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PATHWAYS IN THE BRAIN. Kaan YüceM.D ., Ph.D . . 12. May.2014 Monday. Ascending tracts Sensory Descending tracts Motor General arrangement of both tracts 1st order neuron 2nd order neuron 3rd order neuron. The only difference is the different locations where each order of neuron ends.

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slide1

PATHWAYS IN THE BRAIN

Kaan YüceM.D., Ph.D.

12. May.2014 Monday

slide2

Ascending tracts

  • Sensory
  • Descending tracts
  • Motor
  • General arrangement of both tracts
  • 1st order neuron
  • 2nd order neuron
  • 3rd order neuron

The only difference is the different locations where each order of neuron ends.

Decussation is the cross-over of the tract from one side to the other. Therefore, there are instances where the left side of the body is controlled by the right brain hemisphere. Decussation occurs at different locations for each tracts.

slide3

Descending tracts

1st order neuron

starts at the cerebral cortex in the primary motor cortex

2nd order neuron

axon of the 1st order neuron will synapse with the 2nd order neuron at the level of the brain stem, which commonly decussate (crosses over) to the opposite side

.

3rd order neuron

The 3rd order neuron is located in the ventral horn of the spinal cord, which will exit with the spinal nerve to supply the muscle.

slide4

Types of descending tracts:

  • Lateral corticospinal tract
  • Anterior corticospinaltract
  • Therefore, the descending tract is also known as corticospinal tract.
  • Corticospinal tract arise from long axons of the pyramidal cells of the precentralgyrus (primary motor centre of the cerebral cortex); lies in front of the central sulcus
slide5

MOTOR Homunculus arrangement: arranged upside down;

the finer the movement, the more the cortical representation

fingers, face, tongue – more

trunk, lower limbs – less

medial surface: lower limbs

superolateral surface: everything else

slide6

Sensoryhomunculus

Motor homunculus

slide7

Sensoryhomunculus

Motor homunculus

slide8

1st order neuron

  • Fibres of the 1st order neuron arise from the precentralgyrus
  • These fibres converge and enter a small area
  • internal capsule
  • ALL the fibers (from ascending & descending tracts) converge here
  • bounded medially by the thalamus and caudate nucleus
  • bounded laterally by the lenticular nucleus
  • The descending fibres passes through the LATERAL half of the posterior limb of internal capsule
  • 2nd order neuron
  • Fibres of the 1st order neuron ends when it enters the brain stem and synapse with the 2nd order neuron
  • The fibres pass through the brainstem
  • 1st – through the crus cerebri of midbrain
  • 2nd – through the anterior part of the pons
  • 3rd – in the medulla oblongata
  • 80-85% of the fibres cross to the opposite side: Motor decussation
  • Enters the spinal cord
slide10

2nd order neuron

  • Fibres of the 1st order neuron ends when it enters the brain stem and synapse with the 2nd order neuron
  • The fibres pass through the brainstem
  • 1st – through the crus cerebri of midbrain
  • 2nd – through the anterior part of the pons
  • 3rd – in the medulla oblongata
  • 80-85% of the fibres cross to the opposite side: Motor decussation
  • Enters the spinal cord
slide11

3rd order neuron

2nd order neuron fibres in the medulla oblongata enters the spinal cord and synapse with the 3rd order neuron

Motor decussationin the spinal tract, the crossed tract descend as the lateral corticospinal tract

Therefore, the motor cortex of the cerebral hemisphere controls the opposite side of the body (L – R, R – L)

contra-lateral side.

