Adrenergic antagonists: Alpha blockers

Alpha blocker and beta blockers are two types of postsynaptic anti-adrenergic medications that prevent their respective receptors from being stimulated by catecholamines, like norepinephrine and epinephrine.

The nervous system is divided into the central nervous system, so the brain and spinal cord; and the peripheral nervous system, which includes all the nerves that connect the central nervous system to the muscles and organs.

The peripheral nervous system can be divided into the somatic nervous system, which controls voluntary movement of our skeletal muscles; and the autonomic nervous system, which is further divided into the sympathetic and the parasympathetic, and controls the involuntary movement of the smooth muscles and glands of our organs.

Now, the autonomic nervous system - which includes both the sympathetic and parasympathetic nervous system - is made up of a relay that includes two neurons.

We’ll focus on just the sympathetic nervous system.

Signals for the autonomic nervous system start in the hypothalamus, at the base of the brain.

Hypothalamic neurons have really long axons that carry signals all the way down to the thoracic and lumbar spinal cord nuclei, where they synapse with preganglionic neuron cell bodies.

From there, the signal goes from the preganglionic neurons down its relatively short axon, exits the spinal cord, and reaches the nearby sympathetic ganglion, which is made up of lots of postganglionic neuron cell bodies.

The postganglionic neurons are also called adrenergic neurons because they release the neurotransmitter norepinephrine, which is also called noradrenalin; and to a much lesser degree, epinephrine, or adrenaline.