• starts at cortex, ends at spinal cord
• mediates voluntary movements of skeletal muscles through spinal alpha-motor neurons
• control fine manipulative skills of fingers and toes

• starts in cortex, ends with brain stem at various levels
• controls facial and associated muscles through activation of cranial nerve nuclei in brainstem
• corticobulbar regulation of some cranial nerve lower motor neurons (LMN) is bilateral (i.e. left motor cortex innervates both left and right motor nuclei)

• following cranial nerves receive bilateral projections: trigeminal, facial, vagus, and glossopharyngeal
• clinical implications: muscles of jaw, larynx, and upper face receive bilateral projections
• therefore, unilateral UMN lesion does not profoundly impair the function of these cranial nerves
• spares mastication, phonation, and speech
• if patient has bilateral UMN lesions or a LMN lesion, then observe dramatic deficits

• relate to cell bodies in motor cortex and descending axonal processes before they synapse on cranial or spinal motor neurons
• patient loses precise and delicate motor control of distal limb muscles used in fine manipulative skills and speech and facial expression

• cell bodies in spinal cord (alpha-motor neurons)
• cranial motor nuclei in brainstem
• provide output pathway to peripheral functions via their axons
• innervate muscle fibers

• paralysis (spastic) or weakness
• increased muscle tone
• no twitching or fasciculation
• increased reflexes
• positive Babinski sign
• multiple muscles or limbs (monoplegia, hemiplegia, or quadriplegia)

• neurobiologist strokes bottom of foot with a pointed object
• WNL- 'toes down-going'
• positive babinski sign- 'toes up-going'
• positive babinski in child less than 5-7 years old is not a concern

• paralysis (flaccid) or weakness
• decreased muscle tone
• muscle atrophy (wasting away- visible)
• fibrillations and fasciculations
• decreased reflexes
• no babinski sign or other abnormal reflexes
• involvement in a single limb or selected muscles

• firing of single denervated fiber
• denervated- muscle no longer being served by a nerve
• not visible to naked eye

• spontaneous firing of motor units
• visible with naked eye
• may be most noticeable on tongue
• ex. twitching of the tongue
• also denervated (always LMN)

• cell bodies in gray matter of brainstem
• cross midline
• terminate in thalamus

• cell bodies in thamalus
• project to sensory cortex in parietal lobe

• trigeminal (V)
• facial (VII)
• vestibuloacoustic (VIII)
• glossopharyngeal (IX)
• vagus (X)
• hypoglossal (XII)

trigeminal (V)

sensory component

• principle sensory nerve for head, face, and oral cavity
• mediates sensations of pain, temperature, and discriminative touch (placing paperclip in someone's mouth with eyes closed and asking them to tell you what it is or two pricks on arm--tell between one or two pricks)

trigeminal (V)

motor component

• three branches: opthalmic, maxillary, and mandibular
• loss of sneezing and blinking reflexes because of interrupted innervation of nasal mucosa and exterior surface of eye

• trigeminal motor nucleus controls muscles of mastication
• bilateral projections
• therefore, with a unilateral UMN lesion, likely to see only mild weakness of contralateral mastication muscles

• marked paralysis of mastication muscles bilaterally
• mandible hangs low
• much difficulty chewing foods
• difficulty in production of vowels and labial and lingual consonant sounds (speech will be severely impaired/dysarthric)

• ipsilateral paralysis of muscles of mastication
• jaw slightly deviates toward side of lesion
• jaw deviation is exaggerated upon jaw protrusion
• fasciculations and atrophy on ipsilateral side
• jaw jerk reflex is absent

• patient bites down on tongue depressor
• patient moves jaw laterally against resistance
• patients open and close jaw against resistance (while you're pressing up or down)

facial (VII)

primarily motor nerve

• innervates all muscles of facial expression
• innervates the stapedius muscle
• parasympathetic efferents to lacrimal, sublingual, and submandibular glands

facial (VII)

sensory component

• likely to affect all functions of facial nerve
• paralysis or ipsilateral facial muscles
• excessive secretion from glands
• loss of taste from anterior two-thirds of tongue

