USMLE Step 1 Physiology Review 54 10 Autonomic Nervous System (5 of 5)

USMLE Step 1 Physiology Review 54 10 Autonomic Nervous System (5 of 5)

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Begin 54 10 Autonomic Nervous System (5 of 5) Transcription

Okay, now for some questions about neurotransmission and receptors in the ANS.

What neurotransmitter is secreted by all ANS neurons leaving the central nervous system?

  • Acetylcholine.

The acetylcholine that is released by preganglionic neurons excites what kinds or receptors?  What is the term used to describe the receptors?

  • Nicotinic.

What other kinds of neurons release acetylcholine that in turn excites nicotinic receptors?

  • Somatic motor neurons.

Nicotinic receptors on skeletal muscle are different than ganglionic nicotinic receptors. Evidence of this is the differing effects that drugs, like curare, have on nicotinic receptors of the neuromuscular junction compared to curare’s effect on ganglionic nicotinic receptors.

What is the difference?

  •  Curare blocks nicotinic receptors at the neuromuscular junction but does not block ganglionic nicotinic receptors.

Post ganglionic parasympathetic neurons release what kind of neurotransmitter?

  • Acetylcholine.

What is the term for the acetylcholine receptors on the end organ that are innervated by postganglionic parasympathetic neurons?

  • Muscarinic receptors.

What kind of neurotransmitter is released by postganglionic sympathetic neurons?

  • Noradrenaline.

What is the term for neurons that release noradrenaline?

  • Adrenergic neurons.

Student Doctor, please pause the tape and summarize the information discussed neurotransmission and receptors in the ANS.

  •  The neurotransmitter, acetylcholine is secreted by all ANS neurons leaving the central nervous system.  Nicotinic receptors are excited by acetylcholine.  Somatic motor neurons also release acetylcholine, which in turn excites nicotinic receptors. Nicotinic receptors on skeletal muscle are different than ganglionic nicotinic receptors. Evidence of this is the differing effects of drugs, like curare, have on nicotinic receptors of the neuromuscular junction compared to curare’s effect on ganglionic nicotinic receptors.  Curare blocks nicotinic receptors at the neuromuscular junction but curare does not block nicotinic ganglionic receptors. Post ganglionic parasympathetic neurons release acetylcholine.  The acetylcholine receptors on the end organ that are innervated by postganglionic parasympathetic neurons are called muscarinic receptors. Noradrenaline is released by postganglionic sympathetic neurons. The term for neurons that release noradrenaline is adrenergic neurons.

Now let’s get back to some more questions about neurotransmission and receptors in the ANS.

What are the two types of receptors on effecter organs affected by noradrenaline?

  • Alpha receptors and beta receptors.

Alpha receptors are further sub classified into alpha one and alpha two subtypes. Where are alpha one receptors located?

  • Alpha one receptors are located on target organs and tissues.

What are alpha one receptors primarily responsible for?

  • Alpha one receptors mediate the release of norepinephrine.

Alpha two receptors are located postsynaptically as well as on presynaptic sympathetic nerve terminals.

What effect is produced by the activation of presynaptic alpha two receptors?

  • Activation of presynaptic alpha two receptors produces a feedback inhibition of norepinephrine release. 

Beta adrenergic receptors are sub classified as beta one and beta two receptors. What neurotransmitter do beta adrenergic receptors respond to?

  • Noradrenaline.

Student Doctor, please pause the tape and summarize the information on the alpha receptors that are on the effecter organs that are excited by noradrenaline.

  • The two types of receptors on effecter organs that are excited by noradrenaline are alpha receptors and beta receptors.  Alpha receptors are further sub classified into alpha one and alpha two.  Alpha one receptors are located on target organs and tissues.  Alpha one receptors mediate the release of norepinephrine.  Alpha two receptors are located postsynaptically, as well as on presynaptic sympathetic nerve terminals.  Activation of presynaptic alpha two receptors produces a feedback inhibition of norepinephrine release. 

In what organ do beta one receptors  predominate?

  • The heart.

When beta one receptors are activated, what kind of effect is produced on the heart?

  • Excitatory, such as increased heart rate, conduction velocity and contractility.

In what organ do beta two receptors predominate?

  • The lungs.  Remember one heart, two lungs. Beta one heart, beta two lungs.

What two kinds or effects or actions do beta two receptors mediate?

  • Inhibitory effects of beta receptors and dilator actions.

On what two types of smooth muscle are beta two receptors mediate dilator actions?

  • Vascular and bronchial smooth muscle

What is the adrenal medulla analogous to in the sympathetic nervous system?

  • The adrenal medulla is analogous to postganglionic sympathetic neurons.

What two neurotransmitters does the adrenal medulla secrete into the bloodstream?

  • Norepinephrine and epinephrine, also known as adrenaline.

Student Doctor, please pause the tape and summarize the information on beta adrenergic receptors in the ANS.

  • Beta adrenergic receptors are sub classified as beta one and beta two receptors. Beta adrenergic receptors respond to noradrenaline.  Beta one receptors are predominately located in the heart.  When beta one receptors are activated the effect on the heart is excitatory, such as increased heart rate, conduction velocity and/or contractility.  Beta two receptors are predominately located in the lungs. Remember, one heart, two lungs. Beta two receptors mediate inhibitory effects of beta receptors and dilator actions. Beta two receptors mediate dilator action on vascular and bronchial smooth muscle. The adrenal medulla is analogous to postganglionic sympathetic neurons. The adrenal medulla secretes norepinephrine and epinephrine, also known as adrenaline into the bloodstream.

This completes this section on electrophysiology.

****END OF TRANSCRIPTION****

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