The Autonomic Nervous System & Higher Order Functions. An overview of the ANS. Divisions of the ANS. The Sympathetic Division (16-3) 2/19/2015

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1 The Autonomic Nervous System & Higher Order Functions Chapter 16 An overview of the ANS The autonomic nervous system coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions without instruction or interference by the conscious mind Visceral motor neurons called preganglionic neurons in the CNS send axons to synapse on ganglionic neurons, which are visceral motor neurons in peripheral autonomic ganglia outside the CNS These ganglionic neurons innervate visceral effectors, such as cardiac & smooth muscle, glands, and adipose tissues (where it modulates glucose and fat metabolism) Divisions of the ANS The ANS is divided into sympathetic and parasympathetic divisions The sympathetic division, or thoracolumbar division prepares p the body for heightened levels of somatic activity When fully activated the fight or flight response readies the body for stresses See summary follows this slide: The Sympathetic division of the ANS includes two sets of sympathetic chain ganglia, one on each side of the vertebral column; three collateral ganglia anterior to the vert. col.; and two adrenal medullae The preganglionic fibers are short, because the ganglia are close to the spinal cord. The post ganglionic fibers are longer and extend to their target organs The sympathetic division has considerable divergence. That is, a single preganglionic fiber may inervate two dozen or more ganglionic neurons in different ganglia. As a result, a single sympathetic motor neuron in the CNS can control a variety of visceral effectors and produce a complex and coordinated response All preganglionic neurons release ACH at their synapses with ganglionic neurons. Most postganglionic fibers release NE but a few release ACh or NO The effector response depends on the second messengers triggered by G-protein activation when NE or E binds to alpha receptors or beta receptors The Sympathetic Division (16-3) 1

2 Divisions of the ANS The parasympathetic division, or craniosacral division, stimulates visceral activity The parasympathetic division is responsible for the rest and repose state after a meal Parasympathetic activity conserves energy but stimulates digestive activity by increasing digestive motility and bloodflow See summary on following slide The parasympathetic division includes visceral motor nuclei associated with cranial nerve III, VII, IX, and X, and with sacral segments S 2 -S 4 Ganglionic neurons are located in ganglia within or next to their target organs The parasympathetic division innervates areas serviced by the cranial nerves and organs in the thoracic and abdominopelvic cavities All parasympathtetic neurons are cholinergic. Ganglionic neurons have nicotinic receptors, which are excited by Ach. Muscarinic receptors at neuromuscular and nueroglandular junctions produce either excitation or inhibition, depending on the action of enzymes triggered by G protein activation when Ach binds to the receptor The effects of parasympathetic stimulation are generally brief and restricted to specific organs and sites. The Sympathetic Division The sympathetic division consists of preganglionic neurons that are located in the lateral gray horns between T 1 and L 2 of the spinal cord, and ganglionic neurons that are located in ganglia near the vertebral column The ganglionic neurons occur in three locations Sympathetic chain ganglia Collateral ganglia The adrenal medullae The Sympathetic Division (16-3) 2

3 Sympathetic activation The sympathetic division changes the activities of tissues and organs by releasing NE at peripheral synapses and by distributing E and NE via the bloodstream While reflexes can involve only single effectors, during crisis the entire sympathetic division responds in an event called sympathetic activation The effects of sympathetic activation 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 preganglionic neurons leads to the release of ACh at synapses with ganglionic neurons This stimulation of the ganglionic g neurons leads to the release of neurotransmitters at target organs The synaptic terminals of the ganglionic neurons are called varicosities and look like a string of pearls lying along the surface of the effector cells 3

4 Neurotransmitters and Sympathetic Function Most sympathetic ganglionic neurons release NE at their varicosities, a small number release ACh NE affects the target for a few seconds, much longer than does ACh, principally p because of the low concentrations of Monoamine oxidase (MAO) and Catechol-O-methyltransferase (COMT), the enzymes that break NE down Adrenal effects are of considerably longer duration because the bloodstream does not contain either enzyme The Parasympathetic Division The parasympathetic division of the ANS consists of: Preganglionic neurons in the Brain Stem and Sacral segments of the spinal cord Ganglionic neurons in peripheral ganglia within or adjacent to target organs Parasympathetic Activation The effects produced by the parasympathetic division include those listed below: Constriction of the pupils and focusing the lens on nearby objects Secretion by digestive glands and the liver Secretion of hormones that promote absorption and utilization of nutrients by peripheral cells An increase in smooth muscle activity along the digestive tract Parasympathetic Activation The stimulation and coordination of defecation Contraction of the urinary bladder during urination Constriction of the respiratory passageways A reduction in heart rate and force of contraction Sexual arousal and the stimulation of sexual glands in both sexes Changes in blood flow and glandular activity associated with sexual arousal These functions, with the exception of those related to sexual arousal, center on relaxation, food processing, and energy absorption 4

5 Neurotransmitters and parasympathetic functions All parasympathetic fibers release ACh which induces a short-lived response There are two types of receptors found on the postsynaptic p membranes Nicotinic receptors exhibit an excitatory response to ACh by opening chemically gated channels in the postsynaptic membrane Muscarinic receptors are G-proteins and their stimulation produces a longer term response (excitatory or inhibitory) characteristic of G-protein interactions Interactions between sympathetic and parasympathetic Most vital organs receive dual innervation by both the sympathetic and parasympathetic divisions Where dual innervation occurs, the two divisions work antagonistically such as in the digestive tract, heart, and lungs At other sites, the responses may be separate or complementary 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 Integration and Control The ANS is organized into a series of interacting levels At the bottom are the visceral motor neurons in the lower brain stem and spinal cord Visceral reflexes provide automatic motor responses from the ANS that can be modified, facilitated, or inhibited by higher centers Visceral Reflexes All visceral reflexes are polysynaptic Long reflexes involve the CNS, and processing there leads to the activation of motor neurons commanding visceral effectors Short reflexes bypass the CNS entirely; they involve sensory neurons and interneurons whose cell bodies are located within autonomic ganglia In general, short reflexes control activity in a small portion of the target organ, whereas long reflexes coordinate activity for the entire organ 5

