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Anatomy and Physiology I Chapter 15 The Autonomic Nervous System and Visceral Reflexes.

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Presentation on theme: "Anatomy and Physiology I Chapter 15 The Autonomic Nervous System and Visceral Reflexes."— Presentation transcript:

1 Anatomy and Physiology I Chapter 15 The Autonomic Nervous System and Visceral Reflexes

2 Autonomic Nervous System (ANS) Motor nervous system that controls glands, cardiac muscle, and smooth muscle (visceral motor) – Viscera of thoracic and abdominopelvic cavities – Blood vessels – Sweat glands – Piloerector muscles Involuntary Homeostasis

3 Visceral Reflexes Unconscious, automatic, stereotyped responses to stimuli Slower responses- visceral receptors and effectors Visceral reflex arc – Receptors – Afferent neurons- to CNS – Interneurons – Efferent neurons- away from CNS – Effectors

4 ANS divisions 2 subdivisions – Sympathetic – Parasympathetic Often innervate same organ Cooperative or contrasting effects Autonomic tone- balance b/t divisions – Both systems are active simultaneously – Shifts in accordance to body’s changing needs

5 Sympathetic Adapts body for physical activity Fight or flight Subtle effects

6 Parasympathetic Calming effect on functions Reduced energy expenditure and normal bodily maintenance

7 Neural Pathways Signal passes across 2 neurons to get to target organ Cross synapse – Autonomic ganglion Preganglionic neuron – Soma in CNS – Axon terminates in ganglion Postganglionic neuron – Axon extends to target cells

8 The Sympathetic Division Thoracic and lumbar regions Short preganglionic fibers – Myelinated – Spinal nerve to ganglion Long postganglionic fibers – Unmyelinated – Ganglion to target organ

9 The Parasympathetic Division Brain and sacral regions Long preganglionic fibers – Brain to ganglion – Almost to target cells Short postganglionic fibers – Ganglion to target cell

10 Neurotransmitters and Receptors ANS division has contrasting effects Sympathetic and Parasympathetic fibers secrete different neurotransmitters Target cells respond in different ways – Depends of type of receptor

11 Neurotransmitters All autonomic nerve fibers either secrete ACh or norepinepherine – ACh- secreted by preganglionic neurons of both divisions and postganglionic neurons of the parasympathetic division – NE- secreted by all sympathetic postganglionic neurons Sympathetic effects lasts longer – Ach secreted by parasympathic- quickly broke down by AChE

12 Dual Innervation Viscera receive nerve fibers from both sympathetic and parasympathetic divisions – Antagonist or cooperative effects Antagonist effects- oppose each other Cooperative effects- 2 divisions act on different effectors to produce unified overall effect

13 Control w/out Dual Innervation Dual innervation is not always necessary to produce opposite effects on an organ – Regulation of BP and blood flow – Sympathetic fibers keep vessels in partial constriction- vasomotor tone Increase firing rate- constricts vessel – Smooth muscle contracts Decrease firing rate- dilates vessel – Smooth muscle relaxes Sympathetic division can shift blood flow from organ to organ according to body’s needs

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