Neuroscience 9 - The autonomic nervous system Flashcards
Is the trachea and bronchioles innervated by sympathetic fibres?
No, the smooth muscle in the tissue is instead influenced by catecholamines that are released into circulation. This is the same with blood vessels dilating as a result of catecholamines.
What happens when you denervate the heart? And why?
The heart rate would increase. This is because the heart is normally parasympathetic dominant.
How many parasympathetic nerves are there? And what are they?
- 4 cranial nerves:
- Oculomotor nerve (CN III).
- Facial nerve (CN II).
- Glossopharyngeal nerve (CN IX).
- Vagus nerve (CN X). - 1 sacral nerve:
- Splachnic nerve.
What does the Vagus nerve (CN X) innervate?
It innervates the organs such as the heart, lungs, stomach, pancreas and small intestine.
Describe the structure of the parasympathetic nervous system.
- Starts at the cranial or sacral region.
- Very long pre-ganglionic fibre.
- Ganglion located close to the target organ.
- Short post-ganglionic fibre innervates from the target organ.
What is the important neurotransmitter in the parasympathetic nervous system?
Acetyl choline (released by both the pre and post ganglionic fibres).
Where do sympathetic nerves originate from?
Thoracolumbar outflows, from the thoracic and lumbar regions.
Describe the structure of the sympathetic nervous system.
- Starts at the thoracic or lumbar region.
- Short pre-ganglionic fibres leave spinal cord and form the sympathetic trunk (row of linked ganglia adjacent to spinal cord).
- Long post-ganglionic fibres then innervate the target tissue. One pre-ganglionic fibre can link to many post-ganglionic fibres.
What are the neurotransmitters of the sympathetic nervous system?
Acetyl choline released by the pre-ganglionic fibres and noradrenaline released by the post-ganglionic fibres.
What are 2 exceptions to the normal sympathetic nervous system?
- There is only one pre-ganglionic fibre going to the adrenal gland (there is no post-ganglionic fibre). The adrenal gland then releases adrenaline and noradrenaline and acts like a post-ganglionic fibre.
- Some post-ganglionic fibres to the skin and sweat glands release ACh instead of noradrenaline.
Why does the adrenal gland release noradrenaline?
Noradrenaline released by neurones are removed very quickly from synapses. Hence the effect is very short lived. However, noradrenaline released into the blood stream stays for a longer time and hence has an effect for a longer period.
How is noradrenaline removed from the blood?
It is metabolized in the liver.
Why are most of the pre-ganglionic fibres of the sympathetic nervous system synapsed to form the sympathetic trunk?
To allow highly coordinated responses. Lots of tissues being activated together.
Explain how pupillary constriction works.
- The cranial parasympathetic pre-ganglionic nerve projects down to the ganglion located close to the eye.
- The parasympathetic post-ganglionic nerve then innervates the iris muscle (releases ACh).
- Pupil constriction.
- Sympathetic system has opposite effect (dilation).
How does the ciliary muscle contract?
As a result of the parasympathetic nervous system. Releases ACh and causes lens to bulge.
How is the stomach controlled by the parasympathetic nervous system?
- The vegas nerve from the cranial region projects down to the ganglion close to the stomach.
- The short post-ganglionic fibre innervates the stomach to stimulate the secretion of acids and enzymes as well as muscle contraction.
What is the enteric nervous system?
- It is a system that controls the GI.
- It can work independently of the brain.
- Sensory neurones detect chemical substances or tension caused by food = motor neurones then change secretions or cause vasoconstriction/vasodilation.
How does sympathetic and parasympathetic affect the GI?
- Sympathetic - decreases motility, stimulates contraction of sphincters and inhibits secretory activity.
- Parasympathetic - increases motility, causes relaxation of sphincters and stimulates secretory activity.
How does the sympathetic and parasympathetic affect the heart?
- SNS increases heart rate.
2. PNS decreases heart rate.
How is blood pressure measured by the body?
Baroreceptors in large arteries measure the pressure and an afferent nerve conducts the signal to the CNS.
What effect does increased sympathetic activity have on TPR (total peripheral resistance)?
Increased TPR.
How does increased sympathetic activity increase BP?
Increased CO (from increased HR) and increased TPR.
Are the lungs innervated by sympathetic or parasympathetic nerves?
Only innervated by parasympathetic nerves.
How does the sympathetic nervous system increase oxygen delivery to the lungs?
Via noradrenaline/adrenaline from the adrenals = dilation of airways.
What is the micturition reflex?
- Pressure build up in bladder.
- Stimulation of parasympathetic = detrussor muscle contracts.
- Inhibition of sympathetic = internal sphincter relaxes.
- External sphincter needs to be opened via voluntary control (not ANS).
What are the main neurotransmitters used by the autonomic nervous system?
- Acetyl Choline.
- Noradrenaline.
- Adrenaline.
Last two are catecholamines.
Which neurotransmitters does the PNS use?
Acetyl Choline.
Which neurotransmitters does the SNS use?
- Acetyl Choline in pre-ganglionic fibres.
- Noradrenaline in post-ganglionic fibres.
- Adrenaline released by adrenal medulla.
- ACh in some post-ganglionic fibres.
What is the effect on the heart when you block ACh action in autonomic ganglia?
Depends:
- At rest = parasympathetic dominant, hence inhibition of ACh increases HR.
- During exercise = sympathetic dominant, hence inhibition of ACh decreases HR.
What are the receptors for ACh?
- Nicotinic - ion channel receptor, K+ in Na+ out (quick).
2. Muscarinic - G-protein receptor. In target organ (slower response).
Where are nicotinic receptors located?
In ganglions.
Where are muscarinic receptors located?
At the end of parasympathetic nerves and a few exceptions of sympathetic nerves (pos-ganglionic nerves). At target organs.
What is an effect of blocked nicotinic receptors in an individual at rest?
Constipation.
What are the receptors for adrenaline?
- Adrenoreceptors (G-protein)
2. A1, A2, B1. B2.
Where are adrenaline receptors located?
At effector organs
- A1 in blood vessels (constriction).
- B2 in skeletal muscle (dilating).
How is Acetyl Choline synthesised?
Acetyl CoA + Choline using Choline acetyl transferase.
How is Acetyl Choline released into the synapse?
- ACh is stored in vesicles close to the membrane.
- Action potential stimulates Ca2+ influx.
- ACh released into synapse.
How is ACh metabolised?
Using Acetylcholinesterase to form Choline + Acetate.
How is noradrenaline synthesised?
- Tyrosine => DOPA => Dopamine.
2. Dopamine => Noradrenaline (in vesicle).
How is Noradrenaline degraded?
- First taken into neurone or tissue.
2. Broken down by enzymes.
How is Adrenaline synthesised?
- Tyrosine => DOPA => Dopamine.
- Dopamine => Noradrenaline (in vesicle).
- Noradrenaline => Adrenaline.
Where is Adrenaline produced and by what cells?
Medulla in the adrenal glands by Chromaffin cells.
Where is adrenaline released to?
Released into the interstitial space and diffuses into the capillaries.
