Autonomic and Somatic Nervous System: Structure, Function, and Neurotransmitters

What is the primary function of the Autonomic Nervous System (ANS)?

To maintain homeostasis by adjusting input from the parasympathetic and sympathetic systems.

What are the components of the efferent pathway in the ANS?

Preganglionic neurons, autonomic ganglion, postganglionic neurons, and effector organs.

What is dual innervation in the context of the ANS?

Most effector organs receive input from both the parasympathetic and sympathetic divisions, usually with antagonistic effects.

What is the anatomical origin of the parasympathetic division?

Craniosacral spinal cord.

What is the anatomical origin of the sympathetic division?

Thoracolumbar spinal cord.

Describe the lengths of neurons in the parasympathetic division.

Long preganglionic neurons and short postganglionic neurons.

Where are the ganglia located in the sympathetic division?

Ganglia are linked together in the sympathetic chain.

What neurotransmitter do cholinergic neurons use?

Acetylcholine (ACh).

What neurotransmitters do adrenergic neurons use?

Epinephrine (E), Norepinephrine (NE), and Dopamine (DA).

What are the two main classes of adrenergic receptors?

Alpha (α) and beta (β) receptors.

What is the role of the adrenal medulla in the sympathetic division?

It contains chromaffin cells that release catecholamines, primarily epinephrine.

What is the neuroeffector junction?

The site between the postganglionic neuron and the effector organ where neurotransmitters are released.

What is the primary function of the Somatic Nervous System (SNS)?

To control voluntary movements by innervating skeletal muscles.

Where do motor neurons of the SNS originate?

In the ventral horn of the spinal cord.

What neurotransmitter is released at the neuromuscular junction (NMJ)?

Acetylcholine (ACh).

What type of receptors are found on muscle fibers at the NMJ?

Nicotinic cholinergic receptors.

What is a motor unit?

A motor neuron and all the muscle fibers it innervates.

What is the effect of the parasympathetic activity on heart rate?

It decreases heart rate.

What is the effect of sympathetic activity on gastrointestinal functions?

It decreases gastrointestinal functions.

What is the role of the hypothalamus in regulating the ANS?

It is responsible for overall activation of the sympathetic system and regulates body temperature, food intake, and water balance.

What happens at the neuroeffector junction when an action potential arrives?

Voltage-gated Ca²⁺ channels open, triggering the release of neurotransmitters.

What is the role of Acetylcholinesterase (AChase) at the NMJ?

It breaks down acetylcholine after it binds to receptors.

What is the effect of the sympathetic nervous system on pupil size?

It dilates the pupils.

What is the significance of the adrenal medulla in the fight-or-flight response?

It releases epinephrine and norepinephrine, enhancing the body's response to stress.

What are agonists in the context of the ANS?

Substances that increase neurotransmitter release or mimic neurotransmitter action.

What are antagonists in the context of the ANS?

Substances that block receptor activity or increase neurotransmitter breakdown.

What is the primary effect of parasympathetic activity on blood pressure?

It decreases blood pressure.

What type of receptors are nicotinic cholinergic receptors?

Ionotropic receptors that cause depolarization.