Pathways Flashcards
1
Q
UMN lesions
A
- hemiplegia: contralateral if lesion in cortex before deccusation; ipsilateral if lesion in spinal after deccustion
- paresis/paralysis
- spacitity (increase tone)
- hyper-reflexia
- upward going plantar reflex (babinski sign)
- no/not as much atrophy
- no fasiculations
2
Q
LMN lesions
-6 signs
A
- ipsilateral weakness because after decussation **
- usually ind. muscles not grp
- flaccidity (decrease tone) or normal
- hypo-reflexia
- atrophy
- fasciculations
- *EXCEPT Trochlear (CN1V) nuclei because they cross at nucleus level! (but if lesion at the CN4 nerve, will be ipsilateral
3
Q
UMN
A
- 1ry neuron in motor pathway
- in CNS
- synapse to LMN
4
Q
LMN
A
- cell body in brainstem (CNs) /spinal cord (ventral horns)
- axons in PNS
- synapse to muscles
- LMN pathway = “final common pathway”
- IPSILATERAL innervation
5
Q
Describe the corticospinal tract pathway
A
-for skilled limb movements
-1ry neuron: 1ry motor cortex
> corona radiata
> post. limb internal capsule > cerebral peduncles > CST in ant pons > pyramids
> deccusate at spinomedullary junction (pyramids)
> descend in lateral corticospinal tract (LCST) in lateral column of spinal cord
> synapse 2ry neuron: cervical and lumbosacral enlargements
> distal limbs
6
Q
Which side is affected if CNs are lesioned?
A
IPSI b/c LMN after deccusation
7
Q
Which side is affected if CN nuceli are lesioned?
A
IPSI except for Trochlear nuclei = contralateral
CST tract
8
Q
Describe Corticobulbar Tract
A
-cortex > brainstem
-motor path for cranial nerves (5,7,9,10,11,12)
-same as CST except through genu of internal capsule
(although 7,11,12 more complicated)
9
Q
Which CN does CBTract not innervate?
A
- sensory CNs
- eye motors : 3,4,6
10
Q
Which CNs are bilaterally innervated? what is the implication?
A
- CN 5,9,10
- redundancy - if lesioned on one side in CBTract (UMN), still ok!
- but lesion at nerve level (LMN) (after CBT > nuclei) > ipsilateral effects
11
Q
Describe the UMN, LMN lesions involved with the Mastication Nucleus
A
-CNV3: chewing, jaw movements
-UMN lesion: bilaterally innervated > function preserved
-LMN lesion: IPSIlateral defecit:
opening mouth, chewing diff due to paresis/paralysis jaw drop to lesioned side, atrophy of muscles > asymmetrical face
12
Q
Describe the UMN, LMN lesions involved with the Nucleus Ambiguus
A
-CN 9, 10: larynx (10), pharynx, speech, swallowing
-UMN lesion: bilaterally inn > func ok
-LMN lesion: IPSIlateral def
gag reflex loss
hoarse voice
sagging palate
13
Q
Describe the UMN, LMN lesions involved with Hypoglossal nucleus
A
-CN 12: tongue movements
-UMN lesion: before decussation > no input to CONTRALateral tongue > tongue protrudes to contralateral side of cortex and paresis/paralysis
-LMN lesion: after decussatin > IPSIlateral to lesion
tongue protrudes
paresis/paralysis
fasciculations then atrophy
*Tongue always goes to side of lesion
14
Q
Describe the UMN, LMN lesions involved with Accessory nucleus
A
- CN 11: sterno, trap : shoulder shrug and head turn
- UMN lesion: IPSI for sterno (difficulty turning head to opposite side), CONTRA for trap weakness in should shrug (because UMN of trap crosses before synapsing in nuclei)
-LMN lesion: ipsilateral both muscles
15
Q
Describe the UMN, LMN lesions involved with Facial nucleus
A
- CN 7 - facial expression, taste ant 2/3 tongue, all glands (except parotid)
- Facial Nucleus is different because it has 2 subnuclei controlled by different UMNs to forehead and face
- UMN lesion: rostal subnuclei (forehead) is bilaterally inn; caudal (face) is unilateral. Thus, lesion will only affect CONTRA lower face
- LMN lesion: IPSI face and forehead affected - paralysis
16
Q
Describe STT
A
- Spinothalamic tract
- for pain, T, crude touch
1: periphery > DRG into dorsal roots then synapse
2: in dorsal horn > DECUSSATE > CONTRA STT (ventral-lateral white matter of cord) > travels in Spinal Lemniscus in brain stem > synapse at VP thalamus
