neurons that function within the brain and spinal cord are called

Most postganglionic neurons release acetylcholine onto target organs, although some release nitric oxide. Acetylcholine acts on two types of receptors, the muscarinic and nicotinic cholinergic receptors.

The axons of the preganglionic neurons release acetylcholine on the postganglionic neurons, which are generally located very near the target organs. Parasympathetic preganglionic neurons have cell bodies located in the brainstem and in the sacral (toward the bottom) spinal cord, as shown in Figure 2. One way to remember this is to think that during a restful situation like a picnic, the parasympathetic nervous system is in control (“picnic” and “parasympathetic” both start with “p”).

While the sympathetic nervous system is activated in stressful situations, the parasympathetic nervous system allows an animal to “rest and digest.” The parasympathetic system’s functions conserve energy: slowing down the heart rate, reducing contractile forces of both cardiac and gastrointestinal muscle, and reducing conduction velocity of the sinoatrial node and atrioventricular node. The strength and speed of the sympathetic response helps an organism avoid danger, and scientists have found evidence that it may also increase LTP-allowing the animal to remember the dangerous situation and avoid it in the future. The physiological effects of this norepinephrine release include dilating the trachea and bronchi (making it easier for the animal to breathe), increasing heart rate, and moving blood from the skin to the heart, muscles, and brain (so the animal can think and run). This is both because one preganglionic neuron synapses on multiple postganglionic neurons, amplifying the effect of the original synapse, and because the adrenal gland also releases norepinephrine (and the closely related hormone epinephrine) into the blood stream. As anyone who has ever felt a rush before a big test, speech, or athletic event can attest, the effects of the sympathetic nervous system are quite pervasive. Postganglionic neurons then release norepinephrine onto target organs. The acetylcholine activates the postganglionic neurons. The axons of these neurons release acetylcholine on postganglionic neurons within sympathetic ganglia (the sympathetic ganglia form a chain that extends alongside the spinal cord). Most preganglionic neurons in the sympathetic nervous system originate in the spinal cord, as illustrated in Figure 2. Figure 2. The sympathetic and parasympathetic nervous systems often have opposing effects on target organs.

Neurons that function within the brain and spinal cord are called