Week 4 Learning Issues Part 1 Flashcards
Caudal brainstem contains which divisions
medulla, pons, and midbrain
cd brainstem receives input from
SA and VA from PNS (via cranial nerves) and input from special sense organs
cd brainstem contains ___ neurons
efferent neurons that control that control motor fxs and is involved in relatively basic reflex fxs
contains neuron populations involved in more complex processing of somatic and visceral information as well as UMNs which control motor activity in brainstem and spinal cord LMNs
clinical relevance cd brainstem
important in controlling respiration, cardiovascular fx and gait
D to V division cd brainstem
tectum (midbrain), tegmentum (rostral continuation of spinal cord runs throughout all 3 divisions), and ventral pons
tegmentum relative to tectum and v pons
tectum D to tegmentum in midbrain/ mesencephalon and ventral pons is ventral to tegmentum in pons/ metencephalon
tegmentum path
continuous structure that spans length cd brainstem; no abrupt changes in structure of tegmentum at transition between medulla, pons, and midbrain and functional neuron populations within tegmentum may span multiple brain divisions
cd brainstem neuron groups
discrete nuclear groups: CN nuclei Tectum and pretectal nuclei projection nuclei red nucleus Reticular formation - origin of reticulospinal tracts - neurocircuitry coordinating visceral and homeostatic functions - ascending reticular activating system - monoamine pathways
Tectum (Rostral and Caudal Colliculi) and Pretectal nuclei
involved in visual and auditory processing
projection nuclei
synaptic stations along sensory pathways to cerebellum and cortex
red nucleus
UMNs of rubrospinal tract involved in voluntary movement
reticular formation
contains many neuron populations that are more diffusely organized
- origin of reticulospinal tracts
- neurocircuitry coordinating visceral and homeostatic functions
- ascending reticular activating system
- monoamine pathways
The reticular formation is a histological distinction
It spans medulla, pons, and midbrain
Is a rostral extension of intermediate gray of spinal cord but more developed
origin of reticulospinal tracts
UMNs involved in locomotion
neurocircuitry coordinating visceral and homeostatic fxs
ex. brainstem micturition center, respiratory center and cardiovascular center
ascending reticular activating system
ARAS monoaminergic neurons involved in arousal, maintaining consciousness, sleep/ wake cycle and attention
monoamine pathways
modulate activity in sensory and motor pathway
reticular formation histological vs functional entity
- composed of neurons not included in major nuclear groups of brainstem bc neurons don’t form tight clusters with clear boundaries; there are distinct neuron populations w diff fxs, morphology, and neurochemistry although not histologically visible
axon tracts cd brainstem
- neurons in forebrain project to cd brainstem, cerebellum, and spinal cord to control motor activity and regulate sensory processing
- neurons in spinal cord send axons carrying sensory info to cd brainstem, cerebellum, and forebrain
medial lemniscus
axon tract running through cd brainstem; carry proprioceptive information to forebrain
crus cerebri, longitudinal fibers of pons, and pyramids
axon tract running through cd brainstem; carry motor information to spinal cord
medial longitudinal fasciculus
axon tract running through cd brainstem; associated with vestibular system
axon tracts running through cd brainstem
medial lemniscus, crus cerebri, longitudinal fibers of pons, pyramids, and medial longitudinal fasciculus
pathways that travel through caudal brainstem to get where they are going
locomotion, postural reactions, and conscious perception of sensory stimuli
hypoglossal nucleus location
caudal medulla, ventral to 4th ventricle
path of hypoglossal nerve
- hypoglossal nucleus
- ventrally through medulla
- lateral to pyramids as rootlets
- rootlets merge at hypoglossal canal forming hypoglossal nerve
- exit skull cd to TOF (hypoglossal canal)
- courses medial to mandibular salivary gland
- enters tongue adjacent to lingual artery
CN XI nucleus
- spinal accessory nucleus