3: thalamus > postcentral gyrus
17
Q
Describe DCML
A
- Dorsal column - medial lemniscus
- for fine touch, vibration, conscious proprioception
1: periphery > DRG > dorsal horn > ascend via FASCICULUS GRACILIS (medial, leg) /FASCICULUS CUNEATUS (lateral, arm) > synapse in NUCLEUS GRACILIS/CUNEATUS
2: nuclei > deccusate @ medial lemniscus in brain stem > synapse in VP thalamus
3: thalamus > postcentral gyrus
18
Q
What are the touch submodalities
A
nociception (tissue damage) Temp (T) crude touch fine touch vibration proprioception
19
Q
Name the 5 sensory modalities and where in cortex they are perceived
A
- smell - 1ry olfctory cortex - uncus, amygdala
- vision - 1ry visual cortex - alone calcarine fissure in occipital lobe
- hearing - 1ary auditory cortex - transverse temporal gyri on superior temporal gyrus
- touch - 1ry somatosensory cortex - postcentral gurus
- taste - 1ry gustatory cortex - inf. postcentral gyrus
20
Q
Describe Somatosensory pathway neurons
A
3 neurons:
- pseudounipolar located in DRG or Trigeminal gangion (face)
- in dorsal horn of spinal cord or brain stem
- CROSSES and goes to CONTRA VP thalamus (location of deccusation depends on tract) - thalamus to appropriate cortex
21
Q
Describe clinical expression of an ventral intramedullary lesion
ex: tumour compression from within cord
A
-affect STT
-loss of pain, T at level of lesion, then appears to DESCEND if lesions grows
(distal dermatome further out)
22
Q
Describe clinical expression of an ventral extramedullary lesion
ex: meninegoma, disc compression from outside cord
A
-affect STT
-loss of pain, T at level of lesion then appears to ASCEND
(proximl dermatomes more central on cord)
23
Q
where is the border between running through fasciculus graciclis vs cuneatus
A
above T6: ascend through cuneatus (no FG)
24
Q
Describe clinical expression of midline dorsal compression
A
Loss of conscious proprioception, fine touch, vibration sensation legs moving up
25
What is different about somatosensation of the face?
1ry neuron goes via CNV to trigeminal ganglion not DRG > synpase then deccusate > VP thalamus, synapse > cortex
26
Sensory Trigeminal Nuclei (3)
- posterior brainstem
1. Mesencephalic Nucleus (midbrain)
- 1ry sensory neurons
- proprioception of jaw; reflex arc of masticator muscles
2. Chief Sensory Nucleus (pons)
- 2ry neurons
- touch, vibration (like dorsal column for body)
3. Spinal Trigeminal Nucleus (medulla)
- 2ry neurons
- pain, T, crude touch (like STT)
- fibres enter at pons, descend to medulla to reach nucleus, deccusate and joins SPINAL LEMNISCUS tract to go to thalamus with body signals
27
What is suspended sensory loss?
-loss of sensation at level of lesion but above and below is OK
28
What is dissociated sensory loss?
- one side loss STT modalities, while the other side loss DCML mods
ex: spinal cord unilateral lesion - affect contralateral STT because cross and can't ascend and ipsilatearl DCML because can't ascend. deficit below level of lesion
29
What are muscle spindles? How do they work
-stretch receptors for muscle - length
-located along striate muscles
-fire on 1a afferent axon
-when muscle contract, spindle get sggy so need intrfusal muscle to contrct to maintain spindle
< alpha-gamma co-activtion: ALPHA to contract muscle, GAMMA to contract intrafusal muscle of spindle
30
What are golgi tendon organs?
- receptor for muscle tension/contraction
- located along tendons
- fire on 1b afferent axons
31
Describe 1a stretch reflex pathway.
- muscle stretch
- spindle stretch
- fires on 1a afferent axon > through DRG > dorsal horn > synapse on ALPHA motor neuron > out ventral horn > Contract muscle = reflex movement
- while, reflex also contract synergistic muscles and inhibit antagonistic muscles vi 1a inhibitory neurons
32
How are reflexes modulated?
reflexes are not hardwired...can be modulated with exposure
33
Describe 1b pathway.
