Neuroscience/Objectives/Lecture 22

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Objectives: 1–3 - 4 - 5 - 6 - 7 - 8 - 9–10 - 11 - 12 - 13–14 - 15 - 16 - 17 - 18 - 19 - 20 - 21 - 22 - 23 - 24 - 25 - 26

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Cranial nerve motor systems II: Branchial motor nuclei and parasympathetic nuclei

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Identify the location in the brainstem of the branchiomotor (SVE) nuclei for cranial nerves V, VII, IX, X, and XI.

Cranial nerve Motor nucleus Location
CN V Motor trigeminal nucleus Rostral pons (level of middle cerebellar peduncle); medial to principal trigeminal nucleus
CN VII Motor facial nucleus Caudal pons; sends its nerve dorsally and medially to wrap around the abducens nucleus (forming the facial colliculus)
CN IX Nucleus ambiguus Spans medulla; medial to spinal trigeminal nucleus and tract
CN X Nucleus ambiguus (See above.)
CN XI Accessory nucleus Rostral spinal cord (C1-C5) and into spinomedullary junction; medial to spinal trigeminal nucleus and tract in medulla
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Identify the muscle groups in the periphery innervated by each of these cranial nerves.

(H:7-15, 7-16)

Cranial nerve Motor nucleus Muscle Primary action Notes
CN V Motor trigeminal nucleus

Main muscles of mastication:

  • Temporalis
  • Lateral pterygoid
  • Medial pterygoid
  • Masseter

Others:

  • Mylohyoid
  • Anterior belly of digastric
  • Tensor tympani
  • Tensor veli palatini
Mastication Motor innervation carried only in mandibular branch
CN VII Motor facial nucleus
  • Muscles of facial expression
  • Stapedius
Facial expression
CN IX Nucleus ambiguus
  • Stylopharyngeus
Swallowing
CN X Nucleus ambiguus
  • Pharynx
  • Larynx
  • Esophagus
  • Swallowing (pharynx, esophagus)
  • Speaking (larynx)
  • Cough reflex
  • Gag reflex
CN XI Accessory nucleus
  • Trapezius
  • Sternocleidomastoid
Shrug shoulders, turn head
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Describe the visceral motor component of cranial nerves VII, IX, and X.

(H:7-16) All of the following nuclei contain preganglionic neurons carrying parasympathetic input that ultimately reaches a target organ.

Cranial nerve Motor nucleus Target organ
CN VII Superior salivatory nucleus
  • Lacrimal gland
  • Mucous membranes of nose and mouth
  • Submandibular gland
  • Sublingual gland
CN IX Inferior salivatory nucleus
  • Parotid gland
CN X Dorsal vagal motor nucleus
Nucleus ambiguus (to heart)
  • Thoracic and abdominal viscera
  • Smooth and cardiac muscle
  • Glandular epithelium
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Discuss the clinical effects of damage to the peripheral nerve fibers or the nuclei of these cranial nerves.

