review session: (1) brain development 3: modification of neural circuits (map plasticity and...
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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 Jacobskmjacobs@vcu.edu
804 827-2135
http://www.people.vcu.edu/~kmjacobs/teach.htm
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?
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
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
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
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
Somatosensory Information from the Body to Consciousness
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
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
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
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
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
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