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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