- 1b fire > dorsal horns > synapse on 1b inhibitory neuron > integration node to regulate sensory activity
- more complicated
- reflex control
34
What is the withdrawal reflex?
- contract one leg while extending other to maintain balance
- circuit for walking
- withdrawing when have noxious stimulus (stepping on pin)
- uses sensory input
35
What are 4 descending motor pathways?
1. corticospinl
2. subrospinal
3. vestibulospinal
4. reticulospinal
36
What are the fncs of descending motor pathways?
- control reflex
- select motor programs
- activate motorneurons > muscles
- activate muscles
37
What is tone?
-resistance as joint moves
38
What is spasticity? What are treatment options?
-increased velocity-dependent tone with exagerated stretch reflex (increase amplitude/briskness)
-spastic catch
-Tx: PT, stretching
reduce 1a afferent axons and motorneuron: baclofen
weaken muscle: botulinum toxin reduce ACh release
39
What is clonus?
rapid succession of stretch reflex
| -ankle dorsiflexion: 3-4 beats is normal
40
What is the classic hemiplegic posture? cause?
-stroke
-one side:
facial droop
flexed arm
pronated wrist
hip circumduction
extended leg
ankle planter flexed
41
What is the clasped-knife phenomenon?
-spasticity with flexion reflex
42
What are the 4 cortical sensory modalities? What 1ry sensory modality is needed for each?
- based on 5 touch primary sensories:
1. graphesthesia (need nociception)
2. stereognosis (T)
3. 2-pt discrimination (vibration)
4. extinction (proprioception, light touch)
43
Classes of receptors: exteroceptors vs proprioceptors vs enteroreceptors
extero: light, sound, tissue damage, T, touch, pressure
proprio: muscle, tendon, joints - muscle spindle
entero: viscera
44
Threshold of receptors to fire?
- intensity to activate receptor 50% of time
| - tactile sensations need lower threshold than nociception
45
What is receptor adaptation? Rapid vs slow adapting Receptors?
- reduce firing with continued stimulation
- rapidly adapting R: report onset and end. good for high-f vibration, movements
- slowly adapting R: continuous firing. good for pressure, shape, low f vibration, intensity
46
What is a receptor field size?
area of skin innervted by same sensory axon
- within area, can't do 2pt discrimination
- plastic - alter by use/amputation
47
How is sensitivity of nerves coded? where is it highest?
increase number of innervation
| -highest in fingers, mouth, genitals
48
```
Describe classes of somatosensory nerve fibres:
Aalpha
Abeta
Agamma
A delta
B
C
```
Aalpha - fastest, biggest xons
-1a fibres: limb positio, motion, muscle spindle extrafusal muscle
Abeta
-1b fibres: golgi - tension
-II: skin for consciou proprio, touch, pressure, vibration
Agamma: spindle fibre intrafusal muscle
A delta: fast pain, cold, hair follicles
B: pregang ans, white rami
C: slow pain, warmth, postgang ans grey rami
49
```
How is sensory coded?
intensity
location
modality
quality
```
intensity - f of APs
location - receptive fields of axons
modality - fibre type
quality - popultion of firing axons
50
Relay - Projections along somatosensory pathway of DCML? why?
ex: touch stimulus
ex: touch stimulus activating DCML
1. project to STT to inhibit pain perception
2. project to reticular formation to stimulate alertness
3. project to superior colliculus to drive orientation
51
3 sensory integrations on somatosensory pathway of DCML at 2ry neuron?
1. cortical descending inhibition refines attention
2. lateral inhibition sharpens localization - 2nd neuron inhibits neighbours from firing
3. no mixing of modalities
52
Describe the 1ry somatosensory area
- postcentral gyrus
| - 4 regions: 1 for mechnoreceptors, 1 proprioreceptors
53
Describe the 2ry somatosensory area
- inferior on postcentral gyrus
- inputs from 1ry S1 and thalamus
- projects to medial temporal lobe via insula
- TACTILE MEMORY: graphestesia, stereognosis
54
Describe the sensory association area
- bt postcentral gyrus and occipital lobe
- integrate ss and visual
- project to motor cortex
55
What are sources of input to cerebellum?
