B&B Week 3 Flashcards
list the ascending tracts of the brainstem
anterolateral system (spinothalamic)
dorsal column medial lemniscus system
spinocerebellar tracts
list the descending tracts of the brainstem
corticospinal tract
corticobulbar tract
what are the pontine nuclei?
connections from the brainstem to the cerebellum
name the three intrinsic systems of the brainstem
- reticular formation
- neurotransmitter systems
- central pattern generators
list the general components of the brainstem
- ascending and descending tracts
- cranial nerve nuclei
- connections to the cerebellum/pontine nuclei
- intrinsic systems
where are the cranial nerve nuclei found?
brainstem
describe the general organization of the brainstem
motor fibers are derived from the basal plate, located medially
sensory fibers are derived from the alar plate, located laterally
what fibers are derived form the brainstem basal plate?
motor
what fibers are derived from the brainstem alar plate?
sensory
what gross structures make up the brainstem?
midbrain
pons
medulla
what is the otic capsule?
The otic capsule refers to the dense osseous labyrinth of the inner ear that surrounds the cochlea, the vestibule and the semicircular canals. It is surrounded by the less dense / pneumatised petrous apex and mastoid part of the temporal bone.
in the petrous portion of temporal bone
describe the components of the membranous labyrinth contained within the otic capsule
3 semicircular canals, 2 otoliths (utricle and saccule)
the semicircular canals detect angular accelerations, and head rotations (are arranged orthagonally to each other)
otoliths sense body orientation and linear motion (utricle is detects horizontal and saccule detects sagittal)
what is the function of the semicircular canals in the vestibular system?
the semicircular canals detect angular accelerations, and head rotations (are arranged orthagonally to each other)
each canal is sensitive to head rotations in the plane of that canal
together, the 3 canals can specify the direction and amplitude of any head rotation
what is the function of the otoliths in the vestibular system?
otoliths sense body orientation and linear motion (utricle is detects horizontal and saccule detects sagittal)
name and describe the composition of the labyrinth fluids found in the vestibular system
- perilymph–> found between bony and membranous labyrinth
- is similar to extracellular fluid and CSF
- ultrafiltrate of CSF or blood
- low K+, high Na+ - endolymph–> found inside the membranous labyrinth lumen
- unique extracellular fluid as it is more similar to intracellular fluid (high K+ and low Na+)
- produced by DARK cells of the sensory epithelium
describe the vestibular sensory epithelium
contains HAIR CELLS, which are receptor cells for detecting movement of endolymph by projecting into labyrinth lumen
60-100 stereocilia and ONE kinocilium per hair cell
supporting cells are microvilli
tight junctions
terminals of the vestibulocochlear nerve (VIII)
name the two otoliths
utricle
saccule
what does the utricle do?
detects body position and horizontal linear motion
what does the saccule do?
detects body position and sagittal linear motion
describe the pathway of the vestibulocochlear nerve (CN VIII)
follows internal auditory meatus with facial nerve (VII)
enters brainstem at pontine-medullary junction/the cerebellopontine angle
projects to vestibular nuclear complex, cerebellum
what are the 4 major functions of the vestibular system?
- it is a sensory organ that detects BODY POSITION relative to gravity and the MOTION of the body in space and the motion of the body in space
- maintains equilibrium–> balance, postural stability
- motor output–> reflex and controlled motor movements
- vision–> control of head and eye motion, stabilization of visual gaze during head, body movement
name the 3 semicircular ducts
anterior
horizontal
posterior
what are the 5 vestibular sensory organs?
3 semicircular canals
2 otoliths
what are otoliths?
2 sac like organs between the semicircular canals and the cochlea
sense body orientation and linear motion
how does perilymph drain?
via venules and middle ear mucosa
how does endolymph drain?
absorbed by endolymphatic sac
what are the types of sensory epithelia in the vestibular system?
5:
the cristae of the semicircular canals (3)
the maculae of the utricle and saccule (2)
sensory epithelia contain hair cells which are sensory cells that detect movement of the endolymph
how many stereocilia are there per hair cell?
60-100
how many kinocilia are there per hair cell
1
what neurotransmitter is released from the stereocilia and kinocilia of the hair cells in the vestibular system?
glutamate
how many hair cells do the utricles and saccules have?
about 35 000 hair cells
how many hair cells are in the ampulla of the semicircular canals?
about 8000
what is particularly important about the hair cells?
they are the terminals of the vestibulocochlear nerve (CN VIII)
afferent fibers send output to CNS
bipolar cells with cell bodies in the vestibular ganglia
what are the ampullae of the vestibular system?
swellings at the end of the semicircular canals
what are the cristae of the vestibular system?
hair cell sensory epithelium within the ampullae
what is the cupula of the vestibular system?
acellular, gelatinous mass
hinged gate spanning the ampulla lumen
hair cell cilia embedded in the cupula project into the endolymph
ALL hair cells in the ampulla are oriented in the same direction, with the kinocilium closest to the utricle
describe the functional planes and pairings of the semicircular canals
arranged in three functional planes with right-left pairing
- right anterior // left posterior
- right posterior //left anterior
- right horizontal // left horizontal
* pairs of cristae are arranged as mirror opposites
describe how the semicircular canals would detect a head turn to the left
turning of the head to the left causes fluid motion in the canals and a change in the axis of the hair cells
on the left, afferent fibers of CN VIII increase firing while the afferent fibers of the right side decrease firing
what is the otolithic membrane?
acellular gelatinous mass
what are otoconia?
calcium carbonate crystals that sit on top of the otolithic membrane
**pressure of otoconia deflects hair cell cilium
what is another name for the vestibular ganglion?
scarpa’s ganglion
where is the vestibular nuclear complex found?
in the dorsal pons and medulla beneath the 4th ventricle
list the vestibular nuclei
- lateral vestibular nucleus
- medial vestibular nucleus
- superior vestibular nucleus
- lateral vestibular nucleus
what is the function of the lateral vestibular nucleus in the vestibular nuclear complex?
aka Deiter’s nucleus
innervates gravity-opposing muscles of limbs to MAINTAIN POSTURE
what is the function of the medial vestibular nucleus in the vestibular nuclear complex?
reflex adjustment of the head and trunk muscles to restore head position after disturbance
stabilizes head in space
what is the function of the superior and medial vestibular nuclei in the vestibular nuclear complex?
eye movements
vestibulo-ocular reflex (VOR)
what is the function of the inferior vestibular nucleus in the vestibular nuclear complex?
integrates multi-sensory input and the cerebellum to regulate VOR gain
what are the inputs to the lateral vestibular nucleus?
utricle, saccule, semicircular canals
what is the pathway of the lateral vestibulospinal tract?
from the lateral vestibular nucleus
descends entire spinal cord
UNCROSSED (ipsilateral)
runs in the white matter in the anterior of the spinal cord (ventral horn)
what is the target of the lateral vestibulospinal tract?
ventral horn alpha and gamma motor neurons that innervate gravity opposing muscles of limbs
what is the input to the medial vestibular nucleus?
primarily the semicircular canals
what is the pathway of the medical vestibulospinal tract?
it becomes the descending medial longitudinal fasciculus (MLF)
it is bilateral (but the ipsilateral projection is more dense)
what is the target of the medical vestibulospinal tract?
cervical and upper thoracic spinal cord
motor neurons innervating the neck musculature
what vestibular nuclei are responsible for the VOR?
superior and medial
what is the function of the superior and medial vestibular nuclei (combined)? input?
VOR–> reflex to stabilize image in response to head turn
*input is semicircular canals
what is the pathway of the superior and medial vestibular nuclei/VOR fibres?
pathway is a 3 neuron arc
- bipolar neurons
- medial and superior vestibular nuclei
- motor neurons in the abducens nucleus (VI) and the oculomotor nuclei (III) that innervate oculomotor muscles
what muscles are coordinated by the horizontal VOR?
