Exam #1: Physiology of the ANS I Flashcards
What is the ANS?
Portion of the nervous system that controls most visceral functions & accommodates coordinated responses to external stimuli.
What are the components of the CNS?
- Brain
- Spinal cord
What are the components of the PNS?
1) Somatic Nervous System
2) Autonomic Nervous System
What are the three divisions of the ANS?
1) Sympathetic
2) Parasympathetic
3) Enteric division
What is the key neuron in the somatic nervous system?
Alpha motor neuron
What is the neurotransmitter in the somatic nervous system?
ACh
How does the autonomic nervous system differ from the somatic nervous system in terms of neruons?
- In the somatic nervous system, there is one large neuron that synapses directly on the effect cell
- In the ANS, there are two neurons (preganglionic & post ganglionic, with an intervening ganglia)
How do the sympathetic & parasympathetic nervous systems differ organization of the neurons?
- Sympathetic= Short pre-ganglionic & long post-ganlgionic fiber
- Parasympathetic= Long pre-ganglion & short post-ganglionic
*Note that the the ganglia of the PNS are clustered within the walls of visceral organs
What is the alternate name for the sympathetic nervous system?
Thoraco-lumbar division
What is the intermediolateral cell column?
- Lateral horn of the spinal cord
- Location of the cell bodies of autonomic ganglia
Describe the path of sympathetic outflow.
1) Cell body in the intermediolateral column
2) Preganglionic axon exits the spinal cord via the ventral root w/ somatic motor neurons
3) Diverge from somatic & enter the white rami communicantes
What are the three modes of innervation in the SNS?
1) Preganglionic neuron goes to a) paravertebral ganglia or b) prevertebral ganglia, and then synapses with post-ganglionic neuron
2) Preganglionic neuron goes to a specialized ganglia, which then synapses with the target organs
3) Preganglionic neuron goes straight to the organ e.g. adrenal medulla
Specialized ganglia include: superior cervical ganglion, celiac ganglion, superior mesenteric ganglion, & inferior mesenteric ganglion
What is the alternate name for the PNS?
Cranio-Scaral Division
Describe cranial outflow.
- Preganglionic fibers follow certain cranial nerves
- Ganglia lie very close to target organs
Specific cranial nerves= oculumotor, fascial, glossopharyngeal, & vagus
Describe sacral outflow.
- Parasymathetic fibers emerge from the spinal cord in a bundle known as the nervi erigentes
- Synapse with pelvic ganglia
- Short postganglionic fibers to target organs
What is the enteric nervous system?
Two ganglia sandwhiched between the layers of the gut:
- Myenteric (Auerbach’s)
- Submucosal (Meissner’s)
Specifically, where is the myenteric plexus located? What does the myenteric plexus control?
- Between the external longitudinal & deep circular smooth muscle layers
- Motility
Specifically, where is the submucosal plexus located? What does the submocosal plexus control?
- Between the circular muscularis mucosae
- Ion & fluid transport
Where does the enteric nervous system receive input from? Can the enteric nervous system function without this input?
PNS & SNS
*However, the enteric nervous system can function normally without extrinsic input
What does dual innervation mean?
Most organs receive input from both SNS & PNS; thus, their action is controlled by both systems
What are the exceptions to dual innervation that only receive SNS innervation?
- Hair follicles
- Thermoregulatory sweat gland
- Liver
- Adrenal Gland
- Kidney
In what organs do the SNS & PNS produce similar effects?
Salivary glands
*Both increase the production of saliva
What NT is released from all of the preganglionic fibers?
ACh
*Regardless of system, all preganglionic fibers release ACh
What do the postganglionic fibers of the PNS release?
ACh
What do the postganglionic fibers of the SNS release?
NE/Epi or DA
What is the exception to postganglionic fibers of the SNS releasing NE/Epi or DA?
Thermoregulatory sweat glands, which posses muscarinic receptors & respond to ACh
What neurotransmitter do postganglionic fibers to the renal vascular smooth muscle release?
DA
What NTs are released by the adrenal medulla?
