
SVE - pharyngeal arch 4 forms rest of pharyngeal muscles + cricothyroid muscle
AA - endoderm forms lining of common pharynx + larynx, aortic arch 4 forms root of aorta / right subclavian
AE - endoderm of gastrointestinal tract
What does segment 6 ventral root contain
Ventral root nerve = XII Hypoglossal
SE - somite 6 forms muscle of tongue
What does segment 6 dorsal root contain
Dorsal root nerve = none
Pharyngeal arch 5 lost
What does segment 7 ventral root contain
Ventral root nerve = XII hypoglossal
SE - somite 7 forms muscles of the tongue
What does segment 7 dorsal root contain
Dorsal root nerve = X/XI vagal-accessory complex
SA - none
SVE - pharyngeal arch 6 forms rest of laryngeal muscles
AA - endoderm forms lining of larynx caudal to vocal folds/trachea/lungs/gastrointestinal tract, aortic arch 6 forms pulmonary artery/ductus arteriosus
AE - endoderm of gastrointestinal tract
