Chapter 18: Autonomic Nervous System

Question 1

Describe basic similarities and differences between the somatic nervous system (SNS) and the autonomic nervous system (ANS).

Answer 1

Somatic Nervous System (SNS)

• Voluntary control
• Uses one motor neuron; therefore faster
• Myelinated (faster)
• ACh

Autonomic Nervous System (ANS)

• Involuntary Control
• Sympathetic and Parasympathetic Divisions
• Fight or Flight, Rest and Digest
• Uses 2 motor neurons (pre- and post-ganglionic neuron), therefore slower
• Unmyelinated (slower)
• ACh and norepinephrine (NE)

Both SNS and ANS

• Part of the PNS
• Work together to regulate body organs and maintain normal internal functions
• Use sensory and motor neurons

Question 2

Discuss the location, structure, and basic function of pre and post ganglionic ANS neurons.

Answer 2

Parasympathetic

• Preganglionic axon: Long
• Postganglionic axon: Short
• Preganglionic neuron cell bodies originate in brainstem or lateral gray matter of S2-S4

Sympathetic Division

• Preganglionic axon: Short
• Postganglionic axon: Long
• Preganglionic neuron cell bodies originate in lateral horns of T1-L2

Question 3

Explain the consequences of neuronal convergence and divergence

Answer 3

Convergence:

• axons from numerous preganglionic cells synapse on a single ganglionic cell
• “a lot to a little”

Divergence:

• axons from one preganglionic cell synapse on numerous ganglionic cells
• “A little to a lot”

Question 4

List the 2 divisions of the ANS.

Answer 4

Parasympathetic Division

Sympathetic Division

Question 5

Describe the Parasympathetic Division of the ANS.

Answer 5

• “Rest and Digest” Division, “Craniosacral” Division
• Most active when you are resting or digesting a meal
• Primarily concerned with conserving energy and replenishing nutrient stores
• Helps regulate/maintain homeostasis
• Preganglionic axon: Long
• Postganglionic axon: Short
• Preganglionic neuron cell bodies originate in brainstem or lateral gray matter of S2-S4
• Structurally more simple
• Ganglionic neurons located close to, or within the walls of, the target organ
• Lack of divergence prevents mass activation; more discrete and localized

Question 6

Describe the Sympathetic Division of the ANS.

Answer 6

• “Fight-or-flight” Division, “Thoracolumbar” Division
• Mass activation; large # of ganglionic neurons activate many effector organs
• Primarily concerned with preparing body for emergency
• Increased alertness and metabolic activity; fear
• Also helps regulate homeostasis
• Preganglionic axon: Short
• Postganglionic axon: Long
• Preganglionic neuron cell bodies originate in lateral horns of T1-L2
• More complex

Question 7

Describe the right and left sympathetic trunks.

Answer 7

• Located lateral to the vertebral column on both sides
• “Chain ganglia”
• String of pearls appearance
  
  • Pearls: sympathetic trunk ganglia
  • String: bundles of axons
• One for each spinal nerve except C-spine only has 3 (superior, middle, and inferior)

Question 8

Compare and contrast the white rami and the gray rami.

Answer 8

White Rami

• myelinated preganglionic axons
• “entrance ramps”

Gray Rami

• unmyelinated axons
• “exit ramps”

Question 9

Discuss the structure and function of autonomic plexuses and list examples.

Answer 9

• Collections of sympathetic postganglionic axons and parasympathetic preganglionic axons
• Close to one another but DO not interact or synapse

1. Cardiac Plexus
   - Increase sympathetic activity = increase HR, BP, etc
   - Increase parasympathetic activity = decreases HR, etc
2. Pulmonary Plexus
   - Sympathetic activity = bronchiodilation
   - Parasympathetic activity = bronchioconstriction
3. Esophageal Plexus
   - Parasympathetic activity = controls swallowing reflex
4. Abdominal Aortic Plexus
5. Hypogastric Plexus

Question 10

List and describe the effects of the principle neurotransmitters in the ANS.

Answer 10

2 Neurotransmitters:

1. Acetylcholine (ACh)
2. Norepinephrine (NE)

Neurotransmitters:

• Released by presynaptic cell
• Bind to specific receptors on postsynaptic cell
• Either excitatory or inhibitory effect on effector (depending on receptor)

Question 11

Discuss neurotransmitters. (Which system uses which neurotransmitter?)

Answer 11

• Parasympathetic division: pre and post ganglionic axons release ACh and are called “cholinergic”
• ALL preganglionic axons release ACh as their neurotransmitter
• Sympathetic division: Most postganglionic axons release NE and are called “adrenergic”

Question 12

Discuss ways the ANS maintains homeostasis and describe the hierarchy that controls this system.

Answer 12

• Dual innervation: many organs innervated by postganglionic axons from both ANS divisions and their effects oppose each other
• Autonomic reflexes: contraction of smooth or cardiac muscle, secretion of glands, alteration of pupil diameter, HR, RR, BP, regulation of digestive activities, etc
• Controlled by CNS: Cerebrum, hypothalamus, brainstem, spinal cord
• Sensory processing in thalamus and emotional state in limbic system both effect hypothalamus
• Hypothalamus: command center for ANS; controls visceral functions in both divisions of the ANS; communicates with other CNS regions; emotions
• Brainstem: visceral reflexes
• Spinal cord: ANS reflex center for defecation and urination