Erection requires three things: sinusoidal relaxation in the corpora cavernosa, arteriole dilatation to increase blood flow, and venous compression to maintain the erection. During sexual stimulation, neurotransmitters are released that cause smooth muscle relaxation in the arteries and compression of the subtunical veins, allowing blood to fill the corpora cavernosa and produce an erection. Both the autonomic nervous system (sympathetic and parasympathetic) and somatic nerves are involved in the neurophysiology of erection through the release of various neurotransmitters in both the peripheral and central nervous systems.

1. PHYSIOLOGY OF ERECTION
Dr. Maria Idrees; PT

3. Mechanism of Erection
 CORPORA CAVERNOSA
• Flaccid state – smooth muscles are tonically contracted allowing only a
small portion of arterial flow into corpora.
 Sexual stimulation -
 Release of certain neurotransmitter -
 Relaxation of smooth muscles -
 Dilatation of arteriole -
 Increased blood flow
 Compression of subtunical venous plexux by tunica
 contraction of ischio cavernosus

4.  Erection requires
 Sinusoidal relaxation
 Arteriole dilatation
 Venous compression

5.  CORPORA SPONGIOSUM -
• Thin tunical covering
• Less venous occlusion
• Less pressure increase
Despite the same increase in arterial flow

6. Neurophysiology
 Autonomic- Pelvic plexus
Sympathetic-T11-L2 - ejaculation
Parasympathetic-S2-4 - erection
 Somatic
A D and C fibres- sensation
Onuf nucleus-S2-4 ---Ischio-cavernosus- rigid erection
---- Bulbo-spongiosus - expulsion

7. Peripheral neurotransmitters
FLACCIDITY ERECTION
NE NO
Endothelin Ach
PGI2,F2a CO
TXA2 EDGF
ATII

8. Central neurotransmitters
Increases sexual function Decrease sexual function
dopamine serotonin
NE opiods
Oxytocin GABA
NO prolactin
Melanocortin cannabinoids