P: Autonomic nervous system

Question 1

Definition of cardiac output (CO), how to calculate it and its value

Answer 1

• 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

Question 2

How are heart rate (HR) and stroke volume (SV) regulated?

Answer 2

ANS

Question 3

ANS comprises a reflex arc which has:

Answer 3

• Afferent (sensory) limb
• Central regulatory component in brain stem, spinal cord and hypothalamus
• Efferent (effector pathway)

Question 4

Where does central integration of information take place?

Answer 4

Hypothalamus and brain stem

Question 5

What’s the main integration centre for sensory input?

Answer 5

Hypothalamus

Question 6

Where is the cell body of preganglionic neuron embedded?

Answer 6

In CNS (brain/spinal cord)

Question 7

Where is the cell body of postganglionic neuron embedded?

Answer 7

In an autonomic ganglion (clusters of cell bodies outside CNS) —> its axon extends from ganglion to target organ

Question 8

Where do preganglionic neurons synapse?

Answer 8

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

Question 9

Parasympathetic nerves to organs consist mainly of ___ because terminal ganglia are located ___

Answer 9

Preganglionic neurons, close to or within target organs

Question 10

How do post-ganglionic nerve fibres innervate the tissue?

Answer 10

• 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

Question 11

How does sympathetic system stimulate a fight or flight response?

Answer 11

By releasing norepinephrine (noradrenaline) from postganglionic neurons onto effector organs (adrenergic response)

Question 12

What is the name for noradrenaline and adrenaline?

Answer 12

Catecholamines

Question 13

What do sympathetic nerves release in sweat gland, piloerector muscles and some blood vessels of skeletal muscles?

Answer 13

Acetylcholine (cholinergic response)

Question 14

What does the parasympathetic do in relation to sympathetic system and how?

Answer 14

It opposes the effects of sympathetic system by releasing acetylcholine onto target organs (cholinergic response)

Question 15

What are the 2 main signalling cascades activated in the ANS?

Answer 15

• Adenylyl cyclase - cAMP pathway
• Phosphoinositide pathway

Question 16

What does noradrenaline bind to and what are the subtypes + their general activity?

Answer 16

• 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)

Question 17

What does acetylcholine bind to? What are the subtypes, where are they located and what’s their general activity?

Answer 17

• 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)

Question 18

What are post-ganglionic cells in the adrenal medulla called and what do they release in response to activation by pre-ganglionic cells?

Answer 18

• Chromaffin cells
• Release adrenaline

(mnemonic: ADRENAL medulla releases ADRENALINE)

Question 19

What is the adrenal medulla important for?

Answer 19

Organising the fight or flight response to a threatening situation

Question 20

ACh released from ___ fibres binds to ___ ACh receptors on ___ (adrenal medulla) cells and stimulates synthesis and secretion of ___

Answer 20

• pre-ganglionic sympathetic fibres
• nicotinic
• chromaffin
• catecholamines

Question 21

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 ___)

Answer 21

• HR, CO, BP
• vasodilation, beta2, relaxation
• vasoconstriction, alpha1 and alpha 2, contraction