The Brain Exam 1 Flashcards
the spinal cord has ___ pairs of spinal nerves
31
ventral surface of spinal cord blood supply
- single anterior spinal artery that supplies the anterior 2/3 of cord
dorsal surface of spinal cord blood supply
- a pair of posterior spinal arteries
CSF flow
- acts as shock absorber
- elaborated by choroid plexus in ventricles
- 1/2 L per day
- exits though foramina in brain stem then reabsorbed to keep constant volume
location of blood vessels & cerebrospinal fluid
subarachnoid space
3 layers of meninges
- dura, arachnoid, pia
- specializations in pia anchor cord to dura (denticulate ligaments & filum terminale)
vertebra function
- normally protective but may become a liability in cases of increased mass due to swelling or tumors
development of spinal cord
- 1st trimester: spinal cord & vertebral column grow at same rate, then sc slows
- birth: sc ends btwn L2/L3
- adult: sc ends btwn L1/L2
spinal taps
- performed below L2 (after spinal cord ends)
- needle won’t damage nerve roots
nerve root length
- become progressively longer from cervical to sacral levels stemming from differences in growth of spinal cord & spinal column
- allows it to exit intervertebral foramen at appropriate level
C1-C7
- exit above vertebra of name
C8-S4
- C8 exits above T1 (no C8 vertebra)
- exit below vertebra of name
spinal cord enlargements
- cervical enlargement: C5-T1
- lumbar enlargement: L3-S2
- accommodates neurons required for upper/lower extremities
segmental organization
- segment defined by a pair of spinal nerves
- dorsal (sensory) & ventral (motor)
- primary sensory neurons located in dorsal root ganglion
dermatome
- cutaneous territories innervated by spinal nerves (segmental organization)
myotome
- muscles innervated by a single nerve root (segmental organization)
reflex arc
- occur at spinal cord level (segmental organization)
- stretch reflex
- can involve multiple neurons (as in reciprocal inhibition, nociception, crossed extension)
gray matter
- contains cell bodies
- dorsal horn: sensory neurons
- ventral horn: motor neurons
white matter
- contains axons (myelin stain)
- divided into funiculi (bundle of nerves): dorsal, lateral & ventral
substantia gelatinosa
- caps dorsal horn & contains neurons that deal w/ pain & temperature (poorly myelinated)
transverse sections through spinal cord enlargements
- higher levels of cord have more white matter
- cervical & lumbar enlargements seen in ventral horn expansion
axial muscles are controlled ___ & limb muscles are controlled ___.
medially & laterally
autonomic nervous system division
- preganglionic sympathetic neurons: T1-L2
- pregnaglionic parasympathetic neurons: S2-S4
phrenic nucleus
- C3-C5
- motor neurons of diaphragm
longitudinal organization principles
- long tracts bringing info to/from cortex must dessucate during ascent or descent
somatotopic organization
- arranged systematically according to parts of body surface
ascending spinal cord pathways
- 3 neuron pathways
- 1: 1st order neuron (DRG)
- 2: 2nd order neuron; crosses midline (SC or BS)
- 3: 3rd order neuron (thalamus)
- information then sent to cortex
dorsal column pathway
- position sense, vibration sense, 2 point discrimination
- fasciculus gracilis & cuneatus
- ipsilateral to where info entered
- large neurons w/ heavily myelinated axons
- irrigated by 2 dorsal arteries
fasciculus gracilis
- medial
- info from T6 & below
- 1st order neurons end in gracile nucleus (BS)
fasciculus cuneatus
- lateral
- info from T5 & above
- 1st order neurons end in cuneate nucleus (BS)
somatotopic organization of dorsal column pathway
- sacral levels more medial
- cervical levels more lateral
- continues to cortex
spinothalamic pathway
- localization of pain & temperature
- 2nd order neuron in dorsal horn (SC). must then pass through ventral white commissure
- small neurons w/ poor or no myelination
- contralateral to where info entered
- anteriolateral to anterior horn
somatotopic organization of spinothalamic pathway
- lower levels more lateral
- higher levels more medial
dorsal column lesion causes ___ deficit.
