Autonomic Nervous System Flashcards
Which neurotransmitters does the adrenal medulla release?
It releases adrenaline, noradrenaline, and dopamine
Are all catecholamines
What does the parasympathetic & symapthetic NS target?
smooth muscle, cardiac muscle, and glands
Outline the innervation of blood vessels in the sympathetic nervous system
- Sympathetic neurons are tonically active & will release norepinephrine onto the a-adrenergic receptor
- This causes a change in signal rate
- Increase in norepinephrine = blood vessel constriction
- Decrease in norepinephrine = blood vessel dilation
Blood vessel constriction –> so we increase the blood pressure and get more venous return
Outline the neural supply of pupillary constrictor and pupillary dilator muscles
Pupillary constrictor (parasympathetic supply): Edinger-Westphal nucleus –> III cranial nerve –> ciliary ganglia –> pupilloconstrictor muscle in iris
Pupillary dilator (sympathetic supply): Preganglionic neurons found in spinal cord –> synapse onto superior cervical sympathetic ganglion –> post-ganglion neuron goes to supply the pupillodilater muscle in iris
Outline the sympathetic innervation of the heart
- In the spinal cord in the intermediolateral cell column, there are preganglionic neurons taht synapse with a postganglionic neuron
- Synapses onto ganglia near the heart
- Noradrenaline released onto a B1-receptor
- Activates Ga protein
- Activates cAMP
- Na+ and Ca2+ enter
- Causes depolarization of the** SA node**
Outline the parasympathetic innervation of the heart
- The preganglionic neuron in brainstem exits via 10th cranial nerve
- ACh released onto a muscarinic receptor
- Ga (inhibitory) activated that decreases cAMP
- Na+ and Ca2+ entry decreases
- The beta & gamma subunits increase activity of K+ channel
- Reduced depolarization and cell takes longer to reach threshold
What happens to cardiac activity in response to a decrease of blood flow to the brain?
- Sympathetic nerve activity increases
- TPR increases
- Stroke volume, heart rate, and cardiac ouput increase
- Arterial pressure increases
An increase in exercise results in a rise in cardiac output. How does this affect blood supply to different organs?
- Blood supply to liver, kidneys, bone, and other tissues decreases
- Blood supply to heart, skeletal muscle, and skin increases
How does addition of glycine to system affect arterial pressure?
- Drops
- Integrated renal sympathetic activity drops too
Glycine has been shown to increase the production of nitric oxide (NO) in endothelial cells. Nitric oxide is a vasodilator, meaning it relaxes the smooth muscles of blood vessels, leading to increased blood flow and potentially reduced arterial pressure.
Glycine may also impact renal function, potentially influencing fluid and electrolyte balance, which are key determinants of arterial pressure.
In order to determine whether the spinal cord is involved in autonomic functions, scientists injected a dye into the dorsal root ganglion which filled up the spinal root afferents. They then took a piece of distal colon and cut it. Using a microscope, what did they observe?
- They observed the ends of the afferents in the mucosa
- These afferents contained an ion channel that opens when it is deformed (Piezo-2 channel) in response to mechanical distension of the lumen of the colon
- These afferents were spread out over a large region and were sparesly innervating the colon
Spinal visceral afferents send info that you perceive about organs, whereas cranial visceral afferent send info about the functions
What is referred pain?
- when you have an injury in one area of your body but feel pain somewhere else
- you may receive nerve from heart AND skin - overlapping of neurons can cause pain to be more dispersed
Random note: sensory visceral afferents sense MECHANICAL and CHEMICAL and TEMP stimuli
Where are the cell bodies for cranial visceral afferent found?
- the odose / inferior ganglion of the vagus
- the jugular / superior ganglion of the vagus
- petrosal ganglion
The primary central termination site for cranial visceral afferents is the NTS
What are 2 sites that contain baroreceptors?
aortic arch
carotid sinus
sensory nerves like the VAGUS nerve and the CAROTID SINUS nerve
Distinguish b/w A-fibers and C-fibers
These are the 2 classes of baroreceptor afferents that will respond to stretch / heart pressure
- A fibers are myelinated whereas C fibers are not
- A fibers about 10% whereas C fibers around 90%
- A fibers active at rest whereas C fibers have a very high threshold (activated at HIGHER blood pressure)
- A fibers have synchronous glutamate release whereas C fibers have asynchronous glutamate release
C fibers express TRPV1
The activation thresholds for myelinated fibers are much broader (spread over a larger range, although lower) compared to unmyelinated fibers
How do baroreceptors respond to low blood pressure in the aortic arch receptor vs the carotid sinus receptor
1) signal passes along vagus nerve for the aortic arch receptor
2) signal passes along Nerve IX (glossopharyngeal) nerve for carotis sinus receptor
3) Both synapse onto NTS
4) Release of glutamate at NTS
5)** Pathway 1 = nucleus ambiguous (AMB); cells of AMB exit via VAGUS nerve and SLOW the heart**
6) Pathway 2 = caudal ventral lateral medulla (CVLM)
In pathway 2, CVLM sends projections to RVLM (rostral ventral lateral medulla) –> this drives sympathetic nerve activity –> increases HR and constricts vessels to pressure rises
If blood pressure is high, GABA is released to inhibit SANS
Also inhibits the intermediolateral column
Explain the pathway of the cranial viscerosensory afferent neurons
Periphery –> vagus nerve –> Xth cranial nerve –> solitary tract –> NTS
Periphery = cardiovascular, respiratory, hepatic, gastrointestinal system (all SENSORS)
The vagus nerve becomes the Xth cranial nerve, then it forms the solitary tract along with the IXth and VII cranial nerves
Integration happens at the NTS
Injection of tracing dyes into ganglia known to contain the cell bodies of these neurons (such as the nodose) reveals that their terminal fields are in the NTS. The presence of which protein suggests that they are forming synapses with NTS neurons?
Synaptophysin
Synaptic input occurs very close to the axon initial segment where action potentials are being generated - for the anterograde aortic depressor nerve / nodose ganglion labelling
Action potentials in the visceral neurons eventually result in . . . . . at the ST-NTS synapse.
glutamate release
acts as both AMPA and NMDA neurons
What is frequency dependent depression?
when subsequent action potentials cannot release enough glutamate to match the first - it is a feature of sensory neurons
What are some features of the solitary tract (cranial visceral) input to the NTS?
- A relatively sparse excitatory network where one primary afferent dominates the info pathway
- Dedicated lines of info (usually involved in homeostasis)
- Convergent primary afferent input (usually connect to hypothalamus & involved in complex brain processing)
Why is capsaicin added to cells?
Capsaicin activates the TRPV1 receptor
TRPV1 receptors can also be activated by acid and heat
This channel allows the passage of Na+ and Ca2+; it is involved in nerve cell stimulation
By causing TRPV1 to open, we can inhibit neurons, allowing a lot of Ca2+ to rush in
The cell will become depolarized, but due to the high internal positive charge, it will be very difficult for it to become hyperpolarized to allow another action potential to be fired
Cells that can be blocked by capsaicin have. . .
asynchronous release
cells that had no capsaicin never had asynchronous glutamate release
How does asynchronous release affect excitation?
Asynchronous release extends the post-synaptic excitatory period
Capsaicin inhibits the activation of 2nd order NTS neurons as evoked by electrical activation of the solitary tract. By what mechanism does this occur?
Depolarization block in the presynaptic terminal
If capsaicin is added at a very low concentration, how does this help the researchers understand transmission?
They can activate the TRPV1 receptor specifically and identify those NTS neurons that they are recording from - what type of sensory neuron is talking to it
