The Cranial Nerves

Question 1

What are the segmental trunk nerves

Answer 1

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

Question 2

What do segmental trunk nerves have additionally

Answer 2

Has additional ganglion where pre and post ganglionics synapse

Question 3

What are different about segmental head nerves from segmental trunk nerves

Answer 3

Autonomic efferent neurons leave via dorsal root
Dorsal and ventral roots do not unite
Head has 5th neuronal component

Question 4

Where does striated muscle arise from and how is it innervated

Answer 4

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

Question 5

What does segment 1 not have

Answer 5

No pharyngeal arch so it borrows its dorsal root nerve from segment 2 = opthalmic division of V

Question 6

What are the 2 major divisions of the dorsal root of segment 2

Answer 6

Maxillary
Mandibular divisions of V

Question 7

What do segments 4,5 + 6 loose

Answer 7

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

Question 8

What do segments 6 and 7 do

Answer 8

Somites unite to form tongue muscles so does their ventral root XII

Question 9

What do segments 5 and 7 do

Answer 9

Share their dorsal root nerve (X/XI)

Question 10

What are cranial nerves I, II and VIII

Answer 10

I = olfactory nerve - smell
II = optic nerve - sight
VIII = vestibulo-cochlear (auditory) - balance and hearing

Question 11

What should each segment have

Answer 11

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

Question 12

What does segment 1 ventral root contain

Answer 12

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

Question 13

What does segment 1 dorsal root contain

Answer 13

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

Question 14

What does segment 2 ventral root contain

Answer 14

Ventral root nerve = IV Trochlea
SE - so it’s forms dorsal oblique orbital muscle

Question 15

What does segment 2 dorsal root contain

Answer 15

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

Question 16

What does segment 3 ventral root contain

Answer 16

Ventral root nerve = IV abducent
SE - somite forms lateral rectus + retractor oculi/bulbi

Question 17

What does segment 3 dorsal root contain

Answer 17

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

Question 18

What does segment 4 ventral root contain

Answer 18

Ventral root = none
Somite 4 = lost

Question 19

What does segment 4 dorsal root contain

Answer 19

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

Question 20

What does segment 5 ventral root contain

Answer 20

Ventral root nerve = none
Somite 5 lost

Question 21

What does segment 5 dorsal root contain

Answer 21

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

Question 22

What does segment 6 ventral root contain

Answer 22

Ventral root nerve = XII Hypoglossal
SE - somite 6 forms muscle of tongue

Question 23

What does segment 6 dorsal root contain

Answer 23

Dorsal root nerve = none
Pharyngeal arch 5 lost

Question 24

What does segment 7 ventral root contain

Answer 24

Ventral root nerve = XII hypoglossal
SE - somite 7 forms muscles of the tongue

Question 25

What does segment 7 dorsal root contain

Answer 25

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