ipsilateral
spinothalamic column lesion causes ___ deficit.
contralateral
deficits caused ___ level of lesion
below
suspended sensory loss
- lesions that affect roots (not long tracts)
- reveal band-like distribution of deficit
spinothalamic collaterals
- part of multisynaptic spinal reticular pathway that deals w/ affect of pain
referred pain
- pain seeming to originate from specific area of body surface as a result form damaged internal organ
- visceral pain is poorly localized to diseased organ
referred pain mechanism
- visceral afferents conducting pain enter same spinal cord segment as afferents that supply skin
- collaterals from visceral afferents send signals to somatosensory tract that innervates region of referred pain
ascending pathways to the cerebellum
- all end ipsilaterally in the cerebellum (right controls right)
- dorsal spinocerebellar, ventral spinocerebellar, cuneocerebellar
corticospinal pathway
- voluntary fine movement of distal extremities
- upper motor neuron in cortex crosses in medulla & travels down lateral corticospinal tract
- lower motor neuron in ventral horn sends axon to skeletal muscle
- 15% fibers travel in anterior corticospinal pathway & cross at level of synapse
UMN lesion
- hyperreflexia
- spastic paralysis
- increased muscle tone (flexers of upper ex & extensors of lower ex)
- mild atrophy
- clasp knife reflex
- clonus
- babinski sign present
- large area of body affected (from level of lesion & below)
- location: lateral corticospinal tract
clonus
- rapid series of alternating muscle contractions in response to a sudden stress
LMN lesion
- flaccid paralysis
- loss of deep tendon reflexes
- decrease in muscle tone
- pronounced atrophy
- fasciculations (anterior horn cel involvement)
- segmental distribution of deficit
- location: ventral horn
fasciculations
- spontaneous contractions of muscle fibers visible through the skin as small twitches
neuron
- 50%
- neurotransmitter-dependent classification
glia
- function-dependent classification
- macroglia: astroglia (15-20%), oligodendrocyte (15%), oligodendrocyte precursors (5-10%), ependymal
- microglia (10-15%): originate from mesoderm
schwann cells
- produce myelin in PNS
stains for brain structure & pathological conditions
- H & E (hemotoxylin/eosin): nucleus/cytoplasm
- Nissl: nucleus, rER/RNA granules (loss of staining w/ degeneration)
basic structure of neuron
- dendrites, cell body (soma), axon, & axon terminals
- polar: signal transmission is directional; impulses carried away from cell body
- cell signals are electrical
neuron types
- bipolar (interneuron): axon & dendrites from both sides
- unipolar (sensory): axon & dendrites from one side
- multipolar (motoneuron): 1 axon & multiple dendrites
axon hillock
- initial segment of axon
- action potential originates here
nodes of Ranivier
- location of VG Na channels
neuron communication
- through synapses
- axon terminal releases NT to activate receptors on dendritic spines
- synapse strength matters; amt NT released, # receptors activated, t of activation, & # receptors available
conserved properties of in vivo mature gray matter astroglia
- non-electrically excitable, very low input resistance (leaky)
- uptake glutatmate through excitatory aa transporters
- morphologically ramified & complex
- extensive intercellular coupling through gap-junctions
tripartite synapse
- has glial component in addition to neural component so glial cell can also sense neuronal signal & respond
glutamate-glutamine cycle
- one way that glutamate is replenished in neurons
- in synapse, glutamate is taken up by both neuron & glial cells
- in glial cells, converted to glutamine
- glutamine taken up by neuron to become glutamate
astrocytes in neurological diseases
- astrocytes become GFAP+ to form glial scars in injury
- why axons cannot regenerate
- certain reactive astroglia are toxic & able to induce neuronal cell death
microglia
- immuno cell type
- surveillance
- release cytokines following activation
- cluster around amyloid plaques
- phagocytosis: clear debris
- high motility
oligodendrocytes
- myelin formation in CNS
how do you know disease is in spinal cord?
