PATHWAYS IN THE BRAIN

1. PATHWAYS IN THE BRAIN Kaan YüceM.D., Ph.D. 12. May.2014 Monday

2. 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.

3. 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.

4. 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

5. 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

6. Sensoryhomunculus Motor homunculus

7. Sensoryhomunculus Motor homunculus

8. 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

10. 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

11. 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?

13. AScendingtracts Spinothalamictracts Lateralspinothalamictract pain & temperature Anteriorspinothalamictract lighttouch & pressure Dorsalcolumntract deeptouch & pressure proprioception vibrationsensation Spinocerrebellartract posture & coordination

14. 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

15. 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

16. 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

17. What is limbicsystem? survival YOUR MISSION IN LIFE?

18. Two main functions Emotionalprocessing Motivation TheAnatomy of Behaviour

19. Emotion Memory MedialTemporalLobe • Hippocampus • Parahippocampalgyrus • Amygdala

20. 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

23. James Papez PapezCircuit A list of structures in the brain and a closed circuit related to emotions

24. 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.

27. LimbicSystem • added • Amygdala • Septum • Pre-frontal cortex • to the Papez circuit Paul D. MacLean

29. 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

31. the most famous two guys of the limbic system hippocampus & amygdala

32. 3.1. Hippocampal formation/Hippocampus Temporalhorn of lateralventricle HC

34. TERMINOLOGY HIPPOCAMPAL FORMATION VS. HIPPOCAMPUS 1. Hippocampus (proper) CornuAmmonis (CA) CA1-CA4 2. Dentategyrus 3. Subicular complex

36. Fornix [Arch] Theroad/whitemattertractfromthehippocampus Precommissural fibers 25% Septal area Postcommmissural fibersoriginatefromthesubicularcomplex Mamillary bodies

37. Fornix

39. 3.4.1. Anterior cingulate cortex (ACC) 1=BA25 (subcallosalgyrus) 2=BA24sg (SGPFC) 3=BA32 (paracingulategyrus)

40. 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

41. 3.6. Hypothalamus Glaser R, Kiecolt-Glaser JK. Stress-induced immune dysfunction: implications for healthNat Rev Immunol. 2005 Mar;5(3):243-51.

42. 3.7. Thalamus Limbicthalamicnuclei • Anteriorthalamicnuclei • Mediodorsal thalamic nuclei

43. 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

44. Anterior hippocampus rostral hypothalamus and amygdala HPA-axis control Stress Posterior hippocampus spatial memory

45. Multiple functions of the hippocampus Learning and memory Mood regulation - Affect - Emotional Behavior Regulation of HPA axis Pain Erectile function Attention

46. When you meet someone you know at the street Hippocampus...... Context Amygdala..... Emotions

47. Emotional Memory Fear Amygdala

48. 4.4. Anatomy of cognition & emotion Two circuits & Crossing roads cognition means thinking and emotion means feeling

49. TWO MAIN CIRCUITS IN THE BRAIN COGNITIVE CIRCUIT EMOTION CIRCUIT DORSAL CIRCUIT VENTRAL CIRCUIT The cognitive networks inhibit the ventral circuit.

50. 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.