1. CONTRA: Motor cortex > Pontine nucleus > middle CB peduncle > cerebrocerebellum
IPSI:
2. vision, hearing > sup. and inf colliculi > superior CB p > spinocerebellum
3. vestibular apparatus and proprioception > inferior CB p > vestibulocerebellum
56
Which side is affected if cerebellar is issue? why?
ipsilateral b/c double crossed
1. leaves cerebellum, cross over to contralateral cortex
2. descending motor pathway crosses over @ pyramids
57
What are signs of cerebellar damage?
- ataxia: speech, limbs, wide base gait, "drunk"
- dysmetria: failure to coordinate multiple joints - overshoot and correct
- intention tremor: oscillation as approach target
- dysdiadochokinesia: trouble with repetitive movements
- nystagmus
- vertigo
58
What is the cerebellum? fncs?
- 10% brain V
- 50% brain neurons
- adjust output of descending motor pathways
- coordination, eye movement, speech, balance
59
What are teh 3 fnc lobes of cerebellum? where do they output?
1. cerebrocerebellum > dentate nucleus > sup CB p > red nucleus > VL thalamus > motor, premotor cortex: skilled motor movements, learning, planning
2. vestibulocerebellum (floculonodular lobe) > vestibulo nucleus via inf CB p: balance, eyes and head movements
3. spinocerebellum (vermis, paravermis) > descending motor systems via inf CB: locomotion, limb movements position
60
Head-eye movements
-Head turn
-endolymph turn in OPPOSITE direction > hair cells
>excitation on same side of turn
>inhibition on opposite side of turn
61
What is the vestibular ocular reflex?
- head move, eyes move in opposite direction
- endolymph moves in opposite directon > activaet Abducens Nucleus > activate ipsilateral occulomotor nucleus and contralateral abducens nucleus
62
What is nystagmus and 4 ways to induce?
: repetitive eye movements, sign of vertigo
jerky/pendular oscillations, direction defined by fast phase
1. Disease:
- cerebellar damage
- retina
- meniere's disease
- VIII neuropathy
- brainstem damage
2. Toxicity: alcohol, antiobiotics
3. spinning > nystagmus fast phase in direction of spin, slow phase in trying to maintain fixation
4. Optokinetics
63
What are the semi-circular canals?
- detect angular velocity
- 3 at 90deg of each other
- contain endolymph > moves hair cells > bend > depolarization/repolarization
64
What is utricle? saccule?
- contain of Otolith organs, hair cells, crystals
- detect linear motion
- utricle: horizontal plane
- saccule: vertical plane
65
What is the purpose of the Vestibular system?
=VOR: keeps eyes fixed durign head movements
- vestibulo-colic reflex: keep head balanced during body movements
- upright
- perception of acc/deccleration, angular motion
66
What is vertigo?
- hallucination of movements
| - not dizziness
67
What are inputs to basal ganglia?
via striatum (putamen + caudate) from cortex
68
What are outputs from basal ganglia?
via globus pallidus interna > thalamus > motor cortex
69
What is hemiballismus?
- involuntary unilateral large flinging movements
- rotatory
- lesion to contralateral subthalamic nucleus
70
What is athetosis?
continuous slow sinuous writhing
| -involuntary flexion, extension, pro-supination
71
What is chorea?
-random, purposeless, flitting movements
72
What is dystonia?
-persistant muscle contraction
73
4 signs of Parkinson's D? Tx?
TRAP
- tremor
- rigidity
- akinesia
- postural instability
74
What is the basal ganglia? Fnc?
- extrapyramidal motor system
- doesn't interact with spinal cord directly
- motor planning, cognition
75
Why is nigrostriatal projection importnt?
- substantia nigra contains dopaminergic neurons
| - dopamine pathway to striatum
76
Describe the direct pathway from basal ganglia > cortex using dopamine
Substantia nigra > dopamine > striatum > inhibit direct pathway to Globus pallidus interna > less inhibition to thalamus > excite thalamus to cortex
77
Describe the indirect pathway from basal ganglia > cortex using Dopamine
Substantia nigra > dopamine > striatum > inhibit indirect pathway to Globus pallidus externa and inhibit subthalamic nucleus > inhibit globus pallidus interna > less inhibition to thalamus > excite thalamus to cortex
78
Signs of Basal ganglia issues?
- dystonia
- dyskinesia
- athetosis
- chorea
- hemiballism
- parkisonism (hypokinetic, while the others are hyperkinetic above)
79
What is dyskinesia?
