why nor-adrenaline which is released from substantia nigra has excitatory effect on works of basal nuclei while dopamine has inhibitory effect
I'm sorry, but that statement is not accurate. Norepinephrine (nor-adrenaline) is not released from the substantia nigra, but rather from neurons in the locus coeruleus, which is located in the brainstem. The substantia nigra, on the other hand, releases dopamine.
Dopamine released from the substantia nigra has an excitatory effect on the basal ganglia, particularly the direct pathway. It helps facilitate movement by promoting the activation of the motor cortex and inhibiting unwanted movement.
Norepinephrine, on the other hand, has a modulatory effect in the brain that varies depending on the receptor type it binds to. In general, it can have both excitatory and inhibitory effects depending on the specific brain region and receptors involved.
It's important to note that the functioning of the basal ganglia is a complex process involving interactions between various neurotransmitters, including dopamine, GABA, and glutamate. The exact mechanisms and effects of these neurotransmitters on the basal ganglia are still being studied and understood.
Noradrenaline and dopamine are both neurotransmitters that are involved in the regulation of movement and play different roles in the basal ganglia circuitry.
Noradrenaline (also known as norepinephrine) is released from neurons originating in the substantia nigra and has an excitatory effect on the basal nuclei. The substantia nigra is divided into two parts: the substantia nigra pars compacta (SNpc) and the substantia nigra pars reticulata (SNpr).
The SNpc contains dopaminergic neurons that release dopamine, whereas the SNpr contains noradrenergic neurons that release noradrenaline. In the context of the basal nuclei, the release of noradrenaline by the SNpr has an excitatory effect.
This is because noradrenaline acts on receptors in the basal nuclei, specifically the D1-like receptors, which are typically excitatory. When these receptors are activated by noradrenaline, they lead to an increase in neuronal excitability and enhance movement. Therefore, the release of noradrenaline from the substantia nigra has an overall excitatory effect on the basal nuclei.
On the other hand, dopamine released by the SNpc has an inhibitory effect on the basal nuclei. This is because dopamine acts on D2-like receptors in the basal nuclei, which are generally inhibitory. When these receptors are activated by dopamine, they inhibit neuronal activity and dampen movement.
The balance between noradrenaline and dopamine within the basal nuclei is crucial for proper motor control. Changes in the levels or activity of these neurotransmitters can lead to movement disorders such as Parkinson's disease, where there is a deficiency of dopamine in the basal nuclei.
The effects of noradrenaline and dopamine in the basal ganglia are complex and multifaceted. While it is true that noradrenaline has an excitatory effect on the basal ganglia, and dopamine has an inhibitory effect, it is important to understand the underlying mechanisms to fully understand why this occurs.
The substantia nigra is a region in the midbrain that contains two main parts: the substantia nigra pars compacta (SNc) and the substantia nigra pars reticulata (SNr). The SNc predominantly produces dopamine, while the SNr releases both dopamine and noradrenaline.
Let's first consider why dopamine has an inhibitory effect. In the basal ganglia, dopamine acts as a modulator, helping to regulate the balance of excitatory and inhibitory signals. When released onto the medium spiny neurons (MSNs) in the striatum (part of the basal ganglia), dopamine binds to specific receptors called D1 receptors. Activation of D1 receptors leads to an increase in the production of cyclic adenosine monophosphate (cAMP) and subsequent activation of protein kinase A (PKA). This signaling pathway ultimately results in the suppression of the activity of the MSNs, leading to an inhibitory effect.
On the other hand, the noradrenaline released from the substantia nigra pars reticulata has an excitatory effect on the basal ganglia. The exact mechanism is not yet fully understood, but it seems to involve the activation of alpha-1 adrenergic receptors on the MSNs. This activation leads to an increase in intracellular calcium levels, which promotes neuronal excitation.
To summarize, dopamine and noradrenaline have opposing effects in the basal ganglia due to their interactions with different receptor systems on the MSNs. Dopamine inhibits the activity of MSNs, while noradrenaline enhances their excitability. The fine balance between these neurotransmitters is crucial for proper functioning of the basal ganglia and motor control.