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* 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.
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