Autonomic Nervous System

Comprehensive practice flashcards covering the organization, motor pathways, neurotransmitters, and physiological actions of the somatic, sympathetic, and parasympathetic nervous systems.

What structures are innervated by somatic motor neurons, and what type of control governs them?

Somatic motor neurons innervate skeletal muscles and operate under voluntary / conscious control.

What is the primary role of the Autonomic Nervous System (ANS), and what effectors does it regulate?

The ANS is concerned with physiological homeostasis (such as blood pressure, breathing, digestion, urination, and sexual arousal) and exerts involuntary / subconscious control over cardiac muscle, smooth muscle, and glands.

How are the functions of the sympathetic and parasympathetic divisions of the ANS generally contrasted?

The sympathetic division is responsible for "fight-or-flight" responses, whereas the parasympathetic division is responsible for "rest-and-digest" (or "rest and repair") responses.

How many neurons in series comprise the motor pathways of the Autonomic Nervous System?

Two neurons in series: a preganglionic neuron and a postganglionic neuron.

What are the structural features and myelination status of an autonomic preganglionic neuron?

Its cell body is located in the CNS, its axon is myelinated, it exits the CNS via a cranial nerve or spinal nerve, and it synapses with a postganglionic neuron in an autonomic ganglion.

What are the structural features and myelination status of an autonomic postganglionic neuron?

Its cell body is located outside the CNS in an autonomic ganglion, it lies entirely within the PNS, its axon is unmyelinated, and it synapses on the target organ.

Which neurotransmitter is released by all somatic motor neurons?

Acetylcholine ($\text{ACh}$).

Which neurotransmitter is released by all autonomic preganglionic fibres?

Acetylcholine ($\text{ACh}$).

Which neurotransmitter is released by postganglionic parasympathetic fibres?

Acetylcholine ($\text{ACh}$).

Which neurotransmitter is released by most postganglionic sympathetic fibres?

Noradrenaline ($\text{NA}$), except at sweat glands where acetylcholine ($\text{ACh}$) is released.

Where are the cell bodies of sympathetic preganglionic neurons located?

In the lateral horns of gray matter in the 12 thoracic and first two lumbar segments of the spinal cord ($T1\text{--}L2$), which is why the sympathetic division is called the thoracolumbar division.

Where do sympathetic preganglionic neurons synapse with postganglionic neurons?

In autonomic ganglia, specifically within the sympathetic trunk ganglia (sympathetic chain) or other ganglia located in the abdominal cavity.

What structure is shown in this diagram running alongside the vertebral column from the base of the skull to the coccyx?

The sympathetic trunk ganglia (also called sympathetic chain ganglia).

Which visceral effectors receive sympathetic postganglionic innervation?

Skin, blood vessels, salivary glands, sweat glands, bronchi, heart, stomach & intestine, and bladder.

What are the major physiological effects of sympathetic stimulation on target organs?

Increased heart rate and blood pressure, bronchodilation, pupillary dilation, piloerection, sweating, reduced peristalsis, and sphincter contraction ("fright, fight or flight").

What are the "four E's" associated with sympathetic division activation?

Exercise, Emergency, Excitement, and Embarrassment.

Where are the cell bodies of parasympathetic preganglionic neurons located?

In the brainstem nuclei of four cranial nerves—III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus)—and three sacral spinal cord segments ($S2\text{--}S4$), giving it the name craniosacral division.

Where do parasympathetic preganglionic axons synapse with postganglionic neurons?

In terminal ganglia that are located close to or inside the target organs.

What does the acronym SLUDD stand for in describing parasympathetic stimulation responses?

Salivation, Lacrimation, Urination, Digestion, and Defecation (all of which are increased).

How do parasympathetic and sympathetic stimulation differ regarding their effects on the pupils, bronchi, and heart rate?

Sympathetic stimulation causes pupillary dilation, bronchodilation, and increased heart rate; parasympathetic stimulation causes pupillary constriction, bronchoconstriction, and decreased heart rate.

How do the distribution and duration of responses compare between the sympathetic and parasympathetic divisions?

Sympathetic responses are widespread and long-lasting, whereas parasympathetic responses are localised and transient ('local effect').

How do target tissue supplies differ between the sympathetic and parasympathetic divisions?

The sympathetic division supplies skin, blood vessels, and viscera, whereas the parasympathetic division supplies only viscera.

Which brain structure provides overall control of the Autonomic Nervous System (ANS), and how does it execute this role?

The hypothalamus provides overall control; it integrates sensory input regarding olfaction, gustation, temperature, osmolarity, and blood chemicals, and projects directly to autonomic nuclei in the brainstem and spinal cord.