- LMNs in spinal cord segments C1-C7
CN XI path
- spinal accessory nucleus
- rootlets exit lateral cervical spinal cord
- roots travel crly lateral to spinal cord
- roots merge to form CN XI
- foramen magnum
- lateral to medulla
- jugular formamen
- TOF
CN IX nuclei
- nucleus of the solitary tract (VA)
- parasympathetic nucleus of CN IX (VE)
- Nucleus ambiguous (SE)
Nucleus of solitary tract
- extends from rostral to cd medulla; just v to 4th ventricle
- only VA nucleus of brainstem; important for autonomic fx
- receives VA information from CN IX, X, and spinal cord (via symp pathways)
Nucleus of solitary tract CN X
- Afferent neurons carry visceral sensory info from sensory receptors in pharynx, larynx, trachea, esophagus, and thoracic and abdominal viscera
- VA neuron cell bodies in distal ganglia of the vagus
- enter medulla laterally via TOF
- jugular foramen
- enter brainstem at lateral medulla
- synapse in nucleus of solitary tract ( medulla)
distal ganglion of the vagus
near the TOF
Nucleus of solitary tract CN IX
- Afferent neurons carry visceral sensory info from sensory receptors in cd tongue and pharyngeal muosa and baro and chemoreceptors in proximal neck
- cell bodies in glossopharyngeal ganglion
- TOF
- Jugular foramen
- Enter brainstem at lateral medulla
- synapse in nucleus of solitary tract (medulla)
glossopharyngeal ganglion
near TOF
nucleus of solitary tract and autonomic reflexes and functions
projects to brainstem reticular formation and other CN nuclei (PNX, NA) to mediate these
nucleus of solitary tract and higher level processing of visceral sensory information
projects to hypothalamus and thalamus for this
parasympathetic nucleus CN X location
- located in dorsal caudal medulla, runs from mid to cd medulla
parasympathetic nucleus CN X path
???
- 1st neuron parasympathetic nucleus CN X (dorsal cd medulla)
- enter medulla laterally via TOF
- jugular foramen
- enter brainstem at lateral medulla
- synapse in nucleus of solitary tract ( medulla)
Parasympathetic nucleus CN IX
- cell bodies in parasympathetic nucleus CN IX
- Axons enter crainial cavity via Tympanooccipital Fissure -Jugular Foramen
- Enter brainstem at lateral medulla
- Synapse in Nucleus of the Solitary Tract
Nucleus ambiguus
- LMN cell bodies for X and IX innervation skeletal muscles of pharynx, larynx, esophagus here (these are skeletal muscles involved in swallowing, gagging, breathing, and vocalizing)
- Ventrolateral location in medulla runs from mid to cd medulla
Path from nucleus ambiguus
- Nucleus ambiguus located in medulla
- axons emerge from lateral aspect medulla and contribute to CN IX and X
- exit skull via jug formamen -TOF
LMNs that innervate skeletal muscles of pharynx
via CN IX
LMNs that innervate skeletal muscles pharynx, larynx, and esophagus
via CN X
endoscopic evaluation of laryngeal function can identify a CN __ deificit
CN X
gag reflex
- afferents from cd tongue (IX), pharynx (IX and X), and larynx (X) travel in CNs IX and X and synapse in nucleus of solitary tract
- reflex center in medulla
- somatic efferents from nucleus ambiguous travel in CN IX and X -> elevation of the palate, contraction of pharynx and larynx, and sometimes retching (involves more than CN IX and X)
autonomic and respiratory fx
- visceral sensory info carried on CN X and CN IX processed in autonomic regulatory centers in cd brainstem
- regulate important physiological fxs including respiration, maintanece blood pressure, HR
- nucleus solitary tract and parasympathetic nucleus of CN X= pt of these regulatory centers
- severe lesions cd brainstem -> autonomic and respiratory dysfunction but many non-neuron causes can -> these issues too so not useful for lesion localizing
Nuclei of CN V
- Trigeminal sensory nuclear complex
- motor nucleus of trigeminal nerve
Trigeminal sensory nuclear complex
- 3 CN nuclei that receive sensory info from branches trigemnial nerve span cd brainstem
- axons carrying input nociceptors travel cdly w/ in brainstem and synapse in medulla
- axons carrying input mechanoreceptors synapse in pons
trigeminal sensory nuclei in medulla and pons involvedin
