Autonomic Nervous System: Sympathetic vs Parasympathetic, Animation

Summary

The autonomic nervous system (ANS) controls involuntary functions of internal organs, with two divisions: the sympathetic (SNS) and parasympathetic (PSNS). The SNS prepares the body for action in stressful situations by increasing heart rate, respiration, and energy release, while inhibiting non-essential processes like digestion. In contrast, the PSNS conserves energy during rest by slowing the heart rate and promoting digestion. These systems work together to maintain a balance, though some organs only receive input from one system. The SNS affects a wide range of functions, while the PSNS focuses on more localized responses.

Takeaways

• 🧠 The autonomic nervous system (ANS) regulates involuntary functions of internal organs and operates without conscious control.
• ⚡ The ANS has two divisions: sympathetic (SNS) and parasympathetic (PSNS).
• 💪 The sympathetic division (SNS) is responsible for activating the 'fight or flight' response, increasing heart rate, breathing rate, and energy release in stressful situations.
• 😌 The parasympathetic division (PSNS) manages the 'rest and digest' response, slowing down the heart rate, stimulating digestion, and conserving energy during relaxation.
• ⚖️ Both the SNS and PSNS are active simultaneously, maintaining a balance called 'autonomic tone', which adjusts based on the body's needs.
• 💉 Some organs receive input from only one division, like blood vessels that only receive sympathetic fibers to regulate blood pressure.
• 🔄 Autonomic nerve pathways consist of two neurons: preganglionic and postganglionic, which synapse in an autonomic ganglion.
• 🌀 In the SNS, preganglionic neurons arise from the thoracic and lumbar spine, with fibers that can follow various routes before synapsing with postganglionic neurons.
• 🔀 The SNS exhibits a high degree of neuronal divergence, leading to widespread effects, as one preganglionic fiber can connect to up to 20 postganglionic neurons.
• 🎯 The PSNS has less neuronal divergence, leading to more localized effects, with shorter postganglionic fibers that synapse near or within target organs.

Q & A

What is the autonomic nervous system (ANS)?

The autonomic nervous system (ANS) is the part of the nervous system that regulates the activities of internal organs and operates largely independently of conscious control.

What are the two main divisions of the ANS?

The two main divisions of the ANS are the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS).

What is the primary function of the sympathetic nervous system (SNS)?

The primary function of the SNS is to mobilize the body for action in situations that require alertness and energy, such as in emergencies or during physical activity.

What are some physiological effects of SNS activation?

Activation of the SNS increases cardiac output, accelerates the respiratory rate, releases stored energy, and dilates the pupils. It also inhibits non-essential processes like digestion and urination.

What is the primary function of the parasympathetic nervous system (PSNS)?

The PSNS conserves and restores the body's energy by slowing the heartbeat, reducing respiratory rate, stimulating digestion, and aiding in waste removal.

Why is the SNS called the 'fight or flight' response?

The SNS is called the 'fight or flight' response because it prepares the body for quick and vigorous action in stressful or dangerous situations.

Why is the PSNS referred to as the 'rest and digest' system?

The PSNS is called the 'rest and digest' system because it promotes relaxation and recovery by conserving energy, slowing heart rate, and facilitating digestion.

How do the SNS and PSNS interact with each other in the body?

The SNS and PSNS are not mutually exclusive. They both are active at the same time in most organs, producing a balance known as 'autonomic tone,' which shifts based on the body's needs.

What is autonomic tone?

Autonomic tone refers to the balance of activity between the sympathetic and parasympathetic systems, which adjusts according to the body's changing needs.

How do blood vessels receive input from the autonomic nervous system?

Blood vessels only receive sympathetic inputs, which keep them partially constricted to maintain normal blood pressure. Increased sympathetic firing causes more constriction, raising blood pressure, while decreased firing dilates vessels, lowering pressure.

What is the difference in neuronal divergence between the SNS and PSNS?

The SNS has a high degree of neuronal divergence, meaning one preganglionic neuron can synapse with up to 20 postganglionic neurons, leading to widespread effects. In contrast, the PSNS has much less divergence, leading to more specific and localized responses.

Where do preganglionic neurons of the SNS and PSNS originate?

Preganglionic neurons of the SNS arise from the thoracic and lumbar regions of the spinal cord, while those of the PSNS originate from the brainstem and sacral regions of the spinal cord.

What is the significance of the autonomic ganglion in the ANS pathway?

The autonomic ganglion is where preganglionic and postganglionic neurons meet and synapse. It plays a crucial role in transmitting signals from the central nervous system to target organs.