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