Lecture 8 - Autonomic Nervous System Flashcards
What type of neurons are present in the peripheral nervous system?
Unipolar neurons i.e. only has one extension from the cell body
What 2 types of glial cell are present in the PNS?
Schwaan cells - wrap around axon to form myeline sheath, increases signal speed
Satellite cells - surround cell bodies in ganglia, regulates gas, neurotransmitter and nutrient levels
Where are ganglia and what is within them?
Always outside the CNS
Collections of the cell bodies of the peripheral neurons
Also where the autonomic neurons synapse with eachother
What 3 things does the autonomic nervous system act on?
Smooth muscle (including vasculature and GI tract) Endocrine and exocrine glands Cardiac muscle
Pathway of a SNS response, including where it originates from
Originates craniosacral
Short preganglionic fibre exits through dorsal horn, release Ach to synapses with nAchR on postganglionic fibre in ganglion, long postganglionic fibre releases NA
OR
Short preganglionic that synapses directly onto the target organ (if endocrine gland)
Pathway of a PSNS response
Originates throracolumbar
Long preganglionic fibre exits through dorsal horn, release Ach to synapses with nAchR on postganglionic fibre in ganglion, short postganglionic fibre releases Ach
Which organs are only innervated by the SNS and not the PSNS?
Adrenal gland
Sweat glands
Some blood vessels
Examples of two organs that have dual innervation
Heart
Liver
2 advantages of dual innervation
Faster control
More fine-tuned control
Describe the process of Ach synthesis and breakdown
In nerve terminals, acetyl coeznyme A from mitochondria, and choline uptaken from interstitial fluid that comes from the diet, form Ach.
Ach broken down by acetylcholine esterase
Describe the process of adrenaline synthesis
Tyrosine consumed in diet or protein breakdown
Tyrosine hydroxylase converts it into L-Dopa
Dopa decarboxylase converts it into dopamine
Dopamine hydroxylase converts it into norepinephrine
PNMT converts it into epinephrine
How is noradrenaline signalling stopped?
Inactivated by monoamine oxidase The NET (norepinephrine transporter) re uptakes it back into cells
What receptors can Ach bind to?
nAchR - on muscle, in ganglia or in the CNS
mAchR - M1-5
What receptors can adrenaline bind to?
alpha 1,2
beta 1-3
Are preganglionic neurons and postganglionic neurons excitatory or inhibitory?
Preganglionic always excitatory as release Ach
Postganglionic can be either - M2 and M4 coupled to Gai subunit, which is inhibitory
Which g protein subunit is each receptor linked to?
Gs - b1, b2, b3
Gi - a2, M2, M4
Gq - a1, m1, m3, m5
Describe how preganglionic firing can result in a more delayed/prolonged EPSP?
Low frequency firing = Ach release = activates nAchR = fast EPSP
High frequency firing = Ach release and LHRH peptide release = LHRH binds postsynaptic peptidergic receptor = activation of GIRK channels = delayed EPSP
What is the name for drugs that enhance and oppose the action of the parasympathetic and sympathetic nervous systems?
Parasympathomimetic
Parasympatholytic
Sympathomimetic
Sympatholytic
Name two parasympathomimetic drugs and explain how they work
- Carbachol - Stimulation of cholinergic receptors
2. Neostigmine - Reversible inhibition of AchE, acts on motor end plate, treats myasthenia gravis
Name two parasympatholytic drugs and and explain how they work
- Atropine - Competitive antagonism of muscarinic Ach receptors
- Nicotine - Persistent depolarisation of Ach receptors, preventing repeated excitation
Name 2 examples of sympathomimetic drugs and explain how they work
- Salbutamol - b2 agonist used to treat asthma
2. Amphetamine - antagonist of NET
Name 2 examples of sympatholytic drugs and explain how they work
- Reserpine - antihypertensive, blocks VMAT to prevent NA packaging into vesicles
- Methyldopa - inhibitor of DOPA decarboxylase
How does parasympathetic innervation exert control over heart rate?
- PSNS releases Ach
- Ach binds M2 receptors on heart
- Gby subunit activates GIRK channels in pacemaker cardiomyocytes, potassium efflux, less frequent depolarisation
- Gi subunit inhibits adenylate cyclase, reducing cAMP and PKA, less phosphorylation of L-type calcium channels, reduced contractility
How does sympathetic innervation exert control over heart rate?
- SNS releases NA
- NA binds B1 and B2 receptors on the heart
- Gs subunit activates adenylate cyclase, increasing cAMP and PKA, phosphorylation of L-type calcium channels
Which part of the brain is in charge of autonomic nervous system control?
Hypothalamic paraventricular nucleus
What is the mechanism of action of alcohol and the short term effects?
Positive allosteric modulator of the GABAa receptor
Anxiety relief, sedation, hypnosis, anaesthesia, death
What are the effects of chronic alcohol intake?
Chronic intake can lead to demyelination, causing
- Conduction block
- Slowed conduction
- Impaired ability to conduct high frequency impulses
Name 3 symptoms of acute alcohol withdrawal
Tachycardia
Diaphoresis (Increased sweating)
Hypertension
