autonomic nervous system & visceral reflexes chapter 15 autonomic nervous system & visceral...
TRANSCRIPT
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Chapter 15Autonomic Nervous System & Autonomic Nervous System &
Visceral ReflexesVisceral Reflexes
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Subdivisions of Nervous System
p. 444
ANS
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General Properties of the ANSGeneral Properties of the ANS
• Motor nervous system that controls glands, cardiac and smooth muscle
– also called visceral motor systemvisceral motor system• Regulates unconscious, primitive processes that
maintain homeostasis– blood pressure, body temperature, respiratory airflow
• ANS carries out its actions without our intent or awareness (automatically)
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Visceral ReflexesVisceral Reflexes
• Unconscious, automatic responses to stimulation of glands, cardiac or smooth muscle
• Receptors detect internal stimuli -- stretch, blood chemicals, body temperature, etc.
• Afferent neurons connect to interneurons in the CNS• Efferent neurons carry motor signals to the effectors
– ANS is the efferent neurons of these reflex arcsANS is the efferent neurons of these reflex arcs
– glands, smooth or cardiac muscle is the effectors
• ANS modifies effector activity rather than causing it– Heart will still beat if autonomic n. supply is cut off, however it
will be unmodulated
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Visceral Reflex to High Blood PressureVisceral Reflex to High Blood Pressure
• High BP detected by arterial baroreceptors, signal transmitted to CNS, efferent signals travel to the heart, heart slows reducing BP
• Separate reflex arc for low BP exists
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Divisions of the ANSDivisions of the ANS• Two divisions that innervate the same target organs• Two divisions may have cooperative or contrasting
effects
• SympatheticSympathetic division prepares body for physical activity (‘fight or flight’ response)– increases heart rate, BP, airflow, blood glucose levels, etc
• ParasympatheticParasympathetic division has calming affect on many body functions & assists in bodily maintenance– digestion and waste elimination– (‘resting and digesting’)
• Autonomic toneAutonomic tone is the normal rate of background activity that represents the balance of the two systems
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Somatic versus Autonomic Pathways
ANS = 2 neurons span the distance from CNS to effectors• presynaptic neuron cell body in CNS -- brain or spinal cord
• postsynaptic neuron cell body in peripheral ganglion
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• Origin of presynaptic neurons– lateral hornslateral horns of gray matter of thoracic to lumbar cord
(T1-L2)
• Sympathetic chain ganglia (paravertebral)– 3 cervical, 11 thoracic, 4 lumbar, 4 sacral & 1
coccygeal ganglia– communicating rami suspend ganglia from spinal
nerve– variety of pathways of preganglionic fibers
• enter ganglia & synapse, OR• travel to higher or lower ganglia & synapse, OR• pass through chain without synapsing to reach collateral
ganglia via splanchnic nervessplanchnic nerves
Sympathetic (thoracolumbar) NSSympathetic (thoracolumbar) NS
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Pathways of Preganglionic Sympathetic Fibers
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• Neuronal divergence predominates – each preganglionic cell branches and synapses on
multiple postganglionic cells– produces widespread effects on multiple organs
Sympathetic Nervous System
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Efferent Pathways of Sympathetic NS
Sympathetic splanchnic nerves synapse at celiac, superior mesenteric and inferior mesenteric ganglia. Postganglionic fibers then travel to target organs in abdominal cavity.
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Summary of Sympathetic InnervationSummary of Sympathetic Innervation
• Effectors in the body wall are innervated by sympathetic fibers found in spinal nerves
• Effectors in head and thoracic cavity are innervated by fibers in sympathetic nerves
• Effectors in abdominal cavity are innervated by sympathetic fibers in splanchnic nerves.
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Adrenal GlandsAdrenal Glands
• Paired glands sit on superior pole of each kidney• Cortex
– secretes steroid hormones (Ch. 17)
• MedullaMedulla– modified sympathetic ganglion that secretes
neurotransmitters (hormones) into blood and not onto other neurons
• Sympathoadrenal system is the closely related functioning adrenal medulla and symphathetic NS
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Parasympathetic (craniosacral) NSParasympathetic (craniosacral) NS• Origin of preganglionic fibers
– pons and medulla oblongata for cranial nerve nuclei
– spinal cord segments S2-S4
• Pathways of preganglionic fibers– CN III – control lens and pupil
– CN VII – control tear, salivary and nasal glands
– CN IX - salivation
– CN X – 90% of all preganglionic parasympathetic fibers• cardiac, pulmonary, esophageal, abdominal aortic plexus
– Spinal Nerves S2-S4 (sacral)• pelvic splanchnic nerves to inferior hypogastric plexus
• To distal colon, rectum, urinary bladder, reproductive organs
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Parasympathetic (craniosacral) NSParasympathetic (craniosacral) NS• Terminal ganglia in target organs due to long preganglionic and short
postganglionic fibers
CN Plexus/Terminal Ganglia Effector
CN III Ciliary Lens, pupil
CN VII Pterygopalatine Lacrimal, nasal glands
Submandibular Submandibular (salivary) gland
CN IX Otic ganglion Parotid (salivary) gland
CN X Cardiac plexus heart
Pulmonary plexus lungs
Esophageal plexus swallowing
Abdominal aortic plexus Stomach, liver, pancreas, small intestines, kidneys, ureters, proximal colon
S2-S4 Inferior hypogastric plexus Distal colon, rectum, bladder, repro organs
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Efferent Pathways of Parasympathetic NSEfferent Pathways of Parasympathetic NS
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Enteric Nervous SystemEnteric Nervous System
• Nervous system of the digestive tract
• Composed of 100 million neurons found in the walls of the digestive tract (no components found in CNS)
• Has its own reflex arcs
• Regulates motility of viscera and secretion of digestive enzymes and acid in concert with the ANS
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Neurotransmitters & ReceptorsNeurotransmitters & Receptors
• Types of neurotransmitters released and types of receptors on target cells determines effects of ANS
• Sympathetic NS has longer lasting effects – reaches bloodstream before being broken down
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Cholinergic Receptors for ACh
• Acetylcholine binds to 2 classes of receptors– nicotinic receptors
• occur on allall ANS postganglionic neurons, in the adrenal medulla, and at neuromuscular junctions (skeletal muscle)
• excitatory when ACh binding occurs
– muscarinic receptors• occur on all gland, smooth muscle & cardiac muscle cells
that receives cholinergic innervation
• either excitatory or inhibitory when ACh binding occurs due to subclasses of muscarinic receptors
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Adrenergic Receptors for NE• NE released by nearly all sympathetic postganglionic
neurons
• Norepinephrine binds to 2 classes of receptors – alpha adrenergic receptors
• NE binding is usually excitatory
– beta adrenergic receptors• NE binding is usually inhibitory
• Exceptions to normal results (EPSP or IPSP)– existence of subclasses of each receptor type
• alpha 1 and 2; beta 1 and 2
• Function by means of 2nd messengers– beta receptors activate cyclic AMP, alphas2 receptors
suppress it and alpha1 receptors use calcium
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Dual Innervation• Most of viscera receive nerve fibers from both
parasympathetic & sympathetic divisions– antagonistic effects oppose each other
• exerted through dual innervation of same effector cells– heart slowed down or speeded up
• exerted because each division innervates different cells– pupillary dilator muscle & constrictor pupillae change pupil size
– cooperative effects seen when 2 divisions act on different effectors to produce a unified effect(salivation)
• parasympathetic NS increases salivary serous cell secretion• sympathetic NS increases salivary mucous cell secretion
• Both divisions do not normally innervate an organ equally
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Dual Innervation of the Iris
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