local brainstem reflexes (palpebral, corneal, facial twitching in response to facial stimulation) involve interneuron connections between trigeminal sensory and facial motor nuclei
trigeminal nuceli project via
trigeminal-thalmic tract -> forebrain for conscious perception higher level processing of sensory info from face
somatic sensory fx CN V
mechanoreception, nociception, thermoception, proprioception
- sensory input from face, oral, and nasal cavities and jaw carried to CNS via pseudo unipolar neurons w. cell bodies in trigeminal ganglion
V1 path
- enters cr cavity via orbital fissure
- cavernous sinus
- cell bodies in trigeminal ganglion (rostral tip PTB)
- trigeminal canal (tip of PTB)
- joins brainstem at lateral pons
- synapse in trigeminal sensory nuclei (medulla, pons)
V2 path
- enters cr cavity via round foramen
- cavernous sinus
- cell bodies in trigeminal ganglion (rostral tip PTB)
- trigeminal canal (tip of PTB)
- joins brainstem at lateral pons
- synapse in trigeminal sensory nuclei (medulla, pons)
V3 SA path
- enters cr cavity via oval foramen (cd to cavernous sinus)
- cell bodies in trigeminal ganglion (rostral tip PTB)
- trigeminal canal (tip of PTB)
- joins brainstem at lateral pons
- synapse in trigeminal sensory nuclei (medulla, pons)
- ** DOES NOT GO THROUGH CAVERNOUS SINUS***
motor nucleus of trigeminal nerve
located in pons
- contains LMN cell bodies for muscles mastication
V3 SE path
- LMN cell bodies in motor nucleus of trigeminal nerve in pons
- LMN axons run through trigeminal canal in PTB
- Exit skull via oval foramen as part of V3
- ** DOES NOT GO THROUGH CAVERNOUS SINUS***
Facial nerve nuclei
- Facial nucleus
- parasympathetic nucleus of CN VII
- trigeminal sensory nuclei
facial nucleus
- located in rostral ventral medulla
- cell bodies of LMNs to muscles of facial expression and cd digastrics
CN VII path
- LMNs in facial nucleus in rostral ventral medulla
- axons exit brainstem at lateral aspect trapezoid body
- axons enter petrous temporal bone via internal acoustic meatus
- through petrous temporal bone (via facial canal) and middle ear (near ossicles in dorsal middle ear)
- exit skull via stylomastoid foramen (cd to external acoustic meatus)
- courses ventrolateral to horizontal ear canal
- at cd border of masseter muscle divides into auriculopalpebral and dorsal and ventral buccal branches
parasympathetic nucleus CN VII
in rostral medulla
- contains parasympathetic VE neurons to lacrimal and nasal glands, mandibular and sublingual salivary glands
trigeminal sensory nuclei
sensory neurons from skin on concave surface of pinna synapse here
CN VII dry eye
seen with lesions of CN VII axons to lacrimal gland split form CN VII within PTB so only very proximal facial nerve lesions will present with decreased tear production
trigeminal-facial reflex loop
- blink or twitch of lips, face, whiskers, ear ect = normal response
- behavioral response like pulling head back or pawing at stimulus = conscious perception of sensory stimulation ie conformation that pathway from stimulated branch trigeminal nerve to trigeminal sensory nuclei to contralateral thalamus and cerebral hemisphere is in tact
CN II nuclei
- suprachiasmatic nucleus
- lateral geiculate nucleus (LGN)
- rostral colliculus
- pretectal nuclei
suprachiasmatic nucleus
- hypothalamus
- entrainment of circadian rhythms
lateral geniculate nucleus (LGN)
- thalamus
- relays info from visual cortex for conscious perception and higher level processing
rostral colliculus
- tectum
- visual orienting response
- connections to CNs III, IV, VI to control eye movements toward visual targets
- tectospinal tract controls movement of head to turn toward visual targets
pretectal nuclei
- located at junction rostral mesencephalon and cd diencephalon
- mediates PLR via connections to parasympathetic nucleus CN III
optic chiasm
greater than half of the axons in each optic nerve cross to travel in optic tract on contralateral side here
CN II path
- optic nerve enters cr cavity via optic canal
- optic chiasma at Jnx rostral and middle cr fossa
- optic tract (lateral aspect diencephalon)
- termination: LGN of thalamus, pretectal nuclei, rostral colliculus, suprachiasmatic nucleus
PLR pathway decussates
