P: Autonomic nervous system

Question 1

Cardiac output:

Answer 1

Stroke volume x heart rate

Question 2

Preganglionic neuron

Answer 2

cell body is embedded in CNS. Its axon forms a synapse with a postganglionic neuron.

Question 3

Postganglionic neuron

Answer 3

cell body is embedded in an autonomic ganglion. Its axon extends from ganglion to target organ.

Question 4

Sympathetic division of ANS - where do preganglionic neurons originate from and where do they synapse?

Answer 4

Preganglionic neurons in sympathetic division: originate in thoracic + lumbar levels of spinal cord (T1-L2 segments) and synapse in ganglia in 3 sites:
- Paravertebral ganglia: lie on either side of spinal cord + are interconnected to form a sympathetic chain of ganglia
- Prevertebral ganglia: not segmentally arranged but lie in abdominal cavity
- Within adrenal medulla

Question 5

Parasympathetic division

Answer 5

• Preganglionic neurons originate in brain + in sacral level of spinal column
• Terminal ganglia are located close to, or within target organs
• Parasympathetic nerve to organs consist mainly of preganglionic neurons.

Question 6

Post-ganglionic nerve fibres

Answer 6

• Fibres do not form specific synapses within the tissue they innervate
• Fibres have varacosities which pass into the close proximity with cells
• Neurotransmitters are synthesised + released from varacosities
• Sites are known as neuroeffector junctions.

Question 7

Catecholamines

Answer 7

noradrenaline and adrenaline

Question 8

Adrenergic response

Answer 8

Noradrenaline binds to adrenergic receptors (adrenoceptors) and can have excitatory or inhibitory effects depending on subtypes of adrenergic receptors expressed in the effector organ.

Question 9

A-adrenoreceptors

Answer 9

A-adrenoceptors activate the phosphoinositide pathway + inhibit the cAMP cascade.

Question 10

b-adrenoreceptors

Answer 10

B-adrenoceptors activate the cAMP cascade.

Question 11

Cholinergic response

Answer 11

• Ach binds to cholinergic receptors: nicotinic/ muscarinic receptor subtypes.
• Nicotinic receptors in ANS are located at synapses between preganglionic and postganglionic neurons of both sympathetic and parasympathetic systems.
• Ach released by parasympathetic postganglionic neurons bind to muscarinic - Ach receptors –> can have excitatory or inhibitory effects depending on muscarinic subtype expressed.

Question 12

Nicotinic signal transduction mechanism, target cell & effect on target cell

Answer 12

1. opens channels for sodium and potassium ions
2. postganglionic cell body, chromaffin cells, skeletal muscle cells
3. excitatory

Question 13

Muscarinic signal transduction mechanism, target cell & effect on target cell

Answer 13

1. G-protein coupled: opens/closes specific ion channel
2. Effector organs of parasympathetic nervous system
3. Excitatory or inhibitor

Question 14

Adrenal medulla

Answer 14

Innermost area of adrenal gland. Ganglion of sympathetic nervous system.
Preganglionic sympathetic nerve fibres pass all the way from the lateral horn cells of the spinal cord.

Post-ganglionic cells are chromaffin cells which release adrenaline in response to activation by pre-ganglionic cells.

Question 15

Catecholamine secretion

Answer 15

Ach released from pre-ganglionic sympathetic fibres binds to nicotinic Ach receptors on chromaffin cells and stimulates synthesis + secretion of catecholamines.
- 80% of cells release adrenaline into circulation
- 20% of cells release noradrenaline into circulation
- Act as hormones.

Question 16

CV effects of adrenaline

Answer 16

• Increase heart rate, cardiac output
• Raised blood pressure
• Vasodilation of skeletal muscle blood vessels: adrenaline has a high affinity for B adrenergic receptors which triggers smooth muscle relaxation
• Vasoconstriction of gastrointestinal, renal and splenic beds: a-adrenergic receptors trigger smooth muscle contraction.