4 muscles:
left and right lateral recti
left and right medial recti
describe the basic neural mechanisms of the VOR based on a head turn to the right
if you turn your head to the right, but keep your eyes forward and want the image to be stable, your eyes need to remain pointing forwards
thus, if you turn your head to the right, the VOR causes excitatory signals to be sent to the lateral rectus muscle of the left eye and the medial rectus muscle of the right eye
the excitatory signal that goes to the lateral rectus of the left eye and the medial rectus of the right eye comes from the right semicircular canals, crossing over after the vestibular nucleus
at the same time, inhibitory signals are being sent to the lateral rectus of the right eye and the medial rectus of the left eye from the left semicircular canals
the excitatory and inhibitory signals synapse at the abducens nucleus and then at the oculomotor nucleus
what does the inferior vestibular nucleus do?
adjust the VOR
receives feedback from eyes and can then modulate the vestibular nerve to modulate the VOR
what is nystagmus?
rhythmic alteration of slow and fast eye movements during VOR
VOR –> slow
saccade–> fast
how can you induce a saccade?
by introducing warm or cold water to the ear canal
fast phase direction of the nystagmus: COWS
cold–opposite
warm–same
i.e if you introduce warm water to the right ear, the fast phase of the nystagmus will be towards the right (opposite for cold)
define benign paroxysmal positional vertigo (BPPV)
vestibular disorder
displaced otoconia lodged in the semicircular canals
define meniere’s disease (endolymphatic hydrops)
vestibular disorder
increased endolymph in the inner ear
define vestibular neuritis
vestibular disorder
viral infection of the vertibulo-cochlear nerve
define perilymph fistula
vestibular disorder
breach in the oval and/or round window
define ototoxicity
vestibular disorder
toxicity induced death of hair cells
define mal de debarquement
vestibular disorder
failure of CNS system plasticity to respond to prolonged movement
how do aging, dizziness and balance relate?
as we age we get visual and motor deficits, BPPV and gradual hair cell loss
when would you get bilateral vestibular dysfunction? how does it present?
occurs with toxicity–i.e aminoglycosides
slow onset of loss of vestibular function
instability of eyes with head movements
instability when walking in the dark (without visual input)
how does unilateral vestibular dysfunction present? what might cause it?
severe acute symptoms
extreme dizziness, nausea, vomiting
deviation towards the side of the lesion when walking
abnormal nystagmus
displaced otoconia, viral infection may cause it
how might the body adapt to unilateral vestibular dysfunction?
gradual recovery from unilateral lesions
learning induced changes to central circuits
vestibular inputs become ignored in favor of vision and proprioception
what can happen when there is a mismatch between vestibular and visual inputs?
dizziness
i.e rotation induced, optical illusions, motion sickness, alcohol (bed spins)
where do general somatic efferents (GSEs) go?
give examples of GSEs
to skeletal muscle
cranial nerves: III IV VI XII XI
here do general visceral efferents go?
give examples of GVEs
these are the parasympathetics
cranial nerves: III VII IX X
where do special visceral efferents (SVEs) go?
give examples of SVEs
to skeletal muscle (pharyngeal arches)
cranial nerves: V VII IX X
what do general visceral afferents sense?
give examples of GVAs
visceral sensory
cranial nerves:
IX
X
what do special visceral afferents (SVAs) sense?
give examples of SVAs
taste
cranial nerves:
VII
IX
X
what do general somatic afferents (GSAs) sense?
give examples of GSAs
general sensory
cranial nerves:
V
IX
X
what so special somatic afferents (SSAs) sense?
give examples of SSAs
hearing and balance
cranial nerve VIII
how are the afferent and efferent nuclei generally arranged in the brain stem?
lateral (alar plate)–> from lateral towards the sulcus limitans
SSA–> GSA–> SVA–> GVA–> sulcus limitans
medial (basal plate)–> from sulcus limitans towards the midline
GVE–> SVE–> GSE
what nerve innervates the following extra-ocular muscles:
- superior rectus
- inferior rectus
- medial rectus
- inferior oblique
- superior oblique
- lateral rectus
1-4–> innervated by CN III (oculomotor)
5–> innervated by CN IV (trochlear)
6–> innervated by CN VI (abducens)
what nerve innervates the lateral rectus muscle of the eye?
CN VI (abducens)
what nerve innervated the superior oblique muscle of the eye?
CN IV (trochlear)
what nerve innervates the superior rectus muscle of the eye?
CN III (oculomotor)
what does the MLF do?
connects the abducens (VI) nucleus to the oculomotor nucleus (III)
define gaze
the coordinated, synergistic movement of both eyes to a target
define saccadic eye movements
rapid eye movements to redirect gaze to an object of importance, generated by the FRONTAL EYE FIELDS int he CORTEX
how do the pathways of the impulses that control reflexive saccades and volitional saccades differ?
REFLEXIVE saccades go through the superior coliculus
VOLITIONAL saccades BYPASS the superior colliculus
list and describe the types of volitional saccades
- anti-saccades –> away from stimulus
- predictive saccades–> towards where stimulus is expected to be
- memory saccades –> to where the stimulus was
define smooth pursuit
tracks a slowly moving object
keep object on fovea (the area of highest visual acuity)
what controls vertical gaze?
vertical gaze center
what is disconjugate gaze?
failure of eyes to turn together in the same direction
how do eyes converge? why?
eyes converge through adduction by both medial rectus muscles to focus on a NEAR object
how do eyes diverge? why?
eyes diverge through abduction by both lateral rectus muscles
this shifts the focus from the near object to a farther away object
how many layers make up the retina?
3
list the layers of the retina
- photoreceptors–rods (ro-sco-no) and far fewer cones (co-pho-co)
- bipolar cells–many rods to one bipolar, few cones to one bipolar
- retinal ganglion cells are designated as M cells or P cells
what is the nerve-chiasma tract of the visual system?
the optic nerve fibres from the nasal hemiretina cross over at the chiasma to the contralateral optic tract
optic nerve fibers from the temporal hemiretina do not cross over and reach the thalamus by the ipsilateral optic tract
describe the structure of the lateral genticulate nucleus (LGN) of the visual system, and state what types of cells are found there
2 lamina–> M cells from ipsilateral eye
most ventral: #1 lamina --> M cells from the contralateral eye
most dorsal: #6 lamina--> P cells from contralateral eye
what are M cells?
ganglion cells of the visual system that generate APs
“magnocellular” cells
mostly rods tuned to movement
what are P cells?
ganglion cells of the visual system that generate APs
“parvocellular cells”
mostly cones tuned to fine detail
once the impulses from the optic nerve reach the LGN, what happens to them?
leaving the LGN, fibres fan out in a wide band to reach the visual cortex in the occipital lobe
where is the visual cortex?
in the occipital lobe
where is the LGN?
thalamus
what are optic radiations?
superior optic radiations are fibers that reach the visual cortex from above, via the PARIETAL lobe–> carry information from the INFERIOR retina
inferior optic radiations (Meyer’s) are fibres that reach teh visual cortex from below, via the TEMPORAL lobe–> carry information from the SUPERIOR retina
what is monocular scotoma?
loss of vision in the center of the visual field of one eye
what is the lesion behind monocular scotoma in the right eye?
damage to right retina, partial damage to right optic nerve
what is the lesion behind monocular vision loss in the right eye?
entire right retina or right optic nerve complete lesion
a lesion to the optic nerve of one eye will lead to loss of the complete visual field in that eye
the other eye can still perceive the entire visual field
what can cause the lesions that lead to monocular scotoma or monocular vision loss?
retinal infarct
hemorrhage
infection
trauma
glaucoma
schwannoma
elevated ICP
neuropathy
several diseases of the eye
what is bitemporal hemianopsia?
vision loss in the lateral/temporal fields of both eyes
what is the lesion that leads to bitemporal hemianopsia?
damage to OPTIC CHIASM (often not perfect symmetry)
a lesion to the optic chiasm leads to loss of the nasal retinal fibers from both eyes–> these nasal retinal fibers carry information about the temporal visual field and thus a lesion to the optic chiasm (where the nasal fibers cross) leads to the loss of the temporal visual field in both sides
what can cause the lesions (damage to the optic chiasm) that lead to bitemporal hemianopsia?
