How does Parkinson's cause a slowing of movement when ACh is in excess, and it is an excitatory..?
if ACh is in excess in comparison to dopamine, why is it that there is a slowing of movement in Parkinson's if ACh propagates action potentials
- izzyLv 78 years agoFavorite Answer
"Dopamine is vital for normal movements because it allows messages to be transmitted from the substantia nigra to the striatum, which then initiates and controls the ease of movement and balance. Furthermore, the loss of dopamine causes the neurons in the basal ganglia to fire randomly accounting for involuntary movements.
Acetylcholine is another neurotransmitter that is needed to produce smooth movements. In normal individuals there is a balance between acetylcholine and dopamine. In Parkinson's patients there is not sufficient dopamine to maintain the balance with acetylcholine. This irregular disproportion results in a lack of movement coordination leading to the more overt symptoms of Parkinson's."
- MagsLv 78 years ago
Parkinson's disease is very much about balance. As the dopamine neurons in the substantia nigra die, there is a dwindling supply to be transfered to the striatum or the coordination center for several brain chemicals.
The problem in the plentiful acetylcholine instituting action potential is that the decreased number of the balancing, inhibitory dopamine neurons creates a chemical imbalance. This imbalance results in the inability to signal the neurons to relax when ACh is functioning as an excitatory.
The results of this imbalance can be seen clearly in three of the Big 4 PD symptoms: TRAP
Rigidity (growing stiffness of muscles and neuroskeletal muscles)
Akinesia (or Bradykinesia - slowness of movement - reaction time)
The last imbalance is Postural Instability which is complicated but in a way is a failure to maintain the vertical.
So the ACh sends the excitatory impulse and the DA tries to send the relax message. But since the numbers are not balanced, there are far more messages to tense than there are to relax (normalize)
Try it yourself. Tense your arms by making a fist and bending your arms in front of you. Now hold that tension until it hurts (a symptom seldom discussed in PD but every present) Imagine that you can't relax enough. Every time you try to relax, the tension message is there again. You can see it more clearly in a tremor.
In PD the initial tremor is a resting tremor which means that the limb is inactive, supported, not resisting gravity and yet there is movement. The normal chemical balance - homeostasis - is gone. And so the involuntary tremor occurs.
Gradually it is being understood that other areas of the brain are also involved with PD but the basics lie in that imbalance.
- 3 years ago
Never really thought about that