Autonomic Nervous System Flashcards
What do visceral sensory neurons do and where are they found?
Monitor temperature, pain, irritation, chemical changes and stretch in the visceral organs
Fibres run within autonomic nerves, especially vagus and sympathetic nerves
How do sensory neurons carry information to the brain?
Sensory neurons to spinothalamic tract to thalamus to cerebral cortex
What is referred pain?
Pain in visceral organs is often perceived to be somatic in origin: referred to somatic regions of the body that receive innervation from the same spinal cord segments
Describe the sympathetic nervous system communication
Preganglionic axons exit the spinal cord through ventral route and enter spinal nerve, exit spinal nerve via communicating ramus, enter sympathetic trunk, then either synapse in chain ganglia or pass through ganglia and synapse in prevertebral ganglion forming splanchnic nerve
Why is the adrenal gland an exception?
The synapse is within the gland
Neurotransmitters of the sympathetic and parasympathetic division
Sympathetic: ACh pre-synaptic, noradrenaline post-synaptic
Parasympathetic: ACh pre- and post-synaptic
What are visceral reflex arcs?
Include visceral sensory and autonomic neurons
Many are spinal reflexes such as defecation and micturition
Some only involve peripheral neurons: spinal cord not involved e.g. enteric nervous system- 3 neuron reflex arcs entirely within the wall of the gut
Central control of the autonomic nervous system: amygdala, hypothalamus, reticular formation
Amygdala: main limbic region for emotions, stimulates sympathetic activity, especially previously learned fear related behaviour, can be voluntary when recalling frightful experience as cerebral cortex acts through amygdala
Hypothalamus: main integration centre
Reticular formation: most direct influence over autonomic function
What is tone and how is it affected by the autonomic nervous system?
ANS generally gives a basal level of activity in the tissues it innervates called tone
Sympathetic tone provides a constant partially contracted state to the blood vessels giving a degree of blood pressure
Heart is normally modulated by PNS- if vagus nerve cut, heart rate increases
During exercise parasympathetic tone decreases while sympathetic tone increases
Manipulating synaptic transmission
Block synthesis of neurotransmitter
Block breakdown of neurotransmitter
Block uptake of neurotransmitter or metabolite
Affect release or vesicular stores of neurotransmitter
Agonist or antagonist at receptors
Acetylcholine receptors
Nicotinic: ion channels, fast action, excitatory (Na), A1 at NMJ, A3 at autonomic ganglia i.e. different receptors
Muscarinic: G-protein linked family of receptors, M1-M5, M1-3 in parasympathetic targets, M2 inhibitory, M1 and 3 excitatory
Nicotinic agonist, antagonist and pore blocker
Nicotinic agonist- short term hypertension, palpitations, secretions, GI stimulation- no clinical use
Nicotinic antagonist- hypotension, loss of cardiac reflexes, inhibition of secretions, GI paralysis, impaired mictation- no clinical use
Pore blocker- hypotension, loss of cardiac reflexes, inhibition of secretions, GI paralysis, impaired mictation- no clinical use
Muscarinic agonist and antagonist
Muscarinic agonist (parasympathomimetic): M1- secretion of gastric acid, M2- slowing of the heart, M3- contraction of smooth muscle- limited clinical use in glaucoma Muscarinic antagonist (parasympatholytic): M1- reduced secretion of gastric acid, M2- increased heart rate, M3- relaxation of smooth muscle (pupillary dilatation)- clinical use in motion sickness, asthma, GI or menstrual cramps
Noradrenergic/adrenergic receptors
All GPCR
A1 adrenoceptor: post-synaptic receptor, excitatory
A2 adrenoceptor: pre-synaptic, inhibitory
B1 adrenoceptor- post synaptic, excitatory
B2 adrenoceptor- post synaptic, inhibitory/excitatory
B3 adrenoceptor- post synaptic, excitatory
Noradrenergic agonist and antagonist
Noradrenergic agonist: A1 causes vasoconstriction and contraction of smooth muscle, A2 causes vasoconstriction, B1 causes cardiac stimulation and gut relaxation, B2 causes vasodilation and bronchodilation- clinical uses in hypotension shock, migraine and asthma
Noradrenergic antagonist: A1 causes vasodilation and smooth muscle relaxation, A2 causes vasodilation, B1 causes gut stimulation, B2 causes vasoconstriction and bronchoconstriction- clinical uses in hypertension, phaechromocytoma, beta blockers for hypertension, cardiac arrhythmias, anxiety and migraine
