Module 10: Autonomic Nervous System
Learning Objectives:
By the end of this class, students will be able to:
- Compare and contrast the somatic and autonomic nervous systems.
- Compare and contrast the parasympathetic and sympathetic divisions.
- Explain dual innervation by the parasympathetic and sympathetic divisions.
- Describe an autonomic plexus, including the fibers carried within a plexus.
- Describe the anatomy of the parasympathetic divisions.
- Describe the sympathetic chain and the rami connecting it to the spinal nerve.
- Describe the anatomy of the four pathways of the sympathetic division.
- Describe the effects of the parasympathetic and sympathetic divisions on organs and organ systems throughout the body.
- Explain referred pain.
Terms to Know
General
Autonomic Plexuses
Parasympathetic Division
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Sympathetic Division
*Covered only in lecture, not in this text |
Somatic Vs. Autonomic Nervous System
*This content will be covered in the assignment, primarily as self-study. Portions will be briefly reviewed in lecture.
The nervous system can be divided into two functional parts: the somatic nervous system and the autonomic nervous system. The somatic nervous system causes voluntary contraction of skeletal muscles (though contraction can happen without conscious awareness, like breathing). This is the branch of the nervous system we were describing with the corticospinal tract and lower motor neurons in Unit 1. The autonomic nervous system controls involuntary contraction of cardiac and smooth muscle, as well as glandular tissue. You may remember from Unit 1 that lower motor neurons can only excite their effector. That means that, if the lower motor neuron is stimulated, it will cause the muscle to contract. In the autonomic nervous system, stimulation can either excite or inhibit the effector. That means it can cause muscle contraction or secretion from a gland, or it can prevent those actions from occurring.
There are a few key differences in the neurons and neuronal pathways between the somatic and autonomic nervous systems. The somatic nervous system has just one lower motor neuron traveling from the spinal cord to the effector muscle. Since there is only one neuron, there is no synapse between neurons, and thus, no ganglia. That lower motor neuron originates in the ventral (anterior) horn of the spinal cord. In the autonomic nervous system there are two neurons in the pathway from the spinal cord to the effector organ. The synapse between the two neurons occurs at a ganglion, or a collection of cell bodies. The neurons that originate in the spinal cord begin in the lateral horn. In the somatic nervous system, the lower motor neuron axons are highly myelinated, allowing for a very rapid signal transmission from the spinal cord to the effector. In the autonomic nervous system, the axons are either lightly myelinated (meaning a thin layer of myelin) or unmyelinated, resulting in a slower conduction speed.
Divisions of the Autonomic