Lamprey and hagfish are jawless fish, with skeletons composed of cartilage. They do not have scales and are considered primitive fish. They are in the superclass cyclosystoma.
The incorrect among the choices is "<span>direct signaling involves the activation of g proteins"
This is incorrect because direct signaling does not involve the activation of g proteins rather it involves the activation of ion channels resulting to either an excitation reaction (depolarization of the membrane) or an inhibition reaction (hyperpolarization of the membrane); and this will ultimately affect the action of the organ the nerve is innervating.</span>
Answer:
The correct option is: <em>a deficiency of dopamine in the substantia nigra.</em>
Explanation:
The substantia nigra is the principal site involved in the physiopathology of Parkinson´s disease.
Cells from this area degenerate and die progressively causing important degeneration in the central nervous system. The cells that die -with no known reason- are those that produce dopamine and proportionate dopaminergic innervation to the encephalon. In fact, almost all the symptoms exhibited by patients with the disease can be explained by the lack of dopamine in the substantia nigra.
This area uses the neurotransmitter to communicate neurons from the base ganglia. Ganglia are responsible of modulating and modifying movements.
The nigrostriatal system participates in planning and automatic execution of learned movements. When the ganglia activity decreases, so it does the amount and velocity of movements, something typical of the disease.
