Autonomic Physiology Flashcards
Describe the anatomy of the sympathetic branch of the Autonomic Nervous System.
Sympathetic:
Outflow is thoraco-lumbar, with nerves coming from T1-12 and L1-2. The ganglia are close to the vertebrae in the sympathetic trunk. Usually the preganglionic fibres enter the trunk, make the synapse and then have a long postganglionic fibre.
Describe the anatomy of the parasympathetic branch of the Autonomic Nervous System.
Parasympathetic:
Outflow is cranio-sacral, with innervation from III, VII, IX and X from the cranial nerves and the sacral nerves. They usually have a long preganglionic fibre, with the ganglion close to the target.
Describe the neurotransmitters, receptors and functional aspects of autonomic innervation.
Acetylcholine acts on Cholinergic receptors
• Muscarinic Receptors
• Nicotinic Receptors
Norepinephrine acts on Adrenergic receptors
• α Receptors
• β Receptors
All preganglionic fibres, whether they’re sympathetic or parasympathetic, release Ach onto nicotinic receptors.
In sympathetic nerves, postganglionic fibres release norepinephrine onto alpha or beta receptors. Except in the special case of in the adrenal gland, where norepinephrine and epinephrine are released directly into the blood.
In parasympathetic nerves, postganglionic fibres release ACh onto muscarinic receptors.
Describe simple autonomic reflexes.
Autonomic reflexes e.g. baroreceptor reflex
• Baroreceptors detect blood pressure
• Plus central control
– From the hypothalamus
• Co-ordinates autonomic, somatic and endocrine activity,
• E.g. defence response
Describe the effect of sympathetic autonomic innervation on major internal organs (e.g. heart, lung, eye, gut and blood vessels).
Parasympathetic “rest and digest”- not so coordinated, but generally rest and digest
• Heart rate and BP decreased
• Pupils constricted, focused closer
• Hair down
• Laying down energy stores
• Digestive system mobilised, defecation and digestion
What effects does ANS signalling have on the eye?
Sympathetic system
– Activates β2 receptors on ciliary muscle round lens so that the ciliary muscle relaxes & eye focuses far away
– Activates α1 receptors on radial muscle of iris so that the radial muscle contracts & makes pupil larger
Parasympathetic system
– Activates muscarinic receptors on ciliary muscle so the ciliary muscle contracts & eye focuses close up
– Activates muscarinic receptors on sphincter muscle to contract the sphincter muscle & makes pupil smaller
What effects does ANS signalling have on the eye?
Sympathetic system
– Activates β2 receptors on ciliary muscle round lens so that the ciliary muscle relaxes & eye focuses far away
– Activates α1 receptors on radial muscle of iris so that the radial muscle contracts & makes pupil larger
Parasympathetic system
– Activates muscarinic receptors on ciliary muscle so the ciliary muscle contracts & eye focuses close up
– Activates muscarinic receptors on sphincter muscle to contract the sphincter muscle & makes pupil smaller
What effects does ANS signalling have on the heart?
Sympathetic system
– Activates β1 receptors on pacemaker cells, which increases heart rate
– Activates (mainly) β1 receptors on myocytes which increases strength of contraction
Parasympathetic system
– Activates muscarinic receptors on pacemaker cells which decreases heart rate
– Little effect on myocytes and strength of contraction
What effects does ANS signalling have on the blood vessels?
• Sympathetic system
– Activates α1 receptors on smooth muscle of vessels
• Makes smooth muscle contract & blood flow decreases
– Activates β2 receptors on smooth muscle of vessels
• Makes smooth muscle relax & blood flow increases
• Parasympathetic system
– Usually no effect
What effects does ANS signalling have on the blood vessels?
Sympathetic system
– Activates α1 receptors on smooth muscle of vessels, which makes smooth muscle contract & blood flow decreases
– Activates β2 receptors on smooth muscle of vessels, which makes smooth muscle relax & blood flow increases
Parasympathetic system
– Usually no effect
What effects does ANS signalling have on the gut?
Sympathetic system
– Activates α/β receptors on smooth muscle of gut, decreases gut motility
– Activates α receptors in pancreas, inhibits secretion of enzymes
Parasympathetic system
– Activates muscarinic receptors on smooth muscle of gut, increases gut motility
– Activates muscarinic receptors in pancreas, increases secretion
What effects does ANS signalling have on energy stores?
Sympathetic system
– Activates α/β receptors on liver cells (hepatocytes), stimulates glycogenolyis & gluconeogenesis
– Activates α/β receptors on fat cells (lipocytes), increases lipolysis
Parasympathetic system
– No effect
What effects does ANS signalling have on the salivary glands?
Sympathetic system
– Activates β receptors
• Stimulates thick secretion rich in enzymes (dry mouth when scared)
Parasympathetic system
– Activates muscarinic receptors
• Stimulates profuse watery secretion
What effects does ANS signalling have on the bladder?
Sympathetic system
– Activates β2 receptors on smooth muscle of bladder wall, relaxes smooth muscle and reduces pressure
– Activates α1 receptors on smooth muscle of sphincter, contracts smooth muscle and stops urination
Parasympathetic system
– Activates muscarinic receptors on bladder wall, contracts smooth muscle and increases pressure
– Activates muscarinic receptors on sphincter, relaxes smooth muscle and causes urination
What effects does ANS signalling have on the reproductive tract?
Sympathetic system
– Activates α1 receptors on smooth muscle of urethra, contracts smooth muscle and causes ejaculation
Parasympathetic system
– Activates muscarinic receptors on smooth muscle of corpus cavernosum
, relaxes smooth muscle & causes erection
