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Review Session:
(1) Brain Development 3: Modification of Neural Circuits (Map Plasticity and Reorganization
(Wed Apr 24th 10 AM)
(2)Somatosensory Circuitry: Touch and Proprioception (Friday Apr 26th 8 AM)
(3) Somatosensory Circuitry: Pain and Temperature (Friday Apr 26th 10 AM)
Kimberle M [email protected]
804 827-2135
http://www.people.vcu.edu/~kmjacobs/teach.htm
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Topographic Map Principles
• There is an ongoing competition for neural space (between adjacent representations)
• Proper formation of the topographic map during development requires normal experience
• Changes in the map due to alteration of sensory afferent input can be called use-dependent or experience-dependent plasticity
• Some aspects of topographic maps can only be altered during a “critical period” of development (thalamic input to cortical layer IV)
• Some aspects of topographic maps can be altered into adulthood (via intracortical connections)
• Presumably more cortex gives you better control over that sense or body region – blind, braille readers have greater spatial resolution in finger tips
• Your patient has lost their index finger – what would you advise in order for them to gain increased sensitivity in adjacent fingers? What effect would this have on cortical representations?
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Time Course of Reorganization of Sensory Representations in Adults
Digit 1
Digit 2
Digit 3
Normal
Digit 1
Unresponsive
Digit 3
Digit 2 Amputation
Immediate
Digit 1
Digit 3
Short term(hours to days)
Digit 1
Digit 3
Days to years
Map Reorganizationtime
Border Shifts
Adjacent representation
s take over
Large scale reorganization –
over 10 cm in Monkey cortex
Unmasking of inputs
normally hidden by inhibition
Synaptic Plasticity
changes (LTP)
Anatomical changes, sprouting, creation of additional synapses
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Basic Plan for Somatosensory Info to Consciousness
le ft rightCortex:
le ft rightThalam us:
SpinalCord
le ft right
Mid
line
Dorsal R ootG anglion
Receptor
Skin
Prim a ry (1 )o
Se c o nd a ry(2 C ro sse s)o
Te rtia ry(3 )o
Quaternary (4 )o
Action PotentialInitiation Site
Outside the CNS!
12
3
4
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Conscious SomatosensationNon-consciousProprioception
Spinocerebellar Tracts
(IPSILATERAL)BODY HEAD
TrigeminalSystem
TouchPain
Spinal Principal(Main)
PAIN& Temp
FineTouch
LateralSpino-
Thalamic
Dorsal Column System
Information reaching consciousness goes to the CONTRALATERAL Neocortex, Nonconscious Sensory Information goes to the IPSILATERAL Cerebellum
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Compare ALS and Dorsal Column
Spinal Cord
M edulla
Spinal Cord
M edulla
DRG
PRIM
AR
Y 1
o
S E C O N D A R Y 2 o
S E C O N D A R Y 2 oM
IDL
INE
Skin
synap se
synapse
P R IM A R Y 1 o
Thalamus VPL
Primary Somatosensory Cortex4 o4 o
synap se
synap se
Ve n tra l W h i te C o m m .
In te rn a l A rc u a te F ib e rs
M edialL em niscus
3 o3 o
Lat
eral
Spi
not
hala
mic
1
1
2
3
2
3
44
Fine Discrim ination Touch
Pain and Tem perature
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Somatosensory Information from the Body to Consciousness
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Cor t ex
44
MID
LIN
E
Tr igeminalNUCLEUS
Sp
ina
l
Main
Mes
ence
pah
lic
2
2
2
2
111
2
2
Trigeminal System: Touch Component
Tr igeminalGangl ion
Br anchesof t he Tr igeminal(V) N er ve
Ma
ndibula
rO
pthalm
icM
axillary
Tr igeminalNer ve
1
1
1
VENTRALTRIGEMIN0-THALAMICTRACTM EDULLA
SPINALCO RD
Pa
in &
Tem
p
PONS
Tou
ch
Thal amus
VP
M
VP
L33
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Gliosis and cavitation in midline of the spinal cord – CSF enters the cord. The larger the cavitation, the more tracts affected. One possible cause is a Chiari Malformation. Other causes include trauma, infection. (anything that compresses the CSF)
http://www.asap4sm.com/
Symptoms:Bilateral loss of pain and temperature at the level of the lesion (segments involved).
Lesions and Clinical Deficits - Syringomyelia
Area of lesion
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Lateral Medullary (Wallenberg’s) Syndrome – Symptoms include loss of pain and temperature on the ipsilateral head/face, contralateral loss of pain and temperature in the body, and ataxia.
ALS (lateral spinothalamic tract)
Trigeminal Nucleus
Spinal Trigeminal Tract
DorsalSpinocerebellar Tract
VentralSpinocerebellar Tract
Lesions and Clinical Deficits - Wallenberg’s
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Degeneration of myelinated afferent fibers in the dorsal columns, (destroys large diameter axons), is a late stage of syphilis.
Symptoms:
Severe deficits in touch and position sense but often little loss of temperature perception and of nociception. Bilateral lesion = bilateral effects.
Lesions and Clinical Deficits – Tabes Dorsalis
Area of Lesion
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LESIONS and Clinical Deficits – Brown-Sequard Syndrome
Hemisection of the spinal cord, often in the cervical spinal cord – (it is rare for the entire hemisection to be affected, but this does occur, more often incomplete hemisection is found).
DC
Symptoms: a) Loss of fine discrimination touch, vibration, and position sense ipsilaterally for body regions
from affected dermatome and down
Arch Neurol (2001) 58: 1470.
b) Loss of pain and temperature contralaterally for body regions from affected dermatome and down (small region of bilateral loss of pain and temp at level of lesion and 2 segments
below)
c) Motor Effects: – Ipsilateral Spasticity and Weakness