Autonomic NS Flashcards
what is the autonomic nervous system?
autonomic nervous system is a component of the efferent nervous system responsible for automatic/ involuntary physiological processes via effectors which are usually smooth muscles and glands.
it plays a major role in homeostasis, fight or flight response
can be further subdivided into parasympathetic and sympathetic NS
sometimes enteric NS is classed as 3rd limb.
what is the enteric NS?
intrinsic nerve plexus in the gut
coordinates peristasis and secretion
communicates with ANS - whereby sympathetic reduces motility and secretion and parasymp the opposite.
consists of myenteric plexus and submucosal plexus which extend from oesophagus to anus.
describe the organisation of the nervous system..
descibe the anatomy of autonomic NS
divided into sympathetic and parasympathetic. each has different organisation but follows basic components…
2 neurons
- preganglionic = myelinated B with cell bodies in CNA
- post ganglionic = unmyelinated C, cell bodies in ganglia of PNS
- Ganglia
simplified diagram, in fact each preganglionic can synapse with multiple post ganglionic fibres.
sympathetic:
- thoraco lumbar origin (T1-L3)
- ganglia are in a chain adjacent to spinal cord
- therefore short pre-ganglionic, long post ganglionic
- preganglionic NT Ach (nAChR), Post = NA
parasympathetic
- craniosacral in orgin
- ganglia are near effector organ
- thereofre long pre-ganglionic fibre and short post.
- both pre and post NT = Ach. (nACHR, mAChR)
describe the anatomy of sympathetic NS…
major branch of ANS involved in fight or flight response inducing a state of alertness and arousal.
pre-ganglionic fibres originate from thoracolumbar regions - T1 to L3 - these are myelinated B fibres
leave via the ventral horn in association with spinal nerves
travel to sympathetic chain. The sympathetic chain consists of 22 ganglia either side of spinal cord
some pre-ganglionic fibres go up/down a few levels.
within sympathetic chain are the ganglia where synapse between pre and post neurons occur.
post ganglionic C fibres emerge from sympathetic chain and go on to innervate effector organ.
NT = ACh (nAChR) , NA (adrenoreceptors)
there are some exceptions
- some ganglia are pre-vertebral. e.g. coeliac and mesenteric ganglia - these are closer to target organ
- adrenal medulla - some pre-ganglionic fibres innervate adrenal medulla which secretes NA/A into blood stream directly. could say it is a specialised post ganglionic fibre.
- some post ganglionic fibres secrete ACh e.g. sweat and erector pilli
name of adrenal medulla cells
chromaffin cells.
describe the anatomy of the sympathetic chain..
consists of 22 ganglia either side of spinal cord
divded into 3 parts - cervical, throacic and lumbar
cervical has superior, middle and inferior ganglia. (inferior ganglia + first thoracic ganglia = stellate ganglia)
12 thoracic ganglia and 4 sacral and 4 lumbar ganglia.
each supplies corresponding body parts e.g. cervical does head and neck.
describe the anatomy of parasympathetic NS?
One of the major branches of ANS. invovled in rest and digest. has a basal tone and thus when sympathetic not activated, parasympathetic dominates.
pre-ganglionic fibres orginates from brainstem nuclei and sacral level (craniosacral output)
cranial parasympathetic nerves:
* originate from CN nuclei - 3, 7, 9, 10
* parasympathetic nerves leave and travel with cranial nerve to near target site.
* here they synapse with ganglia
* e.g. CN3 = ciliary ganglia - pupil constriction
* e.g. CN7 = pterygopalatine and submandibular ganglia = salivation and lacrimation
* CN9 = otic ganglia = saliva
* CN 10 = largest of parasymp fibres = many ganglia e.g. heart, lungs, gut etc
sacral outflow - parasympathetic nerves exist with spinal nerves S2 to 4 and then innervate ganglia that supply lower half of body
NT - Ach = nAChR and mAChR
give an overview of the functions of ANS
overall rest and digest vs fight or flight
by system
CVS -
* tachycardia, vasoconstriction, ionotrophy vs
* bradycardia
respiratory
* bronchodilation, tachypnoea
* bronchoconstriction
GI
* reduced motility, reduced secretions
* increased motility/secretions
metabolism
* stimulates glycolysis and gluconeogenesis
* stimulates insulin secretion
Urinary
* ejaculation , bladder relaxation
* erection , bladder contraction, sphinchter relaxation
cranial
* pupil dilation, inhibits salivation
* opposite
how are the outputs of ANS coordinated?
hypothalamus plays a major role.
recieves inputs from cortex, somatic sensors/ visceral sensors erc
then sends outputs through RAS and synapses with various nuclei in brainstem and spinal cord
Tell me about adrenoceptors…
GPCR - 7 transmembrane domain receptor. coupled to G protein which is made of a,b,g subunits.
there are 2 alpha and 3 beta adrenoceptors
A1 = Gq
A2 = Gi
Beta = Gs
A2 is different in that it tends to be pre-synaptic
describe the mechanism of Alpha 1 adrenoceptor
Gq
found in arteriole smooth muscle and causes vasoconstriciton. also contraction of GI and urethral sphinchters and glycogenolysis.
Gq –> activates phospholipase C which breaks down PIP2 to IP3 and DAG
the IP3 acts to increase intracellular calcium
DAG activates PKC which has a number of down stream effects
not found in heart or brain - to avoid vasoconstriction here.
describe the mechanism of a2 adrenoceptors
Gi
therfore inhibits adenylate cyclase
normally AC will convert ATP to cAMP and cAMP activates PKA
now less of this so less of PKA
less phorphosylation of Ca and K channels
results in hyperpolarisation and reduced Ca influx
hence reduced nerve transmission when acting pre-synaptically.
this reduces NA release
describe the mechanism of B1 adrenaoceptors
found in heart , salivary glands, kidneys and liver.
increase HR, contractility, renin , glucogenolysis, lipolyisis
Gs –> PKA –> phosphorylation of Ca channels to increase Ca in. ionotrophic
also phosphorylates HCN funny current channels - chronotrophy
how do B2 adrenoceptors work?
Gs - PKA - phosphorylates and activates myosin light chain phosphatase in smooth muscle - relaxation
vasodilation of certain vascular beds (skeletal, coronary)
bronchodilation
also glycogenolysis
how are catecholamine synthesised?
come from phenylalanine - essential aa
converted to tyrosine by phenylalanine hydroxylase.
tyrosine hydroxylase = rate limiting step.
