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Lecture 13

Week/Lecture 13: Autonomic Nervous System.pdf

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BIOL 171

Autonomic Nervous System controls smooth muscle, cardiac muscle, muscles of respiration (also voluntary control), glands maintains homeostasis Somatic Nervous System: voluntary excitation of skeletal muscle peripheral pathways consist of one neuron somatic motor neuron (cell body in CNS) efferent fibre (myelinated; extends to effector) Autonomic Nervous System: involuntary excitation/inhibition of smooth muscle, cardiac muscle, glands peripheral pathways consist of two neurons preganglionic neuron (cell body in CNS) preganglionic fibre (myelinated; extends to ganglion) postganglionic neuron (cell body in ganglion) postganglionic fibre (unmyelinated; extends to effector) 2 Divisions of ANS parasympathetic (P) predominates under resting, relaxed conditions sympathetic (S) activated by stress ("fight or flight" response) on any given structure, the 2 divisions have opposite effects Sympathetic preganglionic fibres emerge from SC between levels T1 to L2 sympathetic ganglia (group of cell bodies outside CNS) near CNS paravertebral chain on either side of spinal column "para" = close or nearby prevertebral ganglia near large blood vessels in gut preganglionic cell bodies in lateral horn of SC T1 to L2 fibres emerge in spinal NN postganglionic cell bodies in sympathetic chain & pre vertebral ganglia splanchnic nerves formed by preganglionic fibres that pass through ganglia without synapsing synapse in prevertebral ganglia Parasympathetic preganglionic fibres emerge from brainstem and sacral level of SC (S2-S4) long fibre parasympathetic ganglia near or in effectors terminal ganglia in wall of organ preganglionic cell bodies in 4 CN nuclei in brainstem S2-S4 SC postganglionic cell bodies in terminal ganglia near or in the wall of target organ pelvic splanchnic nerves formed by sacral parasympathetic nerve fibres innervate smooth muscle, glands in colon, ureters, bladder, reproductive organs preganglionic cell body—>preganglionic fibre—>ganglion—>postganglionic cell body—>effector Autonomic Plexuses tangle of sympathetic and parasympathetic fibres in thorax, abdomen, pelvis many lie along major may contain sympathetic ganglia, sensory axons Fibres and Receptors neurons are classified chemically by the neurotransmitter they produce receptors are classified on basis of the neurotransmitter they bind cholinergic neurons release ACh, cholinergic receptors bind ACh adrenergic neurons release norepinephrine (NE), adrenergic receptors bind NE (*released from adrenal glands; hormone; co
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