Cranial Nerves

Question 1

Describe upper motor neuron

Answer 1

Usually located in the cerebral cortex
Axons project to owner motor neurons in brain stem and spinal cord

Question 2

Describe location of lower motor neurons

Answer 2

Usually located in brain stem or spinal cord

Question 3

Damage to upper motor neuron results in..

Answer 3

Paresis or paralysis
Spastic paralysis
Exaggerated tendon reflexes

Question 4

Damage to lower motor neuron results in…

Answer 4

Paresis or paralysis
Flaccid paralysis
Loss of tendon reflexes
Rapid muscle atrophy of affected muscles
Fasciculation

Question 5

Describe 1st to 3rd order neuron

Answer 5

1st - arise in cerebral cortex
2nd - internuncial, grey column of SC
3rd - lower MN in ant. Grey column

Question 6

Describe the corticobulbar tract

Answer 6

Arises mainly in the lateral aspect of the primary motor cortex
• Synapse with cranial nerve nuclei. Most innervate cranial nerve nuclei bilaterally
• Unilateral innervation to the area of the facial nerve nuclei which supplies the muscles of the lower quadrant of the face

Question 7

Fibre types of cranial nerves

Answer 7

Efferent motor fibres
Afferent sensory fibres

Question 8

3 types of efferent fibres

Answer 8

General somatic efferents (GSE)
• Cell bodies in brainstem
• Innervate skeletal muscle derived from somites (III, IV, VI, XII)
Special visceral / Branchial motor efferents (SVE)
• Functionally identical to GSE
• Cell bodies in brainstem and innervate skeletal muscle derived from pharyngeal arches
• Visceral = in less developed animals (fish) pharyngeal arches give rise to smooth muscle or glands (V, VII,
IX, X, XI)
General visceral efferent (GVE)
• Cell bodies within brainstem – parasympathetic
• Innervate smooth muscles or glands (III, VII, IX, X)

Question 9

Describe the Afferent fibres

Answer 9

General somatic afferents (GSA)
• Cell bodies outside the CNS (ganglia)
• From joint, tendon, skin, muscle
• Pain, temperature, proprioception, touch and pressure
• Innervate specific nuclei in brainstem (V, VII, IX, X)
Special somatic afferents (SSA)
• Similar to GSA
• Transmit specialised sensory inputs e.g. sight, hearing (II, VIII)
Special visceral afferents (SVA)
• Similar to SSA
• Take information from chemoreceptors associated with viscera and senses e.g. taste and smell (I, VII, IX, X)
General visceral afferents (GVA)
• Receptors located in serous lining or smooth muscle of body viscera
• thirst, hunger, visceral pain, chemoreception (VII, IX, X)

Question 10

Describe the Olfactory nerve (CN1)

Answer 10

Sensory
Special sensory Afferent SVA fibres
Cell bodies in olfactory epithelium of nasal mucosa - no ganglion
Axons transmitted through cribriform plate of ethmoid bone to olfactory bulb
Postsynaptic fibres of secondary neurons form olfactory tract
Complex communication network sending fibres to autonomic centres and limbic system
Function : sense of smell

Question 11

Describe the optic nerve CN2

Answer 11

Sensory
Special sensory Afferent SSA fibres
Cell bodies in retina (first order) and retinal ganglia (second order)
Myelinated second order axons grouped together as the optic nerve and leave orbit via optic canal
Terminate in lateral geniculate body of thalamus and protectable area of midbrain
Cells in lateral geniculate body form geniculocarine tract, travel to primary visual cortex
Function: vision

Question 12

What are the cranial nerves of the midbrain

Answer 12

Oculomotor 3
Trochlear 4

Question 13

Describe the oculomotor nerve 3

Answer 13

Motor
General somatic efferents:
• Emerges from the midbrain
• All extraocular (skeletal) muscles except lateral rectus and superior oblique
• Control eye movements
• Also levator palpebrae superioris (elevates upper eyelid)
• From oculomotor motor nucleus
General visceral efferents:
• Parasympathetic
• Constrict pupils via sphincter pupillae and ciliary (smooth) muscles
• From Edinger-Westphal nucleus
• Sympathetic fibres leave ciliary ganglion with post ganglionic parasympathetic fibres
• Terminate in ciliary body
• Pupillary light and accommodation reflex

Question 14

Parasympathetic effect on iris

Answer 14

Sphincter pupillae muscle contracts: pupil size decreases

Question 15

Sympathetic effect on iris

Answer 15

Dilator pupillae muscle contracts
Pupil size increases

Question 16

Describe the Trochlear nerve 5

Answer 16

Motor
Emerges on dorsal aspect of brainstem
General somatic efferents:
• Innervate superior oblique extraocular muscle: abducts, depresses and medially rotates eyeball
• Cell bodies in trochlear nucleus of midbrain
• the only cranial nerve formed by axons that cross the midline before their exit.

