* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download INTRODUCTION - Faculty & Staff Webpages
Embodied language processing wikipedia , lookup
Single-unit recording wikipedia , lookup
Mirror neuron wikipedia , lookup
Proprioception wikipedia , lookup
Neuroregeneration wikipedia , lookup
End-plate potential wikipedia , lookup
Biological neuron model wikipedia , lookup
Neural coding wikipedia , lookup
Haemodynamic response wikipedia , lookup
Signal transduction wikipedia , lookup
Axon guidance wikipedia , lookup
Microneurography wikipedia , lookup
Neurotransmitter wikipedia , lookup
Development of the nervous system wikipedia , lookup
Caridoid escape reaction wikipedia , lookup
Optogenetics wikipedia , lookup
Chemical synapse wikipedia , lookup
Nervous system network models wikipedia , lookup
Neuromuscular junction wikipedia , lookup
Pre-Bötzinger complex wikipedia , lookup
Synaptogenesis wikipedia , lookup
Central pattern generator wikipedia , lookup
Synaptic gating wikipedia , lookup
Premovement neuronal activity wikipedia , lookup
Endocannabinoid system wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Molecular neuroscience wikipedia , lookup
Neuroanatomy wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
INTRODUCTION • The autonomic nervous system (ANS) operates via reflex arcs. • Operation of the ANS to maintain homeostasis, however, depends on a continual flow of sensory afferent input, from receptors in organs, and efferent motor output to the same effector organs. • Structurally, the ANS includes autonomic sensory neurons, integrating centers in the CNS, and autonomic motor neurons. • Functionally, the ANS usually operates without conscious control. • The ANS is regulated by the hypothalamus and brain stem. Chapter 15 The Autonomic Nervous System • Regulate activity of smooth muscle, cardiac muscle & certain glands • Structures involved – general visceral afferent neurons – general visceral efferent neurons – integration center within the brain • Receives input from limbic system and other regions of the cerebrum SOMATIC AND AUTONOMIC NERVOUS SYSTEMS • The somatic nervous system contains both sensory and motor neurons. • The somatic sensory neurons receive input from receptors of the special and somatic senses. • These sensations are consciously perceived. • Somatic motor neurons innervate skeletal muscle to produce conscious, voluntary movements. • The effect of a motor neuron is always excitation. SOMATIC AND AUTONOMIC NERVOUS SYSTEMS • The autonomic nervous system contains both autonomic sensory and motor neurons. – Autonomic sensory neurons are associated with interoceptors. – Autonomic sensory input is not consciously perceived. • The ANS also receives sensory input from somatic senses and special sensory neurons. • The autonomic motor neurons regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities of cardiac muscle, smooth muscle, and glands. – Most autonomic responses can not be consciously altered or suppressed. SOMATIC vs AUTONOMIC NERVOUS SYSTEMS • All somatic motor pathways consist of a single motor neuron • Autonomic motor pathways consists of two motor neurons in series – The first autonomic neuron motor has its cell body in the CNS and its myelinated axon extends to an autonomic ganglion. • It may extend to the adrenal medullae rather than an autonomic ganglion – The second autonomic motor neuron has its cell body in an autonomic ganglion; its nonmyelinated axon extends to an effector. AUTONOMIC NERVOUS SYSTEM • 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. • Table 15.1 summarizes the similarities and differences between the somatic and autonomic nervous systems. Sympathetic Ganglia • These ganglia include the sympathetic trunk or vertebral chain or paravertebral ganglia that lie in a vertical row on either side of the vertebral column (Figures 15.2). • Other sympathetic ganglia are the prevertebral or collateral ganglia that lie anterior to the spinal column and close to large abdominal arteries. – celiac – superior mesenteric – inferior mesenteric ganglia – (Figures 15.2 and 15.4). Dual Innervation, Autonomic Ganglia • Sympathetic (thoracolumbar) division – preganglionic cell bodies in thoracic and first 2 lumbar segments of spinal cord • Ganglia – trunk (chain) ganglia near vertebral bodies – prevertebral ganglia near large blood vessel in gut (celiac, superior mesenteric, inferior mesenteric) • Parasympathetic (craniosacral) division – preganglionic cell bodies in nuclei of 4 cranial nerves and the sacral spinal cord • Ganglia – terminal ganglia in wall of organ Autonomic Plexuses • These are tangled networks of sympathetic and parasympathetic neurons (Figure 15.4) which lie along major arteries. • Major autonomic plexuses include – – – – – – – cardiac, pulmonary, celiac, superior mesenteric, inferior mesenteric, renal and hypogastric Structures of Sympathetic NS • Preganglionic cell bodies at T1 to L2 • Rami communicantes – white ramus = myelinated = preganglionic fibers – gray ramus = unmyelinated = postganglionic fibers • Postganglionic cell bodies – sympathetic chain ganglia along the spinal column – prevertebral ganglia at a distance from spinal cord • celiac ganglion • superior mesenteric ganglion • inferior mesenteric ganglion Postganglionic Neurons: Sympathetic vs. Parasympathetic • Sympathetic preganglionic neurons pass to the sympathetic trunk. They may connect to postganglionic neurons in the following ways. (Figure 17.5). – May synapse with postganglionic neurons in the ganglion it first reaches. – May ascend or descend to a higher of lower ganglion before synapsing with postganglionic neurons. – May continue, without synapsing, through the sympathetic trunk ganglion to a prevertebral ganglion where it synapses with the postganglionic neuron. • Parasympathetic preganglionic neurons synapse with postganglionic neurons in terminal ganglia (Figure 17.3). Organs Innervated by Sympathetic NS • Structures innervated by each spinal nerve – sweat glands, arrector pili mm., blood vessels to skin & skeletal mm. • Thoracic & cranial plexuses supply: – heart, lungs, esophagus & thoracic blood vessels – plexus around carotid artery to head structures • Splanchnic nerves to prevertebral ganglia supply: – GI tract from stomach to rectum, urinary & reproductive organs Circuitry of Sympathetic NS • Divergence = each preganglionic cell synapses on many postganglionic cells • Mass activation due to divergence – multiple target organs – fight or flight response explained • Adrenal gland – modified cluster of postganglionic cell bodies that release epinephrine & norepinephrine into blood Structure of the Parasympathetic Division • The cranial outflow consists of preganglionic axons that extend from the brain stem in four cranial nerves. (Figure 15.3). – The cranial outflow consists of four pairs of ganglia and the plexuses associated with the vagus (X) nerve. • The sacral parasympathetic outflow consists of preganglionic axons in the anterior roots of the second through fourth sacral nerves and they form the pelvic splanchnic nerve. (Figure15.3) Parasympathetic Cranial Nerves • Oculomotor nerve – ciliary ganglion in orbit – ciliary muscle & pupillary constrictor muscle inside eyeball • Facial nerve – pterygopalatine and submandibular ganglions – supply tears, salivary & nasal secretions • Glossopharyngeal – otic ganglion supplies parotid salivary gland • Vagus nerve – many brs supply heart, pulmonary and GI tract as far as the midpoint of the colon Cholinergic Neurons and Receptors • Cholinergic receptors are integral membrane proteins in the postsynaptic plasma membrane. • The two types of cholinergic receptors are nicotinic and muscarinic receptors (Figure 15.6 a , b). – Activation of nicotinic receptors causes excitation of the postsynaptic cell. • Nicotinic receptors are found on dendrites & cell bodies of autonomic NS cells (and at NMJ.) – Activation of muscarinic receptors can cause either excitation or inhibition depending on the cell that bears the receptors. • Muscarinic receptors are found on plasma membranes of all parasympathetic effectors Adrenergic Neurons and Receptors • The main types of adrenergic receptors are alpha and beta receptors. These receptors are further classified into subtypes. – Alpha1 and Beta1 receptors produce excitation – Alpha2 and Beta2 receptors cause inhibition – Beta3 receptors (brown fat) increase thermogenesis • Effects triggered by adrenergic neurons typically are longer lasting than those triggered by