Neurology - CN, tracts Flashcards
CN II
Optic nerve: sight
- optic nerves converge to form optic chiasm then goes on as optic tract
- synapse on LGN
- Middle cranial fossa, sphenoid bone - optic canal + opthalmic artery and centra retinal vein
CN I
Olfactory nerve ( bulb + tract)
- only CN nerve that bypasses thalamic relay to cortex
- synapses directly in the uncus
- anterior fossa, cribriform plate
CN III
Oculomotor nerve: Motor
- Oculomotor nucleus (midline midbrain): SR, IR, MR, IO, levator palpebrae (opens eyelid)
- Nucleus of Edinger Westfall (pretectum of midbrain): preganglionic parasympathetic -> pupillary constriction (sphincter m.) & accomodation (ciliary m.)
- Middle cranial fossa, sphenoid bone - superior orbital fissure + opthalmic vein
CN IV
Trochlear nerve: motor
- Trochlear nucleus (midline midbrain): SO
- Middle cranial fossa, sphenoid bone –> superior orbital fissure
CN V
Trigeminal nerve: Both
-V1: opthalmic sensation; superior orbital fissure
-V2: maxillary sensation; foramen rotundum
-V3: mandibular sensation + motor to muscles of mastication + somatosensory of anterior 2/3 of tongue; formen ovale
Trigeminal nuclei: Trigeminal motor nucleus (midline pons) = mastication; Spinal nucleus (lateral pons/medulla/upper spine) = Protopathic; Main sensory nucleus (lateral pons = sonsory
CN VI
Abducens: motor
Abducens nucleus: LR
-Middle cranial fossa, sphenoid bone–> superior orbital fissure
CN VII
Facial nerve: Both
- Facial nucleus (midline pons): facial movement, closes eyelid, stapedius muscle in the ear
- Nucleus solitarius (lateral pons): anterior 2/3 taste
- Superior salvatory nucleus: lacrimation & salivation (submandibular and sublingual glands
- Posterior cranial fossa, temporal bone –> internal acoustic meatus
CN VIII
Vestibulocochlear nerve: sensory
- Vestibular nucleus (lateral pons/medulla): balance
- Cochlear nucleus (lateral pons): hearing
- posterior cranial fossa, temporal bone–> internal acoustic meatus
CN IX
Glossopharyngeal nerve: both
- Nucleus ambiguus (lateral medulla): stylopharyngeus m. (elevates pharynx and larynx) = swallowing
- Nucleus solitarius (lateral pons) : taste & somatosensory from from posterior 1/3 of tongue, carotid body monitoring
- Inferior salivatory nucleus: (preganglionic parasympathetic) salivation of parotid gland
- Posterior fossa, temporal bone –> jugular foramen
CN X
Vagus nerve: Both
- Nucleus solitarius (lateral pons): taste of epiglottis, barorecptors of aortic arch, thorachoabdominal viscera (lungs, gut distention)
- Nucleus ambiguus (lateral medulla): motor innervation of pharynx, larynx and upper esophagus = talking, swallowing, coughing, midline uvula
- Dorsal motor nucleus (midline low pons/upper medulla): pre-ganglionic parasympathetic fibers to heart, lungs, and upper GI
- Posterior fossa, temporal bone–> jugular foramen
CN XI
Accessory nerve: motor
-Accessory nucleus: motor to SCM, trapezius = turning head, shoulder shrugging
-Posterior fossa, temporal bone, jugular foramen
Note spinal roots of Xi exit through foramen magnum
CN XII
Hypoglossal nerve: motor
-hypoglossal nucleus (midline medulla): tongue movement
What cranial nerves arise from the midbrain?
III, IV
What cranial nerves arise from the pons?
V-VIII
What cranial nerves arise from the medulla?
IX, X, XII
Recall: XI arise from the spinal cord
Nucleus solitarius
visceral sensory information - taste, baroreceptors, gut distention
-CN VII, IX, X
Nucleus ambiguus
:Lateral medulla; motor innervation of pharynx, larynx, and upper esophagus = swallowing, palate elevation
-CN IX, X, XI (cranial portion)
Dorsal motor nucleus
:midline low pons/upper medulla; sends autonomic pre-ganglionic parasympathetic fibers to heart lungs and upper GI
-CN X
Contents of optic canal
CN II, opthalmic artery, central retinal vein
Contents of superior orbital fissure
CN III, IV, V1, VI, opthalmic vein, sympathetic fibers
Significance of foramen spinosum
external carotid–> maxillary artery –> middle meningeal artery which enters the skull through the foramen spinosum of the temporal bone to supply the meninges and calvarium
Contents of the jugular foramen
CN IX, X, XI, jugular vein
What runs through the foramen magnum?
