P: Autonomic nervous system Flashcards
Definition of cardiac output (CO), how to calculate it and its value
- Volume of blood pumped out of each ventricle per minute
- CO = stroke volume (SV) x heart rate (HR) = 70-80 ml x 70 bpm
- CO = 5.5 litre/min
How are heart rate (HR) and stroke volume (SV) regulated?
ANS
ANS comprises a reflex arc which has:
- Afferent (sensory) limb
- Central regulatory component in brain stem, spinal cord and hypothalamus
- Efferent (effector pathway)
Where does central integration of information take place?
Hypothalamus and brain stem
What’s the main integration centre for sensory input?
Hypothalamus
Where is the cell body of preganglionic neuron embedded?
In CNS (brain/spinal cord)
Where is the cell body of postganglionic neuron embedded?
In an autonomic ganglion (clusters of cell bodies outside CNS) —> its axon extends from ganglion to target organ
Where do preganglionic neurons synapse?
Preganglionic neurons synapse in ganglia which are in 3 sites:
- Paravertebral ganglia: form sympathetic chain
- Prevertebral (collateral) ganglia: generally in abdominal cavity
- Within adrenal medulla
Parasympathetic nerves to organs consist mainly of ___ because terminal ganglia are located ___
Preganglionic neurons, close to or within target organs
How do post-ganglionic nerve fibres innervate the tissue?
- Do not form specific synapses within the tissue
- Neurotransmitters are synthesised in and released from the fibre’s varacosities which pass into the close proximity with the cell
- These sites = neuroeffector junctions
How does sympathetic system stimulate a fight or flight response?
By releasing norepinephrine (noradrenaline) from postganglionic neurons onto effector organs (adrenergic response)
What is the name for noradrenaline and adrenaline?
Catecholamines
What do sympathetic nerves release in sweat gland, piloerector muscles and some blood vessels of skeletal muscles?
Acetylcholine (cholinergic response)
What does the parasympathetic do in relation to sympathetic system and how?
It opposes the effects of sympathetic system by releasing acetylcholine onto target organs (cholinergic response)
What are the 2 main signalling cascades activated in the ANS?
- Adenylyl cyclase - cAMP pathway
- Phosphoinositide pathway
What does noradrenaline bind to and what are the subtypes + their general activity?
- Adrenergic receptors (adrenoceptors)
- Subtypes: alpha 1, alpha 2, beta 1, beta 2, beta 3
- Alpha-adrenoceptors activate the phosphoinositide pathway and inhibit the cAMP cascade
- Beta-adrenoceptors activate the cAMP cascade
(mnemonic: camp CBB —> cAMP = activated by Beta ; AP = afterparty —> alpha activate phosphoinositide pathway and inhibit cAMP)
What does acetylcholine bind to? What are the subtypes, where are they located and what’s their general activity?
- Cholinergic receptors : nicotonic or muscarinic receptor subtypes —> activate the phosphoinositide pathway and inhibit the cAMP cascade (generally)
- Nicotonic: synapses between preganglionic and postganglionic neurons of sympathetic and parasympathetic systems + bound by ACh released from somatic motor neurons
- Muscarinic: bound by ACh released from parasympathetic postganglionic neurons —> 5 subtypes (M1-M5)
What are post-ganglionic cells in the adrenal medulla called and what do they release in response to activation by pre-ganglionic cells?
- Chromaffin cells
- Release adrenaline
(mnemonic: ADRENAL medulla releases ADRENALINE)
What is the adrenal medulla important for?
Organising the fight or flight response to a threatening situation
ACh released from ___ fibres binds to ___ ACh receptors on ___ (adrenal medulla) cells and stimulates synthesis and secretion of ___
- pre-ganglionic sympathetic fibres
- nicotinic
- chromaffin
- catecholamines
Cardiovascular effects of adrenaline:
- Increased ___, ___ and ___
- ___ of skeletal muscle blood vessels (adrenaline has high affinity for ___ receptors which triggers smooth muscle ___)
- ____ of gastrointestinal, renal and splenic beds (___ and ___ adrenergic receptors triggers smooth muscle ___)
- HR, CO, BP
- vasodilation, beta2, relaxation
- vasoconstriction, alpha1 and alpha 2, contraction