cholinergic neurons. • Table 15.2 describes the location of the subtypes of cholinergic and adrenergic receptors and summarizes the responses that occur when each type of receptor is activated. Receptor Agonists and Antagonists • An agonist is a substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone. • An antagonist is a substance that binds to and blocks a receptor, preventing a natural neurotransmitter or hormone from exerting its effect. • Drugs can serve as agonists or antagonists to selectively activate or block ANS receptors. Physiological Effects of the ANS • Most body organs receive dual innervation – innervation by both sympathetic & parasympathetic • Hypothalamus regulates balance (tone) between sympathetic and parasympathetic activity levels • Some organs have only sympathetic innervation – sweat glands, adrenal medulla, arrector pili mm & many blood vessels – controlled by regulation of the “tone” of the sympathetic system Sympathetic Responses • Dominance by the sympathetic system is caused by physical or emotional stress -- “E situations” – emergency, embarrassment, excitement, exercise • Alarm reaction = flight or fight response – – – – – – dilation of pupils increase of heart rate, force of contraction & BP decrease in blood flow to nonessential organs increase in blood flow to skeletal & cardiac muscle airways dilate & respiratory rate increases blood glucose level increase • Long lasting due to lingering of NE in synaptic gap and release of norepinephrine by the adrenal gland Parasympathetic Responses • Enhance “rest-and-digest” activities • Mechanisms that help conserve and restore body energy during times of rest • Normally dominate over sympathetic impulses • SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and 3 “decreases”--decreased HR, diameter of airways and diameter of pupil • Paradoxical fear when there is no escape route or no way to win – causes massive activation of parasympathetic division – loss of control over urination and defecation PHYSIOLOGICAL EFFECTS OF THE ANS - Summary • The sympathetic responses prepare the body for emergency situations (the fightor-flight responses). • The parasympathetic division regulates activities that conserve and restore body energy (energy conservation-restorative system). – Table 15.4 summarizes the responses of glands, cardiac muscle, and smooth muscle to stimulation by the ANS. Autonomic or Visceral Reflexes • A visceral autonomic reflex adjusts the activity of a visceral effector, often unconsciously. – changes in blood pressure, digestive functions etc – filling & emptying of bladder or defecation • Autonomic reflexes occur over autonomic reflex arcs. Components of that reflex arc: – – – – – sensory receptor sensory neuron integrating center pre & postganglionic motor neurons visceral effectors Control of Autonomic NS • Not aware of autonomic responses because control center is in lower regions of the brain • Hypothalamus is major control center – input: emotions and visceral sensory information • smell, taste, temperature, osmolarity of blood, etc – output: to nuclei in brainstem and spinal cord – posterior & lateral portions control sympathetic NS • increase heart rate, inhibition GI tract, increase temperature – anterior & medial portions control parasympathetic NS • decrease in heart rate, lower blood pressure, increased GI tract secretion and mobility Autonomic versus Somatic NS - Review • Somatic nervous system – consciously perceived sensations – excitation of skeletal muscle – one neuron connects CNS to organ • Autonomic nervous system – unconsciously perceived visceral sensations – involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion – two neurons needed to connect CNS to organ • preganglionic and postganglionic neurons Autonomic Dysreflexia • Exaggerated response of sympathetic NS in cases of spinal cord injury above T6 • Certain sensory impulses trigger mass stimulation of sympathetic nerves below the injury • Result – vasoconstriction which elevates blood pressure – parasympathetic NS tries to compensate by slowing heart rate & dilating blood vessels above the injury – pounding headaches, sweating warm skin above the injury and cool dry skin below – can cause seizures, strokes & heart attacks