at both the optic chasm and the midbrain
pathway for PLR
- optic nerve
- optic tract
-optic chiasm (some axons stay in optic nerve and tact on same side some cross to contralateral side via optic chiasma) - pretectal nuclei (ganglion cell axons carry visual info from 1 retina to both pretectal nuclei (at jxn rostral mesencephalon and cd diencephalon) )
- pretectal nuclei project bilaterally into parasympathetic nucleus of CN III in midbrain
- Cavernous sinus
oribtal fissure - PN CN III contains parasympathetic preganglionic neurons that project via CN III to ciliary ganglion
- post ganglionic neurons ciliary ganglio project to pupillary constrictor muscles to mediate pupil constriction
direct PLR
light shined in one eye elicits pupillary constriction in same eye
indirect or consensual PLR
light shined in one eye elicits pupillary constriction in opposite eye; occurs bc bilateral projections in PLR pathway (PLR pathway decussates at both optic chiasm and midbrain)
horners syndrome
caused by interruption to sympathetic innervation of pupil, 3rd eyelid, and periorbital smooth muscle
purpose of sympathetic innervation to eye
dilate pupil in response to threatening stimulus
VE neurons in LH know threatening situation has occured
information comes from processing of visual, auditory, olfactory, and somatosensory nociceptive pathways and is relayed to autonomic control centers in hypothalamus and brainstem autonomic control centers then project to symp preganglionic neurons in LH spinal cord segments T1-T3
Path symp innervation to eye
- symp preganglionic neurons LH T1-T3
- sympathetic trunk
- cr cervical ganglion
- TOF
- carotid canal
- cavernous sinus
- orbital fissure
3 nuclei containing LMNs to extraolcular muscles
- Oculomotor nucleus
- Trochlear nucleus
- Abducent nucleus
medial longitudinal fasciculus
MLF; interconnects oculomotor nucleus, trochlear nucleus, and abducens nucleus with each other, with vesicular nuclei and with LMNs in neck; interconnections permit coordination of eye movements and head movements
Oculomotor nucleus location
rostral midbrain near midline v to periaqueductal grey
CN III path
- oculomotor nucleus
- tegmentum
- emerge from V midbrain medial to crus cerebri
- cavernous sinus
- orbital fissure
- ventral rectus, dorsal rectus, medial rectus, ventral oblique, and levator palpebrea muscles
trochlear nucleus location
- cd midbrain in same location relative to periaqueductal grey (PAG) as oculomotor nucleus
CN IV path
- Trochlear nucleus
- axons pass D around PAG
- decussate in rostral medullary vellum (roof 4th ventricle rostral to cerebellum)
- over lateral aspect midbrain
- cavernous sinus
- orbital fissure
- dorsal oblique muscles
Abducens nucleus location
rostral medulla near midline ventral to 4th ventricle
CN VI path
- abducens nucleus
- tegementum
- lateral to pyramids at level of trapezoid body
- cavernous sinus
- orbital fissure
- lateral rectus and retractor bulbi muscles
LMNs in oculomotor, trochlear, and abducens nuclei are controlled by
UMN projection from many areas of brain including vestibular nuclei, rostral colliculus, and motor cortex
parasympathetic nucleus CN III
located medial to oculomotor nucleus (rostral midbrain near midline v to periaqueductal grey)
path through parasympathetic nucleus CN III
- parasympathetic nucleus CN III
- axons travel as part CN III (cavernous sinus -> orbital fissure)
- synapse in ciliary ganglion w/ in periorbita
- postganglionic neurons form ciliary nerves which innervate ciliary muscles and pupillary constrictors
normal eye position depends on
intact vesicular system and MLF as well as CNs III, IV, and VI
strabismus
deviation form normal eye position; occurs with normal head position suggesting lesion to LMN (cell body or axon)
oculomotor damage -> strabismus
ventrolateral strabismus
trochlear damage -> strabismus
rotated (cat vs calf)
abducens damage -> strabismus
medial strabismus
positional strabismus
occurs when head moved into certain position; suggests lesion affecting MLF or vestibular nuclei
normal VOR
- move animals head side to side eyes move in opposite direct as head so gaze is fixed