- motor sensory level means sc disease
- LMN involvement means sc involvement (or root, nerve)
- suspended sensory loss for pain & temp means spinal cord disease (vwc)
dermatomes: C4, T4, T10, L1, L5, S4-S5
- clavicle
- nipple line
- umbilicus
- inguinal crease
- lateral calf
- perianal area
myotomes: C3,C4,C5; C5; C7; C8; L3; S1
- diaphragm
- biceps brachii
- triceps
- intrinsic hand muscles
- quadriceps femoris
- gastrocnemius
Brown-Sequard syndrome
- when a lateral half of sc is disrupted
- ipsilateral loss of position & vibration sense
- contralateral loss of pain & temperature sense
syringomyelia
- lesion in ventral white commissure
- syrinx that can start small & grow to be more disruptive
- progression: suspended sensory loss to LMN weakness
ALS
- amyotrophic lateral sclerosis
- combined UMN & LMN disease
- affects corticospinal tract & ventral horn
- rare, elderly, insidious onset, progressive, average survival 2-3 yrs, death from infection
- mixed UMN & LMN signs; LMN signs predominate & fasciculations
- sensory pathways normal
ALS variants
- spinal muscular atrophy (LMN)
- primary lateral sclerosis (UMN)
- Bulbar ALS (LMN cranial nerves)
tabes dorsalis
- form of tertiary neurosyphilis
- affects dorsal roots & ganglia
- patchy loss of pain & temperature
- predominant posterior column findings: loss of position/vibratory sense; difficulty maintaining erect posture; romberg sign
Romberg sign
- patient can stand w/ eyes open, but cannot stand w/ eyes closed
- tests for posterior column dysfunction
subacute combined degerneration
- posterolateral sclerosis
- vit B12 deficiency; pernicious anemia
- dorsal columns & corticospinal tract
- UMN signs & Romberg sign
Poliomyelitis
- viral infection w/ predilections for anterior horn cells
- pure lower motor neuron syndrome in setting of acute febrile illness
post-polio syndrome
- new weakness years after acute olio
- often in same distribution as original weakness
anterior spinal syndrome
- dorsal column preserved
motor axons exit via ___ & sensory axons enter via ___.
ventral horn & dorsal horn
what happens during sc injury?
- axons damaged, interrupting efficient nerve conduction
- small % neurons die
- damaged neurons release glutamate = excitotoxicity = cell death
- loss of axon transmission causes neurotrophin-deprived cell death
- swelling = compression
- site fills w/ cytokine fluid causing glial cell growth = glial scar
neurotrophin
- nerve cell growth factor
- efficient connection needed in order to deliver to cell body
glial scar
- inhibits regeneration preventing reconnection & restored neural function
- normally keeps nervous system properly sculpted & prevents inappropriate connections
neuronal survival
- reduce swelling: methylpredisone (approved), surgical decompression, hypothermia
- apply factors directly or engineered cells
altering terrain
- PNS graft at CNS injury, stops once it reaches CNS
- CNS to PNS prevents PNS growth across it
- natural inhibitors in CNS that prevent growth
What interventions could enhance growth & reconnection after spinal cord injury?
- preventing swelling
- providing permissive substrate for growth
- blocking myelin & glial scar based inhibitors
- providing neurotrophins
- adding local guideposts
- stem cells
- neuroengineering
what factors exacerbate severity after spinal cord injury?
