Autonomic Nervous System Physiology

Flashcards covering the key concepts, definitions, and physiological mechanisms of the autonomic nervous system as discussed in Lecture 18.

Where do sympathetic preganglionic neurons originate?

Spinal cord levels T1–L2 (thoracolumbar).

Where do sympathetic preganglionic axons synapse?

Sympathetic chain ganglia OR collateral ganglia.

What is the sympathetic chain?

A series of interconnected ganglia alongside the vertebral column.

How do sympathetic preganglionic axons enter the chain ganglia?

Through the ventral root.

What can a sympathetic preganglionic axon do in the chain?

1. Synapse at the same level 2. Ascend rostrally 3. Descend caudally 4. Pass through to collateral ganglia.

What phenomenon does the branching of sympathetic neurons create?

High divergence → broad, coordinated response.

What neurotransmitter is released by ALL sympathetic preganglionic neurons?

Acetylcholine (ACh).

What neurotransmitter is usually released by sympathetic postganglionic neurons?

Norepinephrine (NE).

Which receptor does ACh bind on sympathetic ganglia?

Nicotinic receptors.

What happens to the pupils during sympathetic activation?

They dilate.

What happens to heart rate during sympathetic activation?

It increases.

What happens to bronchi during sympathetic activation?

They dilate for increased air intake.

How does sympathetic activation affect digestion?

It slows down (decreased motility & secretions).

How does sympathetic activity affect blood vessels?

• Vasodilation to skeletal muscle • Vasoconstriction to GI organs.

What happens to glucose levels during sympathetic activation?

They increase due to glycogen breakdown.

Where do parasympathetic preganglionic neurons originate?

• Brainstem (cranial nerves III, VII, IX, X) • Sacral spinal cord (S2–S4).

Where do parasympathetic ganglia reside?

Near or within the target organ (terminal ganglia).

What neurotransmitter is released by parasympathetic preganglionic neurons?

Acetylcholine (ACh).

What neurotransmitter is released by parasympathetic postganglionic neurons?

Acetylcholine (ACh).

Which receptor type is on the target organs for the parasympathetic nervous system?

Muscarinic receptors.

What happens to heart rate during parasympathetic activation?

It decreases.

What happens to digestion during parasympathetic activation?

It increases—motility and secretions rise.

What happens to the pupils during parasympathetic activation?

They constrict.

What happens to the bladder during parasympathetic activation?

It contracts for urination.

What is the purpose of the orthostatic reflex?

Maintain blood pressure when standing up.

What causes orthostatic hypotension?

Failure of autonomic compensatory feedback.

What are symptoms of orthostatic hypotension?

• Lightheadedness • Dizziness • Fainting.

What triggers neurocardiogenic syncope?

A sympathetic surge followed by paradoxical parasympathetic overactivation.

What happens physiologically during the parasympathetic overreaction in neurocardiogenic syncope?

• Heart rate drops • BP drops • Leads to fainting.

Which neuron directly synapses onto the adrenal medulla?

Sympathetic PREganglionic neuron.

What does the adrenal medulla release?

Epinephrine and norepinephrine into the bloodstream.

What is the effect of the adrenal medulla's release?

Prolonged sympathetic activation.

How many neurons are in the somatic motor pathway?

One.

What does the somatic motor pathway control?

Skeletal muscle (voluntary).

How many neurons are in the autonomic motor pathway?

Two (preganglionic + postganglionic).

What does the autonomic motor pathway control?

Smooth muscle, cardiac muscle, glands (involuntary).

Does the ANS operate consciously?

No—it is automatic.

What is the overall goal of ANS regulation?

Maintain homeostasis.

Which ANS division is faster in activation?

Sympathetic (due to chain ganglia & divergence).

Which ANS division controls long-term recovery?

Parasympathetic.