pituitary adenoma
lesions
meningioma
hypothalamic glioma
craniopharyngioma
what is contralateral homonymous hemianopia?
loss of the temporal visual field in one eye, and the nasal field in the other (i.e both right or both left visual fields are gone)
what is the lesion that leads to contralateral homonymous hemianopia?
lesion in the contralateral optic tract or LGN
i.e if both left visual fields were gone, lesion would be in the right optic tract or LGN/occipital lobe
a lesion to the optic tract will affect the nasal (crossed) fibres from the contralateral eye and the temporal fibres from the ipsilateral eye
these fibers carry information from the contralateral visual field
**in addition, a lesion of the entire primary visual cortex on one side will lead to the loss the contralateral visual field from both eyes
what can cause lesions to the optic tracts etc leading to contralateral homonymous hemianopia?
infarct
bleeding
tumour
demyelination
infection (i.e toxoplasmosis)
what is contralateral superior quadrantanopia?
loss of vision in the upper quadrant of the visual field in both eyes (i.e both upper left quadrants)
“pie in the sky”
what lesion causes contralateral superior quadrantanopia?
lesion of the contralateral temporal lobe, lower bank (meyer’s loop)
a lesion to the Meyer loop will affect the fibers from the upper portion of the contralateral visual field in both eyes
what causes the lesion (lesion of the contralateral temporal lobe) that causes contralateral superior quadrantanopia?
MCA inferior division infarct (“pie in the sky”), tumour, demyelination
what is contralateral inferior quadrantinopia?
loss of the lower quandrants on the same side of the visual field
“pie on the floor”
what lesion causes contralateral inferior quadrantinopia?
lesion of parietal lobe or upper bank of calcarine fissure
a partial lesion of the optic radiations before they are joined by fibres from meyers loop will affect fibres from the lower portion of the contralateral visual field from both eyes
what causes the lesion (lesion of parietal lobe or upper bank of calcarine fissure) that causes contralateral inferior quadrantinopia?
MCA superior division infarct, bleed, trauma, tumour
how do you test the functioning of the extraocular muscles?
H test
also tests all cranial nerves that innervate these muscles
NOTE: the H test does NOT test all the extraocular muscles, but it does test all the CRANIAL nerves that innervate these muscles
how does the H test test each cranial nerve that innervates the ocular muscles?
- the patient is asked to look laterally (i.e left)
- the left eye ABDUCTS through the action of the lateral rectus muscle innervated by CN VI
- abduction of the eye aligns the axis of the eyeball with the axis of the orbit and the muscles attaching to the tendinous ring
- when the eye is abducted, the patient is asked to look UP–> this tests the superior rectus, innervated by CN III
the action of the superior rectus can only be isolated when the patient has already abducted their eye
- patient is then asked to look to the right, ADDUCTING the eye being examined–> tests the medial rectus muscle (CN III)
- with the eye adducted, the patient is asked to look DOWN—> a downward movement will isolate the action of the superior oblique muscle (CN IV)
same movements are repeated for each eye
how do you isolate the function of the eye’s superior rectus muscle, clinically?
abduct the eye and then look up
how do you isolate the function of the eye’s superior oblique muscle, clinically?
adduct the eye, and then look down
what is the sensory innervation of the lacrimal gland?
sensory neurons from the lacrimal gland return to the CNS thru the lacrimal branch of the ophthalmic nerve (V1)
what is the secretomotor/parasympathetic innervation of the lacrimal gland?
secretomotor fibres from the parasympathetic part of the autonomic division of the PNS stimulate fluid secretion from the lacrimal gland
these preganglionic parasympathetic neurons leave the CNS in the FACIAL nerve (CN VII), enter the GREATER PETROSAL nerve (a branch of the facial nerve VII) and continue with the greater petrosal nerve until it becomes the nerve of the PTERYGOID CANAL
the nerve of the pterygoid canal then eventually enters the PTERYOPALATINE GANGLION where the preganglionic parasympathetic neurons synapse on postganglionic parasympathetic neurons
the postganglionic neurons join the MAXILLARY nerve (V2) and continue with it until the ZYGOMATIC nerve branches from it and travel with the zygomatic nerve until it gives off the ZYGOMATICOTEMPORAL nerve, which eventually distributes postganglionic parasympathetic fibers in a small branch that joins the lacrimal nerve
the lacrimal nerve passes to the lacrimal gland
what happens if the BBB is breaches by infectious diseases?
increased protein and water permeation–> edema, accumulation of inflammatory cells to inflammation sites and increased adhesion molecules (ICAM, VCAM)
list 4 of the major bacterial infections of the CNS
- bacterial meningitis
- brain abscess
- tuberculous meningitis
- syphilis
what happens in bacterial meningitis?
inflammatory reaction in SUBARACHNOID space with lots of PMNs and other WBCs
acute inflammation of walls of arteries and veins, may lead to INFARCT over several days
commonly see EPENDYMITIS (inflammation of ventricles)
persistent meningitis causes brain damage from vasculitis, brain infection, fibrosis in subarachnoid space, cranial nerve damage and obstruction of CSF space
what organisms commonly cause bacterial meningitis?
H. influenza
pneumococcus
meningococcus
how would you develop a brain abscess?
bacteria reach CNS via blood from an infection outside the CNS (i.e an ear infection)
what is the causative agent in tuberculous meningitis?
secondary to TB infection elsewhere in the body
what are the characteristics of tuberculous meningitis?
characterized by meningitis, vasculitis, cranial inflammation, tuberculomas
multinucleated giant cells are frequent
tubercles consist of central area of caseous necrosis with epithelioid cells and lymphocytes around
how does syphilis affect the brain? (i.e paretic vs. tabetic vs. meningovascular)
brain disease is a tertiary manifestation of the disease
paretic neurosyphillis–> progressive dementia and death; nerve cell destruction; microglia proliferation; WBC inflammatory response
tabetic neurosyphillis–> spinal and cranial nerves exclusively affected, especially lumbar region
meningovascular neurosyphillis–> vasculitis, chroic meningitis with lymphocytes, plasma cells
list 7 viruses that can cause CNS infection
- acute –> poliomyelitis or smallpox
- herpes simplex/zoster
- subacute sclerosing panencephalitis
- progressive multifocal leukoencephalopathy
- rubella
- cytomegalic inclusion disease
- HIV
how would poliomyelitis or smallpox affect the brain?
elicit inflammatory response
recovery is common
microglial and WBC response concentrated in the PERIVASCULAR spaces
how does herpes simplex/zoster affect the brain?
acute infection that is followed by recovery with relapses later in life
virus is not killed by the immune system and it lives on in the dorsal root ganglion (usually of CN V)
herpes encephalitis –> uncommon, acute, hemorrhagic, necrotizing, usually fatal
what cranial nerve root often harbours herpes virus?
CN V
what is subacute sclerosing panencephalitis?
a rare, chronic destructive disease of the brain
caused by MEASLES
WBC response with intranuclear viral inclusions
microglial proliferation
what is the causative agent behind subacute sclerosing panencephalitis?
measles
what is progressive multifocal leukencephalopathy and how does it affect the brain?
mainly seen in IMMUNOCOMPROMISED patients
patchy destruction of gray and white matter with some demyelination, astrocytes are formed
caused by JC virus
what is the causative agent behind progressive multifocal leukencephalopathy?
