lecture 1 ANS and homeostasis

define homeostasis

control of the internal environment, failure results in pathophysiology

why is homeostasis necessary

maintain equilibrium, maintain variables, involving multiple organ systems

explain homeostatic control

continuous, involves monitoring multiple parameters, then coordinating appropriate responses to minimise disturbance

explain the homeostatic pathway

1st stimulus, sensor, controller, effector, response

which systems are the control mechanisms

CNA/PNS, endocrine system, paracrine systems

explain negative feedback

effector leads to reduction in stimulus

how is the ANS organised

sensory nerve fibres, control centres, efferent pathways

what are the control centres

hypothalamus, brain stem, spinal cord

what are the efferent pathways

sympathetic fight and flight, parasympathetic rest and digest

what are common features of the ANS

2 neurons in series, preganglionic neurons originate in CNS, post in autonomic ganglia

how many postsynaptic ganglionic neurons can 1 preganglionic neuron synapse with

8-9 average

explain fight or flight

adrenaline, noradrenaline and cortisol release, osteocalcin inhibits parasympathetic neurons

what is osteocalcin

bone derived compound, stimulated from amygdala centre, makes sure sympathetic nervous system is unopposed

explain the parasympathetic nervous system

short preganglionic neuron, long postganglionic neuron

which cranial nerves does the preganglionic neuron originate from in PSNS

3 (eye), 7 (facial), 9 (glossopharyngeal) and 10 (vagus)

where does the postganglionic neuron originate from in PSNS

autonomic ganglia, ganglia on or near target organ

where does the preganglionic neuron originate from in SNS

thoracic 1 T1 and lumbar L2/3

where does the postganglionic neuron originate from in SNS

autonomic ganglia, 2 paravertebral sympathetic chains

explain the sympathetic NS

short preganglionic neuron, long postganglionic neuron

what role does the adrenal medulla play in SNS

directly innervated by preganglionic neurons of SNS, secretes adrenaline and noradrenaline

list some neurotransmitters of ANS

Ach, NAdr, Adr, NANC neurotransmitters

list the synapse types in ANS

cholinergic (nicotinic or muscarinic) or adrenergic (alpha or beta)

explain nicotinic receptors

in ganglia SNS and PNS, at neuromuscular junctions, blocked by curare

explain muscarinic receptors

target organ PNS, blocked by atropine (mushroom or belladonna)

explain alpha 1 adrenoreceptors

postsynaptic, Nadr> Adr, vasoconstriction and smooth muscle contraction

explain alpha 2 adrenoceptors

presynaptic, NAdr> Adr, reduction in adrenergic and cholinergic transmission, blocked by phentolamine

explain beta 1 adrenoceptors

in the heart, Adr=NAdr, increases heart rate and contraction force

explain beta 2 adrenoceptors

Adr>NAdr, vasodilation and smooth muscle relaxation

what drug blocks both beta adrenoceptors

propanolol

explain the eye muscle contractions

explain the general neuron path

CNS along a preganglionic neuron to a synapse (autonomic ganglion) along a postganglionic neuron to a target tissue