6 Higher Levels of Autonomic Control More complex ANS reflexes are coordinated by processing centers in the medulla oblongata The medulla oblongata contains centers controlling salivation, swallowing, digestive secretion, peristalsis, and urinary function, which are in turn regulated by the hypothalamus Higher Levels of Autonomic Control While autonomic was originally applied because responses were thought to be independent of other CNS activities subsequent research has shown this view to be erroneous Activity in the limbic systems, thalamus, and cerebral cortex can affect autonomic function When you become angry your blood pressure, heart rate, and respiratory rate all increase; Likewise, when you think about food your stomach growls and your mouth waters Higher order functions Higher order functions share the following characteristics They are performed by the cerebral cortex and involve complex interactions among areas of the cortex and other regions of the brain They involve conscious and unconscious information processing They are not part of the wiring of the brain and are subject to modification and adjustment over time Memory Memories are stored bits of information gathered through experience Fact memories are specific, the color of a stop sign, g, the smell of a perfume Skill memories are learned motor behaviors, lighting a match, tying your shoes, opening a jar With repetition skill memories become incorporated at the unconscious level 6

7 Memory Short term memories, or primary memories, do not last long, but while they exist, the information can be recalled instantly; someone s s name, a telephone number With effort a short term memory can be converted into a long term memory The conversion of short term memories to long term memories is called memory consolidation Memory Long term memories last much longer, some an entire lifetime There are two types of long term memories Secondary memories fade with time and may require effort to recall Tertiary memories seem to be part of your consciousness, such as your name Martini Passage follows Information on one subject is parceled out to many different regions of the brain. Your memories of cows are stored in the visual association area (what a cow looks like, that the letters c-o-w mean cow ), the auditory association area (the moo sound and how the word cow sounds) the speech center (how to say cow), and the frontal lobes (how big cows are, what they eat). Related information, such as how you feel about cows and what milk tastes like, is stored in other locations. If one of these areas is damaged your memory will be incomplete in some way. How these memories are access and assembled on demand remains a mystery. Cellular mechanisms of Memory Memory consolidation at the cellular level involves anatomical and physiological changes in neurons and synapses, Time, effort, and repetition result in: Increased neurotransmitter release (repeated use aids consolidation) Facilitation at synapses (repeated use makes recall easier, aiding consolidation) The formation of additional synaptic connections (repeated use increases the number of synaptic connections, which makes consolidation more likely) Cellular mechanisms of Memory These physiological processes create anatomical changes that facilitate communication along a specific neural circuit A single circuit that corresponds to a single memory is termed a memory engram Efficient conversion of a short term memory into a memory engram takes time, at least an hour Very pleasant or unpleasant events are easily converted to longterm memories 7

8 States of Consciousness Healthy individuals cycle between the alert, conscious state and the sleep state each day The degree of wakefulness at any given moment is an indication of the level of ongoing gcns activity Conscious implies a state of awareness and attention to external events and stimuli Unconscious can imply a range of conditions from anesthetized to nodding off Sleep is the state when one is considered unconscious but can still be awakened by normal sensory stimuli Sleep Two general levels of sleep are recognized During deep sleep, aka slow wave or non-rem sleep, your entire body relaxes and activity at the cerebral cortex is at a minimum, energy utilization declines by around 30% During rapid eye movement, or REM sleep, active dreaming occurs, although EEG traces are similar to awake individuals, you become even less receptive to outside stimuli. Inhibition of somatic motor neurons prevents one from physically responding to dream stimuli Sleep The significance of sleep must lie with its impact on the CNS, but the physiological or biochemical basis remains undetermined. We do know that proteins synthesis in neurons increases during sleep and that extended periods without sleep lead to a disturbance of mental function Arousal Arousal, or awakening from sleep, appears to be a function of the reticular formation. The reticular formation has extensive connections with the sensory, motor, and integrative nuclei and pathways along the brain stem. The reticular activating system (RAS), a diffuse network in the reticular formation is one of the most important brain stem components Output from the RAS projects to thalamic nuclei that influence large areas of the cerebral cortex Arousal Sleep may be ended by any stimulus sufficient to activate the reticular formation and RAS Arousal occurs rapidly but transiently lasting less than a minute Thereafter consciousness is maintained by positive feedback as brain activity continues RAS stimulation After many hours of activity the reticular formation becomes less responsive to stimuli and the individual becomes more lethargic Arousal Evidence suggests that the regulation of sleepwake cycles involves the interplay between brain stem nuclei using different neurotransmitters One group stimulates the RAS with norepinephrine and keeps us awake and alert The other group depresses RAS activity with serotonin and promotes deep sleep 8

9 Brain Chemistry and Behavior Changes in the normal balance between two or more neurotransmitters can profoundly affect brain function Several specific neurotransmitters have been identified as impacting behavior Low levels of serotonin production can lead to severe depression NE release causes elation, insufficiency causes depression Dopamine deficiency causes the motor problems of Parkinson s disease, an excess of dopamine may be associated with schizophrenia 9