Question 17

What is the cranial nerve of the pons

Answer 17

Trgeminal 5

Question 18

Describe the trigeminal nerve

Answer 18

General somatic afferents (sensory root) Portio major
• 3 divisions transmit sensations of touch, pressure, nociception and thermal changes;
• Ophthalmic (V1), sup. Orbital fissure – upper eyelid, forehead &scalp
• Maxillary (V2), foramen rotundum – lower eyelid, upper lip & teeth, maxillary aspect of the face, lateral strip in temporal area
• Mandibular (V3) foramen ovale– lower lip & teeth, oral cavity, skin over mandible and lateral side of head rostral to ear
• 3 sensory nuclei form a continuous column from C2 to the midbrain
• Spinal trigeminal nucleus
• Principal sensory nucleus
• Mesencephalic nucleus
Special visceral efferents (motor root) Portio minor
• Bypasses trigeminal ganglion, travels with V
• Innervate muscles of mastication (temporalis, masseter, medial pterygoid and lateral pterygoid)
• Also mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatine
• 1 motor nucleus
Fibres conveying discriminative touch from the face and oral cavity terminate in the primary sensory nucleus
• Fibres carrying proprioceptive information from the masticatory muscles, extraocular muscles and periodontal
ligament receptors have their cell bodies in the mesencephalic nucleus not in the trigeminal ganglion.

Question 19

What are the cranial nerves of the pons-medulla junction

Answer 19

Abducens 6
Facial 7
Vestibulocochlear 8

Question 20

Describe the abducens nerve 6

Answer 20

General somatic efferent
• Innervates the lateral rectus
• Nucleus located in the pons
• Facial axons loop around it forming facial colliculus
• Leaves superior orbital fissure
• Interneurons go to contralateral oculomotor nucleus
• Allows lateral and medial rectus muscles to work together

Question 21

Describe the facial nerve

Answer 21

Mixed
• Special visceral efferent axons leave facial nucleus and are joined by GVE neurons from superior salivatory nucleus before leaving pons-medullary junction as nerve
• Mixed with these fibres are somatic afferents (taste from ant. 2/3 of tongue) and pinna form intermediate nerve
• Facial nerve exits stylomastoid foramen
Branchial motor component/ Special visceral efferent
• innervation to muscles of facial expression, platysma, stylohyoid, stapedius and posterior belly of digastric.
• Cell bodies in facial motor nucleus of pons
• Five motor branches
• Temporal
• Zygomatic
• Buccal
• Mandibular
• Cervical

Question 22

What are the 5 motor branches of the facial nerve

Answer 22

Temporal
Zygomatic
Buccal
Mandibular
Cervical

Question 23

Describe the parts of the facial nerve carried by the intermediate nerve

Answer 23

General visceral efferent (secretomotor)
• innervation to lacrimal, sublingual and submandibular glands, all glands of head except parotid and integumentary glands
• Cell bodies in superior salivatory nucleus
• Travel in nervus intermedius – divide to become greater petrosal & chorda tympani
Special visceral afferent
• (taste) innervation to anterior 2/3 of tongue
• Cell bodies in geniculate ganglion
• Enters solitary tract and terminates in gustatory nucleus within solitary nucleus
General somatic afferent
• (pain, touch, temperature) fibres transmit information from external ear and external acoustic meatus travel in nervus intermedius and terminate in the spinal trigeminal tract
General visceral afferent
• (sensation from soft palate, nasal cavity and middle ear) fibres with cell bodies in geniculate ganglion
• terminate in the spinal trigeminal tract

Question 24

Describe the vestibulocochlear nerve 8

Answer 24

Sensory
2 separate nerves enclosed within the same connective tissue sheath - vestibular nerve and cochlear nerve
Both enter brainstem at pontomedullary junction

Question 25

Describe the vestibular nerve

Answer 25

Cell bodies in vestibular ganglion • Neurons project to vestibular nuclei of pons and medulla • Medial and inferior vestibular nuclei have connections to cerebellum • Lateral vestibular nucleus sends a large group of axons ipsilaterally down the spinal cord to form the lateral vestibulospinal tract • All nuclei in vestibular complex send axons bilaterally to CN III, IV & VI nuclei via MLF • Vestibular axons in descending MLF (medial vestibulospinal tract) inflorescence lower motor neurons in cervical spinal cord

Question 26

Describe the cochlear (auditory) nerve

Answer 26

Cell bodies in spinal ganglion of cochlea Neurons project to cochlear nuclei of medulla Cross midline to enter superior olivary nucleus - medial geniculate nucleus of thalamus Small number of axons leave sup. Olivary nucleus and provide innervating to stapedius