Spinal roots of CN XI, brain stem, vertebral arteries
Corneal reflex
V1 opthalmic (nasocilary branch) + VII (orbicularis oculi)
Lacrimation
V1 + VII
Note: loss of corneal reflex does not also cause loss of emotional tears
Jaw Jerk
V3 (sensory- muscle spindle from masseter) + V3 (motor- masseter)
Pupillary light reflex
II + III
Gag reflex
IX + X
CN V motor lesion
Jaw deviates toward side of lesion due to unopposed force from the opposite pterygoid muscle.
CN X lesion
Uvula deviates away from the side of the lesion. Weak side collapses and uvula points away
CN XI lesion
weakness turing head to contralateral side of lesion (SCM). Shoulder droop on side of lesion (trapezius)
Note: left SCM contracts to turn head to the right
CN XII lesion (LMN)
tongue deviates toward the side of the lesion due to weakened tongue muscles on the affected side.
CST
Extends from motor cortex -> corona radiata-> internal capsule (posterior limb) -> cerebral peduncle-> basis pontis -> decussate at caudal pyramids -> continue as lateral CST in lateral
- lateral CST organized laterally to medially : LTACervical
- anterior CST
Epicritic sensation
: Receptors are muscle spindles, golgi tendon organs, pacinian corpuscles, meisseners corpuscles, etc.; detect pressure, vibration, touch proprioception
- primary sensory cell bodies in the DRG, axons travel in:
1. Fasiculus gracilus (below T6 = lower body, legs)
2. Fasiculus cutneatus (above T6= upper body, arms) - synapse in nucleus grasiclus/cuneatus in medulla and decussate –> medial lemniscus -> VPL
Protopathic sensation
: receptors are C fibers and A-delta fibers that detect pain and temperature
- cell bodies in the DRG, axons enter spinal cord synase on rexed laminae ->decussate @ anterior white commissure -> spinothalamic tract -> spinal lemniscus -> VPL
- Lateral spinothalamic tract organized laterally to medially: LTACervical
- anterior spinothalamic tract: crude touch and pressure
What thalamic nucleus mediates sensation of the face?
VPM –> primary motor cortex
- Protopathic (pain & temp) mediated by spinal trigeminal nucleus
- Epicritic mediated by main nucleus of trigeminal nerve
What thalamic nucleus mediates vision?
LGN –> primary visual cortex @ calcarine sulcus
“lateral for light”
What thalamic nucleus mediates hearing?
MGN -> temporal lobe (transverse gyrus of Heschl)
“Medial for music”
What thalamic nucleus mediates motor function?
VL
-basal ganglia and cerebellum communicate via VL to thalamus which relays to motor cortex
What thalamic nucleus mediates general epicritic sensory?
VPL
Recall: epicritic = pressure, vibration, touch, proprioception
What thalamic nucleus mediates genera protopathic sensory?
VPL
Recall: protopathic= pain, temperature, crude touch, pressure
Conductive hearing loss
Rinne: bone> Air
Weber: localizes to affected ear
“goes to bad ear, but its not too bad just conductive hearing loss”
Sensorineural hearing loss
Rinne: air> bone
Weber: localizes to unaffected ear
“ goes to good ear, but that not good its sensorineuro loss”
Paralysis of the lower face with forehead sparred. Where is the lesion?
contralateral UMN lesion
- CBT provides contralateral innervation to upper and lower portion of facial nerve; CBT on ipsilateral side only provides innervation to upper portion
- if contralateral CBT lesioned = denervated lower portion of CN VII
Paralysis of upper and lower portion of the face. Where is the lesion?
Ipsilateral CN VII (LMN lesion)
Peripheral paralysis of one side of face - drooping smile and inability to close eye on involved side. Diagnosis? Treatment?