• motor nucleus that controls lower half of face only receives projections from contralateral motor cortex
• however, motor nucleus that controls upper half of face receives bilateral projections

• contralateral lower face weak
• loss of nasolabial fold
• sagging of mouth
• upper face intact
• able to furrow forehead bilaterally
• able to tightly close both eyes

• ipsilateral signs
• entire half-face is paralyzed
• decreased forehead furrows
• weakness noted in closing eye
• loss of nasolabial fold
• sagging of mouth

• two branches
• vestibular division- mediates head position (equilibrium) in space
• acoustic division- serves hearing

• impaired equilibrium
• vertigo or dizziness
• sensation of moving around in space
• nystagmus
• rhythmic movement of eye in which eye moves slowly away from center and then returns rapidly

• sensorineural hearing loss
• involvement of cochlear nuclei, cochlear nerve, and/or central auditory pathways
• tinnitus, possible symptom
• sensation of ringing, buzzing, or other noises

glossopharyngeal nerve (IX)

sensory component

• mediates touch, pain, muscle tension, and temperature sensations from upper pharynx, tonsils, Eustachian tube, soft palate, and posterior third of tongue
• mediates taste from posterior third of tongue

glossopharyngeal nerve (IX)

efferent component

• because of overlapping nuclei and proximity to other cranial nerves and nuclei, selective lesion affecting only glossopharyngeal is rare
• usually assessed with functions of vagus cranial nerve (X)

• only IX (very rare)
• loss of general and taste sensation from ipsilateral posterior third of tongue
• loss of cutaneous sensation from posterior third causes loss of gag reflex
• poor control of parotid gland leads to excessive oral secretion (saliva production)

vagus nerve (X)

visceral afferent

• afferent- toward brainstem
• mediates general sensation from muscles of pharynx, larynx, thorax, and abdomen
• important for safe swallowing function

vagus nerve (X)

visceral efferent

• innervates viscera: cardiac muscles; and smooth muscles of trachea, esophagus, stomach, and intestines

vagus verve (X)

special visceral afferent

• mediates taste sensation from pharyngeal area

• unilateral lesion of nerve fibers and/or nucleus itself results in ipsilateral paralysis of soft palate, pharynx, and larynx
• nucleus is shared with glossopharyngeal nerve (IX)

• lesion specific to pharyngeal branch of vagus
• results in paralysis of pharynx and soft palate
• leads to swallowing difficulty
• may result in hypernasal speech

• unilateral LMN lesion of recurrent laryngeal nerve
• leads to unilateral vocal fold paralysis (both vocal folds will not come to midline--only one)
• breathy and hoarse vocal quality (too much extra air b/c vocal folds are not together)
• may also lead to aspiration

• normal soft palate
• paralysis of left soft palate and pharyngeal wall from LMN lesion
• left palatal arch sags
• uvula moves to right
• bilateral soft palate analysis
• palatal arch remains symmetrical but hangs lower than normal

• controls tongue movement
• innervates all intrinsic (both attachments on tongue) and most extrinsic tongue muscles (one point of attachment in tongue-other somewhere else)
• only contralateral projections
• all fibers cross over to contralateral side. none stay ipsilateral which results in severe weakness on one half of the tongue

• ipsilateral half of tongue paralyzed
• tongue becomes flaccid and wrinkled
• atrophy
• on protrusion, tongue deviates toward side of lesion
• leads to dysarthria
• results in swallowing difficulty
• difficulty with formation and control of bolus

• bilateral paralysis of tongue
• entire tongue flaccid and wrinkled
• bilateral atrophy
• patient may not be able to protrude (move tongue out) his tongue
• results in severe dysarthria 
• leads to severe difficulty in swallowing and eating