USMLE Step 1 Physiology Review 54 08 Autonomic Nervous System (3 of 5)

USMLE Step 1 Physiology Review 54 08 Autonomic Nervous System (3 of 5)

 

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Play USMLE Audio MP3 54 08 Autonomic Nervous System (3 of 5) Below

Begin 54 08 Autonomic Nervous System (3 of 5) Transcription

Okay, now for some more questions about the ANS.

What is another term for the sympathetic nervous system?

  • Thoraco-lumbar division of the ANS.

What does the term thoraco-lumbar tell you about the location of sympathetic preganglionic neuronal cell bodies?

  • Thoraco-lumbar tells you that the neuronal cell bodies are in spinal cords segments T1 to L3.

Be more specific with regard to the location of the neuronal cell bodies. Please pause the tape.

  • They are in the intermediolateral cell column in spinal cord segments T1 to L3.

Sympathetic or thoraco-lumbar preganglionic neurons have fairly short axons. In what two places do they synapse with other neurons?

  • Sympathetic preganglionic neurons synapse with neurons located in paravertebral ganglia more distal prevertebral ganglia.

What gland is innervated by sympathetic preganglionic neurons?

  • The adrenal medulla.

Student Doctor, please pause the tape and summarize the information on the peripheral control of the autonomic nervous system covered since the last summary.  The first question asked for another term for the sympathetic nervous system.

  • The other term for the sympathetic nervous system is the thoraco-lumbar division of the ANS.  The term thoraco-lumbar tells you that the neuronal cell bodies are in the intermediolateral cell column in spinal cord segments T1 to L3. Sympathetic or thoraco-lumbar preganglionic neurons have fairly short axons. Sympathetic preganglionic neurons synapse with neurons located in paravertebral ganglia or the more distal prevertebral ganglia.  The adrenal medulla is innervated by sympathetic preganglionic neurons.

Is the postganglionic axon in the sympathetic nervous system longer than or shorter than the preganglionic axon?

  • Longer than

So, remember sympathetic pre-short, post-long and parasympathetic is pre-long, post-short. A short hand is sym-pre-short, para-pre-long.

In the sympathetic nervous system what do the relatively long postganglionic axons directly innervate?

  • The end organs.

What is the exception for direct sympathetic innervation? In other words, what organ is innervated by the sympathetic nervous system, but not directly by the postganglionic axon?

  •  The GI Tract.

Since the innervation is not direct how do the postganglionic neurons innervate the GI Track; through what intermediate structure, rather?

  • The postganglionic neurons innervate enteric nerve plexuses.

From recent evidence does it appear that sympathetic outflow is generalized or that the sympathetic nervous system can produce discrete reactions to appropriate stimuli?

  • Evidence shows that the sympathetic nervous system can produce discrete reactions to appropriate stimuli.

Student Doctor, please pause the tape and summarize the information on the peripheral control of the ANS covered since the last summary. The first question asked about the length of the postganglionic axon in the sympathetic nervous system.

  • The postganglionic axon in the sympathetic nervous system is longer than preganglionic axon. So, remember sympathetic is pre-short and post-long and parasympathetic is pre-long and post-short. A short hand is sym-pre-short and para-pre-long.  In the sympathetic nervous system the relatively long postganglionic axons directly innervate the end organs. The exception for direct sympathetic innervation is the GI Tract. The postganglionic neurons first innervate enteric nerve plexuses in the GI Tract.  Evidence shows that the sympathetic nervous system can produce discrete reactions to appropriate stimuli.

****END OF TRANSCRIPTION****

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