- excitotoxicity
- swelling w/in vertebral column
- damage at one vertebral level interrupting transmission at all points below
- subsequent loss of neurotrophins leading to cell death
subtypes of neuropathy
- axonal
- demyelinating
- Wallerian degeneration
peripheral nerve
- cell body
- axon
- myelin sheath
- symbiotic but structurally independent relationship btwn axon & myelin sheath
- highly anastomosing vascular supply of arterial branches
- connective tissue
PNS
- includes all neural structures outside the pial membrane of sc & brainstem
- dorsal roots extend into posterior columns & dorsal horns of sc
- peripheral axons of drg are sensory nerve fibers
peripheral fibers divided into different sizes
- type I: larger, heavily myelinated; touch/pressure, spindle afferents
- type II: smaller, thinly myelinated; sharp & lancinating pain & temperature
- type III & IV: small, unmyelinated; dull, burning poorly localized pain
PNS motor
- efferent roots consist of emerging axons of anterior horn cells, lateral horn cells, & motor nuclei of bs
- large myelinated fibers terminate on muscle
- small unmyelinated fibers terminate on sympathetic & parasympathetic ganglia
alpha motor units
- cause muscle contraction
- not heavily myelinated
gamma motor units
- terminate on muscle spindles
- help maintain tension
pre- & postganlionic autonomic units
- slower conduction velocity
- terminate on structure involved in sympathetic & parapsym nervous system
axonal transport
- neurotubules or microtubules are means
- anterograde (away from body) & retrograde
- requires energy (oxphos)
- independent of electrical activity
anterograde transport importance
- necessary to maintain axon itself & in motor nerves is involved in maintaining muscle
- denervated muscles atrophy
- chemo drugs can disrupt neurotubule organization
rapid axonal transport
- carries synaptic vesicles & membrane bound proteins like plasma membrane proteins
- requires kinesin which is thought to link proteins to microtubules & transport them w/ ATP dependent mech
slow axonal transport
- carries soluble enzymes & tubulin, used in making microtubules
- determines rate of recovery from nerve injury
retrograde transport
- occurs often w/ nerve injury; thought to carry signals of nerve injury inducing chromatolysis
- uses dynein
- used by some neurotropic viruses to infect (polio, herpes, rabies)
wallerian degeneration
- dying forward
- degeneration from point of axonal injury peripherally
- elements needed to regenerate nerve can’t migrate to nerve
- chromatolysis, muscle atrophy
axonal degeneration
- dying back
- metabolic derangement results in most distal parts of axon to degenerate in proximal direction
- longest axons die first
- chromatolysis, muscle atrophy
segmental demyelination
- nothing wrong w/ cell body, axon, or connection
- impulse dies in middle of nerve: only myelin damaged
- no chromatolysis OR mucsle atrophy
- may degererate as primary disease or as secondary effect of axonal disruption
nerve conduction studies
- test used to look at peripheral nerves
- measure nerve function by measuring evoked compound motor or sensory nerve action potentials
- can help distinguish type of lesion & refines pattern of sensory or motor involvement
peripheral nerve injury
- sensory & motor studies will both be abnormal
nerve root injury
- abnormal motor study
- normal sensory study
reflexes: biceps, triceps, knee jerk, ankle jerk
- C5
- C7
- L4
- S1
axonal neuropathy
- usually slow and chronic
- stocking-glove distribution: loss of reflexes distally & muscle wasting distally
- low amplitude CMAPS & absent SNAPs
axonal neuropathy causes
- metabolic (diabetes)
- toxic (environmental agents)
- deficiency (thiamine)
- genetic
- paraneoplastic (tumor)
Guillain-Barre Syndrome
- primarily motor
- rapidly progressive ( peaks in 2 weeks)
- areflexia & ataxia belie an afferent component
- NCSs show conduction block
- treatment is w/ “immune modulating” therapies
