The nigrostriatal tract has its source nuclei in the substantia nigra and these project into the basal ganglia. This tract is also often referred to as the extrapyramidal system. In this graphic, it can be seen that the Parkinson's like symptoms of bradykinesia and tremor are caused by (1) lack of dopamine in the basal ganglia (as seen with Parkinson's disease); (2) relative overabundance of serotonin in the region of the basal ganglia or (3) administration of D2 receptor
antagonist drugs (such as antipsychotics).
The next series of illustrations will explain in detail the different types of extrapyramidal side effects and the possible management of each. Since 5-HT2A receptors are present in the nigrostriatal tract, administering drugs that block 5-HT2A receptors will counter-act the blockade of D2 receptors. Thus, some antipsychotics are both D2 receptor antagonists and 5-HT2A receptor antagonists. See atypical antipsychotics.
The nigrostriatal tract projects to the basal ganglia and thus it controls voluntary muscle movements.
Blockade of 5-HT2A receptors in the nigrostriatal tract will increase dopamine neurotransmission.
Symptoms of muscle rigidity, bradykinesia, masked-like face, and postural instability can result from antagonism of 5-HT2A receptors on presynaptic dopamine neurons.