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Biology 141 The Autonomic Nervous System Chapter 15 Overview The CNS spinal cord brain The peripheral nervous system sensory-somatic nervous system Responds to the external environment 12 pairs of cranial nerves and 31 pairs of spinal nerves. autonomic nervous system Responds to the internal environment Parasympathetic nervous system Sympathetic nervous system Divisions of the Nervous System ANS Function: operates without conscious control. Regulation: Control: hypothalamus and brain stem. receives input from limbic system and other regions of the cerebrum Regulate activity of smooth muscle, cardiac muscle & certain glands ANS Sensory receptors associated with interoceptors (receptors that monitor internal environments) Located in blood vessels, viscera, smooth muscle Chemoreceptors Baroreceptors monitor BP Internal pain - angina Mechanoreceptors Monitor vessel stretch Comparison SOMATIC vs. ANS Somatic contains both sensory and motor neurons. input from the special and somatic senses. sensations are consciously perceived. innervate skeletal muscle to produce conscious, voluntary movements. effect of a motor neuron is always excitation. Comparison SOMATIC vs. ANS ANS contains both sensory and motor neurons. Input from interoceptors. input not consciously perceived. may receive input from somatic senses and special sensory neurons. regulate visceral activities Effect: exciting or inhibiting activities of cardiac muscle, smooth muscle, and glands. Comparison SOMATIC vs. ANS Somatic motor pathways consist of a single motor neuron Autonomic motor pathways consists of two motor neurons in series Motor Neurons in Series first autonomic cell body in the CNS myelinated axon extends to an autonomic ganglion or adrenal medullae second autonomic cell body in an autonomic ganglion nonmyelinated axon extends to an effector. Somatic has 1 motor neuron ANS has 2 motor neurons in series First motor neuron: preganglionic Preganglionic neuron cell body in brain or spinal cord axon is myelinated extends to autonomic ganglion Second motor neuron: postganglionic Postganglionic neuron cell body lies outside the CNS in an autonomic ganglion axon is unmyelinated fiber that terminates in a visceral effector First Neuron terminates in a ganglion or adrenal medulla Can use either NE or ACh as the neurotransmitter ANS Efferent Branches The output (efferent) part of the ANS is divided into two principal parts: the sympathetic division the parasympathetic division Organs that receive impulses from both sympathetic and parasympathetic fibers are said to have dual innervation. Parasympathetic and Sympathetic Parasympathetic Sympathetic Dual innervation Dual innervation one speeds up organ one slows down organ Sympathetic NS increases heart rate Parasympathetic NS decreases heart rate Anatomy of Autonomic Motor Pathways Components Preganglionic neuron Sympathetic Parasympathetic Autonomic ganglia Postganglionic neuron Autonomic Plexus Preganglionic Neurons Sympathetic Also called thoracolumbar division Cell bodies in the lateral horns of the gray matter in segments T1-T12 and L1L2 Axons are called the thoracolumbar outflow Parasympathetic Also called craniosacral division Cell bodies in the brain stem cranial nerve nuclei III, VII, IX, and X Cell bodies in the lateral gray horns of segments S2S4 Axons are called craniosacral outflow Autonomic Ganglia Sympathetic 2 groups Sympathetic trunk ganglia (Vertebral chain ganglia) lie in a vertical row on either side of the vertebral column Innervate above the diaphragm Prevertebral ganglia (collateral) Anterior to vertebral column close to large arteries Innervate below the diaphragm Autonomic Ganglia Parasympathetic 1 group: terminal ganglia Located near or in viscera Postganglionic Neurons postganglionic neuron can be branched to receive signals from multiple ganglionic locations. Autonomic Plexuses: Tangled neural networks that lie along major arteries. Major autonomic plexuses Cardiac: supplies the heart, Pulmonary: supplies the lung, Celiac (solar): liver, gallbladder, stomach, pancreas, spleen, kidney, reproductive organs Major autonomic plexuses superior mesenteric: small and large intestines inferior mesenteric: large intestines Renal: kidneys and ureters Hypogastric: pelvic viscera Structure of the Sympathetic Division Preganglionic – leave spinal cord through ventral root Enter the ganglion via the white ramus Synapse with postganglionic Leave via gray ramus Terminates