demyelinating polyneuropathy
- autoimmune
- genetic
chronic demyelinating neuropathy
- hereditary neuropathies
- CIPD (chronic inflammatory demyelinating neuropathy)
- myelin continues to grow over & over again, forming onion bulbs
ischemic mononeuritis multiplex
- seen in a number of conditions but especially in polyarteritis nodosa
- fascicular injury: individual fascicles are injured by interruption of microcirculation of nerve
- individual nerves picked off one by one
- widespread looks like generalized neuropathy
- treat w/ steroids & immune suppressor
focal neuropathies
- compressive or otherwise traumatic
- ischemic, infiltrative, autoimmune
- wallerian degeneration
Seddon’s classification of traumatic nerve injury
- class 1: neurapraxia: compression w/ focal demyelination; no denervation; quick recovery
- class 2: axonotmesis: axonal damage but intact nerve sheath for sprouting to occur; slower & sometimes incomplete recovery
- class 3: neurotmesis; scarred or disrupted nerve sheath; no recovery
features of neuromuscular junction
- VG Ca channel
- ACh vesicles
- post-synaptic membrane folds
- ACh esterase
- ACh receptors
ACh receptor
- 5 subunits
- extracellular portion that sticks into synaptic cleft: main immunogenic region (MIR) & ACh binding site
- 2ACh binding causes opening & Na in/K out
Myasthenia Gravis mech
- post-synaptic disorder
- Anti AChR Ab bind MIR & activate complement cascade = ACh receptor destroyed & sometimes membrane
MG facts
- genetic predisposition to autoimmune disorders
- young women & older men
- 10+% have thymus gland tumor (induces Abs)
MG clinical bottom line
- disorder of striated muscle that causes muscle weakness
MG diagnostics
- fatiguable muscle weakness usually present
- characteristic distribution of muscle involvement
- characteristic examination features
- supportive lab data
MG distribution of muscle involvemnet
- ocular: diplopia, ptosis, ophthalmoplegia
- oropharyngeal: dysarthria, dysphagia, difficulty chewing, nasal regurgitation, choking
- limb
- respiratory (diaphragm)
MG examination features
- fatiguable ptosis/ophthalmoplegia
- fatiguable limb weakness
- normal sensory exam
- no CNS signs
MG diagnostic work-up
- nicotinic ACh receptor Ab
- Tensilon test (AChe inhibitor)
- repetitive nerve conduction studies
- single fiber EMG
- chest CT/MRI
MG treatment
- medications: decrease ACh destruction, reduce Ab, immunosuppressive, block complement
- thymectomy
Lambert Eaton Myasthenic Syndrome (LEMS) mech
- pre-synaptic disorder
- pre-s VGCC damage = reduced Ca influx during AP, reduced ACh release, reduced safety factor for PSM depolarization -> muscle weakness
LEMS etiology
- Ab mediated
- ~ half associated w/ cancer (SCLC)
LEMS clinical features
- slowly progressive proximal muscle weakness most common (shoulder/hip)
- some cranial nerve involvement such as ptosis & ophthalmoplegia but modest
- autonomic symptoms: dry mouth
- weakness can improve w/ repetition
LEMS diagnostic testing
- VGCC Ab test
- repetitive nerve stimulation & SF-EMG (increment - amplitude increases)
LEMS treatment
- turmor search & treatment
- symptomatic treatment 3,4 DAP
- immunosuppressive meds
myopathy
- pathological disorder that impairs normal muscle function, usually but not always alteration of muscle structure
symptoms of myopathy
- muscle weakness: hip girdle, shoulder girdle, oculomotor, facial, bulbar (throat), trunkal, upper airway
when to suspect myopathy
- subacute or chronic symmetric weakness, usually in absence of pain/sensory symptoms
- proximal
- no CNS, peripheral nerve, or nerve root pattern
- may affect cranial nerves awa appendicular & axial
- usually but not always skeletal muscle
- may affect muscle alone or other organ systems
acquired myopathies
- immune mediated: inflammatory (dermatomyositis, polymyositis, inclusion body myositis) & necrotizing myopathy (drugs)
- infectious: HIV, influenza
- toxic/metabolic: steroids, immune checkpoint inhibitors