JC virus
how does rubella affect the brain?
rubella is often a mild disease unless onset in the fetus
meningoencephalitis with WBC response and continued brain destruction
infests endothelial cells leading to vascular damage and ischemia in developing brain
how does cytomegalic inclusion disease affect the brain?
usually only in IMMUNOCOMPROMISED
brain malformation, multiple gyri with distorted architecture and calcific deposits in ependyma
how does HIV affect the brain?
encephalitis and HIV-associated dementia complex are common complications of the disease
list two fungal infections that can affect the brain
- mucormycosis
2. cryptococcosis
how does mucormycosis affect the brain?
propagates in blood vessel walls, leading to thrombosis
how does cryptococcosis affect the brain?
granulomatous reaction with giant cells–> may have no inflammation–> widely disseminated
name two inflammatory diseases of the CNS
MS
primary CNS angiitis
name a class of transmissible CNS diseases
prion diseases
i.e creutzfeldt-jacob
what is creutzfeldt-jacob disease and how does it affect the brain?
prion disease
no immune response, no inclusion bodies, incubation can be very long
prions are normal cell membrane proteins found in nerve cells
conformational changes convert normal prions into pathological ones
accumulation of mutant prions causes neuropathology
progressive destruction of brain with loss of function, vegetative state and death
what is the corona radiata?
sheet of white matter that continues caudally to become the internal capsule
what does the corticobulbar tract arise from? what is its pathway?
corticobulbar tract arises primarily from areas of the motor cortex related to the HEAD and FACE and descends through the corona radiata
fibers converge in the genu of the internal capsule from where they then descend together with corticospinal fibers
where do the corticobulbar fibers terminate?
motor nuclei of the brainstem
what is the internal capsule?
The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus.
what is the nucleus ambiguus?
cell bodies of IX, X, XI (cranial root)
receives bilateral innervation
The nucleus ambiguus (literally “ambiguous nucleus”) is a group of large motor neurons, situated deep in the medullary reticular formation. The nucleus ambiguus contains the cell bodies of nerves that innervate the muscles of the soft palate, pharynx, and larynx which are strongly associated with speech and swallowing.
It is a region of histologically disparate cells located just dorsal (posterior) to the inferior olivary nucleus in the lateral portion of the upper (rostral) medulla. It receives upper motor neuron innervation directly via the corticobulbar tract.
The nucleus ambiguus controls the motor innervation of ipsilateral muscles of the soft palate, pharynx, larynx and upper esophagus. Lesions of nucleus ambiguus results in nasal speech, dysphagia, dysphonia, and deviation of the uvula toward the contralateral side.
what is the trigeminal motor nucleus responsible for?
The trigeminal motor nucleus contains motor neurons that innervate muscles of the first branchial arch, namely the muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric. This nucleus is located in the mid-pons (i.e. in the center of the pons going inferior to superior)
receives bilateral innervation
what is the spinal accessory nucleus (IX) responsible for?
receives IPSILATERAL projecttions for the sternomastoid
mostly CONTRALATERAL projections for the trapezius
where does the spinal accessory nucleus lie?
in the cervical spinal cord
what is the function of the hypoglossal nucleus?
ipsilateral tongue muscle control (XII)
receives bilateral projections but crosses to genioglossus
what is unique about the innervation to the facial motor nucleus (VII)?
there is bilateral innervation to the rostral part of the nucleus –> control UPPER face muscles
contralateral innervation to the caudal part of the nucleus–> controls LOWER face muscles
what cranial nerve nuclei does the corticobulbar tract innervate?
motor nucleus of V
motor nucleus of VII
nucleus ambiguus (IX, X, XI)
hypoglossal nucleus
spinal accessory nucleus
where in the motor cortex does the corticobulbar tract originate from?
precentral gyrus
describe the innervation from the corticobulbar tract to the motor nucleus of V
bilateral
describe the innervation from the corticobulbar tract to the motor nucleus of VII
bilateral for upper face
crossed (contralateral) for lower face –> ie innervation to upper face comes from both sides but innervation to lower face comes from the contralateral side
describe the innervation from the corticobulbar tract to the nucleus ambiguus (IX, X, XI)
all bilateral, except crossed to UVULA
what is the genioglossus?
muscle that runs from chin to tongue–> responsible for action of sticking out your tongue
describe the innervation from the corticobulbar tract to the hypoglossal nucleus (XII)
all bilateral except crossed to GENIOGLOSSUS
describe the innervation from the corticobulbar tract to the spinal accessory nucleus (XI)
ipsilateral to sternocleidomastoid
contralateral to trapezius
what cranial nerves carry the GSA modality
V
IX
X
what cranial nerves carry the SSA modality
VIII
what cranial nerves carry the SVA modality
VII
IX
X
what cranial nerves carry the GVA modality
IX
X
what cranial nerves carry the GVE modality
III
VII
IX
X
what cranial nerves carry the SVE modality
V
VII
IX
X
what cranial nerves carry theGSE modality
III
IV
VI
XII
XI
what modalities does the following cranial nerve carry?
III
GVE and GSE
what modalities does the following cranial nerve carry?
IV
GSE
what modalities does the following cranial nerve carry?
V
GSA and SVE
what modalities does the following cranial nerve carry?
VI
GSE
what modalities does the following cranial nerve carry?
VII
SVA, GVE, and SVE
what modalities does the following cranial nerve carry?
VIII
SSA
what modalities does the following cranial nerve carry?
IX
GSA, SVA, GVA, GVE, SVE
what modalities does the following cranial nerve carry?
X
GSA, SVA, GVA, GVE, SVE
what modalities does the following cranial nerve carry?
XII
GSE
what modalities does the following cranial nerve carry?
XI
GSE
name the following cranial nerve and state what it does
I
olfactory
The functional components of the olfactory nerve include SVA, special visceral afferent, which carries the modality of smell.
contains the afferent nerve fibers of the olfactory receptor neurons, transmitting nerve impulses about odors to the central nervous system
name the following cranial nerve and state what it does
II
optic
paired nerve that transmits visual information from the retina to the brain
name the following cranial nerve and state what it does
III
oculomotor
innervates 4/6 eye muscles
enters the orbit via the superior orbital fissure and innervates muscles that enable most movements of the eye and that raise the eyelid
contains fibers that innervate the muscles that enable pupillary constriction and accommodation (ability to focus on near objects as in reading)
name the following cranial nerve and state what it does
IV
trochlear
motor nerve (a somatic efferent nerve) that innervates only a single muscle: the superior oblique muscle of the eye, which operates through the pulley-like trochlea…on the opposite side (contralateral) from its origin
name the following cranial nerve and state what it does
V
trigeminal
nerve responsible for sensation in the face and motor functions such as biting and chewing
each trigeminal nerve (one on each side of the pons) has three major branches: the ophthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3)
name the following cranial nerve and state what it does
VI
abducens
is a somatic efferent nerve that, in humans, controls the movement of a single muscle, the lateral rectus muscle of the eye.
The abducens nerve carries axons of type GSE, general somatic efferent, which innervate skeletal muscle of the lateral rectus
name the following cranial nerve and state what it does
VII
facial
controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity. It also supplies preganglionic parasympathetic fibers to several head and neck ganglia.
name the following cranial nerve and state what it does
VIII
vestibulocochlear
transmits sound and equilibrium (balance) information from the inner ear to the brain
consists of the cochlear nerve, carrying information about hearing, and the vestibular nerve, carrying information about balance
The vestibulocochlear nerve carries axons of type SSA, special somatic afferent, which carry the modalities of hearing and equilibrium
name the following cranial nerve and state what it does
IX
glossopharyngeal
mixed nerve that carries afferent sensory and efferent motor information
It receives general somatic sensory fibers (ventral trigeminothalamic tract) from the tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue.
It receives special visceral sensory fibers (taste) from the posterior one-third of the tongue.
It receives visceral sensory fibers from the carotid bodies, carotid sinus.
It supplies parasympathetic fibers to the parotid gland via the otic ganglion.
It supplies motor fibers to stylopharyngeus muscle, the only motor component of this cranial nerve.
