Autonomic Nervous System Introduction

Summary

This tutorial provides an introduction to the autonomic nervous system (ANS), explaining its two main divisions: the sympathetic and parasympathetic nervous systems. The sympathetic system is responsible for the body's fight or flight response, while the parasympathetic system governs rest and digest functions. The video details the anatomical differences between the systems, the role of pre- and postganglionic neurons, and the neurotransmitters involved. It also discusses the contrasting physiological effects, such as heart rate and pupil dilation, as well as useful mnemonics like 'point and shoot' to remember their roles in sexual function.

Takeaways

• 😀 The autonomic nervous system consists of two main divisions: the sympathetic and parasympathetic systems.
• 😀 The sympathetic nervous system is responsible for 'fight or flight' responses and originates from the thoracolumbar regions (T1-L2) of the spinal cord.
• 😀 The parasympathetic nervous system is responsible for 'rest and digest' responses and originates from cranial nerves and the sacral regions (S2-S4).
• 😀 The sympathetic and parasympathetic systems have antagonistic functions, meaning they typically do opposite things to each other.
• 😀 The somatic nervous system uses a single motor neuron to control skeletal muscles, while the autonomic nervous system uses two neurons: preganglionic and postganglionic.
• 😀 In the sympathetic nervous system, preganglionic neurons are short and postganglionic neurons are long, while in the parasympathetic nervous system, preganglionic neurons are long and postganglionic neurons are short.
• 😀 Both sympathetic and parasympathetic preganglionic neurons release acetylcholine, but sympathetic postganglionic neurons typically release norepinephrine (except for those controlling sweat glands, which release acetylcholine).
• 😀 The adrenal medulla is directly activated by the preganglionic neurons of the sympathetic nervous system, releasing adrenaline and norepinephrine into circulation.
• 😀 The sympathetic system triggers responses like pupil dilation, increased heart rate, and mobilization of energy reserves (e.g., glycogen breakdown).
• 😀 The parasympathetic system promotes digestion, lowers heart rate, and supports energy storage, stimulating functions like saliva production and gastric acid secretion.
• 😀 A mnemonic to remember the role of the sympathetic and parasympathetic systems in the male genitalia is 'Point and Shoot': parasympathetic causes erection (Point), while sympathetic causes ejaculation (Shoot).

Q & A

What are the two main divisions of the autonomic nervous system?

The two main divisions of the autonomic nervous system are the sympathetic nervous system and the parasympathetic nervous system.

Where does the sympathetic outflow originate?

The sympathetic outflow originates in the thoracolumbar regions of the spinal cord, specifically from spinal segments T1 to L2.

What cranial nerves are involved in the parasympathetic nervous system?

The cranial nerves involved in the parasympathetic nervous system are cranial nerves 3, 7, 9, and 10, which correspond to the ocular motor, facial, glossopharyngeal, and vagus nerves.

How does the somatic nervous system differ from the autonomic nervous system?

The somatic nervous system has a single motor neuron extending from the central nervous system (CNS) to the periphery, whereas the autonomic nervous system has two neurons: the preganglionic neuron and the postganglionic neuron.

What is the role of the preganglionic and postganglionic neurons in the autonomic nervous system?

The preganglionic neuron extends from the CNS and synapses with the postganglionic neuron in a ganglion. The postganglionic neuron then innervates the target organ, such as smooth muscles or glands.

What is the main difference in the length of the preganglionic axons between the sympathetic and parasympathetic systems?

In the sympathetic nervous system, the preganglionic axon is relatively short, whereas in the parasympathetic nervous system, the preganglionic axon is longer, as the ganglia are often located near or within the target organ.

What neurotransmitters are primarily involved in the autonomic nervous system?

The two main neurotransmitters in the autonomic nervous system are acetylcholine and norepinephrine. Acetylcholine is released by both preganglionic neurons in both systems, while norepinephrine is typically released by postganglionic sympathetic neurons.

What is the function of the sympathetic nervous system during the fight-or-flight response?

During the fight-or-flight response, the sympathetic nervous system increases heart rate, dilates pupils, dilates bronchioles, stimulates sweating, and mobilizes energy reserves, preparing the body for intense physical activity.

What effect does the parasympathetic nervous system have on heart rate and digestion?

The parasympathetic nervous system decreases heart rate and enhances digestion by promoting smooth muscle contractions in the gastrointestinal tract, increasing saliva and gastric acid secretion, and relaxing sphincters.

What is the mnemonic to remember the roles of the sympathetic and parasympathetic nervous systems in male genitalia function?

The mnemonic is 'Point and Shoot': the parasympathetic nervous system causes erection (Point), while the sympathetic nervous system causes ejaculation (Shoot).