hereditary myopathies
- dystrophies: progressive; Duchenne/Becker, FSH, myotonic
- congenital: present at or soon after birth; milder
- metabolic: missing enzyme; glycogen/lipid storage mitochondrial
- channelopathies: periodic paralysis myotonia congenita
dermatomyositis
- any age/gender
- subacute onset
- rash
- weakness: proximal, symmetric, neck flexors, dysphagia
- associations w/ other CTD & malignancy
- biopsy: diagnostic or suggestive (perifascicular atrophy)
- responsive to immunomodulation
inclusion body myositis
- > 60 yrs; mostly men
- chronic; slow onset
- weakness: quadriceps, wrist/finger flexors, neck flexors, dysphagia
- associations w/ CTD but rarely malignancy
- biopsy diagnostic in appropriate clinical context
- unresponsive to immunomodulating treatment
endocrine myopathies
- weakness: limb girdle; hip flexors
- biopsy: type II muscle atrophy
- EMG, CK - normal
necrotizing myopathy
- toxins (statins), autoimmune, or paraneoplastic
- weakness: limb girdle
- biopsy: myofiber necrosis
- EMG, CK: abnormal
muscular dystrophies
- heritable, progressive disorders
- related to mutations in genes producing proteins requisite for myofiber integrity & function
- biopsy associated w/ destructive changes in muscle
- historically referred to by eponym or characteristic pattern of weakness
dystrophinopathies
- duchenne’s - beckers
- x-linked mutation of dystrophin gene
- symptomatic @ 2-3; life expectancy: end of 30s
- weakness: limb girdle, calf hypertrophy, tight heel cords
- associated cardiomyopathy, ventilatory muscle weakness, id
fascioscapulohumeral
- AD - types 1 & 2
- recognition from 1st decade to adulthood
- weakness: face, scapular fixators, biceps/triceps, foot dorsiflexors
myotonic MD
- AD - DM1 (myotonin protein kinase), DM2 (zinc finger protein)
- DM1 trinucleotide repeat disease, variable age of onset, variable severity
- weakness: cranial, distal limb weakness, ventilatory
- associated myotonia & systemic features including cardiac conduction defects, cataracts, smooth muscle involvement, frontal balding
congenital myopathy
- heritable, often evident at birth, slow progression
- AD, AR, X-linked
- associated dysmorphic & orthopedic features common
glycogen storage disease
- Pompe: a-glucosidase, AR, weakness: limb girdle/ventilatory, associated cardiac/liver
- McArdle: myophosphorylase, AR, exertional muscle pain/cramping/myoglobinuria
lipid storage disease
- multiple mutations
- fixed muscle weakness or dynamic depending on mutation
- other end-organs may be involved
- symptoms precipitated by fasting, pregnancy, or intercurrent illness
mitochondrial myopathy
- mutations in mito genome or nuclear genes coding for mito proteins
- variable phenotype w/ involvement of end organs (w/ high energy requirement)
characteristics of spinal cord lesions involving long tracts
- effects observed at a level of the body & below
- pain & temperature loss on side opposite lesion
- weakness, position sense, & vibration sense lost on side of lesion
characteristics of brainstem lesions
- lesions of long tracts in brainstem result in contralateral deficit
- cranial nerve signs reveal level of lesion in brainstem
- cranial nerve signs observed onside of lesion
corticospinal tract travels through the ___ of the ___ in brainstem.
pyramids; medulla
the olive is
- a relay station for info heading to cerebellum
dorsal column pathways travel under ___ in the brainstem
bulges on dorsal aspect
medial medullary lesions involve _____.
the dorsal column pathways & potentially corticospinal tract
motor cranial nerve nuclei receive cortical input via the ___.
corticobulbar pathway (except those innervating muscles of eye)
corticobulbar pathway
- neurons in cortex
- axons branch off & bilaterally synapse on motor nuclei of brainstem (except lower face neurons)
alar plate
- gives rise to sensory neurons
basal plate
- gives rise to motor neurons
in brainstem, motor nuclei are ____ to sensory nuclei.
