Autonomic Nervous System: Neurotransmitters, Receptors, and Pathways

Target neurotransmitter used in sympathetic pathways

Norepinephrine (SN)

Target neurotransmitter used in parasympathetic pathways

Acetylcholine (PA)

Symbol/Abbreviation for Sympathetic Norepinephrine

SN

Symbol/Abbreviation for Parasympathetic Acetylcholine

PA

First receptor type hit after signal leaves CNS in all autonomic pathways

Nicotinic receptor

Location of nicotinic receptors in autonomic pathways

On the autonomic ganglion

Receptor located on target tissue in sympathetic pathways

Adrenergic receptor

Receptor located on target tissue in parasympathetic pathways

Muscarinic receptor

Full sequence of a sympathetic signal from CNS to target tissue

CNS -> Nicotinic receptor on ganglion -> Norepinephrine -> Adrenergic receptor on target tissue

Full sequence of a parasympathetic signal from CNS to target tissue

CNS -> Nicotinic receptor on ganglion -> Acetylcholine -> Muscarinic receptor on target tissue

Location of sympathetic ganglia relative to spinal cord

Close to the spinal cord

Location of parasympathetic ganglia relative to target tissues

Close to (or in) target organs

Spinal regions where sympathetic nerves exit

Thoracic or lumbar regions

CNS exit points for parasympathetic nerves

Cranium or sacrum

Types of neurons present in sympathetic division

Noradrenergic and cholinergic neurons

Types of neurons present in parasympathetic division

Cholinergic neurons

Coexistence of sympathetic and parasympathetic fibers in a single nerve

Impossible (a nerve CANNOT have both)

Neurotransmitter matching: Sympathetic target = ___

Norepinephrine

Neurotransmitter matching: Parasympathetic target = ___

Acetylcholine

Receptor matching: Sympathetic target = ___

Adrenergic receptor

Receptor matching: Parasympathetic target = ___

Muscarinic receptor

Receptor matching: Ganglion (both divisions) = ___

Nicotinic receptor

Exit origin matching: Thoracic and Lumbar = ___

Sympathetic nervous system

Exit origin matching: Cranium and Sacrum = ___

Parasympathetic nervous system

Ganglion location matching: Close to spinal cord = ___

Sympathetic nervous system

Ganglion location matching: Close to or inside target = ___

Parasympathetic nervous system

Fill in the blank: Sympathetic pathways use ______ (SN)

Norepinephrine

Fill in the blank: Parasympathetic pathways use ______ (PA)

Acetylcholine

Fill in the blank: CNS -> ______ receptor on autonomic ganglion

Nicotinic

Fill in the blank: Sympathetic target tissues have ______ receptors

Adrenergic

Fill in the blank: Parasympathetic target tissues have ______ receptors

Muscarinic

Fill in the blank: Sympathetic ganglia exit from ______ or ______ regions

Thoracic; Lumbar

Fill in the blank: Parasympathetic ganglia exit from ______ or ______

Cranium; Sacrum

Fill in the blank: A single nerve ______ have both sympathetic and parasympathetic fibers

CANNOT

True or False: Sympathetic and parasympathetic fibers can run in the same nerve

False (A nerve CANNOT have both)

True or False: Nicotinic receptors are located on target tissues in autonomic pathways

False (Nicotinic receptors are on autonomic ganglia; target tissues have adrenergic or muscarinic receptors)

True or False: Parasympathetic pathways contain both noradrenergic and cholinergic neurons

False (Parasympathetic pathways contain only cholinergic neurons; sympathetic contains both)

True or False: Sympathetic ganglia are located close to or inside target tissues

False (Sympathetic ganglia are close to the spinal cord; parasympathetic ganglia are near/in targets)

Which division uses noradrenergic neurons?

Sympathetic division

Which division uses ONLY cholinergic neurons?

Parasympathetic division

Comparative Length: Preganglionic axon in Sympathetic vs Parasympathetic

Sympathetic preganglionic axons are short (ganglia near cord); Parasympathetic preganglionic axons are long (ganglia near target)

Comparative Length: Postganglionic axon in Sympathetic vs Parasympathetic

Sympathetic postganglionic axons are long; Parasympathetic postganglionic axons are short

Anatomical nickname for Sympathetic division based on exit points

Thoracolumbar division

Anatomical nickname for Parasympathetic division based on exit points

Craniosacral division

Scenario: A drug blocks adrenergic receptors. Which division's target response is inhibited?

Sympathetic division

Scenario: A drug blocks muscarinic receptors. Which division's target response is inhibited?

Parasympathetic division

Scenario: A drug blocks nicotinic receptors at ganglia. Which division is affected?

Both Sympathetic and Parasympathetic divisions

If a spinal cord injury occurs at the lumbar region, which autonomic division's outflow is directly affected?

Sympathetic nervous system

If cranial nerves are involved in an autonomic response, which division is active?

Parasympathetic nervous system

Summary: Sympathetic Nervous System Key Features

• Neurotransmitter: Norepinephrine (SN) | • Target Receptor: Adrenergic | • Ganglia: Close to spinal cord | • Exit: Thoracic / Lumbar | • Neurons: Noradrenergic & Cholinergic

Summary: Parasympathetic Nervous System Key Features

• Neurotransmitter: Acetylcholine (PA) | • Target Receptor: Muscarinic | • Ganglia: Close to/in targets | • Exit: Cranium / Sacrum | • Neurons: Cholinergic only

Core rule regarding nerve composition in ANS

A nerve CANNOT have both sympathetic and parasympathetic fibers.