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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. - PowerPoint PPT Presentation
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PATHWAYS IN THE BRAIN
Kaan YüceM.D., Ph.D. 12. May.2014 Monday
Ascending tractsSensoryDescending tractsMotor
General arrangement of both tracts1st order neuron2nd order neuron3rd 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.
1st order neuronstarts at the cerebral cortex in the primary motor cortex
2nd order neuronaxon 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 neuronThe 3rd order neuron is located in the ventral horn of the spinal cord, which will exit with the spinal nerve to supply the muscle.
DESCENDING TRACTS
Lateral corticospinal tractAnterior corticospinal tract
Therefore, the descending tract is also known as corticospinal tract.Corticospinal tract arise from long axons of the pyramidal cells of the precentral gyrus (primary motor centre of the cerebral cortex); lies in front of the central sulcus
Types of descending tracts:
MOTOR Homunculus arrangement: arranged upside down; the finer the movement, the more the cortical representationfingers, face, tongue – moretrunk, lower limbs – lessmedial surface: lower limbssuperolateral surface: everything else
Motor homunculusSensory homunculus
Motor homunculusSensory homunculus
1st order neuronFibres of the 1st order neuron arise from the precentral gyrusThese fibres converge and enter a small areainternal capsuleALL the fibers (from ascending & descending tracts) converge herebounded medially by the thalamus and caudate nucleusbounded laterally by the lenticular nucleusThe descending fibres passes through the LATERAL half of the posterior limb of internal capsule 2nd order neuronFibres of the 1st order neuron ends when it enters the brain stem and synapse with the 2nd order neuronThe fibres pass through the brainstem1st – through the crus cerebri of midbrain2nd – through the anterior part of the pons3rd – in the medulla oblongata80-85% of the fibres cross to the opposite side: Motor decussationEnters the spinal cord
2nd order neuronFibres of the 1st order neuron ends when it enters the brain stem and synapse with the 2nd order neuronThe fibres pass through the brainstem1st – through the crus cerebri of midbrain2nd – through the anterior part of the pons3rd – in the medulla oblongata80-85% of the fibres cross to the opposite side: Motor decussationEnters the spinal cord
3rd order neuron2nd order neuron fibres in the medulla oblongata enters the spinal cord and synapse with the 3rd order neuronMotor decussation in the spinal tract, the crossed tract descend as the lateral corticospinal tractTherefore, 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 affectedbelow the motor decussation same side of body affected ipsilateral sideUncrossed fibres: in the spinal tract, the uncrossed tract descent as the anterior corticospinal tractits fibres cross at spinal level?
Spinothalamic tractsLateral spinothalamic tractpain & temperatureAnterior spinothalamic tractlight touch & pressure
Dorsal column tractdeep touch & pressureproprioceptionvibration sensation
Spinocerrebellar tractposture & coordination
ASCENDING TRACTS
SPINOTHALAMIC TRACTS1st order neuronArise from sensory receptors of the body; The fibres enter the white mater from the tip of posterior gray horn2nd order neuron:The fibres of 1st order neuron synapse with the 2nd order neuron at the substantia gelatinosa. These fibres then cross to the opposite sidePain & temperature fibres enters the lateral spinothalamic tractLight touch & pressure fibres enters the anterior spinothalamic tractThese tracts ascends to brainstemtracts flattened in the brainstem: spinal lemniscusEnds @ the ventral posterolateral nucleus of the thalamus 3rd order neuronArise from the thalamus and pass through the internal capsulethalamocortical fibres pass through the medial part of the posterior limb of the internal capsuleEnters the postcentral gyrus
1st order neuronArise from the sensory receptors of the bodyFibres enter the dorsal column of the SAME side (post column of spinal cord)
ascends to the medulla oblongata(does not synapse and end here like spinothalamic tract)Ends in the gracile and cuneate nucleus
2nd order neuron Starts at the gracile & cuneate nucleus of the medulla oblongataThese fibres crosses to the opposite side of the medulla oblongata.Ascends through the brain stem as flattened bundle medial lemniscusEnds in the ventral posterolateral nucleus of the thalamus.3rd order of nucleus Arise from the thalamus Pass through the internal capsule; medial aspect of the posterior limb of internal capsule.Ends @the postcentral gyrus
DORSAL COLUMN TRACT
1st order neurons:Arise from the sensory receptors of the bodyEnters the spinal cordEnds in the Clarke’s Column of the posterior grey hornSynapse
2nd order neurons:Arise from the Clarke’s Columnsynapse with 1st order neuronsAscends in the spinocerebellar tracts, enters the cerebellum through the interior and superior cerebellar pedunclesthe only tract that enters the cerebellum
These tracts decussate 2 times; therefore cerebellum controls same side of bodyİpsilateral; eg. right spinocerebellar tract controls the right side vice versa
SPINOCEREBELLAR TRACT
What is limbic system?