medial
columns of CN nucleai medial to lateral in medulla
- somatic motor (hypoglossal)
- pharyngeal motor (ambiguous)
- visceral motor (dorsal X)
- visceral sensory (solitarius)
- somatic sensory (spinal V)
- special senses (vestibular)
hypoglossal lesion
- paralysis of tongue on side of lesion
- fasciculations - LMN sign
- upon protrusion, tongue deviates to side of lesion
nucleus ambiguus lesion
- hoarseness
- difficulty swallowing
- arch of soft palate droops on affected side
- uvula is deviated away from side of lesion
dorsal motor nucleus of X
- preganglionic parasym for throacic & abdominal viscera
nucleus solitarius
- taste & sensation from viscera via CN VII, IX, X (tongue/epiglottis/glottis)
spinal nucleus of V
- pain & temp info from face & oral cavity
- lesions result in ipsilateral defect
reticular formation
- contains centers for respiration, HR, BP & reticular activating system important for arousal & consciousness
- extends through entire bs & forms a core
- descending pain & motor pathways
- NT production
- disruption = coma
caudal medulla
- motor decussation
- sensory decussation (superior)
rostral medulla
- cranial nerve nuclei
columns of CN nuclei from medial to lateral in pons
- somatic motor (abducens)
- branchial motor (facial n & motor n)
- visceral motor (superior salivary)
- visceral sensory (solitarius)
- somatosensory (spinal V, principal sensory V)
- special senses (vestibular cochlear)
cranial nerve VIII & associated nuclei
- hearing to spiral ganglion to ventral & dorsal cochlear nuclei
- equilibrium to vestibular ganglion to vestibular nuceli
auditory info is distributed:
- bilaterally in the CNS
- info from cochlear nucleus crosses midline in trapezoid body
- lesion: difficulty localizing sound/eliminating background noise
paramedian pontine reticular formation
- lateral gaze center
- receives input from cortex & communicates via medial longitudinal fasciculus
neurons that control the upper face receive ____ innervation. neurons that control the lower face receive ____ innervation.
- bilateral corticobulbar
- only contralateral (paralysis indicates contralateral corticobulbar lesion)
nuclei of CN V
- principal sensory: relay touch, position, vibration sense
- spinal V: relay pain, temp
- mesencephalic V: relay sensation from mastication muscles
- motor V: innervates mastication muscles
- sensory travel via trigeminothalamic pathway
locked in syndrome
- results from bilateral damage to base of pons
- lesion of corticospinal & corticobulbar pathways
columns of CN nuclei from medial to lateral in midbrain
- somatic motor (trochlear, oculomotor)
- visceral motor (Edinger-Westphal)
- somatosensory (mesencephalic nucleus of V)
locus coeruleus
- major noradrenergic nucleus of brainstem
- provides most output to cerebral cortex
- may play role in maintaining attention & vigilance
tectum
- top of bs
- only in midbrain
- relevant for inferior & superior colliculi
substantia nigra
- area of dopaminergic neurons in midbrain
- loss of these neurons leads to parkinson’s
vergence
- converging eyes on 1 target
saccade
- rapid eye movement
- horizontal signal from frontal lobe
- vertical signal from midbrain
pursuit
- follow things moving slowly across environment
- requires a lot of cerebellar input
vestibulo-ocular reflex
- gyroscope that keeps eyes steady despite eye movement
optokinetics
- identification of things when things move rapidly by
- combined saccades & pursuit
exotropia
- fixed separation of eyes
- form of strabismus where eyes deviate outward
exophoria
- eyes drift apart
horizontal gaze palsy
- damage to PPRF
internuclear ophthalmoplegia
- lesion to MLF
- medial rectus slowing & incomplete movement
- nystagmus is secondary
vestibular nucleus damage
- results in nystagmus
- the intact vestibular nucleus forces eyes toward damaged side w/ corrective movement(s)
- lateropulsion & Bruyn’s nystagmus
disruption of vertical upgaze
- tumor of midbrain blocks neurons responsible for upgaze
accompanying signs: CN lesion inside brainstem
- CN lesion + limb weakness, ataxia, or sensory symptoms
accompanying signs: CN lesion in subarachnoid space
- multiple CN lesions withouth long tract signs
accompanying signs: CN lesion at skull base or beyond
- multiple CN, contiguous, unilateral
CN group lesion patterns
- 3, 4, 5, 6: cavernous sinus
- 5, 7, 8: CP angle
- 9, 10, 11, 12: skull base
cerebellar peduncle connections
- inferior: medulla; non-cortical (spino/vestibulo) input to cerebellum
- middle: pons; cortical input to cerebellum
- superior: midbrain; output from cerebellum
cerebellar blood supply
- SCA, AICA, PICA (from vertebrals/basilar)
Mollaret’s triangle
- inferior olive, red nucleus, dental nucleus
- lesion causes palatal myoclonus
cerebellar cortex layers
- internal granular: densely packed neurons receive input
- molecular: dominated by tracts
- purkinje: large neurons
what does not synapse at granular cell layer?
