Changes

* Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Hypothalamus|Hypothalamus]].

* Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Endocrine_System_-_Hypothalamus_-_Anatomy_%26_Physiology#Hypothalamus|Hypothalamus]].

* Hypothalamic neurones synapse with parasympathetic and sympathetic efferent neurons that control penile vascular smooth muscle (vascular tone).

* Hypothalamic neurones synapse with parasympathetic and sympathetic efferent neurons that control penile vascular smooth muscle (vascular tone).

* Firing of Nonadrenergic, noncholinergic (NANC) parasympathetic neurones causes erection.

* Firing of '''Nonadrenergic, noncholinergic (NANC) parasympathetic neurones''' causes erection.

** Release nitric oxide (NO) from their terminals.

** Release '''nitric oxide (NO)''' from their terminals.

** NO is the principle neurotransmitter that drives the erectile process.  

** NO is the principle neurotransmitter that drives the erectile process.  

** NO activates the enzyme guanylate cyclase.

** NO activates the enzyme '''guanylate cyclase'''.

** Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).

** Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).

* Causes corporal smooth muscle relaxation (vasodilation) and results in erection.

* Causes corporal smooth muscle relaxation (vasodilation) and results in erection.

* Under nonerotogenic conditions, cGMP is acted upon by PDE5 (phosphodiesterase 5).

* Under nonerotogenic conditions, cGMP is acted upon by '''PDE5 (phosphodiesterase 5)'''.

* PDE5 promotes conversion of cGMP to GMP.

* PDE5 promotes conversion of cGMP to GMP.

* Breakdown causes increased vascular tone.

* Breakdown causes increased vascular tone.