The Autonomic Nervous System and Higher Order Functions

An Overview of the ANS

ANS

• Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions

• Preganglionic neurons in the CNS send axons to synapse on ganglionic neurons in autonomic ganglia outside the CNS

Divisions of the ANS

• Sympathetic division (thoracolumbar, “fight or flight”)

• Thoracic and lumbar segments

• Parasympathetic division (craniosacral, “rest and repose”)

• Preganglionic fibers leaving the brain and sacral segments

The Sympathetic Division

Sympathetic division anatomy

• Preganglionic neurons between segments T1 and L2

• Ganglionic neurons in ganglia near vertebral column

• Specialized neurons in adrenal glands

Sympathetic ganglia

• Sympathetic chain ganglia (paravertebral ganglia)

• Collateral ganglia (prevertebral ganglia)

Organization and anatomy of the sympathetic division

• Segments T1-L2, ventral roots give rise to myelinated white ramus

• Leads to sympathetic chain ganglia

Postganglionic fibers

• Rejoin spinal nerves and reach their destination by way of the dorsal and ventral rami

• Those targeting structures in the thoracic cavity form sympathetic nerves

• Go directly to their destination

Abdominopelvic viscera

• Sympathetic innervation via preganglionic fibers that synapse within collateral ganglia

• Splanchic nerves

Abdominopelvic viscera

• Celiac ganglion

• Innervates stomach, liver, gall bladder, pancreas, spleen

• Superior mesenteric ganglion

• Innervates small intestine and initial portion of large intestine

• Inferior mesenteric ganglion

• Innervates kidney, urinary bladder, sex organs, and final portion of large intestine

Sympathetic activation

• In crises, the entire sympathetic division responds

• Sympathetic activation

• Affects include increased alertness, energy and euphoria, increased cardiovascular and respiratory activities, elevation in muscle tone, mobilization of energy resources

Neurotransmitters and sympathetic function

• Stimulation of sympathetic division has two distinct results

• Release of ACh or NE at specific locations

• Secretion of E and NE into general circulation

• Most postganglionic fibers are adrenergic, a few are cholinergic or nitroxidergic

• Two types of receptors are alpha receptors and beta receptors

• Sympathetic ganglionic neurons end in telodendria studded with varicosities filled with neurotransmitter

The Parasympathetic Division

Parasympathetic division

• Preganglionic neurons in the brainstem and sacral segments of spinal cord

• Ganglionic neurons in peripheral ganglia located within or near target organs

Organization and anatomy of the parasympathetic division

• Preganglionic fibers leave the brain as cranial nerves III, VI, IX, X

• Sacral neurons form the pelvic nerves

Parasympathetic activation

• Effects produced by the parasympathetic division

• relaxation

• food processing

• energy absorption

Neurotransmitters and parasympathetic functions

• All parasympathetic fibers release ACh

• Short-lived response as ACH is broken down by AChE and tissue cholinesterase

• Postsynaptic membranes have two kinds of receptors

• Muscarinic

• Nicotinic

Interactions Between the Sympathetic and Parasympathetic Divisions

Sympathetic and parasympathetic divisions

• Sympathetic

• Widespread influence on visceral and somatic structures

• Parasympathetic

• Innervates only visceral structures serviced by cranial nerves or lying within the abdominopelvic cavity

• Dual innervation = organs that receive input from both systems

Anatomy of dual innervation

• Sympathetic and parasympathetic systems intermingle to form autonomic plexuses

• Cardiac plexus

• Pulmonary plexus

• Esophageal plexus

• Celiac plexus

• Inferior mesenteric plexus

• Hypogastric plexus

Comparison of the two divisions

• Important physiological and functional differences exist

Figure 16.10 Summary: The Anatomical Differences between the Sympathetic and Parasympathetic Divisions

Integration and Control of Autonomic Functions

Visceral reflexes

• Visceral reflex arcs are the simplest function of the ANS

• Long reflexes (interneurons)

• Short reflexes (bypassing CNS)

• Parasympathetic reflexes govern respiration, cardiovascular function and other visceral activities

Higher levels of autonomic control

• Activity in the ANS is controlled by centers in the brainstem that deal with visceral functioning

SNS and ANS organized in parallel

• Integration occurs at the brainstem and higher centers

High Order Functions

Higher order functions

• Are performed by the cerebral cortex and involve complex interactions

• Involve conscious and unconscious information processing

• Are subject to modification and adjustment over time

Memory

• Short term or long term

• Memory consolidation is moving from short term to long term

• Amnesia is the loss of memory due to disease or trauma

Consciousness

• Deep sleep, the body relaxes and cerebral cortex activity is low

• REM sleep active dreaming occurs

• The reticular activating system (RAS) is important to arousal and maintenance of consciousness

Brain Chemistry and Behavior

Neurotransmitters and the brain

• Neurotransmitters and brain function

• Changes in balance between neurotransmitters can profoundly alter brain function

• Personality and self-awareness

• Characteristics of the brain as an integrated system rather than one specific component

Aging and the Nervous System

Age-related changes

• Reduction in brain size and weight

• Reduction in the number of neurons

• Decrease in blood flow to the brain

• Changes in synaptic organization of the brain

• Intracellular and extracellular changes in CNS neurons