- depends on intact vestibular system, intact MLF, and functioning LMNs to extra ocular muscles
resting nystagmus
oscillating moevement of eye occurs spontaneously with head in normal position
positional nystagmus
occurs when head moved into certain positions
resting and positional nystagmus suggest
a lesion affecting the vestibular system or cerebellum bc damaged vestibular system is reporting head movements that are not occurring and eye movement system is generating eye movements based on faulty input
visual following
tests CN II visual pathways through cerebral cortex, descending pathways from cerebrum to brainstem, cerebellum and CNs III, IV, and VI
vestibular nuclei location
located in rostral medulla slightly cd and immediately medial to cd cerebellar peduncle
auditory system
- hair cells in cochlea transduce auditory stimulus and release neurotransmitter onto dendrites of primary afferent neurons
- cell bodies of primary afferents in spiral ganglion in PTB
- through PTB
- internal acoustic meatus
- join brainstem at level of trapezoid body
- synapse on cochlear nuclei in rostral medulla
auditory information used locally
in brainstem for more reflexive types of behavior such as auditory orienting
unilateral auditory deficits
difficult to detect, animal with lesion in PTB, brainstem, or forebrain that disrupts auditory pathway patient will like present for more noticeable and serious problems than hearing loss
vestibular apparatus
- located within PTB
- bony labyrinth (semicircular canals and the vestibule) houses epithelial lined membranous labrynth (composed of semicircular ducts and saccule and utricle)
- filled with endolymph (fluid that flows within the ducts in response to movements of the head)
endolymph
movement of endolymph detected by hair like processes of specialized receptor cells (hair cells) located in ampullae of semicircular canals; hair cells release neurotransmitter from their basal surface onto vestibular afferents
primary vestibular afferents
- dendrites near basal surface of hair cells of vestibular apparatus
- cell bodies located w/ in vestibular ganglion in PTB
- axons join those of auditory afferents run through PTB -> int acoustic meautus into cr cavity
- fibers enter brainstem at level trapezoid body to synapse in vestibular nuclei and cerebellum
where do primary vestibular afferents synapse in cerebellum
flocculonodular lobe and vermis
vestibular apparatus detects
acceleration and rotation of head
semicircular canals
oriented to be in 3 perpendicular planes so they can encode angular rotation of the head
semicircular canals on L and R of head
designed to function in pairs based on orientation in common plane
movement exciting vestibular afferents from semicircular duct on one side
inhibits vestibular afferents from paired duct on opposite side; this info is then conveyed to the vestibular nuclei (ie rotation head to right increases activity in vestibular afferents on right and decreases activity in vestibular afferents on left based on how hair cells respond to movement)
vestibular nuclei gives rise to what 3 major motor pathways
- Medial vestibulospinal tract/ pathway
- lateral vestibulospinal tract/ pathway
- pathway for vestibule-ocular reflex (VOR)
medial vestibulospinal tract/ pathway location
- projects bilaterally to cervical spinal cord via MLF and ventromedial funicilus
Medial vestibulospinal tract/ pathway fx
provides innervation to the neck muscles that control head position; controls movements of head for maintaining posture and balance
lateral vestibulospinal tract/ pathway location
- projects ipsilaterally to all levels spinal cord via ventromedial funiculus
- excites LMNs to ipsilateral axial and proximal limb extensors and inhibits lens innervating ipsilateral flexors
lateral vestibulospinal tract/ pathway fx
- turning or tilting head in one direct increases activity in ipsilateral vestibular nucleus which produces increased ipsilateral extensor tone to maintain balance
- pathway also facilitates ipsilateral stretch reflex for extensor muscles and inhibits contralateral stretch reflex
lesions involving vestibular nuclei can afffect