Epi & NE
What receptors are present in the target organs of the PNS?
Muscarinic ACh
What receptors are present in the thermoregulatory sweat glands?
Muscarinic ACh
What receptors are present in the target organs of the SNS? What are the two exceptions to this?
- Alpha & Beta Adrenergic
- Exceptions: 1) thermoregulatory sweat, 2) renal vasculature
What receptors are present in the renal vasculature?
DA-1
What receptors are present in skeletal muscle?
Nicotinic ACh
How is ACh synthesized?
1) Uptake of choline from the ECF via the Na+ dependent choline transporter (CHT)
2) Conjugation by ChAT (AcetylCoA + Choline)
3) Final product: ACh
Note that acetylcholine is synthesized in BOTH the cytoplasm & in the mitochondria. ChAT= choline acteyltransferase
What drug can block the choline transporter (CHT)?
Hemicholiniums
*Note that these are not used clinically.
How is ACh stored?
Once ACh is synthesized, it is transported into the storage vesicle via the “vesicle assocaited transporter” (VAT)
What drug blocks VAT?
Vescamicol
How is ACh released?
1) Depolarization of nerve
2) Voltage-dependent Ca++ entry
3) Ca++ binds Calmodulin, activating “vesicle associated membrane proteins,” VAMPs & “synaptosome-assocaited proteins,” (SNAPs)
4) Exocytosis
What is the function of the VAMPs & SNAPs?
- Docking storage vesicles on the inner surface of the nerve terminal facing the synapse
- Fusion of the synaptic vesicle with the neural membrane
What does botulinum toxin block?
VAMPs & SNAPs
*Botulinum toxin enzymatically removes two amino acids from one or more of these fusion peptides
How is ACh action terminated?
1) Rapid hydrolysis of ACh via acetylcholine esterase (AChE)
2) Choline re-uptake into terminals
3) ACh interaction with ACh autoreceptors
What does acetylcholine esterase break ACh into?
Choline & Acetate
What drug blocks Acetylcholine esterase? What happens at the synapse in response to these drugs? Give an example of an AChE inhibitor.
- AChE inhibitors
- Increase ACh concentrations & over-stimulation of receptors
*Neostigmine is an AChE inhibitor
What are the two major types of ACh receptors?
- Muscuarinic
- Nicotinic
What are muscarinic receptors?
Transmembrane G-protein coupled receptors
*The type of G-protein associated with the particular receptor will result in a differential effect
What are nicotinic receptors?
Transmembrane Na+ ion channel
*ACh acts as a ligand that causes the channel to undergo a conformational change & opening when bound; both Na+ & K some K+ flow down their electrochemical gradients
How is aqueous humor produced? Describe the path that aqueous humor takes after being secreted.
- By the ciliary body epithelium
- Passes anterior to the lens
- Drains into the canal of schlemm (deep in the angle formed by the cornea & iris)
What increases intra-ocular pressure in glaucoma?
- Increased production of aquenous humor by the ciliary body epithelium
- Decreased drainage of aqueous humor from the Canal of Schlemm
What are two functions of the ciliary muscle?
1) Contraction= near accomodation & miosis
2) Opening of the Canal of Schlemm
What will contraction of the ciliary muscle do to intra-ocular pressure?
Decrease
What two receptors are located on the ciliary muscle? What action does stimulation of each receptor produce?
M3= Contraction, PNS, ACh
B2= Relaxation, SNS, NE
What type of alpha subunit is associated with M1 & M3? What does their activation ultimately lead to?
- Gq
- Increased Ca++
- Increased PKC
What type of alpha subunit is associated with M2? What does the activation of M2 ultimately lead to?
- Gi/o
- Decreased cAMP
- Decreased PKA
What muscle controls dilation of the pupil?
Radial (dilator) muscle
What type of receptor controls the function of the radial muscle?
Alpha-1 (SNS)
What types of receptors are associated with the ciliary epithelium? What is the effect of stimulating these receptors?
- Beta-1 & Beta-2
- Increased production of aqueous humor
