Physiology and pharmacology of the parasympathetic nervous system Flashcards
What does stimulation of vagus nerve in the heart result in?
-Stimulation of Vagus nerve release Ach which acts at M2 receptors
-Decreased frequency of electrical activity generated at SA node leading to reduction in heart rate which decreases cardiac output and TPR
What do the parasympathetic not innervate in the heart and what does this mean?
-Parasympathetic nerves do not innervate ventricles or most blood vessels
-This means that this does not affect heart contractility or total peripheral resistance
What do the parasympathetic nerves in the eye regulate?
-Pupil diameter
-Intra-ocular pressure
-Accommodation(focusing)
What receptor is stimulated by the parasympathetic nervous system in the eye which impacts pupil diameter?
-Stimulation of M3 receptors lead to constriction of the circular smooth muscle of the iris(constrictor pupillae)
-Constrict of pupil(miosis)
What is the secondary action as a result of constriction of the pupil due to stimuation of M3 receptor?
-Constriction of the pupil(M3) has a secondary action of opening the canal of schlemm at the back of the pupil
-Drains aqueous humour from eye
-Reducing pressure within the eye
Parasympathetic control for distance vision?
-Ciliary muscle relaxed
-Suspensory ligament taut
-Long thin lens
-Long focal length
Parasympathetic control for close vision?
-Oculomotor nerve(III) releases Ach which stimulates M3 receptor causing:
-Ciliary muscle contracted
-Suspensory ligaments relaxed
-Bulged lens shape
-Reduced focal length
What does bladder voiding involve?
-Bladder voiding involves a series of interactions between parasympathetic,
sympathetic, motor and sensory (afferent) nerves
What muscles are contracted and relaxed in the bladder due to sympathetic nerves?
-Detrusor muscle is relaxed
-Sphincter contracted
What receptor is stimulated by the sympathetic nervous system in detrusor muscles and what does this allow?
-Beta2 receptors in detrusor smooth muscle activated
-This allows the bladder to fill
What receptor is stimulated by the sympathetic nervous system in sphincter and what does this allow?
-alpha1 receptor in internal sphincter smooth muscle activated
-This allows to hold urine
What do stretch receptors activate when the bladder is full and through the activation and inhibition of what nervous system?
-When the bladder is full, SR activates micturition reflex through stimulation of parasympathetic nerves and inhibition of sympathetic nerves
What receptor does the parasympathetic nervous system activate in bladder and what does this cause?
-Stretch receptors activate parasympathetic nerves innervating bladder
-stimulates M3 receptor and detrusor smooth muscle contract
Where do the motor nerves(somatic efferent nerves) originate from and what do they innervate, stimulare and cause in the bladder?
-Innervates the external urethral sphincter nicotinic, stimulating the nicotinic receptor, providing voluntary control over micturition
What receptor does the stimulation of the vagus nerve activate in GI tract and what does this led to and cause?
Stimulation of vagus nerve releases Ach which acts on M3 receptors
-Leads to contraction of circular and longitudinal smooth muscle in GI tract
-This increased motility
What are the afferent(sensory) fibres of the vagus involved in?
-Vagus also contains afferent (sensory) fibres
-These are involved in peristaltic reflex control
What does the vagus nerve act as and to what system and muscles?
-Vagus nerve acts as an afferent(sensory) and efferent(motor) nerve to enteric nervous system, longitudinal smooth muscle and circular smooth muscle
What does the enteric nervous system act as and to what muscles?
-The enteric nervous system acts as an efferent(motor) nerve to longitudinal smooth muscle and circular smooth muscle
What is the salivary gland innervated by and what do those nerves stimulate and increase?
-Innervated by VII (facial) and IX (glossopharyngeal)
-Stimulates acinar cells
-Increase amylase/mucins
What is the gastric glands innervated by and what do those nerves stimulate and increase?
-Innervated by X(vagus)
-Stimulate parietal cells
-Increase gastric acid
What is the pancreatic glands innervated by and what do those nerves stimulate and increase?
-Innervated by X(vagus)
-Stimulate acinar+islet cells
-Increase pancreatic secretions
What is the pancreas innervated by and what do those nerves cause?
-Innervated by X(vagus)
-Increase insulin secretion from beta-cells
What receptors are stimulated in the lungs by the parasympathetic nervous system and what does this cause?
-Stimulation of M3 receptors contract bronchi smooth muscle cells causing bronchoconstriction
What are muscarinic antagonists used as in the lungs?
-Muscarinic antagonists are used as bronchodilators and are used in COPD to increase airway flow
What do muscarinic antagonists do in patients with bladder outflow problems and glaucoma?
-In patients with bladder outflow problems and glaucoma, muscarinic antagonists will reduce urine outflow and increase intraocular pressure
What are possible contraindications for bladder issues or glaucoma?
-Bladder issues or glaucoma might be potential contraindications against using muscaranic antagonists in COPD
What nerves innervate erectile tissue in male genitalia and what does this release?
-Specialised sacra parasympathetic vasodilator nerves innervate erectile tissue
-Stimulation of these nerves release nitric oxide (NO) not Ach
What is nitric oxide?
-Nitric oxide is a lipophilic, membrane-permeable gas
What does nitric oxide cause and what does this produce?
-Nitric oxide causes relaxation of vascular smooth muscle cells composing the corpus cavernosum
-Corpus cavernosum dilates and fills with blood
-Produces and maintains erection
