Exam 5: How Do Neurons Communicate and Adapt

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The sympathetic and parasympathetic nervous systems are two branches of the autonomic nervous system, which controls involuntary body functions. Each system uses specific neurotransmitters to communicate with target organs and tissues through a variety of neurochemical neurons.

In the sympathetic nervous system, the primary neurotransmitter is norepinephrine (also known as noradrenaline). The sympathetic neurons that release norepinephrine are called adrenergic neurons. These neurons are responsible for the "fight or flight" response, which prepares the body for action in stressful situations. The sympathetic nervous system increases heart rate, dilates the pupils, and diverts blood flow to the muscles, among other effects.

The pathway of sympathetic activation typically involves a two-neuron chain: the preganglionic neuron and the postganglionic neuron. The preganglionic neuron originates in the spinal cord and releases acetylcholine at the synapse with the postganglionic neuron, which is located in a sympathetic ganglion. The postganglionic neuron then extends to the target organ and releases norepinephrine to exert its effects.

In contrast, the parasympathetic nervous system is responsible for the "rest and digest" response, which conserves energy and maintains bodily functions during restful periods. The primary neurotransmitter in the parasympathetic nervous system is acetylcholine. The neurons that release acetylcholine are called cholinergic neurons. These neurons slow down the heart rate, constrict the pupils, stimulate digestion, and promote various other functions that help the body relax and recuperate.

Similar to the sympathetic system, the parasympathetic pathway also involves a two-neuron chain: the preganglionic neuron and the postganglionic neuron. However, both the preganglionic and postganglionic neurons in the parasympathetic system release acetylcholine. The preganglionic neurons originate in the brainstem or the sacral spinal cord and synapse with postganglionic neurons located near or within the target organs.

In summary, the sympathetic and parasympathetic nervous systems use different neurochemical neurons to communicate with the body. The sympathetic system primarily uses adrenergic neurons that release norepinephrine, while the parasympathetic system uses cholinergic neurons that release acetylcholine. Both systems work together to maintain homeostasis in the body by balancing their opposing effects.