on visceral effectors 3 Pathways of Sympathetic Fibers Spinal nerve route Sympathetic chain route out same level up chain & out spinal nerve Collateral ganglion route out splanchnic nerve to collateral ganglion Divergence of Sympathetic Neurons Divergence: Mass activation due to divergence 1 preganglionic cell synapses on many postganglionic cells multiple target organs fight or flight response explained Adrenal gland modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood Horner’s Syndrome Sympathetic innervation to one side of the face is lost (mutation, injury, or disease). Affects outflow Drooping of eyelid Constricted pupil Lack of sweating Structure of the parasympathetic division Preganglionic Cranial Sacral From ventral root of spinal nerve Terminal ganglia As part of a cranial nerve In the walls of viscera Postganglionic Innervate smooth muscle and glands of the visceral walls Parasympathetic Cranial Nerves Oculomotor nerve Facial nerve pterygopalatine and submandibular ganglions supply tears, salivary & nasal secretions Glossopharyngeal ciliary ganglion in orbit iris otic ganglion supplies parotid salivary gland Vagus nerve supply heart, pulmonary and GI tract as far as the midpoint of the colon Parasympathetic Sacral Nerve Form pelvic splanchnic nerves ANS Neurotransmitters Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released Adrenergic Cholinergic ANS NEUROTRANSMITTERS Cholinergic Produce and release acetylcholine (ACh) All sympathetic and parasympathetic preganglionic All parasympathetic postganglionic Only sweat gland sympathetic postganglionic Adrenergic Produce and release norepinephrin (NE) Most sympathetic postganglionic neurons(noradrenalin) Cholinergic Neurons Excitation or inhibition depending upon receptor subtype and organ involved. Cholinergic Receptors Cholinergic receptors integral membrane proteins in the postsynaptic plasma membrane. 2 types: Nicotinic and muscarinic Activation of nicotinic receptors excitation Nicotinic receptors are found on postsynaptic cells of ANS cells and at NMJ Activation of muscarinic receptors excitation or inhibition Muscarinic receptors are found on plasma membranes of all parasympathetic effectors (viscera, smooth muscle) Adrenergic Neurons Adrenergic neurons release norepinephrine (NE) ) from postganglionic sympathetic neurons only Excites or inhibits organs NE lingers at the synapse until enzymatically inactivated Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons. Physiological Effects of the ANS Autonomic Tone Sympathetic Response balance between sympathetic and parasympathetic activity regulated by the hypothalamus Supports rigorous functions and rapid ATP production Fight or flight response Parasympathetic Response Enhances rest and digestive functions, storage of ATP Fight or Flight Alarm reaction dilation of pupils Increase heart rate respirations BP Blood flow to skeletal muscles Blood sugar decrease in blood flow to nonessential organs Long lasting lingering NE in synaptic gap Pathway Autonomic Reflexes Receptor Sensory neuron Responds to stimuli Transduce stimuli to action potential Action potential travels to CNS Integrating center (CNS) Interneurons relay sensory info to motor neurons 2 Motor neurons (pre and post ganglionic) Hypothalamus Brain stem Spinal cord Carries action potential from the CNS to an effector Effector Smooth or cardiac muscle, glands Autonomic Control by Higher Centers Major control and integration center: hypothalamus Receives input from Viscera Olfaction Gustation Changes in temp Osmolarity Blood chemistry levels Limbic system Output to Brain stem Heart Blood vessels Salivary glands swallowing Spinal cord Intestines bladder DISORDERS Raynaud’s phenomenon excessive sympathetic stimulation of smooth muscle in the arterioles of the digits Result - vasoconstriction the digits (fingers and toes) become ischemic (lack blood) after exposure to cold or with emotional stress. Digits may become necrotic Autonomic Dysreflexia Exaggerated response of sympathetic NS in cases of spinal cord injury above T6 Sensory impulses from below the injury are unable to ascend to the brain Causes mass stimulation of sympathetic nerves below the injury Result vasoconstriction which elevates blood pressure parasympathetic NS tries to compensate slows heart rate, dilates blood vessels above the injury Produces a pounding headache, hypertension, flushed skin, profuse sweating above the injury and cool dry skin below can lead to seizure, stroke or heart attack