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The somatosensory system is the part of the sensory system concerned with the conscious perception of touch, pressure, pain, temperature, position, movement, and vibration, which arise from the muscles, joints, skin, and fascia.

1st Order Neurons terminate in dorsal column nuclei, located in the medulla, where they form synapses with second order neurons. In the thalamus, 2nd order neurons form synapses with 3rd order neurons, which transmit info to the somatosensory cortex.

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Furthermore, only a select number of substances can pass through the endothelial cells. Such substances include lipid-soluble substances (e.g., oxygen, carbon dioxide). Hydrophilic substances, for example, hydron and bicarbonate, are not permitted to pass through cells and across the blood-brain barrier.

Protective shield for the brain This barrier is formed by the walls of the blood vessels in the brain and spinal cord that are less permeable there than they are in other organs. White blood cells, specifically T lymphocytes and B lymphocytes, can only pass to a minor extent if required for immune defence.

Under normal circumstances, glucose crosses the endothelial cells of the blood-brain barrier by way of GLUT1, as already described. Once in the brain, extracellular space glucose is rapidly taken up by the different types of brain cells including astrocytes, microglia and neurons.

Whereas the skull, meninges and cerebrospinal fluid protect against physical damage, the blood–brain barrier provides a defence against disease-causing pathogens and toxins that may be present in our blood.

Only water, certain gases (e.g. oxygen), and lipid-soluble substances can easily diffuse across the barrier (other necessary substances like glucose can be actively transported across the blood-brain barrier with some effort).

So what happens if the blood–brain barrier is damaged or somehow compromised? One common way this occurs is through bacterial infection, as in meningococcal disease. Meningococcal bacteria can bind to the endothelial wall, causing tight junctions to open slightly.

Nerves are bundles of axons in the peripheral nervous system (PNS) that act as information highways to carry signals between the brain and spinal cord and the rest of the body. Each axon is wrapped in a connective tissue sheath called the endoneurium.

The CNS is comprised of the brain, cerebellum and spinal cord. Remaining neurons, and associated cells, distributed throughout the body form the PNS. The nervous system has three broad functions: sensory input, information processing, and motor output.