week 11

Question 1

1. What are the main functions of the autonomic nervous system?

Answer 1

The autonomic nervous system (ANS) regulates involuntary bodily functions by acting on smooth muscle, cardiac muscle, glands, and adipose tissue. It maintains homeostasis and can augment function in response to internal or external changes, such as stress or changes in the environment.

Question 2

2. How does the ANS differ functionally from the somatic nervous system?

Answer 2

The ANS controls involuntary activities (e.g., heart rate, digestion) and uses a two-neuron pathway (preganglionic and postganglionic), while the somatic nervous system governs voluntary movement and uses a single neuron that directly innervates skeletal muscle. The ANS can have excitatory or inhibitory effects depending on the neurotransmitter and receptor, whereas the somatic system is always excitatory at the neuromuscular junction.

Question 3

3. Which tissue types are targeted by the ANS?

Answer 3

The ANS targets:

Smooth muscle

Cardiac muscle

Glands

Adipose tissues
These tissues allow the ANS to regulate a wide array of physiological functions across various organ systems.

Question 4

4. What is meant by “homeostasis” in the context of ANS function?

Answer 4

Homeostasis refers to the ANS’s role in maintaining internal balance within the body, such as temperature regulation, blood pressure, and digestive activity. It adjusts physiological processes to respond to internal or external stimuli, such as hunger or perceived threats.

Question 5

5. Describe the difference between sympathetic and parasympathetic nervous system roles.

Answer 5

Sympathetic nervous system: Dominates during stress (“fight or flight”), increases heart rate, dilates pupils, and redirects blood to muscles.

Parasympathetic nervous system: Dominates at rest (“rest and digest”), slows heart rate, promotes digestion, and supports maintenance functions.
Both systems are continuously active and balance each other depending on situational demands.

Question 6

6. Where do sympathetic and parasympathetic preganglionic neurons originate in the CNS?

Answer 6

Sympathetic preganglionic neurons originate from the thoracic and lumbar regions of the spinal cord.

Parasympathetic preganglionic neurons arise from the brainstem (cranial nerves) and sacral spinal cord.

Question 7

7. Compare the location of ganglia in the sympathetic and parasympathetic nervous systems.

Answer 7

In the sympathetic nervous system, ganglia are located in two chains (sympathetic chains) that run laterally to the spinal cord.

In the parasympathetic nervous system, ganglia are found near or within the target organs.

Question 8

8. What is the significance of the sympathetic chain ganglia’s position relative to the spinal cord?

Answer 8

Their position allows for rapid communication and coordination of responses across multiple organs—important for the fight-or-flight response.

Question 9

9. Describe the concept of dual innervation and its functional relevance.

Answer 9

Dual innervation means that many organs receive input from both sympathetic and parasympathetic branches. This arrangement allows for fine-tuned antagonistic control, such as sympathetic dilation and parasympathetic constriction of pupils.

Question 10

10. What is divergence in the ANS, and what advantage does it provide?

Answer 10

Divergence refers to a single preganglionic neuron synapsing with multiple postganglionic neurons, allowing one CNS signal to affect multiple organs simultaneously. This enhances the amplification and distribution of autonomic signals.

Question 11

11. Which neurotransmitter is released by all preganglionic neurons in the ANS?

Answer 11

Acetylcholine (ACh) is released by all preganglionic neurons, regardless of whether they are part of the sympathetic or parasympathetic divisions.

Question 12

12. What type of receptor do postganglionic neurons have for acetylcholine?

Answer 12

Postganglionic neurons express nicotinic cholinergic receptors, which respond to acetylcholine released from preganglionic neurons.

Question 13

13. Which neurotransmitters are typically used by sympathetic and parasympathetic postganglionic neurons?

Answer 13

Sympathetic postganglionic neurons typically release norepinephrine (NE)

Parasympathetic postganglionic neurons release acetylcholine (ACh)
Some sympathetic neurons are exceptions and release ACh (e.g., those to sweat glands).

Question 14

14. What is the functional difference between nicotinic and muscarinic receptors?

Answer 14

Nicotinic receptors: Found on postganglionic neurons; always excitatory; ligand-gated ion channels.

Muscarinic receptors: Found on effector organs; can be excitatory or inhibitory, depending on the subtype and target tissue; G-protein coupled receptors.