-involuntary, rthmic mvoements (tongue jaw face)
80
What is Huntington's disease?
-wasting of caudate, putamen, cortical atrophy
81
What are tics? What is an associated dissorder?
- repeated suppressible actions vis urge involving basal ganglia
- Tourette's syndrome
82
What is the rule of 4 for brainstem?
1. 4 M midline structures: motor pathway, medil lemniscus, medial longitudinal fasciculus, motor nuclei and nerves
2. 4 motor nuclei midline: 3,4,6,12
3. 4 S side structures: STT, spinocerebellar tract, sensory nucleus of CNV, sympathethic pathway
4. 4 CNs in each medull, pons, midbrain or above
83
What is dyskinesia?
mix of choreaform, ballistic, dystonic movements
| complication with ldopa use
84
How is pitch coded? What can we perceive?
- frequency: changes in air pressure per seconds
- normal : 20Hz-20KHz
- encoded by firing of specific axons at particular place along basilar membrane that resonate the most at that sound wave > signal is highest
85
Pathway sense organ > primary auditory cortex.
Cochlea > spiral ganglion > CN VIII > synpse on IPSI cochlear nuclei > project BIlaterally to suprior olive > inferior colliculi > Medial geniculate nucleus of thalamus > 1ry auditory cortex (temporal lobe).
86
How is loudness coded?
- intensity - difference in pressure. number of APs
| - decibels (log scale)
87
What happens in the middle ear?
- air filled space-
- tympanic membrane > oval window
- ossciles: MIS
88
What are the ossicle muscles in middle ear? innervation?
```
tensor tympani (V3)
stapedius (VII)
```
lesion : hypercusis
89
Describe the inner ear.
```
-fluid filled cavity
contain bony labyrinth and membranous labyrinth
-2 sense organs:
1. Vestibular apparutus
2. cochlea
```
90
Describe the cochlea.
- bony labyrinth spiral around MODIOLUS (contain nerves and blood vessels)
- cross section looks like 3 spaces but actually continuous at apex of spiral
91
What are the 3 scala of cochlea? What is inside each? what is membrane bt them?
Scala vestibuli - perilymph (stapes hit oval window here to start pressure wave)
-vestibulr membrane-
Scala media (Membranous labyrinth)- endolymph
-basilar membrane-
Scala tympani - perilymph
-round window - release pressure
92
What is endolymph vs perilymph?
endo ~ ICF, high in K+, secreted by stria vascularis in Scala media of cochle
peri ~ CSF
93
What is the spiral lamina (ear)?
- osseous extension (spike of bone from spiral centre) from modiolus into cochlear space. attach basilar membrane and determine width of membrane.
- base > apex: basilar membrane gets wider because lamina is shorter, cochlea narrows
94
What is the organ of Corti?
aka Spiral organ
on basilar membrane (in Scala media)
-covered by tectorial membrane
-contain receptor cells: convert mechanical E > action potential > CNVIII
95
What are stereocilia?
| Outer hair cells vs inner hair cells?
hair cells hve stereocilia = mechanicoreceptors: bend > depolarization.
rows on the hair cell. tallest AWAY from modiolus
-OHCs - extend through endolymph into tectorial membrane. Amplify input.
-IHCs - extend into endolymp but not tectorial membrane. More important for input coding.
-more OHC (3:1) but IHC connected to more neurons
96
How is sound transduced once it reaches cochlea?
stapes hit oval window > endolymph moves > perilymph moves > basilar membrane moves > axons at maximal activtion along basilar membrane fires:
1. vibrations of basilar membrane moves DOWN: hair cells move outward > tip of stereocilia INward toward modiolus, away from tallest = hyperpolarization
2. basilr membrane moves UP > hair cells move inwrd > tip of stereocilia outwward AWAY from modiolus, toward tallest sterocilia = depolarization
97
How do receptor potentials in hair cells work?
stereocilia tips have K+chnnels (perilymph high in K+)
- when bend toward tallest: channels increase conductivity > depolarization > Ca2+ at base of hair cell > vesicles secrete NT > spiral gnglion neurons >>>
- -when bend away tallest: channels decrease conductivity > hyperpolarization > decresase NT release
98
where is lesion if there is unilateral deafness?
below Cochlear nuclei (can't be subcorticl/cortical because of bilateral innervation)
-ear, cochlear nerve, cochler nucleus
