Chapter 15 - Autonomic Nervous System

What is the autonomic nervous system (ANS)?

The division of the nervous system that regulates involuntary activities of cardiac muscle, smooth muscle, and glands.

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

The sympathetic nervous system and the parasympathetic nervous system.

What type of functions does the ANS control?

Involuntary functions such as heart rate, digestion, respiratory rate, glandular secretion, and blood vessel diameter.

How does the ANS differ from the somatic nervous system?

The ANS controls involuntary responses using two neurons, while the somatic nervous system controls voluntary skeletal muscle using one neuron.

What type of muscles does the ANS innervate?

Smooth muscle, cardiac muscle, and glands.

How many neurons are involved in an autonomic motor pathway?

Two neurons: a preganglionic neuron and a postganglionic neuron.

What is a preganglionic neuron?

A neuron that extends from the CNS to an autonomic ganglion.

What is a postganglionic neuron?

A neuron that extends from an autonomic ganglion to the target organ.

What is an autonomic ganglion?

A cluster of neuron cell bodies located outside the CNS where preganglionic neurons synapse with postganglionic neurons.

Where do sympathetic preganglionic neurons originate?

In the thoracic and lumbar regions of the spinal cord (T1-L2).

Where do parasympathetic preganglionic neurons originate?

In the brainstem and sacral regions of the spinal cord (S2-S4).

Why is the sympathetic nervous system called 'fight or flight'?

Because it prepares the body for stress, emergencies, and physical activity.

Why is the parasympathetic nervous system called 'rest and digest'?

Because it promotes relaxation, digestion, and energy conservation.

Which division increases heart rate and blood pressure?

The sympathetic nervous system.

Which division decreases heart rate and promotes digestion?

The parasympathetic nervous system.

What neurotransmitter is released by all preganglionic autonomic neurons?

Acetylcholine (ACh).

What neurotransmitter is released by most sympathetic postganglionic neurons?

Norepinephrine (NE).

What neurotransmitter is released by parasympathetic postganglionic neurons?

Acetylcholine (ACh).

What receptors bind acetylcholine in the ANS?

Cholinergic receptors.

What receptors bind norepinephrine in the ANS?

Adrenergic receptors.

What type of receptor is found on postganglionic neurons in autonomic ganglia?

Nicotinic cholinergic receptors.

What type of cholinergic receptors are found on parasympathetic target organs?

Muscarinic receptors.

What are the two main types of adrenergic receptors?

Alpha (α) receptors and beta (β) receptors.

What effect does stimulation of beta-1 (β₁) receptors have on the heart?

Increases heart rate and force of contraction.

What effect does stimulation of beta-2 (β₂) receptors have on the lungs?

Causes bronchodilation.

What effect does stimulation of alpha-1 (α₁) receptors have on blood vessels?

Causes vasoconstriction.

What is sympathetic tone?

The continuous low-level activity of the sympathetic nervous system that maintains blood pressure and vessel tone.

What is parasympathetic tone?

The continuous activity of the parasympathetic nervous system that helps regulate resting organ function.

Which division has long preganglionic neurons and short postganglionic neurons?

The parasympathetic nervous system.

Which division has short preganglionic neurons and long postganglionic neurons?

The sympathetic nervous system.

What is the adrenal medulla's role in the sympathetic nervous system?

It releases epinephrine and norepinephrine into the bloodstream during stress.

How does epinephrine differ from norepinephrine?

Epinephrine has stronger effects on beta receptors and produces longer-lasting responses.

What is dual innervation?

When an organ receives input from both sympathetic and parasympathetic divisions.

Why is dual innervation important?

It allows precise control of organ function by opposing effects.

Give an example of sympathetic and parasympathetic effects on the heart.

Sympathetic increases heart rate; parasympathetic decreases heart rate.

What happens to digestion during sympathetic activation?

Digestive activity decreases.

What happens to digestion during parasympathetic activation?

Digestive activity increases.

How does the sympathetic nervous system affect pupils?

Causes pupil dilation.

How does the parasympathetic nervous system affect pupils?

Causes pupil constriction.

What is autonomic reflex control?

Automatic regulation of organ function through reflex pathways without conscious control.

Why is the ANS important for homeostasis?

It maintains internal balance by regulating vital functions such as heart rate, blood pressure, and digestion.