Cranial nerve Lesion Deficits
CN V LMN (e.g. motor trigeminal nucleus)
  • Paralysis of ipsilateral muscles of mastication
  • Deviation of jaw towards lesioned side when mouth is open
UMN (e.g. corticobulbar tract) No obvious deficits because trigeminal motor nucleus receives bilateral input from cortex
CN VII LMN (e.g. motor facial nucleus) Bell's palsy
  • Ipsilateral facial paralysis (both upper and lower quadrants)
  • Ipsilateral loss of tear production
  • Ipsilateral loss of hearing
UMN (e.g. corticobulbar tract) Contralateral deficit in lower quadrant of face (ipsilateral innervation to upper face is spared)
CN IX, X LMN (e.g. nucleus ambiguus)
  • Paralysis of ipsilateral stylopharyngeus (CN IX)
  • Droop of ipsilateral soft palate (CN IX, X)
  • Deviation of uvula away from lesioned side (CN X)
  • Paralysis of ipsilateral larynx and pharynx (CN X)
  • Loss of ipsilateral gag and cough reflex (CN X)
UMN (e.g. corticobulbar tract)
  • Contralateral soft palate droop
  • Deviation of uvula towards lesioned side
CN XI LMN (e.g. isolated accessory nucleus lesion)
  • Ipsilateral shoulder droop and winging of scapula
  • Difficulty raising affected arm above 90°
  • Difficulty turning head to side opposite lesion
UMN (e.g. corticobulbar tract)
  • Ipsilateral hemiparesis of sternocleidomastoid and trapezius
  • Inability to turn head to side opposite lesion
Mixed nerve lesions
CN V Trigeminal nerve
  • Ipsilateral hemiparesis of muscles of mastication
  • Ipsilateral loss of general sensations from face and mucous membranes of oral and nasal cavities
  • Loss of afferent limb of corneal blink reflex
  • Jaw droops towards lesioned side
  • Tic douloureux (trigeminal neuralgia)
CN VII Facial nerve
  • Loss of taste from anterior two-thirds of tongue
  • Paralysis of stapedius → hyperacusis
  • Bell's palsy
    • Orbicularum oculi paralysis → drooping of eye, inability to completely close eye
    • Inability to wrinkle forehead
    • Mouth appears pulled to side opposite lesion
    • Loss of efferent limb of corneal blink reflex → corneal ulceration if untreated
    • Loss of parasympathetic input to lacrimal gland → dry eye
CN IX Glossopharyngeal nerve
  • Loss of taste from posterior one-third of tongue
  • Loss of baroreceptor and chemoreceptor input from carotid arch and body → difficulty regulating blood pressure
  • Loss of afferent (pharyngeal) limb of gag reflex
  • Paralysis of elevator muscles of pharynx
CN X Vagus nerve
  • Uvula deviates away from lesioned side
  • Ipsilateral paralysis of soft palate, pharynx, larynx → dysphonia, dyspnea
  • Loss of efferent limb of gag reflex
  • Difficulty swalling, suppression of cough reflex → ↑probability of choking

The motor trigeminal nucleus receives bilateral input from the cortex and innervates the ipsilateral muscles of mastication. Thus upper motor neuron lesions have no functional consequences, while lower motor neuron lesions result in ipsilateral paralysis of the jaw. (H:7-11, 7-16)

The motor facial nucleus has a dorsal zone, which innervates the ipsilateral upper face, and a lower zone, which innervates the ipsilateral lower face. The dorsal zone receives bilateral input from the motor cortex. The ventral zone receives primarily only contralateral input from the cortex. Thus upper motor neuron lesions result in deficits to the contralateral lower quadrant of the face. Lower motor neuron lesions result in ipsilateral facial paralysis. (H:7-11, 7-16)

Lesions affecting the corneal blink reflex may involve the afferent or efferent limb of the reflex, or both. [224]

The nucleus ambiguus contains neurons that innervate the stylopharyngeus (via CN IX) and pharynx, larynx, and upper esophagus (via CN X). These neurons subserve swallowing, some aspects of speech, and the gag and cough reflexes. Corticobulbar projections to the nucleus ambiguus are bilateral except for those to neurons innervating the uvula and soft palate, which receive contralateral corticobulbar input. Consequently, upper motor neuron lesions to the nucleus ambiguus result in paralysis of the muscles of the contralateral uvula and soft palate (CN IX) as well as ipsilateral paralysis of the pharynx, larynx, and esophagus, with loss of ipsilateral cough and gag reflexes (CN X). (H:7-11, 7-16) [225-227]

Because the accessory nucleus receives ipsilateral cortical input and projects to the ipsilateral sternocleidomastoid and trapezius, both upper and lower motor neuron lesions result in ipsilateral hemiparesis of those muscles. (H:7-11, 7-16) [227-230]

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Understand the distinction between upper and lower motor neuron lesions involving these cranial nerves.

See above.

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