Question 15

15. Define varicosities and explain their role in neurotransmission.

Answer 15

Varicosities are swellings along the distal branches of postganglionic neurons in the ANS. They:

Store high concentrations of neurotransmitters

Release neurotransmitter directly onto a broad area of the effector organ

Allow one postganglionic neuron to influence a large area of tissue simultaneously.

Question 16

16. How is neurotransmitter release from autonomic neurons different from somatic neurons?

Answer 16

In the somatic nervous system, neurotransmitter (ACh) is released at a precise neuromuscular junction. In the autonomic nervous system, neurotransmitters are released from varicosities—swellings along the postganglionic axon—which allow diffuse and broad neurotransmitter release across the effector tissue.

Question 17

17. Describe the flow of events when norepinephrine is released at a neuroeffector junction.

Answer 17

Action potential arrives at the varicosity.

Voltage-gated Ca²⁺ channels open, allowing Ca²⁺ influx.

Exocytosis of synaptic vesicles releases norepinephrine (NE).

NE binds to adrenergic receptors on the effector tissue.

NE action ends by:

Diffusion away

Reuptake into the neuron

Degradation by monoamine oxidase (MAO).

Question 18

18. List three mechanisms by which neurotransmitters are removed from the synaptic cleft.

Answer 18

Diffusion away from the synapse

Active reuptake into the neuron

Enzymatic breakdown, e.g., by MAO for norepinephrine.

Question 19

19. How could inhibiting monoamine oxidase (MAO) affect neurotransmission in the sympathetic nervous system?

Answer 19

MAO breaks down norepinephrine. Inhibiting MAO would prolong the action of norepinephrine at the effector organ, enhancing the sympathetic response. MAO inhibitors are used pharmacologically to boost neurotransmitter levels in disorders like depression or Parkinson’s.

Question 20

20. What determines whether a neurotransmitter’s effect is excitatory or inhibitory in the ANS?

Answer 20

The effect depends on the receptor type on the effector organ, not the neurotransmitter alone. For example:

ACh binding to muscarinic receptors may be excitatory or inhibitory.

NE binding to α or β adrenergic receptors produces different responses depending on subtype and location.

Question 21

21. What are the main receptor types involved in sympathetic nervous system signaling?

Answer 21

The sympathetic system primarily uses adrenergic receptors, including:

Alpha (α₁, α₂)

Beta (β₁, β₂, β₃)
These receptors respond to norepinephrine and epinephrine and mediate diverse effects on target tissues.

Question 22

22. What is the effect of acetylcholine binding to muscarinic receptors in smooth muscle?

Answer 22

When acetylcholine (from parasympathetic fibers) binds to muscarinic receptors on smooth muscle (e.g., bronchioles), it stimulates contraction, resulting in narrowing of the airways.

Question 23

23. Why does the ANS use multiple receptor subtypes for its neurotransmitters?

Answer 23

The ANS uses few neurotransmitters but multiple receptor subtypes to diversify responses. This allows the same neurotransmitter to cause different effects (excitatory or inhibitory) depending on the receptor type and location.

Question 24

24. Provide an example of antagonistic control at an effector organ.

Answer 24

An example is pupil size:

Sympathetic activation causes dilation

Parasympathetic activation causes constriction
This shows how both branches innervate the same tissue but produce opposing effects depending on the physiological need.

Question 25

25. How does receptor subtype diversity increase functional flexibility in the ANS?

Answer 25

Different receptor subtypes allow varied sensitivity and responses to neurotransmitters. This lets the ANS fine-tune physiological effects, enabling more target-specific control—some receptors may promote stronger or weaker actions, or even opposite effects, with the same neurotransmitter.

Question 26

26. Why is the adrenal medulla referred to as a “modified sympathetic ganglion”?

Answer 26

The adrenal medulla is called a modified sympathetic ganglion because it receives preganglionic sympathetic input and releases acetylcholine, like other autonomic ganglia. However, instead of a postganglionic neuron projecting to a target organ, chromaffin cells (modified postganglionic neurons without axons) release epinephrine directly into the bloodstream, enabling a widespread systemic response.