Question 27

What are the cranial nerves of the medulla

Answer 27

Glossopharyngeal 9 Vagus 10 Accessory 11 Hypoglossal 12

Question 28

What are the fibre types of the glossopharyngeal nerve 9

Answer 28

• Special visceral afferents: taste from posterior 1/3 of tongue (inferior ganglion) • General visceral afferents: sensation from posterior 1/3 of tongue, pharynx and carotid sinus (inferior ganglion) go to NTS • General somatic afferents: sensation from external ear (superior ganglion) – enter spinal trigeminal tract • Special visceral efferents/ branchial motor: motor innervation to stylopharyngeus muscle from nucleus ambiguus of medulla • General visceral efferents: parasympathetic innervation of parotid gland from inferior salivatory nucleus of medulla

Question 29

Describe the glossopharyngeal nerve 9

Answer 29

Mixed Leaves skull via jugular foramen Inferior ganglion - visceral Afferent Superior ganglion - somatic Afferent Composed of 5 fibre types

Question 30

Describe the Vagus nerve 10

Answer 30

Mixed Extends throughout neck, thorax, and abdomen to colon • Special visceral afferents: taste from epiglottis to solitary nucleus (via inferior ganglion) • General visceral afferents: sensation from abdominal organs, heart lungs etc. pharynx, larynx, oesophagus and trachea as well as inputs from chemoreceptors in carotid body to monitor blood CO2, these go to NTS (cardio respiratory portion) • General somatic afferents: general sensation from pharynx, larynx, oesophagus, trachea external ear and external acoustic meatus (superior ganglion) – nucleus spinal trigeminal tract • Special visceral efferents / Branchial motor: motor innervation to all pharyngeal and laryngeal muscles (except for stylopharyngeus and tensor veli palatini) from nucleus ambiguus of medulla • General visceral efferents: parasympathetic innervation from dorsal motor nucleus to thoracic and abdominal viscera e.g. heart, GI tract, influenced by hypothalamus, olfactory system, reticular formation & NTS. Dorsal nucleus located in vagal trione

Question 31

Describe the accessory nerve CN11

Answer 31

Motor •Once thought to have two parts: cranial and spinal accessory nerve roots • Cranial root since found to be composed of vagus nerve fibres from nucleus ambiguus • Accessory nerve arises from spinal accessory nucleus in posterolateral ventral horn of the cervical spinal cord (C2 – C5 levels) • Emerges from spinal cord in lateral funiculus (between ventral and dorsal spinal nerve roots) and ascends to enter foramen magnum • Special visceral efferent innervation to sternocleidomastoid, trapezius and intrinsic laryngeal muscles

Question 32

Describe the hypoglossal nerve (12)

Answer 32

Motor Cellbodies located in hypoglossal nucleus of the medulla General somatic efferent innervating to extrinsic muscle (except palatoglossus) and intrinsic muscles of ipsilateral side of tongue

Question 33

Where are motor nuclei

Answer 33

• Most medial CN motor nuclei XII, VI, IV, III • Located adjacent to midline and anterior to ventricular space • Alpha motor neurons that these nuclei innervate originate from paraxial mesoderm that migrated to the occipital region (tongue) and orbit • Functional component is SE, they innervate skeletal muscles that migrated through pharyngeal arches • Laterally adjacent to the SE forming a discontinuous column are the nuclei that constitute the craniosacral (parasympathetic) division -Nuclei dorsal motor vagus – X -Inf salivatory nucleus – IX -Sup. Salivatory nucleus - VII (intermediate part) -Edinger-Westphal nucleus – III • Give rise to preganglionic axons that terminate in a peripheral ganglion, that give rise to postganglionic fibres that innervate a visceral structure • Classified as visceral efferent / VE preganglionic parasympathetic Most lateral discontinuous motor column forming by -Nucleus ambiguous – IX & X -Facial motor nucleus – VII -Trigeminal motor nucleus - V • Muscles innervated originate from mesoderm that migrates into pharyngeal arches

Question 34

Describe sensory nuclei

Answer 34

Most medial solitary tract & nucleus • No matter what cranial nerve returns visceral afferent info. The central processes of these primary afferent fibres contribute to the solitary tract, the fibres of which terminate in the solitary nucleus • VA info from VII, IX & X, taste & visceral sensations of thorax & abdomen Vestibular and cochlear nuclei receives sensory input from vestibular apparatus and cochlea Although SA pain and temp sensations enter brain stem on 4 diff nerves, the central processes of these primary Afferent fibres Exeter the spinal trigeminal tract and terminate in the medially adjacent spinal trigeminal nucleus