section 6, chapter 11

Autonomic Nervous System

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Autonomic Nervous System

• Functions without conscious effort• Controls visceral activities• Regulates smooth muscle, cardiac muscle, and glands• Efferent fibers typically lead to ganglia outside of the CNS

• Two autonomic divisions regulate:• Sympathetic division (speeds up)

• Prepares body for ‘fight or flight’ situations

• Parasympathetic division (slows down)• Prepares body for ‘resting and digesting’ activities

Autonomic Nervous System

• The cell bodies of neurons that control effectors in the ANS reside in ganglia outside the central nervous system.

Therefore, Autonomic pathways require and additional motor neuron to reach the effector.

Figure 11.35 Motor pathways. (a) Autonomic pathways include 2 neurons between the CNS and an effector. (b) Somatic pathways usually have a single neuron between the CNS and an effector.

Autonomic Pathway

1. Receptor2. Sensory Neuron3. Interneuron4. Preganglionic Fiber5. Postganglionic fiber6. Effector

Sympathetic Division

Arise from thoracolumbar division of the spinal cord• Location of preganglionic neurons• Originate in lateral horns

• Preganglionic fibers leave spinal nerves through white rami (myelinated fibers) and enter sympathetic chain ganglia (paravertebral ganglia)

• Postganglionic fibers extend from sympathetic ganglia to visceral organs

Figure 11.37 Sympathetic fibers leave the spinal cord as preganglionic fibers, through the ventral roots of spinal nerves, enter sympathetic chain ganglia, and synapse with a postganglionic neuron that extends to visceral effectors.

Figure 11.37 Sympathetic fibers leave the spinal cord as preganglionic fibers, through the ventral roots of spinal nerves, enter sympathetic chain ganglia, and synapse with a postganglionic neuron that extends to visceral effectors.

• Ganglia are near or within various organs = Terminal ganglia

Parasympathetic Division

• Preganglionic fibers arise from the brain and sacral regions of the spinal cord.

• Short postganglionic fibers continue to specific muscles or glands

Figure 11.39. The preganglionic fibers of the parasympathetic division of the ANS arise from the brain and sacral regions of the spinal cord. Ganglia are located near the organs they serve.

Figure 11.39. The preganglionic fibers of the parasympathetic division of the ANS arise from the brain and sacral regions of the spinal cord. Ganglia are located near the organs they serve.