Chapter 18: Autonomic Nervous System Flashcards
Describe basic similarities and differences between the somatic nervous system (SNS) and the autonomic nervous system (ANS).
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
Discuss the location, structure, and basic function of pre and post ganglionic ANS neurons.
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
Explain the consequences of neuronal convergence and divergence
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”
List the 2 divisions of the ANS.
Parasympathetic Division
Sympathetic Division
Describe the Parasympathetic Division of the ANS.
- “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
Describe the Sympathetic Division of the ANS.
- “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
Describe the right and left sympathetic trunks.
- 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)
Compare and contrast the white rami and the gray rami.
White Rami
- myelinated preganglionic axons
- “entrance ramps”
Gray Rami
- unmyelinated axons
- “exit ramps”
Discuss the structure and function of autonomic plexuses and list examples.
- Collections of sympathetic postganglionic axons and parasympathetic preganglionic axons
- Close to one another but DO not interact or synapse
- Cardiac Plexus
- Increase sympathetic activity = increase HR, BP, etc
- Increase parasympathetic activity = decreases HR, etc - Pulmonary Plexus
- Sympathetic activity = bronchiodilation
- Parasympathetic activity = bronchioconstriction - Esophageal Plexus
- Parasympathetic activity = controls swallowing reflex - Abdominal Aortic Plexus
- Hypogastric Plexus
List and describe the effects of the principle neurotransmitters in the ANS.
2 Neurotransmitters:
- Acetylcholine (ACh)
- Norepinephrine (NE)
Neurotransmitters:
- Released by presynaptic cell
- Bind to specific receptors on postsynaptic cell
- Either excitatory or inhibitory effect on effector (depending on receptor)
Discuss neurotransmitters. (Which system uses which neurotransmitter?)
- 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”
Discuss ways the ANS maintains homeostasis and describe the hierarchy that controls this system.
- 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