Autonomic Nervous System (ANS)

1. What is the autonomic nervous system (ANS)?

A part of the peripheral nervous system (PNS) that controls involuntary body functions.

2. What does the ANS control?

Cardiac muscle, smooth muscle, glands, and adipose (fat) tissue.

3. What is the difference between the ANS and somatic nervous system?

→ ANS = involuntary; somatic = voluntary skeletal muscle control.

4. What are the two divisions of the ANS?

→ Sympathetic and parasympathetic.

5. What does the sympathetic division do?

→ Fight or flight: increases heart rate and breathing and slows digestion.

6. What does the parasympathetic division do?

→ Rest and digest: slows heart rate and breathing and increases digestion.

7. What does “dual innervation” mean?

→ An organ receives signals from both sympathetic and parasympathetic divisions.

8. Why do organs have dual innervation?

→ To fine-tune and control their activity.

9. What is autonomic tone?

→ A constant baseline level of stimulation from the ANS.

10. What is sympathetic tone?

→ A constant level of sympathetic activity, especially important for controlling blood vessel diameter.

11. What does sympathetic tone do to blood vessels?

→ It can change their diameter by causing vasoconstriction or allowing vasodilation.

12. What is parasympathetic tone in the heart?

→ Constant parasympathetic activity that slows the heart's natural rate.

13. Where does the parasympathetic division come from?

→ The brain (cranial nerves) and sacral spinal cord.

14. What is another name for the parasympathetic division based on its origin?

→ Craniosacral division.

15. Where does the sympathetic division come from?

→ The thoracic and lumbar spinal cord.

16. What is another name for the sympathetic division based on its origin?

→ Thoracolumbar division.

17. Where can sympathetic neurons synapse?

→ In sympathetic chain ganglia or prevertebral ganglia.

18. Where are sympathetic chain ganglia located?

→ Alongside the vertebral column.

19. What is special about the adrenal medulla?

→ It acts like a modified sympathetic pathway that releases hormones into the blood.

20. What stimulates the adrenal medulla?

→ Preganglionic sympathetic neurons.

21. What does the adrenal medulla release?

→ About 80% epinephrine and 20% norepinephrine.

22. Why does the adrenal medulla release these hormones into the blood?

→ To spread and strengthen sympathetic effects throughout the body.

23. How many neurons are in a somatic motor pathway?

→ One neuron from the CNS directly to skeletal muscle.

24. How many neurons are in an autonomic motor pathway?

→ Two neurons: a preganglionic neuron and a postganglionic neuron.

25. What does the preganglionic neuron do?

→ Carries the signal from the CNS to a ganglion.

26. What does the postganglionic neuron do?

→ Carries the signal from the ganglion to the target organ.

27. What neurotransmitter do all preganglionic ANS neurons release?

→ Acetylcholine (ACh).

28. What neurotransmitter does a somatic motor neuron release?

→ Acetylcholine (ACh).

29. What does a parasympathetic postganglionic neuron release?

→ Acetylcholine (ACh)

30. What does a sympathetic postganglionic neuron usually release?

→ Norepinephrine (NE).

31. What does the adrenal medulla release?

→ Epinephrine and norepinephrine.

32. What are cholinergic receptors?

→ Receptors that bind acetylcholine (ACh).

33. Where are nicotinic receptors found?

→ On skeletal muscle, postganglionic neurons, and adrenal medulla cells.

34. Where are muscarinic receptors found?

→ On cardiac muscle, smooth muscle, and glands.

35. What are adrenergic receptors and what are their main types?

→ Receptors that bind norepinephrine and epinephrine. The main types are alpha-1, alpha-2, beta-1, beta-2, and beta-3:

• Alpha-1 → vasoconstriction

• Alpha-2 → slows digestion

• Beta-1 → increases heart rate and force

• Beta-2 → vasodilation

• Beta-3 → fat breakdown