Question 27

27. Describe the role of chromaffin cells in the adrenal medulla.

Answer 27

Chromaffin cells are modified postganglionic sympathetic neurons that lack axons. When stimulated by acetylcholine from preganglionic neurons, they secrete epinephrine (and some norepinephrine) into the blood, functioning as a neuroendocrine organ for fast systemic responses.

Question 28

28. How does the adrenal medulla contribute to the fight-or-flight response?

Answer 28

The adrenal medulla rapidly releases epinephrine into the bloodstream during sympathetic activation. This amplifies and prolongs the sympathetic effects—such as increased heart rate, blood pressure, and energy availability—enabling a body-wide fight-or-flight response.

Question 29

29. What neurotransmitter is released by the adrenal medulla, and how does it travel through the body?

Answer 29

The adrenal medulla releases epinephrine (and some norepinephrine), which enters the circulatory system and travels via the bloodstream to distant target tissues, affecting multiple organ systems simultaneously.

Question 30

30. What structural difference distinguishes the adrenal medulla from other sympathetic ganglia?

Answer 30

Unlike typical sympathetic ganglia that contain postganglionic neurons with axons that project to target organs, the adrenal medulla contains chromaffin cells that do not have axons. Instead, they release hormones directly into the blood, making it a neuroendocrine structure.

Question 31

31. How do single-unit and multi-unit smooth muscles differ?

Answer 31

Single-unit smooth muscle cells are connected by gap junctions, allowing action potentials to spread and cause coordinated contraction. Multi-unit smooth muscle cells are not electrically connected; each cell must be individually stimulated by autonomic neurons.

Question 32

32. What structural feature allows single-unit smooth muscle to contract as a unit?

Answer 32

Gap junctions between smooth muscle cells enable the spread of electrical signals and allow the entire sheet of muscle to contract simultaneously, even if only part of it receives neurotransmitter input.

Question 33

33. How does neurotransmitter release affect smooth muscle with and without gap junctions? x

Answer 33

In single-unit smooth muscle, neurotransmitter at one varicosity can lead to widespread contraction due to gap junctions. In multi-unit smooth muscle, neurotransmitter only affects specific targeted cells, allowing for fine-tuned, localized control.

Question 34

34. Compare skeletal and smooth muscle control by the nervous system.

Answer 34

Skeletal muscle: Controlled by the somatic nervous system; each fiber is innervated individually by a motor neuron at a neuromuscular junction. Smooth muscle: Controlled by the autonomic nervous system; can be coordinated (single-unit) or independent (multi-unit), with diffuse neurotransmitter release via varicosities.

Question 35

35. How does the ANS achieve broad vs. localized control of smooth muscle?

Answer 35

Broad control is achieved in single-unit smooth muscle through gap junctions and diffuse neurotransmitter release from varicosities. Localized control occurs in multi-unit smooth muscle, where individual cells are independently innervated without electrical coupling.

Question 36

36. What are the three main CNS regions that regulate autonomic functions?

Answer 36

The key CNS control centers of the ANS are: Hypothalamus: Master regulator, coordinates fight-or-flight, thermoregulation, hunger, and water balance Brainstem: Especially the reticular formation, regulates cardiovascular and respiratory functions Spinal cord: Controls autonomic reflexes such as urination and defecation.

Question 37

37. Describe the role of the hypothalamus in autonomic control.

Answer 37

The hypothalamus integrates signals from the cerebral cortex, limbic system, and visceral afferents. It coordinates autonomic responses like temperature regulation, fight-or-flight, hunger, and hydration, making it the top command center of the ANS.

Question 38

38. What functions are regulated by the brainstem in the ANS?

Answer 38

The brainstem, especially through the reticular formation, regulates: Cardiovascular activity (e.g., heart rate, blood pressure) Respiratory rhythms (e.g., breathing rate and airway resistance).

Question 39

39. Which autonomic reflexes are mediated by the spinal cord?

Answer 39

The spinal cord is involved in autonomic reflexes such as: Urination (micturition) Defecation Sexual reflexes (e.g., erection and ejaculation).

Question 40

40. How do emotional states influence autonomic activity via the limbic system?

Answer 40

The limbic system, responsible for processing emotions, sends signals to the hypothalamus, which integrates emotional input with physiological responses. This allows emotional experiences (e.g., fear, stress, pleasure) to influence autonomic outputs such as heart rate, digestion, and pupil size.