10, 11 and 12 - Autonomic Nervous System Flashcards
What is the autonomic nervous system?
The portion of the nervous system that controls most visceral functions and accommodates coordinated responses to external stimuli
Are autonomic disorders being sufficiently considered, suitably investigated and appropriately managed in clinical practice?
NOOOOOO
What accounts for these issues with ANS disorders?
Symptoms are so variable
What does the central nervous system consist of?
Brain
Spinal cord
What does the peripheral nervous system consist of?
Somatic nervous system
Autonomic nervous system
What are the two parts of the somatic nervous system?
Somatic efferent nerves which innervate skeletal muscles
Somatic and visceral afferent nerves
What are the three components of the autonomic nervous system?
Sympathetic division (SANS) Parasympathetic division (PANS) Enteric division (which is closely interconnected with SANS and PANS)
In the sympathetic division of the ANS, the preganglionic fibers are _________ compared to the postganglionic fibers.
Short
In the parasympathetic division of the ANS, the preganglionic fibers are ________ compared to the postganglionic fibers
Long
long pre, short post
Why do parasympathetic fibers have longer presympathetic fibers?
Because they synapse in the wall of the visceral organs, so they have to travel a long way to get there (long pre) but they are very close after they synapse (short post)
What is the one exception to the two-neuron organization of the ANS? (meaning there is a pre and post ganglionic nerve)
The adrenal medulla
Why is the adrenal medulla an exception?
It is considered to be a giant ganglion that does not have post-gaglionic fibers (there fore there is only one nerve, the presynaptic nerve)
What does the adrenal medulla release?
- Epinephrin
- Norepinephrin
- Dopamine
- Peptides
Where are these neurotransmitters released?
Directly into the blood stream
Is activation of the ANS involuntary or voluntary?
Involuntary
Can responses to a stimuli in the ANS be excitatory, inhibitory or both?
Both
What spinal levels contribute to the sympathetic division of the ANS?
The throaco-lumbar section (T1-L3,4) as well as some cranial nerves
At the spinal level, where do the autonomic neurons lie?
The intermediolateral cell column (AKA lateral horn)
Where is the intermediolateral cell column located?
Between the dorsal and ventral horns
Where do axons from preganglionic sympathetic neurons exit the spinal cord?
VENTRAL roots along with axons from somatic motor neurons
From the ventral root, the preganglionic sympathetic neurons branch away from the somatic motor neurons and enter the ____________
White communicantes
Why is the white communicantes white?
Because most preganglionic sympathetic axons are myelinated, making the white communicantes appear white
What is a paravertebral ganglia?
Along the length of the sympathetic trunk are ganglia known as paravertebral ganglia. The ganglia are distinguished as cervical, thoracic, lumbar, and sacral and, except in the neck, they closely correspond to number to the vertebrae.
What is a prevertebral ganglia?
Sympathetic ganglia which lie between the paravertebral ganglia and the target organ
What is the specialized ganglia?
There are four:
- Superior cervical ganglion
- Celiac ganglion
- Superior mesenteric ganglion
- Inferior mesenteric ganglion
There are three modes of innervation in the sympathetic division of the ANS. What are they?
The preganglionic neuron goes to the…
1 - paravertebral OR prevertebral ganglion then becomes a post-ganglionic neuron which then goes to the target organ
2 - specialized ganglion then goes to the target organ
3 - organ directly (adrenal medulla)
The parasympathetic division of the ANS emerges from two separate regions of the CNS. What are they?
CRANIO-SACRAL
What does the cranial outflow consist of?
Preganglionic fibers in certain cranial nerves
Which cranial nerves contain parasympathetic fibers?
Oculomotor nerve
Facial and glossopharyngeal nerves
Vagal nerve
Where do the ganglia for parasympathetics coming from cranial outflow lie?
The ganglia lie close to the target organs
What does the sacral outflow consist of?
Parasympathetic fibers destined for the pelvic and abdominal viscera emerge from the spinal cord ina bundle of nerves known as the nervi erigentes
Where are these parasympathetic fibers destined for?
- Bladder
- Descending large intestine
- Rectum
- Genetalia
Where do the sacral outflow of parasympathetic nerve synapse?
In scattered pelvic ganglia
What is unique about the pelvic ganglia?
They carry both sympathetic and parasympathetic fibers - the two divisions are NOT anatomically distinct in the pelvic region
What is the enteric nervous system?