In upper motor neuron lesions: above the motor decussation (above medulla), opposite side of body affected

below the motor decussation same side of body affected ipsilateral side

Uncrossed fibres: in the spinal tract, the uncrossed tract descent as the anterior corticospinal tract

its fibres cross at spinal level?

slide13

AScendingtracts

Spinothalamictracts

Lateralspinothalamictract

pain & temperature

Anteriorspinothalamictract

lighttouch & pressure

Dorsalcolumntract

deeptouch & pressure

proprioception

vibrationsensation

Spinocerrebellartract

posture & coordination

slide14

SPINOTHALAMIC TRACTS

1st order neuron

Arise from sensory receptors of the body; The fibres enter the white mater from the tip of posterior gray horn

2nd order neuron:

The fibres of 1st order neuron synapse with the 2nd order neuron at the substantiagelatinosa.

These fibres then cross to the opposite side

Pain & temperature fibres enters the lateral spinothalamic tract

Light touch & pressure fibres enters the anterior spinothalamic tract

These tracts ascends to brainstem

tracts flattened in the brainstem: spinal lemniscus

Ends @ the ventral posterolateral nucleus of the thalamus

3rd order neuron

Arise from the thalamus and pass through the internal capsule

thalamocorticalfibres pass through the medial part of the posterior limb of the internal capsule

Enters the postcentralgyrus

slide15

DORSAL COLUMN TRACT

  • 1st orderneuron
  • Arisefromthesensoryreceptors of the body
  • Fibresenterthedorsalcolumn of the SAME side (post column of spinalcord)
    • ascendstothemedullaoblongata
    • (does not synapseandend here likespinothalamictract)
    • Endsin thegracileandcuneatenucleus
  • 2nd orderneuron
  • Starts at thegracile & cuneatenucleus of themedullaoblongata
  • Thesefibrescrossestotheoppositeside of themedullaoblongata.
  • Ascendsthroughthebrainstem as flattenedbundlemediallemniscus
  • Ends in theventralposterolateralnucleus of thethalamus.
  • 3rd order of nucleus
  • Arisefromthethalamus
  • Passthroughtheinternalcapsule; medialaspect of theposteriorlimb of internalcapsule.
  • Ends @thepostcentralgyrus
slide16

SPINOCEREBELLAR TRACT

1st order neurons:

Arise from the sensory receptors of the body

Enters the spinal cord

Ends in the Clarke’s Column of the posterior grey horn

Synapse

2nd order neurons:

Arise from the Clarke’s Column

synapse with 1st order neurons

Ascends in the spinocerebellar tracts, enters the cerebellum through the interior and superior cerebellar peduncles

the only tract that enters the cerebellum

These tracts decussate 2 times; therefore cerebellum controls same side of body

İpsilateral; eg. right spinocerebellar tract controls the right side vice versa

slide17

What is limbicsystem?

survival

YOUR MISSION IN LIFE?

slide18

Two main functions

Emotionalprocessing

Motivation

TheAnatomy of Behaviour

slide19

Emotion

Memory

MedialTemporalLobe

  • Hippocampus
  • Parahippocampalgyrus
  • Amygdala
slide20

The limbic system structures are telencephalic& subcortical structures.

  • The complex network for the process of emotions and is also related to memory and learning in addition to hippocampus, amygdala and parahippocampusincludes:
  • Cingulate gyrus
  • Hypothalamus
  • Major areas in the prefrontal cortex
  • Striatum
  • Somethalamicnuclei
  • Orbitofrontal cortex
  • Septal area
  • Some medial components of the midbrain (e.g. VTA)
  • Habenula …
  • + whitemattertracts
slide23

James Papez

PapezCircuit

A list of structures in the brain and a closed circuit related to emotions

slide24

Hippocampal formation (Subiculum) → fornix → mammillary bodies

Mammillary bodies → mammillothalamic tract → anterior thalamic nucleus

Anterior thalamic nucleus → genu of the internal capsule → cingulate gyrus

Cingulate gyrus → cingulum → parahippocampalgyrus

Parahippocampalgyrus → entorhinal cortex → perforant pathway → hippocampus.

slide27

LimbicSystem

  • added
  • Amygdala
  • Septum
  • Pre-frontal cortex
  • to the Papez circuit

Paul D. MacLean

slide29

Klüver-Bucy Syndrome

bilateral removal of amygdala and hippocampal formation

What happens if we remove the medial temporal lobe of an animal, a monkey?

