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.
Kaan YüceM.D., Ph.D.
12. May.2014 Monday
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 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.
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
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)
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?
pain & temperature
lighttouch & pressure
deeptouch & pressure
posture & coordination
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
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
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
YOUR MISSION IN LIFE?
TheAnatomy of Behaviour
A list of structures in the brain and a closed circuit related to emotions
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.
Paul D. MacLean
bilateral removal of amygdala and hippocampal formation
What happens if we remove the medial temporal lobe of an animal, a monkey?
the limbic system
hippocampus & amygdala
Temporalhorn of lateralventricle
1. Hippocampus (proper)
CornuAmmonis (CA) CA1-CA4
3. Subicular complex
Precommissural fibers 25%
1=BA25 (subcallosalgyrus) 2=BA24sg (SGPFC)
Glaser R, Kiecolt-Glaser JK. Stress-induced immune dysfunction: implications for healthNat Rev Immunol. 2005 Mar;5(3):243-51.
4 major nuclei
(1) corpus striatum
Ventral striatum –nuc.accumbens
internal and external segments
(4) subthalamic nucleus
rostral hypothalamus and amygdala
Learning and memory
Mood regulation - Affect - Emotional Behavior
Regulation of HPA axis
cognition & emotion
Two circuits & Crossing roads
cognition means thinking and emotion means feeling
COGNITIVE CIRCUIT EMOTION CIRCUIT
DORSAL CIRCUIT VENTRAL CIRCUIT
The cognitive networks inhibit the ventral circuit.
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