Physiology and pharmacology of ANS Flashcards
Parasympathetic system, Sympathetic system actions
slide 4, lecture 11
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Fight or flight response
Which system
Sympathetic Nervous System- not usually the case but only if strongly activated
Pupil dialation Increased heart rate Increased bronchioles diameter Stimulates increased glucose release for muscles Increased sweating
Parasympathetics nerves
Cranial nerves III, VII, IX, X: III Oculomotor – pupil constriction VII Facial nerve – Salivation IX Glossopharyngeal – Salivation X Vagus – bradycardia, gastric motility, digestion
Sacral splanchnic nerves S2-4
None from main part of spinal cord
Sympathetic nerves
Where do they eminate from?
Intermediolateral cell column T1-L2
Follow ventral root in motor fibres, diverted through sympathtetic ganglia, synapse into post ganglionic neurones
Sympathetic Chain- between T1 and L3
Anatomy of ANS- diagram
(slide 8, lecture 11)
Difference between sympathetic and parasympathetic
Comes out of spinal cord and synapses into the sympathetic chain
Fibres out of spinal cord= presympathetic/ preautonomic
Pre ganglionic neurones the ones that have synapsed onto cells in the spinal cord which exit the spinal cord into the ganglia
Post ganglionic= after ganglion to the organs
No ganglia outside of target organ in parasympathetic, ganglia in parasympathetic IS IN THE TARGET ORGAN (post ganglionic neurone is in the target organ)
Differences between parasympathetic vs sympathethic Neurotransmitters? Synapses? Exceptions in Sympathetic? Somatic Nervous System Diagram (slide 10, lecture 11)
Parasympathetic
Comes out of CNS, parasympathetic innervates target organs by monosynaptic connection (only one synapse within target organ)
Mostly ACh (at preganglionic and postganglionic) at both stages
Sympathetic
Preganglionic neurones that come down spinal cord use glutamate as NT (exitatory NT)
Pre ganglionic neurones= ALWAYS ACh into ganglionic
Post-ganglionic=mainly noradrenaline into target organs
Exception= sweat glands activated by SNT use ACh at post ganglionic
Exception= renal vessels activated by SNT used Dopamine at post ganglionic
Exception= adrenal medulla targeted by SNT but doesn’t go through sympathetic ganglia, but still ACh is used, adrenal medulla then releases both Adrenaline+ Noradrenaline into bloodstream to target effector organ via hormonal response rather than neuronal response
Somatic/ Voluntary nervous system:
Glutamate coming down to spinal cord which synapses directly onto target organs using ACh (problem in target drugs which only want to use ACh for ANS)
Noradrenaline and acetylcholine biosynthesis
slide 12, lecture 11
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Regulation of function= blood pressure
Baroreceptors in aorta (via vagus nerve)/2 in carotid arteries (via glossopharyngeal) respond to mechanical pressure, transmitting pressure information beat to beat
When BP threshold reached, baroreceptors start to fire
Aortic baroreceptors send impulses down vagus afferents, to brain, causing impulses down vagus efferents via PNS to decrease stroke volume and hence output, while also causing vasodilation via inhibition of SNS, all to decrease pressure
Baroreflex
In hypertensive patients?
Set point is normal blood pressure on a graph of blood pressure by baroreceptor firing (sigmoid curve)
Tiny change in blood pressure causes significant change in baroreceptor firing
Very sensitive system
In hypertensive patients, the sigmoid curve+ set point shifts to the right and brain thinks this is normal (cause could be congenital impaired blood flow to brain so trying to keep it high)
Regulation of GI function
Sensory inputs enter?
Sensory inputs enter hypothalamus for direction to brainstem in the cephalic response
Sight, smell and taste of food leads to cephalic response
Vagus nerve causes:
1) Pancreas releases small amount of insulin in anticipation of increased glucose (neurally mediated)
2) Stomach also secretes gastric juices in response to
Mechanoreceptors: detect stomach wall distension sending information via vagus nerve to brainstem to alert brain that have eaten; degree of distention leads to a proportional increase in firing
Gut hormones released in response to chemoreceptors: GLP-1, PYY and CCK are released from the GI tract to activate chemoreceptors to signal to brain to stop eating via the Vagus nerve
Obesity: decreases the response from mechanoreceptors for a given pressure, and lose satiety hormone receptors
When hungry, Vagus does not express satiety hormone receptors e.g. PYY; expressed when start eating
In obese state, PYY receptor lost
Regulation of function: Respiration
Pontine respiratory centre (coordinates rate and pattern of breathing) in the pons and the ventral (coordinating rhythmicity)/dorsal (inspiration and diaphragm control) groups in the medullary respiratory centre make up the central respiratory centre
Output to respiratory muscles (intercostal+ diaphragm)
Aortic chemoreceptors transmit down vagus nerve (CXIX) and carotid chemoreceptors transmit down 9th cranial nerve, detecting decreased oxygen, decreased pH and increased CO2
Central chemoreceptors respond to decreased pH and increased CO2
All chemoreceptors communicate with the dorsal group of the medulla to increase respiration
Lung mechanoreceptors are stretched, and transmit down vagus nerve, inhibiting respiration to prevent overexpansion in the Hering-Breuer reflex
Mechanoreceptors communicate with the dorsal group of the medulla to decrease respiration
Parts of spinal levels that control respiration
C1-C3 = accessory muscles C3-C5 = diaphragm control (via phrenic nerve) T1-T11 = intercostals T6-L1 = abdominals
Regulation of function- Micturition Muscles Efferent neurones? Afferent? Activation of PNS=? Activation of SNS=? Afferent signalling results in?
Detrusor muscle: outer muscle wall, innervated by sacral cord (S2-S4) (PNS)
Internal sphincter: T10-12 (SNS)
External sphincter: S2-S4; voluntary control by motor neurones
Afferent mechanoreceptors go via S2-S4
Activation of:
PNS = detrusor muscle contraction
SNS = contraction of the internal sphincter
Voluntary control motor nerves= contraction of external sphincter
If bladder is full afferent signalling results in activation of PSN and inhibition of SNS. Overall control of voiding governed by voluntary control of external sphincter
Central regulation of autonomic funtion
Nucleus Tractus Solitarius (NTS): CNX and CNIX inputs, sending info up to hypothalamus (e.g. BP and stomach filling) for integration, returning signals to the dorsal motor nucleus of the vagus, controlling output - or directly to Intermediolateral cell columns; other brain regions can exert some control over ANS (e.g. Can hold breath)
PNS receptors of ANS
Cholinergic Receptors
Types: Nicotinic (ionotropic receptor found in all autonomic ganglia, binding of ACh causes binding of cations into cell= AP) , Muscarinic (G-protein coupled receptor, stimulated by all post-ganglionic PNS neurones+ also by SNS at selected sites, works by binding to external site of GPCR causing downstream pathways)
NB Nicotinic also found at NMJ
