Neuroscience: Gray and White Matter

Gray vs White Matter

• Gray matter contains cell bodies, dendrites, and synapses
• White matter contains bundles of axons, which connect hemispheres
• In the brain, white matter is located on the outside, and gray matter is on the inside
• In the spinal cord, gray matter is located on the inside and white matter is on the outside

Meninges

• There are 3 membranes that surround the brain and spinal cord, these are called the meninges
• Each membrane is composed of connective tissue
• They provide protection and structural framework for arteries and veins, and aid in CSF circulation.
• The dura mater is the outermost layer, and is attached to the inner surface of the cranium.
• It has two layers: the periosteal dura mater, which is equivalent to the periosteum of the skull bones, and the meningeal dura mater, which is internal to the periosteal layer.
• There is a small space between the two layers of the dura mater
• The arachnoid mater is the middle layer, and is attached to the inside of the dura mater.
• It surrounds the brain and spinal cord but is not directly attached to them.
• The subarachnoid space is located between the arachnoid mater and the pia mater, and contains cerebrospinal fluid (CSF), as well as all the cerebral veins and arteries.
• The pia mater is the innermost layer and is very thin. It follows all contours of the brain and arteries and is strongly attached to the brain tissue.

Cerebrospinal Fluid (CSF)

• CSF is clear, colorless liquid that is located in the subarachnoid space, as well as in cavities within the brain called ventricles
• It is produced by the choroid plexus
• The choroid plexus is located in each ventricle and filters blood plasma through capillaries
• Functions of CSF:
  • Protects the brain and spinal cord
  • Nourishes the CNS
  • Maintains the optimal environment for the CNS
  • Cushions the brain
  • Removes waste products

CSF Circulation

• There are four ventricles in the brain, which are interconnected cavities
• CSF is produced in the lateral ventricles and flows into the third ventricle through the interventricular foramen
• From the third ventricle, the CSF flows into the fourth ventricle through the aqueduct of Sylvius
• From the fourth ventricle, the CSF circulates into the subarachnoid space
• CSF is reabsorbed into the bloodstream through the arachnoid villi, which are invaginations of the arachnoid membrane into the dural sinuses.

Blood Brain Barrier

• The blood brain barrier is composed of the lining of microvessels, also known as capillaries in the brain
• It is present almost everywhere in the brain
• It regulates what substances can pass from the bloodstream into the brain's extracellular fluid
• Generally, only lipid-soluble (lipophilic) molecules with a low molecular weight and positive charge can cross this selectively permeable barrier
• Other molecules may require transport systems

Circumventricular Organs (CVOs)

• CVOs are regions in the brain where the blood brain barrier is absent or less effective
• These regions are located in the 3rd and 4th ventricles
• They allow direct access to the brain tissue for the bloodstream, which is essential for monitoring hormonal changes as well as nutrient levels.

Explore the fundamental differences between gray and white matter in the brain and spinal cord. Understand the role of the meninges and their protective function surrounding the central nervous system. This quiz will test your knowledge on neural structure and protective membranes.