: Bell’s palsy; destruction of facial nerve nucleus
- can occur idiopathically and recover in most cases
- Associated with Lyme disease, HSV, herpes zoster, sarcoidosis, tumors, and diabetes
- treatment: corticosteroids
Muscles that close the jaw
Masseter, temporalis, medial pterygoid
-innervated by V3
Muscles that open the jaw
lateral pterygoid
-innervated by V3
Pupillary control miosis
: constriction mediated by parasympathetic
1st neuron: nucleus of Edinger Westfall –> ciliary ganglia via CN III
2nd neuron: short ciliary nerves to pupillary sphincter muscles
Pupillary control mydriasis
: dilation mediated by sympathetic
1st neuron: hypothalamus to ciliospinal center of Budge (C8-T2) and synapses in lateral horn
2nd neuron: exit at T1 to superior cervical ganglion (travels along cervical sympathetic chain near lung apex, subclavian vessels)
3rd neuron: plexus along internal carotid through cavernous sinus, enters orbit as long ciliary nerve to pupillary dilator muscle
Horner syndrome
:Ptosis, anhidrosis, miosis
-associated with lesion of spinal cord above T1
Pupil constricts to consensual but not direct light. Where is the lesion?
CN II lesion = Marcus Gunn pupil
Pupil fails to constrict to direct or consensual light. Where is the lesion?
CN III = hutchinson syndrome
also associated may be with dilated pupil + ptosis + lack of accommodation + down and out gaze
Patient with ptosis. How do you know its parasympathetic or sympathetic lesion?
Look at the pupils:
- Dilated = parasympathetic lesion
- constricted (pinpoint) = sympathetic lesion (above T1)
Explain the pupillary light reflex.
light in either retina sends a signal via CN II to pretectal nuclei in midbrain that activates bilateral nucleus of edinger westfall = pupils contract bilaterally –> consensual reflex
Marcus Gunn Pupil
Deafferented (CN II lesion) that constricts to consensual light but not direct light
Patient presents with ptosis, down and out gaze
CN III motor lesion
- affected primarily by vascular disease (DM) due to decreased diffusion of oxygen and nutrients to the interior fibers from compromised vasculature that resides on outside of nerve
- Note: motor fibers are centrally located within CN III
Patient has absent pupillary light reflex to direct and consensual light & blown out pupil
CN III parasympathetic lesion; often accompanied by ptosis and down and out gaze ( motor portion)
- fibers in the periphery are 1st affected by compression (PICA aneurysm, uncal herniation)
- Note parasympathetic fibers are at the periphery of CN III
Right anopia, where is the lesion?
right cranial nerve II ( nerve portion)
Bitemporal hemianopia, where is the lesion?
optic chiasm
Left homonymous hemianopia, where is the lesion?
RIGHT optic tract, LGN, or optic radiations
Left upper quandrantic anopia, where is the lesion?
right temporal lesion (meyers loop - optic radiations) MCA territory
Left lower quandrantic anopia, where is the lesion?
Right parietal lesion, MCA territory
Left hemianopia with macular sparring, where is the lesion?
Right occipital lobe lesion, PCA territory
Describe the pathway of conjugate gaze when looking to the left.
Saccade- Right frontal eye field activates the left PPRF that stimulates the left CN VI (lateral rectus) –> right MLF to stimulate the right CN III (medial rectus)
C fibers
:free nerve endings; slow unmyelinated fibers, mediate pain and temperature
-located on all skin, epidermis, some viscera
A delta fibers
free nerve endings; fast, myelinated fibers mediate pain and temperature
-located on all skin, epidermis, some viscera
Meissner corpuscles
:large, myelinated fibers, adapt quickly mediate dynamic, fine/light touch; position sense
-located on glabrous (hairless) skin
Pacinian corpuscles
large, myelinated fibers; adapt quickly mediate vibration, pressure
-located in deep skin layers, ligaments, and joints
Merkel discs
large myelinated fibers; adapt slowly; mediate pressure, deep static touch
-located in the basal epidermal layer, hair follicles
Hypothalamus functions
"TAN HATS" Thirst and water balance Adenohypophysis control (regulates anterior pituitary) Neurohypophysis releases hormones produced in hypothalamus Hunger Autonomic regulation Temperature regulation Sexual urges
What are the inputs to the hypothalamus?
Circumventricular organs - not protected by BBB
“Mild SOAP”
Where is ADH produced?
Supraoptic nucleus
Where is oxytocin produced?
Paraventricular nucleus
Lateral area of hypothalamus
Hunger
- Destruction –> anorexia, failure to thrive (infants)
- Inhibited by leptin
Ventromedial area of hypothalamus
Satiety
- destruction (craniopharyngioma) –> hyperphagia
- Stimulated by leptin
Anterior hypothalamus
Cooling, parasympathetic
“A/C”
Posterior hypothalamus
heating, sympathetic
Suprachiasmatic nucleus
circadian rhythm
