Is there a muscle in the brain?

I know there is no muscle in the brain and the brain doesn't have pain or sensation receptors, but when you think real hard or mentally strain yourself, you do feel that your are straining your brain. What is it that I'm feeling - my scalp muscles or the blood vessels on the surface of my brain? What's that sensation coming from?
Answer:
I'm not a doctor, but I know when you concentrate real hard on something, more and more neural receptors in the brain start firing, which causes the brain tissue to need and use more oxygen, which causes the blood vessels supplying the brain with blood and oxygen to widen more and more with each heartbeat. The pressure of the blood vessels pulsing in the brain can be felt in surrounding areas of the head, such as the eyes, ears, neck, and skin tissue, which do have nerve endings that relay the pressure impulses to - you got it - the brain.

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Your brain is a muscle

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