The Clitoris in Your Head
Have you ever seen a cortical homunculus?
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I told you I was thinking about the clitoris this week. I guess that makes this retroactively Clitoris Week, with a big helping of neuroanatomy.
What is a "cortical homunculus?"
A cortical homunculus (from Latin homunculus 'little man, miniature human' is a distorted representation of the human body, based on a neurological "map" of the areas and proportions of the human brain dedicated to processing motor functions, or sensory functions, for different parts of the body. (Wikipedia)
Now you know.
I've been brushing up on my neuroanatomy again, and I'm surprised by this thing I haven't been able to find out. Maybe one of you can tell me. All the cortical homunculi I've ever seen have been male.
Like this guy:
And this slightly more controversial guy:
I've never seen a female somatosensory homonculus.
Why? I suspect it's because a female somatosensory homunculus would have a clitoris bigger than its head – nearly twice the size of the homologous penis – and the scientists responsible for these things just can't quite cope with that.
But.
Would it have that massive clitoris?
It's true that the clitoris has something approaching twice the number of nerve endings as the penis. Not quite, but nearly – which is pretty impressive in something roughly 1/8th the size of its male homologue – but that's the PERIPHERAL nervous system.
What about its CORTICAL sensory representation? These cortical somatosensory homunculi (so fun to say!) are representations of how much sensory cortex is taken up by each body part. You'll notice the penis is fairly large in one and QUITE large in the other; this is because the penis – along with the hand, toes, and lips – takes up a lot of sensory BRAIN space. So is the peripheral hyperenervation of the clitoris reflected in its cortical representation?
I'll ask that again in a different way, for people who have never thought seriously about the nervous system: Body parts have nerve endings that detect sensation – some (like your hands, feet, lips, and genitals) have a LOT. They bundle together in the spine and make their way north to the brain. Those nerves in your body are your peripheral nervous system (PNS). The nerves in your spine and brain are your central nervous system (CNS).
Your brain, in turn, is organized in layers. The outermost layer, with all the wrinkly bits and the split down the middle like an unbaked loaf of French bread, that's your cortex. An adult's cortex is organized into functional units. The part in the front does decision-making and reasoning. The part in the very back processes visual information. Over on the right side you've got motor coordination, sensation, and visuospatial things like music and math, and over on the left you've got language comprehension and production. (Cortical neuroanatomy in one paragraph. Obviously, this is not the whole story.) Now. What I've said about the clitoris having all these nerve endings describes the relevant bit of the PERIPHERAL nervous system.
Those pictures up there of the dudes with massive hands is a representation of the relevant module of the CENTRAL nervous system. What I want to know is: is the difference in PERIPHERAL enervation of the clitoris reflected in the CENTRAL representation of the clitoris?
To put it plainly: would a female somatosensory homonculus have a clitoris nearly twice the size of this penis? I cannot find the answer. No one I know seems to know either. I'm putting out a call to the internet.
Please, someone, tell me if the representation of the clitoris in primary somatosensory cortex is as disproportionate as its representation in the peripheral nervous system?
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