The skin is the largest organ in the body; this doesn’t refer to the topmost skin, which you can see and which you might stroke, scratch, bite, pick or pull hairs from. The internal “thick of the skin,” which is crossed by many blood vessels, vital to the dynamics of life; helping to regulate temperature. Extensive burns which impair this regulatory system can be fatal.
This inner thickness of the skin, with its variety of blood-vessels, forms a large part of the somatosensory system, conveying signals from the outside world, inwards. The word somatosensory means sensing the soma (Greek for “body”) .
This system combines a number of sub-systems which notify the brain of how the different parts of the body are feeling. The signals used by the somatosensory system travel rapidly across nerve fibers from the body to the central nervous system. Signals cross large areas very fast, from the spinal cord and brain stem to the outermost aspects of grey matter in the brain, working in conjunction with chemistry in the bloodstream to report up-to-the second states of each part of the body. During times of high stress and high cortisol, some sensitive individuals can literally feel their skin conducting these signals.
When you stroke a cat’s fur, comfort signals combine in the central nervous system, gathering information from the movement of your body; the sensors in your fingers; and the internal subjective comforting response to the cat and the fur. This last part, the one concerned with your internal responses is constantly active; signalling deep bodily responses to your brain; even when you are still and quiet.
Chemicals flowing in the bloodstream are sensed by nuclei of neurons in parts of the brain stem and hypothalamus . If the chemical concentration is not quite continuous, neurons fire, beginning processes to restore balance, calming you or making you feel edgy and itchy, horny or hungry, depending on what is required.
The brain is protected from large molecules by the blood-brain barrier, which monitors nutrients to the brain tissue. There are a few areas which this blood brain barrier doesn’t get to protect, such as the hypothalamus. Here, substances such as oxytocin are allowed through, and this is vital for functions such as bonding, love, relationships, etc.
These pathways monitor pH, oxygen and carbon-dioxide and carry signals for the body’s pain systems, for example in the head or the stomach, in the womb, joints or muscles; distributing signals via the bloodstream and neural pathways .
Smooth muscle movement adjusts the system’s blood pressure, perhaps paling or flushing the skin which, for sensitive individuals, may feel uncomfortable and prickle or itch.
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