Page 25 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)

NB

The terms adrenergic and cholinergic are used to describe neurons of either division,

according to which neurotransmitter they synthesize and release.

Adrenergic neurons Cholinergic neurons

➢ Release norepinephrine (NE) ➢ release Ach

➢ Receptors for NE on the effector organs are called ➢ receptors for ACh are

adrenoreceptors. called cholinoreceptors.

➢ Adrenoreceptors may be activated by NE, which is

released from adrenergic neurons, or by epinephrine

(E), which is secreted into the circulation by the

adrenal medulla.

Adrenal Medulla

o The adrenal medulla is a specialized ganglion in the sympathetic nervous system.

o The cell bodies of its preganglionic neurons are located in the thoracic spinal cord 

The axons travel in the greater splanchnic nerve to the adrenal medulla, where they

synapse and release Ach  activates nicotinic receptors on chromaffin cells 

secrete catecholamines (E and NE) into the general circulation.

o In contrast with sympathetic postganglionic neurons, which release only

norepinephrine, the adrenal medulla secretes mainly epinephrine (80%) and a small

amount of norepinephrine (20%). Why?

• Due to the presence of phenyl ethanolamine-N-methyltransferase (PNMT) in the

adrenal medulla, but not in sympathetic postganglionic adrenergic neurons.

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