It contributes to the pharyngeal plexus.
name the following cranial nerve and state what it does
X
vagus
vagus nerve supplies motor parasympathetic fibers to all the organs except the suprarenal (adrenal) glands, from the neck down to the second segment of the transverse colon. The vagus also controls a few skeletal muscles
name the following cranial nerve and state what it does
XI
spinal accessory
controls the sternocleidomastoid and trapezius muscles
name the following cranial nerve and state what it does
XII
hypoglossal
innervates muscles of the tongue
name the branches of the trigeminal nerve
V1–ophthalmic nerve
V2–maxillary nerve
V3–mandibular nerve
what does the oculomotor nucleus (III) innervate?
somatic motor to inferior, superior and medial rectus muscles of the eye, and to the inferior oblique muscle of the eye as well as the levator palpebrae superioris
visceral motor to the ciliary and constrictor papillae muscles (parasympathetic)
where is the main oculomotor nucleus located?
rostral midbrain
in anterior part of the periaqueductal gray
efferent fibers pass anteriorly through the red nucleus and emerge from the midbrain in the interpeduncular fossa on the medial surface of the cerebral peduncle
where is the parasympathetic nucleus (edinger-westphal nucleus) of the oculomotor nucleus found?
located posterior to the main oculomotor nucleus in the periaqueductal gray
efferent fibers run with other oculomotor fibres and synapse in the ciliary ganglion
what does the trochlear nucleus innervate?
CN IV
somatic motor to the superior oblique muscle
where is the trochlear (IV) nucleus located?
caudal midbrain, in anterior part of periaqueductal gray
efferent fibres pass POSTERIORLY around the central gray
fibers decussate in superior medullary velum and emerge caudal to the inferior colliculus
this is the ONLY cranial nerve to emerge from the POSTERIOR aspect of the brainstem
what does the abducens nucleus (VI) innervate?
somatic motor to the lateral rectus muscle
where is the abducens nucleus (VI) located?
posterior part of the caudal pons, beneath the floor of the 4th ventricle, near the midline
efferent fibers pass ANTERIORLY through the pons and emerge in the pontomedullary junction
through what fissure does the abducens nerve run?
superior orbital fissure
what innervates the following muscle and what does the muscle do?
levator palpebrae muscle
superior branch of oculomotor nerve (CN III)
elevation of upper eyelid
what innervates the following muscle and what does the muscle do?
medial rectus muscle
inferior branch of oculomotor nerve (CN III)
adduction of eyeball
what innervates the following muscle and what does the muscle do?
lateral rectus muscle
abducens nerve (CN VI)
abduction of eyeball
what innervates the following muscle and what does the muscle do?
superior rectus muscle
superior branch of oculomotor nerve (CN III)
elevation, adduction, medial rotation of the eyeball
what innervates the following muscle and what does the muscle do?
inferior rectus muscle
inferior branch of oculomotor nerve (CN III)
depression, adduction and lateral rotation of the eyeball
what innervates the following muscle and what does the muscle do?
inferior oblique muscle
lower division of oculomotor nerve (CN III)
elevation, abduction, lateral rotation of eyeball
what innervates the following muscle and what does the muscle do?
superior oblique muscle
trochlear nerve (CN IV)
depression when eye is in adduction
medial rotation of eyeball (intorsion) when eye is abducted
list the major nerve of the orbit
CN II–optic
CN V1–frontal + branches and nasociliary + branches
CN III–oculomotor
CN IV–trochlear
CN VI–abducens
what are the two major branches of V1 in the orbit?
frontal nerve and nasociliary nerve
what are the branches of the frontal nerve (branch of V1) in the orbit and what do they do?
- supratrochlear nerve–> conjunctiva, eyelid, lower medial forehead
- supraorbital nerve–> conjunctiva, eyelid, forehead (can extend all the way to mid-scalp
what are the branches of the nasociliary nerve (branch of V1) in the orbit and what do they do?
- long ciliary nerve–> carries afferent info from eyeball
- short ciliary nerve–> carry parasympathetic innervation for CN III (sphincter pupillae muscle and ciliary muscle)
- anterior ethmoidal nerve–> sensory from anterior cranial fossa, nasal cavity, skin of lower half of nose
- infratrochlear nerve–> sensory from eyelids, lacrimal sac, skin of upper half of nose
what type of pathway is the dorsal column medial lemniscus pathway?
ascending
what kind of information is transmitted by the dorsal column medial lemniscus pathway?
role in discriminative touch, vibration, pressure, conscious proprioception
what kind of deficits would arise in response to a lesion in the dorsal column medial lemniscus pathway?
if in spinal cord, would result in deficits in discriminative touch, vibration, pressure or conscious proprioception on the IPSILATERAL side of the lesion
if it is in the caudal medulla, (i.e nucleus gracilis or cuneatus) or above,, deficits will be on the CONTRALATERAL side
what is a “pyramidal pattern of weakness”?
results from UMN lesions
the pattern results in the flexors of the upper limbs being stronger (more spastic) than the extensors, and the opposite (extensors being stronger than the flexors) in the lower limb
WYSIWIS–> “what you see is what is strong”
so you see people with this pattern of symptoms with their arms flexed against their chests and their legs “too long” (ie straight with foot plantar flexed) which affects their gate
what is the Romberg test?
test used in a neuro exam and also as a test for drunk driving
exam based on the premise that a person requires at least two of the three following senses to maintain balance while standing:
- proprioception (body position in space)
- vestibular function (one’s head position in space)
- vision (can be used to monitor and adjust for changes in body position)
what senses do you need to maintain balance?
2/3:
- proprioception (body position in space)
- vestibular function (one’s head position in space)
- vision (can be used to monitor and adjust for changes in body position)
how do you perform the romberg test?
ask subject to stand erect with feet together and eyes closed
stand close by as a precaution in order to stop the person from falling
watch the movement of the body in relation to a perpendicular object behind the subject (i.e door)
a positive romberg sign is noted when a swaying, sometimes irregular swaying and even a toppling over occurs
essential feature is the patient becomes unsteady with eyes closed
how do you interpret the romberg test?
used to investigate the loss of motor coordination (ataxia)
a positive romberg test suggests that the ataxia is SENSORY in nature (i.e loss of proprioception in pathologies affecting the PCML or peripheral sensory neurons)
this is NOT a test of cerebellar function–> patients with cerebellar ataxis will generally be unable to balance even with eyes open
why must the eyes be closed in the romberg test?
basis of test is that balance come from the combination of several neuro systems, namely proprioception, vestibular input, and vision
if any two of these systems are working the person should be able to demonstrate a fair degree of balance
the key to the test is that vision is taken away by asking the patient to close their eyes
this leaves only two of the three systems available and if there is either a vestibular or sensory/proprioception disorder then the patient will become much more imbalanced
where is the optic disc located?
region of the eye where axons of the ganglion cell layer gathers to form the optic nerve
lies 15 degrees medial (nasal) to the fovea
*it is also the entry point for the central artery and vein–supply and drain the inner retina
why is there a blind spot on the optic disc?
there are no photoreceptors (rods or cones) over the optic disc and thus it is a blind spot for each eye (15 degrees lateral and slightly inferior to the central fixation point for each eye)
what is the swinging light test?
shows abnormal light response of the affected eye (initial dilation followed by restriction)
i.e if the left eye were abnormal, both pupils constrict when the light is shown into the right eye but when the light is swung to the left eye, both pupils dilate–> when the light is swung back to the right, both pupils again constrict
this reaction indicates a defect in the afferent pupillary fibers from the left eye(the near reflex is normal)
what is marcus gunn pupil?
relative afferent pupillary defect
medical sign noted during the swinging light test
most common of marcus gunn pupil is a lesion of the optic nerve proximal to the optic chiasm or severe retinal disease
how do you do the swinging light test?
for an adequate test, vision must not be entirely lost
in dim room light, the examiner notes the size of the pupils
patient asked to gaze into the distance, and the examiner swings a beam of a penlight back and forth from one pupil to another and observes the size of pupils and reaction in the eye that is lit
how do you interpret the swinging light test?
normally, each illuminated eye looks or promptly becomes constricted with the opposite eye constricting consensually
when ocular disease (cataracts) impairs vision, the pupils still respond normally
when the optic nerve is damaged, the sensory stimulus sent to the midbrain is reduced and thus the pupil, responding less vigorously to the stimulus, dilates from its prior constricted state
this response is an afferent pupillary defect (marcus gunn pupil)
why do we use the swinging light test?
