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| * When sexual receptivity of the female is established and sufficient arousal is accomplished in the male, erection and protrusion of the penis ensue. | | * When sexual receptivity of the female is established and sufficient arousal is accomplished in the male, erection and protrusion of the penis ensue. |
| * Successful penile erection requires a complex series of neural and vasomotor reactions. | | * Successful penile erection requires a complex series of neural and vasomotor reactions. |
− | * Erection of the penis is necessary for copulation and deposition of [[Copulation_-Sperm_in_the_Female_Tract_-_Anatomy_%26_Physiology|semen in the female reproductive tract]]. | + | * Erection of the penis is necessary for copulation and deposition of [[Sperm in the Female Tract - Anatomy & Physiology|semen in the female reproductive tract]]. |
| * Erection is characterized by a marked increase in rigidity of the penis. | | * Erection is characterized by a marked increase in rigidity of the penis. |
| * Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow. | | * Increased rigidity is the result of increase in arterial inflow of blood compared to venous outflow. |
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| * Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it. | | * Increased blood flow to the penis is brought about by vasodilation of the arterioles supplying it. |
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| == Erection of the Fibroelastic Penis == | | == Erection of the Fibroelastic Penis == |
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| + | [[Image:Erection of the Fibroelastic Penis.jpg|thumb|right|150px|<p>The Fibroelastic Penis in a Flaccid State</p><sup> Copyright Nottingham University 2008.</sup>]] |
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| * Bull,Ram and Boar | | * Bull,Ram and Boar |
| * Involves increased blood flow with subsequent increase in pressure and simultaneous relaxation of the '''retractor penis muscles'''. | | * Involves increased blood flow with subsequent increase in pressure and simultaneous relaxation of the '''retractor penis muscles'''. |
− | * Erection and [[Reproductive_Behaviour_-_Pre-copulatory_Behaviour_-_Anatomy_%26_Physiology#Penile_Protrusion|protrusion]] involve straightening of the penis to eliminate the '''sigmoid flexure'''. | + | * Erection and protrusion involve straightening of the penis to eliminate the '''sigmoid flexure'''. |
| * Does not increase significantly in diameter during erection. | | * Does not increase significantly in diameter during erection. |
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| == Erection of the Musculovascular Penis == | | == Erection of the Musculovascular Penis == |
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| + | * Stallion |
| + | * Increases in diameter during erection. |
| + | * '''Retractor penis muscle''' still relaxes during erection, but '''no sigmoid flexure'''. |
| + | * Engorgement with blood plays a significant role in the highly vascular penis. |
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| + | == Mechanism == |
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| + | Erection of the penis requires: |
| + | * Elevated arterial inflow |
| + | * Dilation of '''corporal sinusoids''' |
| + | * Restricted venous outflow |
| + | * Elevated intrapenile pressure |
| + | * Relaxation of '''retractor penis muscles''' |
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| + | * Engorgement of cavernous sinuses causes a blockage of venous circulation from the penis. |
| + | * Contractions of ischiocavernous muscles cause compression of the penile veins. |
| + | ** Intermittent contractions of the muscles around the two '''crura''' create a pump-like action at the base of the penis. |
| + | ** Result in the build up of blood within the '''corpus cavernosum'''. |
| + | * Very high pressure results. |
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| + | == Sensory Input and Local Vascular Response == |
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| + | '''''Nervous Component''''' |
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| + | * Arousal driven |
| + | * Must be appropriate sensory stimuli (tactile, visual, olfactory, auditory) in order for the central nervous system to be stimulated for efferent events to cause erection. |
| + | ** Extrinsic stimuli are called '''erotogenic stimuli'''. |
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| + | * Stimuli cause afferent sensory nerves to fire. |
| + | * Terminals synapse with neurons in the ''''behaviour centre'''' in the [[Hypothalamus_- Anatomy & Physiology#Hypothalamus|Hypothalamus]]. |
| + | * 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. |
| + | ** Release '''nitric oxide (NO)''' from their terminals. |
| + | ** NO is the principle neurotransmitter that drives the erectile process. |
| + | ** NO activates the enzyme '''guanylate cyclase'''. |
| + | ** Guanylate cyclase converts guanylate triphosphate (GTP) into cyclic guanyosine monophosphate (cGMP). |
| + | * Causes corporal smooth muscle relaxation (vasodilation) and results in erection. |
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| + | * Under nonerotogenic conditions, cGMP is acted upon by '''PDE5 (phosphodiesterase 5)'''. |
| + | * PDE5 promotes conversion of cGMP to GMP. |
| + | * Breakdown causes increased vascular tone. |
| + | ** Tonic contraction of arterial and corporal smooth muscles. |
| + | ** Outflow of blood from '''corpora cavernosa'''. |
| + | * Loss of erection and return to usual flaccid state. |
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| + | '''''Local Vascular Component''''' |
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| + | * When corporal smooth muscles relax because of cGMP, resistance to blood flow by penile arterioles and '''corporal sinusoids''' decreases. |
| + | * Blood flow to the penis triples or quadruples. |
| + | * When erection occurs, sinusoid pressure is so great that '''emissary veins''' are collapsed. |
| + | ** Venous outflow blocked |
| + | * Penile erection maintained for as long as vasodilation of corporal smooth muscle takes place. |
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| + | == Vascular and Biochemical Control of Erection == |
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| + | '''''Anatomy''''' |
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| + | * '''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'''. |
| + | * '''Corporal sinusoids''' are supplied by '''helicine arteries'''. |
| + | * '''Deep dorsal vein''' and '''superficial dorsal vein''' drain the erectile tissues. |
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| + | * For more information on anatomy of the penis follow this link. |
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| + | '''''Flaccid Penis''''' |
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| + | * Sinusoids are flattened because adrenergic nerves secrete noradrenaline (norepinephrine) that causes '''vasoconstriction'''. |
| + | * Blood flow to cavernous tissue is low. |
| + | * No erotogenic stimuli present |
| + | * Nonadrenergic noncholinergic (NANC) parasympathetic neurons do not fire. |
| + | * No release of Nitric Oxide (NO) |
| + | * Vasoconstriction takes precedence over vasodilation. |
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| + | '''''Erect Penis''''' |
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| + | * Erotogenic 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 smooth 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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| + | [[Category:Reproductive Behaviour]] |
| + | [[Category:Bullet Points]] |