ADRENERGIC NERVE FIBRE

nerve fibre that releases the neurotransmitter norepinephrine at the synapse, or junction, between a nerve and its end organ, which may be a muscle, gland, or another nerve. Such fibres make up the sympathetic nervous system, one of two peripheral nervous systems controlling involuntary activities, such as digestion, respiration, and circulation. Adrenergic fibres innervate smooth muscle, cardiac muscle, visceral glands, and various central nervous system structures and sense organs; their stimulating action on these organs is opposite to the inhibiting action of the cholinergic fibres of the parasympathetic system. Peripheral adrenergic neurons (nerve cells) integrate signals from other nerves of the central nervous system and peripheral sense organs; an adrenergic nerve impulse is triggered when one nerve fires repeatedly or when several nerves fire simultaneously.