Biology 218 – Human Anatomy
Lecture Outline
Adapted from Martini Human Anatomy 7th ed. / Session:
Section:
Days / Time: Instructor: / FALL
52999
MW 5:00 PM – 9:20 PM
RIDDELL

Chapter 17

The Nervous System

Authonomic Nervous System

Introduction

The autonomic nervous system functions outside of our conscious awareness

The autonomic nervous system makes routine adjustments in our body’s systems

The autonomic nervous system:

Regulates body temperature

Coordinates cardiovascular, respiratory, digestive, excretory, and reproductive functions

A Comparison of the Somatic and Autonomic Nervous Systems

Autonomic nervous system

Axons innervate the visceral organs

Has afferent and efferent neurons

Afferent pathways originate in the visceral receptors

Somatic nervous system

Axons innervate the skeletal muscles

Has afferent and efferent neurons

Afferent pathways originate in the skeletal muscles

Subdivisions of the ANS

The autonomic nervous system consists of two major subdivisions

Sympathetic division

Also called the thoracolumbar division

Known as the “fight or flight” system

Parasympathetic division

Also called the craniosacral division

Known as the “rest and repose” system

Subdivisions of the ANS

Sympathetic division

Thoracic and upper lumbar nerves synapse in ganglia near the spinal cord

Sympathetic activation results in:

Increased metabolism and alertness

Parasympathetic division

Synapses are located near the target organ

Parasympathetic activation results in:

Energy conservation

Subdivisions of the ANS

Sympathetic division

All preganglionic fibers release acetylcholine. The effects are stimulatory.

Most postganglionic fibers release norepinephrine.The effects are stimulatory.

Parasympathetic division

All preganglionic fibers release acetylcholine. The effects are stimulatory.

Postganglionic fibers release acetylcholine but the effects can be inhibitory.

The Sympathetic Division

Sympathetic division consists of:

Preganglionic neurons between T1 and L2

Two types of ganglionic neurons near the vertebral columns: sympathetic chain ganglia (lateral to the vertebral column) and collateral ganglia (anterior to the vertebral column)

Specialized neurons in the interior of the suprarenal gland

The Sympathetic Division

Sympathetic division

Preganglionic neurons

Cell bodies are in the lateral gray horns

Axons enter the ventral roots

Sympathetic chain ganglia (paravertebral ganglia)

Control effectors in the body wall, head, neck, limbs, and thoracic cavity

The Sympathetic Division

Sympathetic division

Collateral ganglia (prevertebral ganglia)

Neurons innervate effectors in the abdominopelvic cavity

Specialized neurons

Modified sympathetic ganglion in the suprarenal gland

Neurons release neurotransmitters that act like hormones

The Sympathetic Division

Sympathetic Chain Ganglia

The ventral root joins a dorsal root

Forms a spinal nerve

Passes through an intervertebral foramen

White ramus branches off the spinal nerve

Goes to a nearby sympathetic chain ganglion

The Sympathetic Division

Functions of Sympathetic Chain Ganglia

Reduction of circulation to the skin

More circulation to skeletal muscles

Stimulates more energy production by skeletal muscles

Releases stored adipose

Stimulation of arrector pili muscles

Dilation of pupils

Increased heart rate

Dilation of respiratory tubes

The Sympathetic Division

Anatomy of the Sympathetic Chain Ganglia

Each spinal nerve consists of:

Preganglionic and postganglionic fibers

There are:

cervical sympathetic chain ganglia

thoracic sympathetic chain ganglia

lumbar sympathetic chain ganglia

sacral sympathetic chain ganglia

coccygeal sympathetic chain ganglia

The Sympathetic Division

Collateral Ganglia

Preganglionic neurons originate in the inferior thoracic and superior lumbar areas of the spinal cord

Fibers pass through the sympathetic chain ganglia without synapsing

Converge to form the greater, lesser, and lumbar splanchnic nerves

Splanchnic nerves converge on the collateral ganglia

The Sympathetic Division

Functions of the Collateral Ganglia

Reduction of flow of blood to the visceral organs

Decrease in activity of the digestive organs

Stimulation of the release of glucose from glycogen in the liver

Stimulates adipose cells to release energy reserves

Relaxation of smooth muscles in the urinary bladder

Cause ejaculation in males

The Sympathetic Division

Anatomy of the Collateral Ganglia

Splanchnic nerves innervate:

Celiac ganglion: fibers innervate the stomach, duodenum, liver, gallbladder, pancreas, spleen, and kidney

Superior mesenteric ganglion: fibers innervate the small intestine and the first parts of the large intestine

Inferior mesenteric ganglion: fibers innervate the kidney, urinary bladder, sex organs, and terminal ends of the large intestine

The Sympathetic Division

Suprarenal Medullae

Fibers pass through sympathetic chain and the celiac ganglion without synapsing

Proceed to the suprarenal medulla

Fibers then synapse on modified neurons that when stimulated will release neurotransmitters that act as hormones:

Epinephrine and norepinephrine

The Sympathetic Division

Functions of the suprarenal medullae

Increase alertness by activating the reticular activating system

Increase cardiovascular and respiratory activity

Increase muscle tone

Increase the mobilization of energy reserves

Increased release of lipids from adipose cells

Increased breakdown of glycogen in liver cells

The Sympathetic Division

Sympathetic activation and neurotransmitter release

Sympathetic ganglion fibers release acetylcholine at the synapse with ganglionic neurons

These are cholinergic synapses

The stimulation of ganglionic neurons causes the release of norepinephrine at the neuroeffector junction

These terminals are adrenergic

Some ganglionic neurons also release acetylcholine

Especially at the neuroeffector junctions of skeletal muscles

The Sympathetic Division

Summary of the Sympathetic Division

Consists of parallel chains on either side of the spinal
cord

Preganglionic fibers are short and extend from the
spinal cord to the sympathetic chain

Postganglionic fibers are long and extend from the spinal cord to the body organs

The sympathetic division shows considerable divergence

All preganglionic neurons release ACh / most postganglionic neurons release norepinephrine

The Parasympathetic Division

Parasympathetic Division

Preganglionic neurons are in the brain stem and sacral segments

Preganglionic neurons do not diverge as much as the sympathetic division

Therefore, the parasympathetic division is more localized and specific as compared to the sympathetic division

Postganglionic neurons are near (terminal) the target organ or within (intramural) the target organ

The Parasympathetic Division

Organization and Anatomy of the Parasympathetic Division

Preganglionic fibers leave the brain via:

CN III (to the intrinsic eye muscles, pupil, and lens)

CN VII (to the tear glands and salivary glands)

CN IX (to the parotid salivary glands)

CN X (to the visceral organs of the thoracic cavity and abdominal cavity)

Preganglionic fibers leave the sacral region via:

Pelvic nerves (to the visceral organs in the inferior portion of the abdominopelvic cavity

The Parasympathetic Division

Functions of the Parasympathetic Division

Pupil constriction

Secretion of digestive enzymes from digestive glands

Increased smooth muscle activity of the digestive system

Stimulation and coordination of defecation

Contraction of the urinary bladder

Constriction of respiratory passages

Reduced heart rate

Sexual arousal

The Parasympathetic Division

Parasympathetic Activation and Neurotransmitter Release

All preganglionic and postganglionic fibers release ACh at their synapses and neuroeffector junctions

Most stimulations are short lived due to the immediate breakdown of ACh by acetylcholinesterase

The Parasympathetic Division

Plasmalemma Receptors and Responses

Two types of ACh receptors are found on the postsynaptic plasmalemmae:

Nicotinic receptors: respond to nicotine

Found on surfaces of parasympathetic and sympathetic ganglionic neurons

Muscarinic receptors: respond to muscarine

Found on surfaces of parasympathetic cholinergic neuroeffector junctions

The Parasympathetic Division

Summary of the Parasympathetic Division

Involves CN III, CN VII, CN IX, and CN X

Involves sacral segments S2 to S4

All parasympathetic neurons are cholinergic

Release of ACh stimulates nicotinic receptors on ganglionic neurons

Release of ACh on neuroeffector junctions stimulates muscarinic receptors

Relationships between the Sympathetic and Parasympathetic Divisions

Sympathetic

Widespread effect on visceral organs

Parasympathetic

Modifies the activity of structures innervated by specific cranial nerves and pelvic nerves

Most vital organs are innervated by both the sympathetic and parasympathetic nerves

The two often oppose (antagonistic) each other

Relationships between the Sympathetic and Parasympathetic Divisions

Anatomy of Dual Innervation

Head region

The parasympathetic fibers accompany the sympathetic fibers to the target organ

Thoracic and abdominopelvic regions

The parasympathetic and sympathetic fibers mingle together forming plexuses

Cardiac plexus

Pulmonary plexus

Esophageal plexus

Celiac plexus

Inferior mesenteric plexus

Hypogastric plexus

Visceral Reflexes

Provide autonomic motor responses to:

Modify or facilitate higher centers

All are polysynaptic

Reflexes can be:

Long reflexes

Short reflexes

Visceral Reflexes

Long Reflexes

Visceral sensory neurons go to the CNS via the dorsal roots

There are interneurons within the CNS

Information is “interpreted” in the spinal cord or brain

ANS sends motor commands to the visceral organs

Visceral Reflexes

Short Reflexes

Sensory nerve impulses go to the ganglionic neurons

Motor commands are distributed by the postganglionic fibers

Impulses bypass the CNS

© 2012 Pearson Education, Inc. Page 1 of 6 BIO 218 F 2012 CH 17 Martini Lecture Outline