allows the examiner to observe the relative defect in an eye by using the normal eye as a control
what is conjugate gaze?
motion of both eyes in the same direction at the same time
how are saccadic eye movements controlled to allow for conjugate gaze?
ascending MLF connects CN VI on one side with CN III on the opposite side –> driven by the PPRF area in the pons
the ipsilateral visual field–> contralateral frontal eye field in the cortex (area 8)–> stimulate PPRF–> activate ipsilateral VI nucleus and ipsilateral lateral rectus–> MLF contralateral–> contralateral CN III nucleus and contralateral medial rectus
how are pursuit eye movements controlled to allow for conjugate gaze?
stabilizes image on fovea during slow movement of object or during locomotion
input from primary visual cortex, frontal eye fields in cortex, cerebellum, and vestibular nuclei to relay center in CN VI–> results in coordinated movements by connecting VI and III
how is the VOR controlled to allow for conjugate gaze?
adjust eye movements to head movements–image stable on retina
if head rotates to the right, endolymph flows in the opposite direction–> project to ipsilateral vestibular nuclei–> contralateral CN VI nucleus AND ipsilateral CN III–> eyes move to right
what is nystagmus?
rapid back and forth rhythmic eye movements
rapid component (flick) in one direction and slow component in the opposite
named for the RAPID component (i.e L nystagmus is rapid to the left)
what can cause physiological nystagmus?
physiologically by stimulation of the vestibular system or by visual stimuli
what causes physiological vestibular nystagmus?
when head rotation is greater than what can be compensated for by the VOR, the eyes reset with a rapid movement in the same direction as rotation, and then the compensatory movement of the VOR can happen again
the VOR usually moves the eyes opposite to the movement of the head to maintain fixation on the visual stimulus or object–> ie if head moves left, eyes move right, vision stays straight ahead
if you move your head too far to the left then you will get eyes slowly moving right as part of VOR, then the rapid movement will be the “reset” to the left–> nystagmus
how does a rapidly moving object cause nystagmus?
as the eyes follow the moving object in the field of view then rapidly shift focus to the next object in the field of view (i.e tracking a train as it moves by, passing rapidly by power poles as you look out the window of a car)
list 5 mechanisms/problems that can result in a disruption of horizontal conjugate gaze that can lead to double vision
- right abducens nerve palsy
- right abducens nucleus damage
- right PPRF problem
- left MLF damage (INO)
- left MLK and left abducens nucleus damage
how would the following problem disrupt horizontal conjugate gaze and cause double vision?
right abducens nerve palsy
no transmission thru to the right eye, therefore cannot abduct the right eye
how would the following problem disrupt horizontal conjugate gaze and cause double vision?
right abducens nucleus damage
the nucleus synapse is dysfunctional therefore right eye cannot abduct and left eye cannot adduct (because this nucleus tell the contralateral eye when it needs to adduct along with the ipsilateral side abducting)
how would the following problem disrupt horizontal conjugate gaze and cause double vision?
right PPRF problem
results in the same dysfunction as the right abducens nucleus damage
right eye cannot abduct and left eye cannot adduct
the nucleus synapse is dysfunctional therefore right eye cannot abduct and left eye cannot adduct
left MLF damage (INO)
cannot adduct the left eye
nystagmus is also produced in the right eye as it abducts–> theory is that maybe the left eye feels it needs to adduct, and the only other way to do this is through disconjugate conversion of both eyes–> causes right eye to experience nystagmus
the nucleus synapse is dysfunctional therefore right eye cannot abduct and left eye cannot adduct
left MLF and left abducens nucleus damage
same situation as with left MLF damage except now the eyes cannot deviate to the left when attempting to look at something in the left visual field
what is the medial longitudinal fasciculus? (MLF)
fibre tract that interconnects CN III, IV and VI nuclei to each other and to the vestibular nuclei, thus allowing synergistic or coordinated movements of the two eyes and adjustments of eye position in response to movements of the head
facilitates conjugate gaze
where does the MLF originate from?
originates from the vestibular nuclei in the ROSTRAL MEDULLA/CAUDAL PONS and has both descending and ascending components
describe the pathway and function of the ascending part of the MLF
arises from the medial vestibular nuclei, with some input from the superior vestibular nuclei
responsible for the coordination and synchronization of all major classes of eye movements
appears as a small pair of heavily myelinated tracts near the midline, just anterior to the 4th ventricle in the medulla and pons and anterior to the cerebellar aqueduct in the midbrain
what is internuclear ophthalmoplagia? (INO)
lesion of the MLF which interrupts the input to the MEDIAL RECTUS muscle
the eye ipsilateral to the lesion does not fully adduct on attempted horizontal gaze
the eye contralateral to the lesion experiences nystagmus, possible because of mechanisms trying to bring the eyes back into alignment (towards the midline)
- the side of the INO is the side with the lesion
- -> since the ascending MLF crossed almost immediately after leaving the abducens nucleus, the side of the INO is also the side on which the eye adduction is weak (i.e the lesion would never occur before the nerve crosses)
why is the eye with the impairment with adduction with horizontal gaze (in INO) usually spared during convergence?
efferent signal for this travels in a tract separate from the ascending MLF
what are some common causes of INO?
MS
pontine infarcts
neoplasms involving the MLF
list peripheral causes of diplopia
extraocular muscle damage
lens abnormalities (cataracts, opacities, following lens implant, problems with implant)
list central causes of diplopia
cranial nerve dysfunction (CN III/IV/VI)
myasthenia gravis
disorders of the neuromuscular junction between the cranial nerves and the extraocular muscles
retinal dysfunction (detachment, central retinal venous occlusion)
INO
what does it indicate if the diplopia is persistent with one eye covered?
this is monocular diplopia stemming from intrinsic eye problems (corneal abrasions, uncorrected refractive error, cataract, foveal traction)
what does it indicate if the diplopia disappears with one eye covered?
this is binocular diplopia caused by disruption of ocular alignment
how is MS diagnosed?
mostly a CLINICAL diagnosis
clinical evidence of lesions in the CNS that are DISSEMINATED in TIME and SPACE
diagnosis cannot be made unless evidence of TWO or MORE different regions in central white matter have been affected at different times
what are some clinical symptoms of MS used in diagnosis?
clinical symptoms vary widely, depending on where the pathology occurs in the CNS
- motor–> weakness, spasticity, brisk reflexes
- sensory deficits, cerebellar (ataxia, tremor, nystagmus, dysarthria)
- cranial nerve/brainstem (i.e vision, ocular disturbance)
- autonomic (bowel, bladder, sexual)
- psychiatric (depression, euphoria, cognitive)
- fatigue
what imaging is used in the diagnosis of MS?
T1 weighted images (fat is bright)–> show hypointense black holes which are areas of permanent axonal damage
T2 weighted images (water is white)–> bright areas which are demyelinated plaques located in white matter
what lab tests can be done to help diagnose MS?
oligoclonal bands in CSF
these arise from the synthesis of large amounts of homogenous immunoglobins by individual plasma cell clones in CSF
sensitivity –80%
specificity– 92%
how good are MRIs at helping to diagnose MS?
highly sensitive, with abnormalities detected in 90% of MS patients
detects clinically silent AND overt lesions
BUT many infectious, inflammatory, neoplastic and ischemic illnesses can present with T2 weighted abnormalities as well
can be used to monitor disease activity more than clinical exam
how helpful are CSF tests in diagnosing MS?
may help to exclude neoplasm and infection (thus is complementary to MRI)
abnormal findings in 85-95% of patients with MS, but may be normal in early stages
look for: abnormal oligoclonal banding, abnormal leukocytic pleocytosis (elevated CNS leukocytes with lymphocytic predominance)
good specificity but not perfect–> infections and inflammatory processes may have similar findings in CSF)
how helpful are evoked potential tests in diagnosing MS?
brain electrical responses to visual, auditory and somatosensory stimuli are recorded and time averaged by neurologist
evaluates multiple areas of CNS
abnormal tests correlate with CNS demyelination, which is sensitive but not specific for MS
what are the lesions associated with MS? how do they occur? what do they do?
plaques generate in the nervous system
majority of lesions are in the white area near the cerebellum, the spinal cord, the brain stem and the optic nerve
when MS lesions are present, neurons cannot transmit impulses efficiently –> the disease destroys the myelin covering the nervous systems fibers –> results in diminishing or complete disappearance of myelin
a partial restorative process (remyelination) occurs at thea early stages of the disease but as the cells myelin cover cannot completely be rebuilt and there is continued attack against the myelin this leads to fewer successful remyelinations and thus the formation of lesions
what role do T cells play in MS pathology?
in MS T cells infiltrate into the brain via the BBB which is both a physical barrier and a system of cellular transport
this barrier is not normally accessible to T cells unless the CNS is affected by a virus which reduces the strength of the junctions that form the barrier
T cells then remain locked in the brain, wrongly perceiving myelin as an alien agent and attacking it as if it were a virus
this generates an inflammatory process and further damages the CNS via swelling and activation of other immune cells and antibodies
what is the etiology of MS?