  • Becamedocile;”good monkeys”.
  • A tendency towards oral behaviour such as attempting to ingest inedible objects.
  • Hypersexualizedbehaviour by mounting females of the same and different species.
  • A compulsion to attend and react to every visual stimulus
  • No fear.
  • Change in dietary habits
slide31

the most famous two guys of

the limbic system

hippocampus & amygdala

slide32

3.1. Hippocampal formation/Hippocampus

Temporalhorn of lateralventricle

HC

slide34

TERMINOLOGY

HIPPOCAMPAL FORMATION

VS.

HIPPOCAMPUS

1. Hippocampus (proper)

CornuAmmonis (CA) CA1-CA4

2. Dentategyrus

3. Subicular complex

slide36

Fornix [Arch]

Theroad/whitemattertractfromthehippocampus

Precommissural fibers 25%

Septal area

Postcommmissural fibersoriginatefromthesubicularcomplex

Mamillary bodies

slide39

3.4.1. Anterior cingulate cortex (ACC)

1=BA25 (subcallosalgyrus) 2=BA24sg (SGPFC)

3=BA32 (paracingulategyrus)

slide40

3.5. Limbic structures in the Prefrontal cortex (PFC)

  • DLPFC, dorsolateral prefrontal cortex
  • VLPFC, ventrolateral prefrontal cortex
  • FP, frontopolar cortex
  • OFC, orbitofrontal cortex
  • DMPFC dorsomedial prefrontal cortex
  • VMPFC, ventromedial prefrontal cortex
slide41

3.6. Hypothalamus

Glaser R, Kiecolt-Glaser JK. Stress-induced immune dysfunction: implications for healthNat Rev Immunol. 2005 Mar;5(3):243-51.

slide42

3.7. Thalamus

Limbicthalamicnuclei

  • Anteriorthalamicnuclei
  • Mediodorsal thalamic nuclei
slide43

3. 8. Striatum

4 major nuclei

(1) corpus striatum

Caudatenucleus

Putamen

Ventral striatum –nuc.accumbens

(2) globuspallidus

internal and external segments

(3) substantianigra

pars compacta

pars reticulata

(4) subthalamic nucleus

slide44

Anterior hippocampus

rostral hypothalamus and amygdala

HPA-axis control

Stress

Posterior hippocampus

spatial memory

slide45

Multiple functions of the hippocampus

Learning and memory

Mood regulation - Affect - Emotional Behavior

Regulation of HPA axis

Pain

Erectile function

Attention

slide46

When you meet someone you know at the street

Hippocampus......

Context

Amygdala.....

Emotions

slide47

Emotional Memory

Fear

Amygdala

slide48

4.4. Anatomy of

cognition & emotion

Two circuits & Crossing roads

cognition means thinking and emotion means feeling

slide49

TWO MAIN CIRCUITS IN THE BRAIN

COGNITIVE CIRCUIT EMOTION CIRCUIT

DORSAL CIRCUIT VENTRAL CIRCUIT

The cognitive networks inhibit the ventral circuit.

slide50

Dorsal (cognitive) circuit

  • Hippocampus
  • Dorsolateral prefrontal cortex (DLPFC)
  • Dorsal regions of the anterior cingulate cortex (ACC)
  • Parietal cortex
  • Posterior insular region
  • Modulates selective attention, planning and effortful regulation of affective state.
slide51

Ventral (limbic) circuit structures:

  • Amygdala
  • Insula (Particularly, anterior insula)
  • Ventral striatum
  • Ventral regions of the anterior cingulate cortex (ACC)
  • Orbitofrontal cortex (OFC) and medial PFC
slide52

It is possible that the altered emotional regulation or cognition found in all of these syndromes involvesaberrant function of these circuits, but perhaps with different patterns on a molecular level.

Phillips et al. 2003