ANS Flashcards
What is the autonomic nervous system (ANS)?
A division of the peripheral nervous system that regulates involuntary bodily functions
What are the two main divisions of the ANS?
- Sympathetic nervous system
- Parasympathetic nervous system
What is the primary function of the sympathetic nervous system?
To prepare the body for ‘fight or flight’ response
What is the primary function of the parasympathetic nervous system?
To promote ‘rest and digest’ activities
What physiological effects are associated with the parasympathetic nervous system?
- Constricted pupils
- Increased salivation
- Slow heart rate
- Decreased force of contraction of heart
- Decreased blood pressure
- Constricted bronchial smooth muscle
- Stimulated GI tract activity
- Decreased blood flow to skeletal muscle
- Increased blood flow to skin
What neurotransmitter is primarily associated with the sympathetic nervous system?
Noradrenaline/adrenaline
What neurotransmitter is primarily associated with the parasympathetic nervous system?
Acetylcholine
What is the role of acetylcholine in salivary glands?
It signals via muscarinic acetylcholine receptors
Fill in the blank: The sympathetic nervous system is responsible for the ______ response.
fight or flight
Fill in the blank: The parasympathetic nervous system is responsible for the ______ activities.
rest and digest
What is the difference in the length of pre-ganglionic neurons between the sympathetic and parasympathetic systems?
- Sympathetic: Short
- Parasympathetic: Long
Where are the ganglia located in the sympathetic nervous system?
Paravertebral (mainly)
Where are the ganglia located in the parasympathetic nervous system?
Close to the target organ
What are catecholamines?
- Adrenaline
- Noradrenaline
- Epinephrine
- Norepinephrine
What is the role of the adrenal medulla in the sympathetic nervous system?
It secretes catecholamines into the bloodstream
True or False: The sympathetic nervous system decreases blood pressure.
False
True or False: The parasympathetic nervous system increases GI tract activity.
True
What is the effect of Gq signaling in the autonomic nervous system?
Vasoconstriction (increase BP), contraction of visceral smooth muscle, relax GI tract
What is the effect of Gi signaling in the autonomic nervous system?
Decreased heart rate, decreased insulin release
What are the effects of β1 adrenoceptors?
Associated with the Gs G protein
- Increased heart rate
- Increased force of contraction
- Release of renin
What are the effects of β2 adrenoceptors?
Associated with the Gs G protein
- Vasodilation (decrease BP)
- Bronchodilation
- Muscle tremor
- Relax visceral smooth muscle
- Glycogenolysis
What are the effects of α1 adrenoceptors?
Associated with Gq G protein
- Vasoconstriction (increase BP)
- Contraction of visceral smooth muscle
- Relax GI tract
What is the primary function of choline acetyltransferase (ChAT)?
Biosynthesis of acetylcholine
What is the first step in the biosynthesis of adrenaline?
Conversion of tyrosine to L-DOPA
What are the three key enzymes involved in the biosynthesis of noradrenaline?
- Tyrosine hydroxylase
- DOPA decarboxylase
- Dopamine β-hydroxylase
Where are the adrenal glands?
Located on top of each kidney
Secrete adrenaline and noradrenaline
What are afferent neurons?
Sensory neurons that carry information from the body to the central nervous system
What is catechol and catecholamine?
Catechol = chemical structure with benzene ring with 2 adjacent hydroxyl groups, forming the backbone of catecholamines
Catecholamine = group of neurotransmitters and hormones, including dopamine, noradrenaline, and adrenaline, derived from tyrosine and contains catechol group
What is the enteric nervous system?
A division of the ANS located in the gastrointestinal tract, capable of regulating digestion independently of the CNS
What is a monoamine?
Class of neurotransmitters that includes catecholamines, serotonin, histamine and melatonin
What are prevertebral ganglia?
Sympathetic ganglia located near major abdominal arteries, innervating abdominal and pelvic organs
Effects of the SNS
- dilated pupils
- decreased salivation
- increased HR (tachycardia)
- increased force of contraction
- relaxed bronchial smooth muscle (allows more O2)
- inhibited GI tract activity
- increased blood flow to skeletal muscle
- decreased blood flow to skin
- increased blood pressure
- sweating
Organisation of the SNS
CNS connected to ganglion cells (which have ACh nicotinic receptors) by short preganglionic neurons that release ACh
Postganglionic neurons are long and release noradrenaline and are connected to cells which have noradrenaline/adrenoreceptors
Difference between Adrenaline and noradrenaline
Also known as epinephrine and norepinephrine
Adrenaline has an extra methyl group
Noradrenaline has an amine group
Structure of the adrenal medulla
- long preganglionic neurons from the spinal cord attach to the adrenal medulla
- adrenal medulla contains ACh nicotinic receptors and chromaffin cell (secretes into circulation instead of synapse)
- Adrenaline and noradrenaline is released into the circulation in a ratio of 4:1 (A:N)
Biosynthesis of Acetylcholine
Acetyl coenzyme A with a Choline group is turned into ACh
ACh has a permanent positive charge on the N (key to binding receptors) and a ester linkage between the choline and acetyl group (this bond is broken by an enzyme to switch off signalling)
NOT a monoamine
Describe ganglionic transmission
- ACh is released from vesicles in the preganglionic neuron into the synapse
- ACh activates nicotinic ACh receptors on the postganglionic neuron = trigger an action potential
- Signal is turned off by AChE which is present in the synapse
- It breaks down ACh into acetate and choline
- Choline is taken up by a transporter in the preganglionic neuron and is used to make more ACh
Biosynthesis of adrenaline
Describe noradrenergic transmission
- Tyrosine enters via aromatic amino acid transporter (AAAT)
- Noradrenaline is packaged into vesicles by vesicular monoamine transporter (VMAT)
- Noradrenaline is released from vesicles into the synapse to bind to post-synaptic adrenoreceptors
- Noradrenaline is either recycled or metabolised
- This is slow transmission as it relies on G-protein coupled receptors
MAO - monoamine oxidase = metabolises noradrenaline
COMT - catechol-O-methyl transferase = metabolises noradrenaline
NET and Uptake 2 = recycle and package noradrenaline
What are the effects of α2 adrenoceptors?
Associated with Gi G protein
- Decreased transmitter release
- Decreased insulin release
Muscarinic signalling systems
Located in the glands (heart and smooth muscle)
- M1 = Gq pathway
- M2 = Gi pathway —> decreases heart rate
- M3 = Gq —> smooth muscle contraction
Found in the CNS
- M4 = Gi pathway
- M5 = Gq pathway
Sympathetic vs parasympathetic NS
Sympathetic
- Noradrenaline/adrenaline and ACh in salivary glands
- Short pre-ganglionic neuron
- Long post-ganglionic neuron
- Ganglia located paravertebral
- Flight, fright or fight response
Parasympathetic
- ACh
- Long pre-ganglionic neuron
- Short post-ganglionic neuron
- Ganglia located close to target
- Rest and digest