A collection of nerve plexuses that surround the gastrointestinal tract, including the pancreas and biliary system
We say that the enteric nervous system is “sandwhiched” between the ______________
The layers of the gut
The enteric nervous system is connected by a ____________
Dense meshwork of nerve fibers
What does the myenteric plexus of the enteric nervous system control?
Motility
What does the submucosal plexus of the eteric nervous system control?
Ion and fluid transport
Where does the enteric nervous system receive input from?
Both the sympathetic and parasympathetic divisions
Can the enteric nervous system funciton normally WITHOUT extrinsic input?
YES!
One of the characteristics of the autonomic nervous system is DUAL INNERVATION. What does this mean?
***
Most organs receive both sympathetic and parasympathetic innervation, meaning that the actions of the organ are controlled by BOTH systems
What are the exceptions to the dual innervation?
ONLY sympathetic
- Hair follicles
- Thermoregulatory sweat glands
- Liver
- Adrenal glands
- Kidney
There is one place in the body where the sympathetic and the parasympathetic innervations produce SIMILAR rather than opposing effects. Where is this?
Salivary glands
How many somatic nerves release acetylcholine?
ALL OF THEM
How many of the preganglionic fiers of the ANS release acetylcholine?
ALL OF THEM
Do all post-ganglionic fibers have the same receptors and respond the same way to ACh?
No…
What receptor is found at all of the ganglion?
Nicotinic receptors
Where does the variability come from?
You will have a different response based on the receptors on the target organs
What do parasympathetic POSTganglionic fibers release? (we know their preganglionic fibers release ACh)
Post ALSO release ACh
What do sympathetic POSTganglionic fibers release?
They are andrenergic (epinephrine/norepinephrine) or dopaminergic (dopamine)
At what part of the body are postganglionic sympathetic fibers dopaminergic (release dopamine)?
Renal vascular smooth muscle
What is the exception to the rule of postganglionic sympathetic fibers?
Thermoregulatory sweat glands
What do postganglionic sympathetic fibers release at sweat glands?
Acetylcholine because the sweat glands possess muscarinic (muscle) receptors (meaning they respond to acetycholine)
What does cholinergic neurotransmission mean?
Its a shorter way of saying acetylcholine neurotransmission
There is a general four step method of cholinergic neurotransmission. What is it?
1 - Synthesis of the neurotransmitters at the pre-synaptic terminal
2 - Storage of the neurotransmitter
3 - Release of the neurotransmitterand actions of the transmitter at the receptor sites
4 - Termination of the transmitter’s action
What are the three steps that happen in the initial synthesis step of cholinergic neurotransmission?
Occurs at the presynaptic terminal…
1 - Uptake of choline by the choline transporter (CHT)
2 - Conjugation of acetylCoA (mito) plus choline with the enzyme choline acetyltransferase (ChAT)
3 - Final product of acetylcholine is formed
There is an experimental drug being tested that blocks the synthesis of acetylcholine. What step does it function at?
The uptake of choline - it blocks the choline transporter (CHT)
What is the enzyme that conjugates the acetylCoA to the choline?
Cholineacetyltransferase (ChAT)
Describe the storage step in cholinergic neurotransmission
ACh is transported into a storage vesicle by a second carrier called the vesicle-associated transporter (VAT) where it remains until secretion
What experimental drug is working to prevent acetylcholine storage?
Vesamicol
It attempts to block the VAT or vesicle-associated transporter
What is the first step in the release of acetylcholine from a presynaptic terminal
Depolarization of the nerve terminal
What happens after the presynaptic termianl has been depolarized?
Voltage-dependent Ca++ enters the presynaptic terminal
What does the Ca++ do once it enters the terminal?
Binds to calmodulin
What does the Ca++ calmodulin complex associate with (2 things)
VAMP (vesicle associated membrane proteins)
SNAP (synaptosome associated proteins)
Botulinum toxin functions at this point during the release of acetylcholine. What does it block?
SNAPs - synaptosome-associated proteins
What is the final step of acetylcholine release?
The vesicles fuse to the membrane and the neurotransmitter is released via exocytosis
The action of acetylcholine must be terminated once it has had a chance to function… How is it terminated?
First, rapid hydrolysis of ACh to form choline and acetate
Second, choline re-uptake into the terminals