The Autonomic Nervous System

Transcription

1 The Autonomic Nervous System The Autonomic Nervous System and Visceral Sensory Neurons The Autonomic Nervous System Innervates smooth muscle, cardiac muscle, and glands Regulates visceral functions Heart rate, blood pressure, digestion, urination The general visceral motor division of the PNS 1

2 The Autonomic Nervous System and Visceral Sensory Neurons Figure 15.1 Comparison of Autonomic and Somatic Motor Systems Somatic motor system One motor neuron extends from the CNS to skeletal muscle Axons are well myelinated, conduct impulses rapidly 2

3 Comparison of Autonomic and Somatic Motor Systems Autonomic nervous system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons Pre-ganglionic Post-ganglionic Ganglion Copyright 2005 Pearson Education, Inc., publishing as Benjamin Cummings Autonomic and Somatic Motor Systems Figure

4 Divisions of the Autonomic Nervous System Sympathetic and parasympathetic divisions Innervate mostly the same structures Cause opposite effects Divisions of the Autonomic Nervous System Sympathetic fight, flight, or fright Activated during exercise, excitement, and emergencies Parasympathetic rest and digest Concerned with conserving energy 4

5 Anatomical Differences in Sympathetic and Parasympathetic Divisions Issue from different regions of the CNS Sympathetic also called the thoracolumbar division Parasympathetic also called the craniosacral division Figure 15.3 Anatomical Differences in Sympathetic and Parasympathetic Divisions Length of postganglionic fibers Sympathetic long postganglionic fibers Parasympathetic short postganglionic fibers Branching of axons Sympathetic axons highly branched Influences many organs Parasympathetic axons few branches Localized effect 5

6 Neurotransmitters of Autonomic Nervous System Neurotransmitter released by preganglionic axons Acetylcholine for both branches (cholinergic) Neurotransmitter released by postganglionic axons Sympathetic most release norepinephrine (adrenergic) Parasympathetic release acetylcholine Anatomical Differences in Sympathetic and Parasympathetic Divisions Figure 15.4a 6

7 Anatomical Differences in Sympathetic and Parasympathetic Divisions Figure 15.4b The Parasympathetic Division Cranial outflow Comes from the brain Innervates organs of the head, neck, thorax, and abdomen Sacral outflow Supplies remaining abdominal and pelvic organs 7

8 The Parasympathetic Division Figure 15.5 Cranial Outflow Preganglionic fibers run via: Oculomotor nerve (III) Facial nerve (VII) Glossopharyngeal nerve (IX) Vagus nerve (X) Cell bodies located in cranial nerve nuclei in the brain stem 8

9 Outflow via the Vagus Nerve (X) Fibers innervate visceral organs of the thorax and most of the abdomen Stimulates - digestion, reduction in heart rate and blood pressure Preganglionic cell bodies Located in dorsal motor nucleus in the medulla Ganglionic neurons Confined within the walls of organs being innervated Parasympathetic Nervous System: Sacral Outflow Emerges from S 2 -S 4 Innervates organs of the pelvis and lower abdomen Preganglionic cell bodies Located in visceral motor region of spinal gray matter Form splanchnic nerves 9

10 The Sympathetic Division Basic organization Issues from T 1 -L 2 Preganglionic fibers form the lateral gray horn Supplies visceral organs and structures of superficial body regions Contains more ganglia than the parasympathetic division Sympathetic Trunk Ganglia Located on both sides of the vertebral column Linked by short nerves into sympathetic trunks Joined to ventral rami by white and gray rami communicantes Fusion of ganglia fewer ganglia than spinal nerves 10

11 Sympathetic Trunk Ganglia Figure 15.8 Prevertebral Ganglia Unpaired, not segmentally arranged Occur only in abdomen and pelvis Lie anterior to the vertebral column Main ganglia Celiac, superior mesenteric, inferior mesenteric, inferior hypogastric ganglia 11

12 Sympathetic Division of the ANS Figure 15.7 Cholinergic vs. Adrenergic Fibres Cholinergic fibres use acetylcholine (ACh) Adrenergic fibres use norepinephrine (NE) The effect of ACh or NE excitatory or inhibitory will depend on the receptors. 12

13 CHOLINERGIC RECEPTORS Nicotinic receptors Muscarinic receptors Nicotinic receptors Found in somatic system on motor end plates Found in ANS on all postganglionic neurons and the hormone-producing cells of adrenal medulla. ACh binding to a nicotinic receptor is excitatory. 13

14 Muscarinic receptors Found in effectors stimulated by cholinergic fibres. The effect is inhibitory or excitatory based on the target ADRENERGIC RECEPTORS Found on organs stimulated by sympathetic fibers (using NE). They are of two types : Alpha : excitatory Beta : inhibitory, except in cardiac muscle where it is excitatory Both types are found in many organs 14

15 The Role of the Adrenal Medulla in the Sympathetic Division Major organ of the sympathetic nervous system Secretes great quantities epinephrine (a little norepinephrine) Stimulated to secrete by preganglionic sympathetic fibers Visceral Sensory Neurons General visceral sensory neurons monitor: Stretch, temperature, chemical changes, and irritation Cell bodies are located in the dorsal root ganglia Visceral pain perceived to be somatic in origin Referred pain 15

16 12/31/2013 Visceral Reflexes Visceral sensory and autonomic neurons Participate in visceral reflex arcs Defecation reflex Micturition reflex 16

17 Visceral Reflex Arc Figure Central Control of the ANS Control by the brain stem and spinal cord Reticular formation exerts most direct influence Medulla oblongata Periaqueductal gray matter Control by the hypothalamus and amygdala Hypothalamus the main integration center of the ANS Amygdala main limbic region for emotions Control by the cerebral cortex 17

18 Vasomotor Tone: Blood Pressure Blood pressure is controlled almost exclusively by sympathetic system. Vasomotor tone continual state of partial constriction in blood vessels. When blood needs to be delivered faster, impulses are sent more quickly and vessels constrict. Parasympathetic Tone Parasympathetic tone is exhibited by organs that are controlled primarily by the parasympathetic system the heart, the digestive tract, and the urinary tract Also referred to as vagal tone 18

19 Unique Roles of the Sympathetic System Sweat glands Blood vessels Adrenal medulla Response to heat Metabolic effects Increased metabolism of body cells Increased blood glucose Readying of fat to be used as fuel Increased mental awareness Disorders of the Autonomic Nervous System Raynaud s disease characterized by constriction of blood vessels Provoked by exposure to cold or by emotional stress 19

20 Disorders of the Autonomic Nervous System: Hypertension Hypertension high blood pressure Can result from overactive sympathetic vasoconstriction Disorders of the Autonomic Nervous System: Mass Reflex Reaction Mass reflex reaction Uncontrolled activation of autonomic and somatic motor neurons Affects quadriplegics and paraplegics 20

21 Disorders of the Autonomic Nervous System: Achalasia of the Cardia Achalasia of the cardia Defect in the autonomic innervation of the esophagus 21