Autonomic nervous system

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What are alpha motor neurones?

motor nerve fibres supplying skeletal muscle

cell bodies in ventral horn of grey matter of spinal cord

axons leave via ventral root & travel direct to skeletal muscle (no synapsing)

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Homeostatic mechanisms that involve skeletal muscles

ventilation - diaphragm & chest-wall muscles
shivering

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What 2 neurons are involved in the parasympathetic & sympathetic pathways?

preganglionic - myelinated, cell body in CNS, sends axon to autonomic ganglion

postganglionic - cell bodies in the ganglion, axons usually unmyelinated, innervate organ in question

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Where do sympathetic and parasympathetic fibres carry motor signals to?

Smooth muscle, either directly or via the enteric nervous system
cardiac muscle
glands

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Where are most cell bodies for sympathetic nerves found?

intermediolateral column of grey matter

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neurotransmitter of preganglionic SNS fibres

acetylcholine

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neurotransmitter of postganglionic SNS fibres

noradrenaline

often co-transmitted with other substances like neuropeptide Y or ATP

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chromaffin cells

synapse with preganglionic sympathetic fibres in adrenal medulla

AcH causes them to release adrenaline into the blood

thought to be specialised ganglion cells

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What type of adrenergic receptor does adrenaline stimulate/not stimulate?

Activates all sub types

more potent at stimulating beta-2

less potent at stimulating beta-3 on brown fat

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What type of adrenergic receptors does noradrenaline stimulate/not stimulate?

less potent beta-2 receptor stimulator

more potent beta-3 receptor stimulator on brown fat

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What G proteins do beta, alpha-1 & alpha-2 receptors activate?

beta receptors: excitatory G proteins

alpha-1 receptor: works via G_q to activate the inositol phospholipid pathway

alpha-2 receptors: inhibitory G proteins

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parasympathetic nervous system

brain —→ cranial nerves —→ target organs

thoracic & abdominal nerves receive parasympathetic innervation in the vagus nerve

preganglionic synpases in ganglion close to/in the wall of the target organ

acetylcholine is the neurotransmitter

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How do beta-1-adrenoreceptors on SAN cells respond to catecholamines?

activate excitatory G-protein

increase in intracellular cAMP

promote opening of HCN channels

increased funny current

depolarisation increases

heart rate increases

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How do muscarinic receptors respond to vagal ACh?

activate a different G-protein within SAN cells

dissociated alpha subunit inhibits adenylate cyclase

levels of cAMP reduces

beta-gamma subunit directly opens potassium channels in the cell membrane

cell hyperpolarises

heart rate slows

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What was demonstrated by Otto Loewi and how?

Loewi took 2 frog hearts, one with the vagus nerve still attached and placed them in separate containers of Ringer's solution. He stimulated the vagus nerve of one heart and the heartbeat slowed (already known at the time). He then transferred some of the solution from the vagus heart to the non-vagus heart and the other heart began to slow, showing chemical signals were in the fluid, not just electrical.

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sympathetic tone

basal level of vasoconstriction

noradrenergic sympathetic fibres to the blood vessels activate alpha receptors

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