The brain has no pain receptors itself but the brain is surrounded by meninges which covers the brain, it has periosteum which covers the bones of the skill along with the scalp which has pain receptors on them. The brain is however considered as one of the important key factors which allow us to detect pain. Pain is an unpleasant sensation that we experience due to the activation of sensory nerve fibers within the body i.e. nociceptors. The nociceptors are specialized nerve fibers which are present in the muscles, joints, skin along with different organs of the body that helps in the transmission of pain signals from the peripheral part of the brain where the messages are perceived. The brain itself has no nociceptors as mentioned above due to which brain surgeries can be easily performed without any discomfort to the patients. For instance, we are walking and suddenly we feel a nail pinching on our feet which is due to the specialized pain receptors present on the skin that activates once you are potentially injured. The impulse of pain leads through the nerves towards the spinal cord and then moves up towards the brain. The activation of pain occurs within nanoseconds.
Now you must be wondering if the brain has no pain receptors then how does it experience headaches. There are nociceptors in peripheral tissues of the brain like pia matter and dura matter which serves as the protective layer between the skull and brain. In certain conditions, these receptors get activated or result in the release of chemicals from the blood vessels leading to headaches. In migraine headaches, excess blood flow results in the throbbing pain while in tension headaches nociceptors are activated due to the excessive contraction of the surrounding muscles around the brain. The nociceptors are present in different structures of our head such as muscles, nerves or blood vessels within the face, scalp or neck. These nociceptors get activated due to the damage, trauma, pressure, temperature changes or certain chemical changes. For instance, dehydration can lead to headaches and ultimately pain due to the irritation of blood vessels. Another example includes headaches when visiting a dentist due to the overexertion of jaw muscles during the treatment protocol.
The spinal cord has a complex of nerves that transmit signals to and fro towards the brain at all times. The spinal cord plays an essential role to perform reflexes. When the spinal cord is intact, it immediately sends the messages to the brain rather than waiting for the brain to activate and send messages. Pain is a complex response which not only needs a stimulus but needs the proper transmission of signals. Pain just needs to log into the brain so that it can imitate the response. The pain signal transmits through the spinal cord towards the thalamus which then directs to different areas of the brain for interpretation. The cortical areas of the brain then identify the type of pain whether it is sharp, dull, radiating, is it similar to the past painful sensation or is it different. The thalamus also sends the signals towards the limbic system which is known as the emotional center of the brain. The feelings are then linked with the painful sensation that you experience and results in the generation of response by the body.
To conclude, pain is not just a sensory experience but it is a cognitive as well as an emotional experience where the entire body gets affected. Though the brain has no pain receptors it is one of the vital organs involved in the interpretation, evaluation and experiencing the pain sensation.