Autonomic Nervous System and Visceral Reflexes

Flashcards reviewing the autonomic nervous system and visceral reflexes, covering motor divisions, general properties, reflex arcs, somatic vs autonomic pathways, divisions of the ANS, neurotransmitters, dual innervation, and central control.

What is the Autonomic Nervous System (ANS)?

The portion of the nervous system that operates unconsciously and manages the body's homeostasis.

What does the autonomic nervous system control?

Glands, cardiac muscle, and smooth muscle.

What are the primary organs of the ANS?

Viscera of thoracic and abdominal cavities, cutaneous blood vessels, sweat glands, and piloerector muscles.

What are Visceral reflexes?

Unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors.

What are the components of a visceral reflex arc?

Receptors, afferent neurons, interneurons, efferent neurons, and effectors.

How many synapses are in visceral reflexes?

At least two synapses between the CNS and the effector (preganglionic and postganglionic neurons).

Describe the somatic motor division pathway.

Cell bodies in the CNS, a single long myelinated motor neuron from the CNS to the effector.

Describe the autonomic motor division pathway.

A two-neuron chain: preganglionic fibers and postganglionic fibers, meeting at an autonomic ganglion.

What is the function of the sympathetic division of the ANS?

Prepares the body for physical activity; increases heart rate, BP, airflow, and blood glucose levels.

What is the function of the parasympathetic division of the ANS?

Calms body functions, reduces energy expenditure, and assists in bodily maintenance; lowers heart rate and blood pressure.

What is autonomic tone?

Normal background rate of activity that represents the balance of the two systems according to the body's changing needs.

What does parasympathetic tone maintain?

Maintains smooth muscle tone in intestines and holds resting heart rate down.

What does sympathetic tone maintain?

Keeps most blood vessels partially constricted and maintains blood pressure.

What is the origin of the sympathetic division (thoracolumbar division)?

Arises from the thoracic and lumbar regions of the spinal cord.

Where are sympathetic ganglia located?

2 Sympathetic chains of ganglia nearby vertebral column.

What are the relative lengths of fibers in the sympathetic nervous system?

Relatively short preganglionic and long postganglionic fibers.

Where do ganglionic neurons occur?

Lateral chain ganglia (both sides of vertebral column), collateral ganglia, and adrenal medullae.

What are the effects of increased sympathetic activity?

Stimulates tissue metabolism and increases alertness.

What is the origin of the parasympathetic division?

Arises from the brain and sacral regions of the spinal cord (craniosacral division).

Where are the parasympathetic ganglia located?

Terminal ganglia in (intramural) or near target organs.

What are the relative lengths of fibers in the parasympathetic nervous system?

Long preganglionic fibers, short postganglionic fibers.

What does the parasympathetic division control during resting conditions?

Stimulates visceral activity, conserves energy, and promotes sedentary activities.

What does the sympathetic division do during stress?

Increases alertness, metabolic rate, and muscular abilities.

What does the parasympathetic division do during rest?

Reduces metabolic rate and promotes digestion.

What are the neurotransmitters used in the ANS?

All parasympathetic fibers are cholinergic; all sympathetic pre-ganglionic fibers are cholinergic; most sympathetic post-ganglionic fibers are adrenergic.

What is dual innervation?

Most viscera receive nerve fibers from both parasympathetic and sympathetic divisions.

What are antagonistic effects in dual innervation?

Oppose each other, exerted through dual innervation of same effector cells or because each division innervates different cells.

What are cooperative effects in dual innervation?

When two divisions act on different effectors to produce a unified overall effect.

What effectors receive only sympathetic fibers?

Adrenal medulla, arrector pili muscles, sweat glands, and all blood vessels.

What are the levels of CNS that regulate autonomic function?

Cerebral cortex, hypothalamus, midbrain, pons, medulla oblongata, and spinal cord reflexes.