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ANS and Somatic Motor Control Dr. Gary Mumaugh – Bethel University Sensory Neuron Processing Sensory Neurons o Each sensory neuron responds primarily to only one particular type of stimulus This is called it’s normal – Example: photoreceptors, chemoreceptors The dendrite of the sensory neuron transduces (converts) the stimulus into changes in membrane potential. stimulus >>>>> increased permeability of membrane to sodium >>>>>> depolarization >>>>>> AP o The intensity of the stimulus affects: The number of sensory neurons that respond The frequency of the Aps that are generated by each sensory neuron o Sensory adaptation to an ongoing stimulus Continuous stimulation of a sensory neuron resulted in a decreasing Response (sensory adaptation) Somatic Sensory Neurons o Information reaches consciousness (awareness) o Exteroreceptors Provides information about external environment Photoreceptors Chemoreceptors Olfactory receptors Taste buds Somatic nociceptors o Stimulated by chemical mediators or inflammation Mechanoreceptors Touch and pressure receptors Vibration, tickle and itch receptors Auditory (cochlear) receptors Thermoreceptors o Proprioceptors (kinesthesia) Provides information about position of the head and body in space Muscle stretch receptors (muscle spindle fibers) Golgi tendon organs Joint receptors Vestibular apparatus Semicircular canals Utricle Saccule 1 Visceral Sensory Neurons (Interoreceptors) o Information does not reach consciousness, or is only poorly defined and localized. o Chemoreceptors O2, CO2, H Glucose Visceral nociceptors – stimulated by chemical mediators of inflammation o Baroreceptors o Visceral stretch receptors Example – fullness of bladder or rectum o Irritant receptors – triggers coughing, sneezing or nausea Injured Cell Releases >>>>>>>>>> Kinins & Prostoglandins >>>>>>>>>> Pain Sensory Pathways to the Brain Organization of Sensory Pathways o Sensory nerve fibers (1st order neurons) synapses onto myelinated interneurons (2nd order neurons) in the CNS o The 2nd order neurons then: decussate (cross over) travel in bundles (fiber tracts) upwards through the CNS synapse in the Thalamus onto myelinated interneurons (3 rd order neurons) o These 3rd order neurons project to many areas of the brain, including the cerebral cortex. Third Order Neuron Thalamus to Cortex Second Order Neuron Cord to Thalamus First Order Neuron Dorsal Root Ganglion to Cord 2 General Characteristics of Visceral Effectors (organs) Includes: o The heart o All organs containing visceral (smooth) muscle GI tract Blood vessels Lung bronchioles Urinary bladder Iris of the eye Uterus o Glands Sweat glands Mucus secreting glands of the reparatory tract Salivary glands Secretory glands of the GI tract Liver Pancreas Adrenal glands Exhibits intrinsic activity (automaticity) o The visceral effectors are not dependent upon nerve stimulation Example: heart Innervated by autonomic motor neurons that act to influence the rate of activity The Autonomic Nervous System Consists of the hypothalamus, descending autonomic fiber tracts and the autonomic motor neurons o The hypothalamus continuously (and unconsciously) adjusts the activity of the visceral effectors to match the person’s activity and energy requirements Homeostasis o The hypothalamus is influenced by the person’s emotional state o A person’s emotional state indirectly influences the activity of the visceral organs Limbic System There are 2 types of autonomic motor neurons for each visceral effector of the body This is called dual innervation o Parasympathetic autonomic motor neurons influence the organs during states of relaxation (low energy requirements) o Sympathetic autonomic motor neurons influence organs during stated of stress – fight, flight, fright (high energy requirements) 3 General Pattern of Autonomic Outflow of the CNS Parasympathetic (Cranio-Sacral) Division o These neurons are present only in certain Cranial nerves and Sacral spinal nerves III Oculomotor Nerves VII Facial Nerves X Vagus Nerves S2 – S4 Pelvis Nerves Sympathetic (Thoraco-Lumbar) Division o The sympathetic motor neurons are present in the spinal nerves that emerge at the thoracic and lumbar levels. Neural Innervation of Effectors o Somatic Motor Neuron Overflow Under voluntary (conscious) control Originates in the grey matter of the brainstem, and the ventral gray horns of the spinal cord (at all levels) Releases ACh that excites the skeletal muscle fibers to the part Because it releases Ach, it is cholinergic Effect of denervation – neurogenic flaccid paralysis 4 o Autonomic Outflow Functions autonomously (unconscious) control Preganglionic (presynaptic) motor neurons Myelinated Released ACH that excites the postganglionic (post synaptic) motor neurons (Cholinergic) Postganglionic (postsynaptic) motor neuron Unmyelinated Release a neurotransmitter onto the visceral effector cells o Parasympathetic post ganglionic motor neurons release ACH o Sympathetic post ganglionic motor neurons release norephinephrine (Class Drawing – Autonomic Outflow) 5 (Class Drawing – Autonomic Innervation of the Heart 6 Neural Innervation of Effectors o Innervation of the Adrenal Medulla The adrenal medulla actually consists of specialized post ganglionic motor neurons that have no axons!! They produce epinephrine. They release epinephrine directly into the adrenal blood vessels, thus affecting all visceral organs and the brain. The adrenal medulla amplifies a generalized sympathetic response Parasympathetic Effects “Rest and Digest” on the Visceral Organs Generally inhibits the activity of of most visceral organs to conserve energy Stimulates anabolic biochemical processes for growth and repair of body tissues Visualize: The body’s internal state after leisurely enjoying a large dinner and then relaxing with a movie. “S L U D D” o Salivation o Lacrimation o Urination o Digestion o Defecation 7 Sympathetic Effects “Stress” on the Visceral Organs Generally increases the activity of most visceral organs to meet the increased energy demands associated with stress Stimulates catabolic biochemical processes to increase the availability of O 2 and glucose to active tissues, and to increase the generation of ATP (cell respiration) Visualize: The body’s internal state during strenuous exercise “ E SITUATIONS” o Exercise o Excitement o Emergency o Embarassment Clinical Considerations of ANS on the Visceral Organs Use of Parasympathomimetic Drugs Cholinergic Use of Sympathomimetic Drugs Adrenergic Use of Parasympholytic Drugs Anti-cholinergic o Examples: the belladona alkaloids o Widely used to block nasal, salivary and bronchial secretions prior to surgery in OTC cold medications Use of Sympatholytic Drugs Adrogenic Blockers o Examples: the beta-adrenergic blockers – “beta blockers” o Widely used to block the physiologic response to stress The Autonomic Control of the Pupils of the Eyes The Iris of the eyes contains antagonistic smooth muscles o Circular muscle Parasympathetic innervation Contraction of the circular muscle >>>>>>> pupillary constriction o Radial muscle Sympathetic innervation Contraction of the radial muscle >>>>>>> pupillary dilation The pupils are constricted in response to o Bright lights o Near vision o Quiet reflection The pupils are dilated in response to o Dim lights o Distant vision o Stress 8 Autonomic Actions on Visceral Effectors “Rest & Digest” ACh (Muscarinic Cholinergic) “Stress” Epinephrine & Norepinephrine (Adrenergic, Catecholamines) Purpose Decreased Energy Demands Purpose Increased Energy Demands Liver glycogenesis >> hypoglycemia Lipogenesis in fat cells Decreased rate & depth of breathing Liver glycogenolysis >> hyperglycemia Lipolysis in fat cells Increased rate & depth of breathing (Diaphragm is a skeletal muscle) Bronchodilation Decreased bronchial secretions Increased rate & force of cardiac contraction Tachycardia Increased contractility Vasodilation to heart and skeletal muscle Causing increased blood flow Generalized vasoconstriction to the other blood vessels of the body causing decreased blood flow to the GI tract and kidneys Increased blood pressure Pupillary dilation(Mydriasis) Decreased salivation Inhibits emptying of urinary bladder (retention) Increased CNS alertness Orgasm (ejaculation) Increased sweating causing heat loss (From Increased Cell Respiration) Bronchoconstriction Increased bronchial secretions Decreased rate & force of cardiac contraction Bradycardia Decreased contractility Vasoconstriction to heart and skeletal muscle Causing decreased blood flow Generalized vasodilation to the other blood vessels of the body causing increased blood flow to the GI tract and kidneys Decreased blood pressure Pupillary constriction Increased salivation Emptying of urinary bladder Decreased CNS alertness Sexual arousal (penile erection) 9