Muscarinic antagonist brain, involving both increased levels of acetylcholine and degeneration of dopaminergic pathways (nigrostriatal pathway). Thus, in parkinsonism there is decreased level of dopaminergic activity. One method of balancing the neurotransmitters is through blocking central cholinergic activity using muscarinic receptor antagonists. Atropine acts on the M2 receptors of the heart and antagonizes the activity of acetylcholine. It causes tachycardia by blocking vagal effects on the sinoatrial node. Acetylcholine hyperpolarizes the sinoatrial node, which is overcome by MRA and thus increases the heart rate. If atropine is given by intramuscular or subcutaneous injection, it causes initial bradycardia. This is because by i.m/s.c
Sinoatrial node hyperpolarisation-activated cyclic nucleotide–gated (HCN) channels, are activated. Activation of these channels at very negative membrane potential is an unusual property for ion channels, therefore the flow of sodium (Na) and some potassium (K) through the activated HCN channel is referred to as a "funny current" (I). This funny current causes the membrane potential of the cell to gradually increase, as the positive charge (Na and K) is flowing into the cell. Another mechanism involved in pacemaker potential is known as the calcium clock. Here, calcium is released spontaneously from the sarcoplasmic reticulum (a calcium store) into the cell, this is