- climbing fibers from inferior olive
- goes directly to purkinje cells (skips mossy fiber)
deep cerebellar nuclei
- dentate nucleus
- outputs get modulated
- purkinje cells synapse here
functional cerebellar organization
- vermis (midline) & paramedian: trunkal control & leg coordination
- lateral: limb (mostly upper) control
- flocculonodular: balance
cerebellar areas
- vestibulocerebellum (flocculonodular): input/output vestibular neuclei
- spinocerebellum (vermis/paramedian): input/output spinocerebellar tract, olives
- neocerebellum (most): input from cortex via pontine nuclei/output to cortex via VL thalamus
cerebellar syndromes
- vestibulocerebellum: balance & gait ataxia; oculomotor control
- spinocerebellum: truncal incoordination; leg incoordination
- neocerebellum: upper extremity dyscoordination
hemispheric syndromes (cerebellum)
- incoordination - ataxia
- dysmetria
- intention tremor
- dysdiadochokinesis
time course in cerebellar dx
- acute: ischemia, hemorrhage, hypoxia, toxins
- subacute: alcohol, inflammatory, autoimmune
- chronic: genetic, neurodegenerative
structures of basal ganglia
- striatum
- globus pallidus
- subthalamic nucleus
- substantia nigra
striatum
- caudate nucleus
- putamen
- receive inputs from cortex
- blood supply: branches from ACA & MCA
globus pallidus
- externa/interna
- main output to thalamus
- blood supply: anterior choroidal artery, lateral striate arteries
subthalamic nucleus
- key component of indirect pathway
- blood supply: branches of PCA & PCOM
substantia nigra
- pars compacta (dopamine)
- pars reticulata (output to thalamus)
- key inhibitor/activator of striatal activity
- blood supply: branches of PCA & PCOM
basal ganglia function
- extrapyramidal motor system (facilitates voluntary movement & attenuates involuntary movement)
- NT: glutamate/dopamine excite; GABA/dopamine inhibit
direct pathway (basal ganglia)
- facilitate voluntary movement
- default: net activation of cortex
- dopamine activates D1 receptors = net increase in cortical activity
indirect pathway (basal ganglia)
- inhibit involuntary movement
- default: net inhibition of cortex
- dopamine inhibits D2 receptors = net activation of cortex
extrapyramidal disorder
- hypokinetic disorders: parkinsonism (bradykinesia resting tremor, rigidity, postural instability)
- hyperkinetic disorders: tremor, hemiballismus, myoclonus, chorea, dystonia, tics
Parkinson’s
- loss of dopamine producing cells in substantia nigra
- less dopamine present = decreased net activation of cortex
- bradykinesia, resting tremor, rigidity, postural instability
- asymmetry of symptoms
Huntington’s
- movement disorder: chorea & later parkinsonism
- dementia
- psychiatric: depression; psychosis