general muscle tone and stretch reflexes (bc lateral vestibulospinal tract/ pathway facilitates ipsilateral stretch reflex for extensor muscles and inhibits contralateral stretch reflex)
vestibular nuclei projects
into brainstem for reticular formation vomitting center and to cerebral cortex for conscious perception of head position movement and higher level motor processing
Pathway for VOR
- from vestibular nuclei on either side travels rostrally in medial longitudinal fasciculus (MLF) to synapse:
- excitatory synapse on ipsilateral oculomotor nucleus (controls MR)
- excitatory synapse on contralateral abducens nucleus (controls LR)
VOR activity in vestibular nuclei on either side
drives eyes in the contralateral direction
in absence of head movement vestibular nuclei
have baseline level of activity balanced so eyes look straight ahead; if head rotates in horizontal plane eyes will move in contralateral direction
nystagmus
- normal phenomenon that exists to maintain appropriate eye position in face of large rotational movements of head
- 2 phases slow phase and fast phase
slow phase of nystagmus
at beginning of head movement eyes move with equal velocity as head but in opposite direction to keep image stabilized on retina; this stage is slow phase of nystagmus which is VOR
fast phase of nystagmus
head continues to move eyes reach maximal excursion and can no longer maintain the stationary image a fast eye movement occurs to fix gaze at new central location
this is not dependent on VOR pathway
nystagmus naming
named for direction of fast phase should name it nystagmus with slow phase to left and/ or fast phase to the right rather than right nystagmus
when cavity in vestibular nuclei on either side of brain is balanced
motor input to postural muscles on both sides of body is equal ; equal activity in vestibular nuclei results in equal stimulation of medial and lateral rectus muscles for both eyes
lesion that causes unilateral damage to vestibular apparatus, vestibular nerve, or vestibular nuclei in brainstem
will cause an imbalance in the system resulting in somewhat predictable movements of the eyes and postural muscles
lesion of vestibular apparatus, nerve or nucleus may cause abnormal nystagmus with slow phase
directed toward the lesion; nystagmus is initiated by the VOR
when lesion abolishes activity in the vestibular apparatus, nerve, or nuclei on one side
the baseline cavity on the other side is unopposed -> VOR toward side of lesion followed by a fast eye movement away from lesion when eyes reach their maximal excursion in orbit
patient with lesion of vestibular apparatus, nerve, or nuclei often presents with
loss of balance including a tendency to fall, turn (tight circles) or demonstrate a head tilt toward the side of the lesion largely bc decreased extensor tone on side of the lesion; if vestibular apparatus nerve or nucleus on one side is no longer active there is loss of excitatory input to ipsilateral extensors of limbs via lateral vestibulospinal tract; contralateral limb will still have extensor tone
cerebellum plays a critical role in
maintenance of posture and in control of eye movements; combines vestibular input with input from many systems including the visual system and proprioceptors in the limbs, trunk, neck, and eye muscles; determines appropriate movement and feedback to vestibular nuclei to influence their output
axons from cerebellum to vestibular nuclei
travel in caudal cerebellar peduncle
effect of the cerebellum on the vestibular nuclei
is inhibitory
unilateral lesion of cerebellum or cd cerebellar peduncle can result in Turing/ tiltiing/ falling ___ from the side of the lesion
away; this = paradoxical vestibular dx bc clinical signs relative to lesion are reversed; rather than diminishing activity in the vestibular nuclei the cerebellar lesion releases the vestibular nuclei from inhibition resulting in increased activity in vestibular pathways ipsilateral to cerebellar lesion
peripheral vestibular dx
refers to problem affecting PNS components of vestibular system (vestibular apparatus and vestibular nerve)
central vestibular dx
refers to problem affecting CNS components of vestibular system (vestibular nuclei, cd cerebellar peduncle, and cerebellum)
