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* '''Shaft''' of the Penis consists of two dorso-lateral '''corpora cavernosa''' and the '''corpus spongiosum'''.
* '''Shaft''' of the Penis consists of two dorso-lateral '''corpora cavernosa''' and the '''corpus spongiosum'''.
* Arterial blood is supplied by the '''internal pudendal artery''' that supplies '''dorsal and deep cavernosal arteries'''.
* Arterial blood is supplied by the '''internal pudendal artery''' that supplies '''dorsal and deep cavernosal arteries'''.
−
* '''Corporal sinuso'''ids are supplied by '''helicine arteries'''.
+
* '''Corporal sinusoids''' are supplied by '''helicine arteries'''.
* '''Deep dorsal vein''' and '''superficial dorsal vein''' drain the erectile tissues.
* '''Deep dorsal vein''' and '''superficial dorsal vein''' drain the erectile tissues.
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'''''Flaccid Penis'''''
'''''Flaccid Penis'''''
−
* Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine).
+
* Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine)that causes '''vasoconstriction'''.
+
* Blood flow to cavernous tissue is low.
+
* No eretogenic stimuli present
+
* Nonadrenergic noncholinergic (NANC) parasympathetic neurons do not fire.
+
* No release of Nitric Oxide (NO)
+
* Vasoconstriction takes precedence over vasodilation.
+
+
'''''Erect Penis'''''
'''''Erect Penis'''''
+
+
* Eretogenic stimuli present
+
* NANC neurones fire and release NO from their terminals.
+
* NO activates the enzyme guanylate cyclase.
+
* Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP).
+
* Causes smoot muscle of '''corporal sinusoids''' to relax (vasodilation).
+
* '''Cavernous sinusoids''' engorge with blood.
+
* Intracorporal pressure increases dramatically.
+
* Pressure compresses the venules through which blood exits the penis.
+
* Blood trapped within the penis causing an erection.
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== Sensory Input and Local Vascular Response ==
== Sensory Input and Local Vascular Response ==