Autonomic Nervous System Physiology Flashcards
role of autonomic nervous system
involuntary branch of efferent division of PNS
ANS controls internal environment
heart rate, circulation, digestion, respiration
internal organs controlled by ANS
Heart Lungs Stomach & GIT, spleen, pancreas Bladder & rectum Kidney & liver Eye (pupil)
Medulla and Pons in brain stem control
Centres controlling cardiovascular, respiratory & digestive fcts.
Hypothalamus controls
Heart rate, B.P. respiration (via medulla)
spinal cord controls
Integrates autonomic reflexes not subject to higher control
e.g. urination, defecation
Regions regulating the ANS output
Medulla and pons
Hypothalamus
Spinal cord
parasympathetic
rest and digest - promotes normal maintenance of body
secretion and mobility of the body of different parts of the digestive tract
sympathetic
fight or flight - emergency
increase cardiac outputpulmonary ventilation, routes blood to muscles, raises blood glucose and slows down digestion, kidney filtration and other functions not needed during emergencies
each ANS pathway from ___ to ___ is ___
Each ANS pathway from CNS to organ/effector is two-neuron chain
Origin of parasympathetic ANS nerve fibre
cranial (X – vagus nerve) and sacral (lower spinal cord)
structure of parasympathetic pathway
long and myelinated preganglionic nerves
short and unmyelinated postganglionic
Origin of preganglionic sympathetic SNS nerve fibre
Preganglionic - thoracic and lumbar regions of spinal cords (T1-L3)
structure of ANS sympathetic pathways
short and myelinated preganglionic nerves
long and unmyelinated postganglionic nerves
where does the sympathetic ganglia lie
in a chain along either side of the spinal cord - sympathetic trunk
name 2 main neurotransmitters used in ANS
Acetylcholine (ACh)
Noradrenaline (NA)
where is ACh released
preganglionic ANS nerves
Postganglionic parasympathetic nerves
what nerves stimulate the release of Noradrenaline
Postganglionic sympathetic nerves
2 portions of adrenal gland
inner - adrenal medulla
outer - adrenal cortex
how is adrenal medulla innervated
Medulla modified sympathetic ganglion w/out postganglionic fibres
what do the preganglionic fibres of adrenal medulla stimulate
Preganglionic fibre directly stimulates hormone release from chromaffin cells
what neurotransmitter does adrenal medulla stimulate the release of
20% noradrenaline
80% adrenaline
three layers of the adrenal cortex (outer - inner)
zona glomerulosa
zona fasciculata
zona reticularis
exceptions to rules of ANS
Blood vessels
Arterioles & veins (not arteries or capillaries) innervated by sympathetic NS only
Liver (glycogen stores)
Gluconeogenesis (glucose released) by sympathetic NS
Sweat glands
Mainly sympathetic innervation and terminal fibre release ACh(!) not NA(!)
Limitation of neurotransmitters of the ANS
stimulate activity in some tissues but decrease activity in others
NA increases heart rate but decrease contraction of digestive tract
if the tissue/organ targets posses one or more receptor
binding of NT induce tissue specific response
2 types of receptors
ionotrophic receptor - dont open ion channels but change conformation to allow ions - for fast responses
metabotrophic receptor - something must be bound has a cascade and activate other ion channels - for slow responses
where are Acetycholine receptors and Noradrenaline receptors in sympathetic nervous system
AChR at ganglion
NA-R -target tissue
2 types of receptors that bind to acetylcholine
nicotonic
muscarinic
nicotonic cholinergic receptors are found in …
Found on all postganglionic ANS cell bodies
nicotonic cholinergic receptors are activated by ..
R activated by ACh released from preganglionic parasymp. or symp. nerves
R also activated by tobacco derivative nicotine
are nicotonic cholingergic receptors ionotropic or metabotropic
ionotropic - fast responses
depolarisation - fast - new impulse is transmitted
target tissues of muscarinic cholinergic receptors
Found on effector cell membranes - smooth muscle, glands, cardiac muscle
nicotonic cholinergic receptors are activated by …
Binds ACh released from postganglionic parasympathetic nerves
also activated by mushroom poison muscarine
are muscarinic cholingergic receptors ionotropic or metabotropic
metabotrophic receptor
5 types
location and function of inhibitory muscarinic receptors
M2
Located on cardiac tissue
Receptor couples to increase K+ conductance, inhibit calcium channels
e.g. decrease heart contraction
location and function of excitatory muscarinic receptors
M3
Located in digestive system
G protein couples to Ca2+ second-messenger system
e.g. Increase glandular secretions, increase GIT motility
2 Classes of Adrenergic receptors that bind NA and AD
alpha - a1 and a2
Beta - B1, B2, B3
A1 location
excitatory response
Located on most sympathetic target cells
a1 function
G protein couples to Ca2+ second-messenger system
e.g. Increase contraction of arterioles → raised blood pressure
a2 location
: inhibitory response
Located in digestive system
a2 function
G protein couples to inhibit cyclic AMP system
e.g. decreased smooth muscle contraction → reduced GIT motility
b1 location
Located in heart
b1 function
excitatory
Couples via G protein to cyclic AMP/PKA
e.g. contraction of cardiac muscle → increased rate & force
b2 location
Skeletal muscle (AD in blood), smooth muscle of some vessels & organs
b2 function
inhibitory
Couples via G protein to cyclic AMP/PKA
e.g. relaxation of smooth muscle → bronchiolar dilation
how is excess acetylcholine removed
destroyed by acetylcholinesterase
how is excess noradrenaline removed
Re-uptake by pre- and post-synaptic cell then metabolized/re-cycled
potential targets for Pharmacological intervention
NERVE TERMINAL Neurotransmitter release POST SYNAPTIC MEMBRANE Neurotransmitter-receptor interaction NEUROTRANSMITTER EFFECT TERMINATION Neurotransmitter degradation
how do drugs interfere with ANS
mimic agonist or inhibit antagonist ANS response and receptors
function of atropine
Blocks muscarinic R
Blocks parasympathetic actions at effector tissues
Reduces salivary and bronchial secretion (e.g. during surgery
example of muscarine antagonist
atropine
adrenergic agonist
salbutamol
atenolol
function of salbutamol
Activates b2 adrenergic receptors
Dilates bronchioles – treatment of asthma / COPD
Lask of effect at b1 means no effect on heart
function of atenolol
Blocks b1 adrenergic receptors
CVS: Lowers blood pressure - treatment of hypertension
example of autonomic function
Dysautonomia
causes of Dysautonomia
Trauma,
Inflammation
Drugs
Neurodegenerative disease
dysautonomia
deficiency of sympathetic activity to lesion /compression (trauma, tumor)
