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Flashcards in Major neurochemical pathways Deck (18):

Dopaminergic pathways

- 3 types
1. long paths: nigrostriatal, mesocortical and mesolimbic
2. short paths: tuberoinfundibular and incertohypothalamic pathway
3. ultrashort paths: found in amacrine cells in the retina and in the olfactory system


Nigrostriatal pathway

-extrapyramidal pathway that is crucial for motor control
-most of the brain's dopamine
-originates in the substantia nigra and travels to the amygdala and striatum via the medial forebrain bundle
-dopamine deficiency in Parkinsons disease or dopamine blockade due to antipsychotics can cause extrapyramidal side effects


Mesolimbic pathway

-originates from ventral tegmental area and goes to the nucleus accumbens and hippocampus via medial forebrain bundle
-blockade of dopamine produces desirable antipsychotic effect by controlling positive psychotic symptoms


Mesocortical pathway

-Originates in the Ventral Tegmental area and travels to the cingulate cortex and prefrontal regions via medial forebrain bundle
-low levels of dopamine or dopamine blockade in this tract is associated with negative symptoms (alogia, anhedonia, amotivation and apathy)


Tuberoinfundibular pathway

-originates in hypothalamus and travels to the pituitary via the portal vessels
-dopamine acts as prolactin inhibitory hormone
-dopamine blockade serves to increase prolactin level


Incertohypothalamic pathway

-internal connections within hypothalamus
-dopamine blockade causes disturbed thermoregulation and possible weight gain


Cholinergic pathways

2 major cholinergic pathways
1. brainstem pathway
2. basal forebrain pathway


Brainstem pathway

-cholinergic pathway
-forms part of the ARAS -ascending reticular activating system
-important for maintaining wakefulness and REM sleep state
-originates from pedunculopontine and laterodorsal tegmental nuclei and innervates thalamic relay neurons and reticular nuclei


Basal forebrain pathway

-cholinergic pathway
-originates at the nucleus basalis of meynert in the basal forebrain and projects to the hippocampus, frontal cortex and amygdala
-degeneration of this pathway is implicated in Alzheimers


Serotonergic pathways

-originate in the midbrain dorsal and medial raphe nuclei
-ascend to innervate the entire cortex, basal ganglia, thalamus and also descend to the spinal cord


Noradrenergic pathways

-originates at the locus coeruleus (pons) and ascends to most of the cortex via the medial forebrain bundle


Glutamatergic system

-glutamate is the most common excitatory neurotransmitter in the brain
-as a result almost all cortical descending tracts (from pyramidal cells) rely on glutamate for neurotransmission
-this large output of corticofugal fibres makes up most of the corona radiata
-all association and commisural fibres also use glutamatergic transmission
-many thalamic neurons are glutamatergic
-thalamocortical projections are also glutamatergic
-cerebellar output from deep nuclei, subthalamic nuclei to globus pallidus projections and braintem to spinal cord projections are also predominantly glutamatergic


GABAergic system

-primary inhibitory neurotransmitter in the brain
-no specific pathway
-GABA is the major transmitter for cerebral interneurons throughout the cortex



-usually short neurons
-connect two other neurons
-dont carry motor or sensory information but serve to modulate local neural circuitry
-2 subtypes: parvalbumin-expressing interneurons and somatostatin expressing interneurons


Parvalbumin (PV)-expressing interneurons

-40% of interneurons
-reduction of these is seen in the frontal cortex in schizophrenia
-2 subtypes: Basket cells and chandelier cells


Somatostatin (SST)-expressing interneurons

-30% of interneurons
-also called Martinotti cells


Basket cells

-receive direct input from thalamocortical projections
-form synapses with the soma or dendrites of the pyramidal neurons
-provide excitatory-inhibitory balance in the cortex


Chandelier cells

-form csynapses with the proximal axonal hillock of pyramidal neurons
-they may have an overall excitatory role by serving short-circuit the action potential propagation
-role not actually clear