YOUR MISSION IN LIFE?
survival
Two main functions
Emotional processing
Motivation
The Anatomy of Behaviour
Medial Temporal Lobe Hippocampus Parahippocampal gyrus Amygdala
Emotion
Memory
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 parahippocampus includes:• Cingulate gyrus• Hypothalamus • Major areas in the prefrontal cortex• Striatum• Some thalamic nuclei• Orbitofrontal cortex• Septal area• Some medial components of the midbrain (e.g.
VTA)• Habenula …+ white matter tracts
James Papez
A list of structures in the brain and a closed circuit related to emotions
Papez Circuit
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 → parahippocampal gyrus
Parahippocampal gyrus → entorhinal cortex → perforant pathway → hippocampus.
Paul D. MacLean
Limbic Systemadded Amygdala Septum Pre-frontal cortex to the Papez circuit
Klüver-Bucy Syndrome
What happens if we remove the medial temporal lobe of an animal, a monkey? bilateral removal of amygdala and hippocampal formation
Became docile;”good monkeys”.
A tendency towards oral behaviour such as attempting to ingest inedible objects.
Hypersexualized behaviour 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
the most famous two guys of the limbic system
hippocampus & amygdala
3.1. Hippocampal formation/Hippocampus
HC
Temporal horn of lateral ventricle
TERMINOLOGY
HIPPOCAMPAL FORMATION VS.HIPPOCAMPUS
1. Hippocampus (proper) Cornu Ammonis (CA) CA1-CA4
2. Dentate gyrus
3. Subicular complex
Fornix [Arch]The road/white matter tract from the hippocampusPrecommissural fibers 25% Septal areaPostcommmissural fibers originate from the subicular complexMamillary bodies
Fornix
3.4.1. Anterior cingulate cortex (ACC)1=BA25 (subcallosal gyrus) 2=BA24sg (SGPFC) 3=BA32 (paracingulate gyrus)
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
3.6. Hypothalamus
Glaser R, Kiecolt-Glaser JK. Stress-induced immune dysfunction: implications for healthNat Rev Immunol. 2005 Mar;5(3):243-51.
3.7. Thalamus
Limbic thalamic nuclei Anterior thalamic nuclei
Mediodorsal thalamic nuclei
3. 8. Striatum4 major nuclei (1) corpus striatumCaudate nucleusPutamenVentral striatum –nuc.accumbens (2) globus pallidus internal and external segments
(3) substantia nigra pars compacta pars reticulata (4) subthalamic nucleus
Anterior hippocampusrostral hypothalamus and amygdalaHPA-axis controlStress
Posterior hippocampusspatial memory
Multiple functions of the hippocampus
Learning and memoryMood regulation - Affect - Emotional BehaviorRegulation of HPA axisPainErectile functionAttention
When you meet someone you know at the street
Hippocampus......Context
Amygdala.....Emotions
Emotional Memory
Fear
Amygdala
4.4. Anatomy of cognition & emotion
Two circuits & Crossing roadscognition means thinking and emotion means feeling
TWO MAIN CIRCUITS IN THE BRAIN COGNITIVE CIRCUIT EMOTION CIRCUIT DORSAL CIRCUIT VENTRAL CIRCUIT
The cognitive networks inhibit the ventral circuit.
Dorsal (cognitive) circuit o Hippocampuso Dorsolateral prefrontal cortex (DLPFC)o Dorsal regions of the anterior cingulate cortex (ACC)o Parietal cortexo Posterior insular region
Modulates selective attention, planning and effortful regulation of affective state.
Ventral (limbic) circuit structures:o Amygdalao Insula (Particularly, anterior insula)o Ventral striatum o Ventral regions of the anterior cingulate cortex (ACC) o Orbitofrontal cortex (OFC) and medial PFC
It is possible that the altered emotional regulation or cognition found in all of these syndromes involves aberrant function of these circuits, but perhaps with different patterns on a molecular level.
Phillips et al. 2003