MS is a demyelinating, autoimmune disease which affects the CNS
research seems to implicate a small or incomplete slow-growing virus as the causative agent
the measles virus has been suspected because of high titers of measles antibodies in MS patients serum and CSF
an immunological deficiency in MS patients may be linked to genetic factors such as HLA tissues types and histocompatability antigens
genetics and socioeconomic conditions may also result in the distinct geographical pattern of MS distribution globally
describe the course of MS
MS is a PROGRESSIVE autoimmune disease characterized by the presence of acute, focal inflammatory demyelination
generally occurs in the second and third decades of life and it affects women more than men (3:2)
course is unpredictable and induces a wide spectrum of symptoms as lesions can occur anywhere in the CNS
commonly affected sites include the optic nerve, periventricular areas, corpus callosum, brainstem and spinal cord
however, there are still a number of common patterns of initial presentation
what are some commonly affected areas in MS?
optic nerve, periventricular areas, corpus callosum, brainstem and spinal cord
what is l’hermitte’s symptom?
sensation of electric shock down the back and limbs upon neck flexion
can occur in MS
what is uhthoff’s phenomenon?
increased symptoms due to heat (i.e after a hot bath or exercise), altering the conduction of nerves
can occur in MS
what is ephatic transmission?
transmission of charge between neighboring axons resulting in paroxysmal symptoms
can occur in MS
what is the prognosis of MS?
there are 3 general types of MS
80% of people affected initially present with a relapsing/remitting form–> women more than men–> many of these patient experience phases of relapse followed by full recovery until they can no longer recover from relapses (this is secondary progression)
20% of people affected experience primary progression–> there are no relapses and the disease progresses from the onset
25% of patients never experience significant adverse effects upon their daily activities, while another 15% are significantly disabled
what is usually the cause of death in a patient with MS?
most patients die from other reasons and lire expectancy is about 25-30 years after disease onset
what are the 4 major aims of medical tx for MS?
- reduce relapse rates
- prevent permanent disability
- manage permanent disability
- prevent disability due to progressive disease
what are some non-medical aspects to MS tx?
people with MS generally require patient education and counseling
may benefit from physio, support groups, OT, social work, nutrition counseling and other supports
list disease suppressing agents that can help reduce relapse rates in patients with MS
beta interferons
beta 1b–> betaseron can decrease relapse rate and progressive disease
beta 1a–> avonex can decrease relapse rates
copolymer can also decrease relapse rates
what is used to prevent disability in patients with MS (i.e acute tx during relapse)?
corticosteroids–> given as IV methyl prednisone over 3-5 days
since administered in response to a relapse (damage to axons has already occurred) they merely shorten the duration of the relapse without decreasing morbidity
there is evidence that regularly administered or “pulsed” corticosteroids can decrease this morbidity
how is permanent disability managed in MS?
requires the services of an interprofessional team, as well as tx of individual sx
spasticity is effectively treated with baclofen or tizanidine
bladder problems due to a failure to empty can be treated with self catheterization
if the bladder is unable to store well, then the detrusor can be inhibited with an anti-cholinergic such as oxybutinin
pain can be treated with TCA or carbamazepine
erectile impotence can be treated with sildenafil citrate
there has been some success treating fatigue with adamantine and modafanil
depression can be treated with SSRIs
how is spasticity treated in MS?
with baclofen or tizanidine
how might an overactive bladder be treated in MS?
with an anti-cholinergic like oxybutinin
what might you use to treat pain in MS?
TCA or carbamazepine
what might be used to treat erectile impotence in MS?
sildenafil citrate
how might you treat fatigue in an MS patient?
adamantine and modafanil
what symptoms of MS tend to indicate a more benign future course? what about a more difficult course?
patients that present with sensory sx (blurred vision, paresthesias) tend to have a more benign course
patients that present with pressure sores, intractable spasticity with contractures, and recurrent UTIs tend to have a more severe disease progression with little likelihood of significant recovery
function of sclera?
protects eye and anchors muscles
function of cornea?
transparent window
pain nerve endings
function of the pupil?
regulates amount of light entering
function of the ciliary body?
ring of smooth muscle
controls lens shape via suspensory ligament
what are the two layers of the retina? what is their function?
- outer PIGMENTED layer (RPE)
- absorbs light and prevents light scatter
- plays role in photoreceptor regeneration - inner NEURAL layer
- photoreceptors (rods and cones)
- neurons (bipolar, amacrine, horizontal and ganglion cells)
what is the function of rods?
responsible for “scotopic vision” –> high sensitivity in dark, saturate as light increases
low spatial resolution–> input from many rods is summated by one bipolar cell
what is the function of cones?
“photoptic vision” –> best in bright light
“colour vision”–> 3 types of cones, which reflect the type of photopigment (opsin)
R–> long
G–> medium
B–>short
HIGH spatial resolution–> only a few cones converge on one bipolar cell
how doe the phototransduction cascade occur?
photopigments = opsin + retinal (which is a vitamin A derived molecule)
1 photon converts 11-cis-retinal to all-trans-retinal–> this changes the shape of the photopigment
this activates hundreds of G protein TRANSDUCIN–> this activates a cyclic GMP phosphodiesterase–> each of these breaks down thousands of cyclic GMP–> decreased cGMP concentration closes Na+ channels in the membrane–> leads to hyperpolarization
what area of the retina has the highest resolution?
fovea–> only cones
if you have a central scotoma, what types of photoreceptors are likely affected?
cones
what does the bipolar cell do in the eye?
relays from photoreceptor to retinal ganglion cell
there are separate bipolars for rods and cones
ON/OFF bipolar cells
bipolar cells receive inputs from horizontal and amacrine cells–> this creates lateral inhibition by light in neighbouring regions of the retina, giving rise to “center-surround” receptive field organization
what are the two types of retinal ganglion cells?
magnocellular RGCs and parvocellular RGCs
what is the function of magnocellular RGCs?
large cell bodies, long dendrites, large receptive fields–> low spatial resolution
respond transiently to onset/offset of light–> high TEMPORAL resolution
what is the function of parvocellular RGCs?
small cell bodies, short dendrites, small receptive fields–> high SPATIAL resolution
sustained responses to onset of light–> low temporal resolution
“colour opponency”
what is optic atrophy?
lesions of the axons of the retinal ganglion cells, anywhere from the outer retinal layer to the intracranial optic nerve, eventually causing pallor of the optic disc
what is the blood supply to the eye?
from the internal carotid artery
the ophthalmic artery has 2 end divisions–> posterior ciliary arteries (choroid, outer retina, optic disc) and the central retinal artery (inner retina)
what visual hemifield is carried in the left optic tract?
the right visual hemifield
the visual input from the nasal hemiretinas (temporal visual field) decussates at the optic chiasm–> thus the left optic tract represents the left hemiretina which is the right visual hemifield of each eye
where do the axons of the retinal ganglion cells (the optic tracts) project?
most fibres are destined for the Lateral Geniculate Nucleus (LGN) which is the last neuron in the relay to the striate cortex
some fibres do project elsewhere:
- suprachiasmatic nucleus in the hypothalamus (sleep wake cycles)
- pretectal nucleus in the midbrain (input for pupil light reflex)
- midbrain ocular motor structures (i.e superior coliculus… mediates reflexive eye movements)
what is the function of the suprachiasmatic nucleus in the hypothalamus?
regulates sleep wake cycles
what is the function of the pretectal nucleus in the midbrain?
input for pupil light reflex
what is the function of the midbrain ocular motor structures (i.e superior coliculus)?
mediates reflexive eye movements
where do the inputs from the RGCs travel after they reach they LGN?
