Does the T12 (thoracic 12) nerve supply the glans penis?

Innervation of the Glans Penis

No, the T12 (thoracic 12) nerve does not supply the glans penis. The glans penis is primarily innervated by the dorsal nerve of the penis, which is a terminal branch of the pudendal nerve originating from sacral nerve roots (S2-S4).

Anatomical Innervation of the Glans Penis

• The dorsal nerve of the penis is the primary nerve that innervates the glans penis, providing sensory innervation to this structure 1
• Anatomical studies demonstrate that the dorsal nerve of the penis consists of two populations of axons - one innervating the penile shaft and urethra, and the other specifically innervating the glans 2
• The most numerous nerve terminals in the glans are free nerve endings (FNEs) present in almost every dermal papilla and scattered throughout the deeper dermis of the glans 3
• The ratio of free nerve endings to corpuscular receptors in the glans penis is approximately 10:1, which explains its unique sensory properties 3

Distribution of Nerve Endings in the Glans

• Genital end bulbs are present throughout the glans but are most numerous in the corona and near the frenulum 3
• The dorsal nerve of the penis extends branches through the glans ventrolaterally, with the frenulum also receiving innervation from a branch of the perineal nerve 1
• Electrical stimulation studies confirm that the dorsal nerve of the penis innervates the corona, dorsal and ventral mid glans, and penile shaft 1
• The pattern of glanular innervation identifies the glans as a sensory end organ for sexual reflexes 2

Clinical Significance of Glans Innervation

• The integrity of the dorsal nerve of the penis is crucial for normal erectile and ejaculatory function 2
• In patients with low spinal cord lesions, procedures like TOMAX (TO MAXimize sensation) can restore genital sensation by connecting the dorsal nerve of the penis to an intact ilioinguinal nerve 4
• The unique innervation of the glans explains its protopathic sensibility (primitive pain and temperature sensation) as opposed to epicritic sensibility (fine touch and pressure) found in fingertips 3
• The abundance of free nerve endings and absence of Merkel terminals and typical Meissner corpuscles in the glans explains the dissociated sensibility compared to glabrous skin of digits 3

Common Misconceptions and Pitfalls

• The thoracic spinal nerves (including T12) primarily supply the trunk and abdominal wall, not the genital structures 1, 2
• Confusing dermatomes with actual nerve supply can lead to misunderstanding of penile innervation - while T12 dermatome is in the lower abdomen/groin region, it does not extend to the glans penis 2
• Understanding the correct innervation of the glans is important for procedures involving the penis, including surgeries for penile cancer where preservation of sensation is desired 5
• Proper knowledge of penile innervation is crucial for nerve-sparing techniques in penile surgeries and for diagnostic procedures in erectile dysfunction 6