LGN relays info via its axons in the optic radiations to the striate cortex
some modulation by feedback from cortical regions occurs in the LGN
what happens in the striate (V1) cortex? where is it located?
termination of the retino-geniculo-striate pathway
initial stage of cortical processing
information is still highly “retinotropic” (specific for the location on the retina)
instead of spots of light, information is represented as linear segments and boundaries–> cells prefer lines of a specific orientation and these are organized in a regular array of “orientation columns”
located in occipital lobe
what happens in the extrastriate cortex?
beyond the striate (V1) cortex, information fans into a parallel distributed hierarchy of specialized modules
ascending the hierarchy, information is less concerned with retinotropic location and more concerned with specific stimulus properties
modules can be grouped into two streams: ventral (occipitotemporal stream)–> the WHAT; dorsal (occipitoparietal) stream–> the WHERE
what processing is done in the ventral/occipitotemporal stream of the extrastriate cortex?
WHAT
color perception, form processing, object, face and word recognition
what processing is done in the dorsal/occipitoparietal stream of the extrastriate cortex?
WHERE
motion perception, stereopsis, saccadic targeting, manual reaching
list defects resulting from lesions in the ventral/occipitotemporal stream of the extrastriate cortex and what they are
- achromatopsia–> inability to perceive colors
- general visual agnosia–> inability to recognize objects by sight, though able to by touch or sound
selective agnosias:
3. pure alexia–> inability to read, though able to write, talk and comprehend speech
- prosopagnosia–> inability to recognize faces
what is another name for the occipitotemporal gyrus (the WHAT of processing visual stimuli)?
fusiform gyrus
list defects resulting from lesions in the dorsal/occipitoparietal stream of the extrastriate cortex and what they are
WHERE stream
- akinetopsia–> inability to perceive object motion
- hemineglect–> failure to attend to stimuli on the contralateral side
- astereopsis–> inability to perceive depth from binocular cues
- Balint’s syndrome–> triad of:
- ocular motor apraxia (inability to make saccades accurately to visual targets)
- optic ataxia (inability to reach accurately to visual targets)
- simultanagnosia (inability to attend to more than one object at a time)
what regions of the brain are involved in control of eye movements?
frontal, parietal, occipital cortical regions with connections thru the internal capsule to the gaze centers in the brain stem
brainstem structures from midbrain to medulla with cerebellar and vestibular system inputs are responsible for voluntary and reflex eye movements
where is the vergence center?
midbrain
where is the vertical gaze center?
midbrain
where is the horizontal gaze center?
pons
list the supranuclear regions that control eye movements
- frontal gaze center (voluntary movements)
- occipital gaze center (pursuit) center
- descending projections (internal capsule) to brainstem
- vergence center
- vertical gaze center
- horizontal gaze center
- MLF
where is the voluntary gaze center?
frontal lobe
where is the pursuit gaze center?
occipital lobe
list the nuclear structures responsible for control of eye movement
- CN III nerve nuclear complex (including the edinger-westphal nucleus)
- CN IV nerve nucleus
- CN VI nerve nucleus (relationship to VII and PPRF)
list the infranuclear structures responsible for control of eye movement
- CN III nerve–> intramedullary relationships include red nucleus (cerebellar connections) and cerebral peduncle (pyramidal tract); tentorium and MCA/PCom junction; cavernous sinus and pituitary; superior orbital fissure and orbit
- CN IV nerve–> long course from dorsum of brainstem; through cavernous sinus and adjacent to pituitary
- CN VI nerve–> over petrous ridge; through cavernous sinus and adjacent to pituitary
why is the CN III intermedullary relationship with the red nucleus important?
cerebellar connection
what is the fixation system?
supranuclear gaze system
poorly localized in cortex
micromovements to move the object of regard on the fovea
global confusional state and dementia
anxiety
sedative/tranquilizing drugs
what is the saccadic system? and what are some common problems?
supranuclear gaze system
voluntary eye movements and fast eye movements
frontal eye fields crosses to brainstem gaze centers
unilateral–> horizontal gaze palsy
bilateral–> vertical gaze palsy
disorders commonly seen
what is the pursuit system?
supranuclear gaze system
tracking of objects
slow eye movements
occipital-parietal localization
projects to brainstem gaze centers
“cogwheel” pursuits
what is the vergence system?
supranuclear gaze system
slow eye movements
disconjugate
occipital-parietal to midbrain pre-tectum
allows focus on near
what is the non-optic reflex system?
supranuclear gaze system
slow eye movements
brainstem vestibular system-labyrinthine and tonic neck receptor inputs
maintenance of fixation during head movement
what are generalized symptoms of CNS infection?
fever, headache, neck stiffness, confusion, seizures
what are focal symptoms of CNS infection?
seizures, numbness, weakness, visual changes, ataxia, dizziness, memory loss
related to the part of the brain involved
in terms of CNS infection localization, name the type of syndrome that would present in each of the following “spaces”:
- epidural
- subdural
- subarachnoid
- parenchymal (focal vs. diffuse)
- venous
- abscess (enclosed collection of pus)
- empyema (collection of pus in a cavity)
- meningitis (inflammation of the meninges)
- diffuse–> encephalitis//focal–> brain abscess
- septic thrombophlebitis (infected venous clot)
how seriously must you treat CNS infections?
they are all medical/surgical emergencies
what are the two types of meningitis based on causative agent and how do their prognoses differ?
bacterial–> life threatening
viral–> self limited
how can you distinguish bacterial from viral meningitis just based on symptoms?
both get fever, headache, stiff neck
bacterial–> get change in level of consciousness
viral–> no change in LOC
how can you distinguish bacterial from viral meningitis just based on lab tests?
bacterial: +++ WBC, +++ CSF PMNs, low CSF glucose
viral: +/- WBC, + CSF lymph, normal CSF glucose
what two factors in the pathogenesis of bacterial meningitis cause increased BBB permeability?
endothelial cell invasion (from bacteremia) and subarachnoid space inflammation (from meningeal inflammation)–> leads to vasogenic edema
overall what causes death in bacterial meningitis?
disease progresses such that you get increased ICP and cerebral infarction and thus decreased cerebral blood flow
what causes bacterial meningitis in the newborn?
group B strep
e coli
listeria
what causes bacterial meningitis in an infant?
group B strep
haemophilus
neisseria
what causes bacterial meningitis in an adult?
pneumococcus
meningococcus
haemophilus
listeria
staphylococcus
how do you treat bacterial meningitis?
start appropriate antibiotics ASAP
if LP is going to be delayed by need for CT scan, obtain blood cultures and start Abs right away
empiric therapy:
ceftriaxone IV + vancomycin (for penicillin resistant S. pneumo) + ampicillin (for elderly, immunosuppressed, pregnant) + dexamethasone IV (corticosteroid…prior to or with first dose of Abs)
how would you empirically treat a suspected brain abscess?
ceftriaxone + metronidazole +/- vancomycin
-OR-
neropenem +/- vancomycin
glucocorticoids when there is significant swelling (dexamethasone)
how do you distinguish clinically between meningitis and encephalitis?
meningitis has intact brain function, whereas encephalitis does not
i.e in encephalitis you might get: altered mental status motor or sensory deficits change in behavior/personality speech or movement disorder
what type of brain syndrome does rabies or west nile cause?
encephalitis
