Brain and Spinal Cord Overview

Meninges

• The meninges are the plural term for protective coverings surrounding the brain and spinal cord.
• They consist of three layers:
  • Dura Mater (outer layer)
  • Arachnoid Mater (middle layer)
  • Pia Mater (inner layer, attached directly to the brain and spinal cord).
• The longitudinal fissure separates the two cerebral hemispheres.
• The group that separates the frontal lobe from the parietal lobe is called the lateral fissure.

Cerebrospinal Fluid (CSF)

• CSF is a colorless fluid found in the ventricles, subarachnoid space, and central canal of the spinal cord.
• It is a filtrate of blood, differing from mucus, which is produced by goblet cells.
• Functions of CSF:
  • Supplies the brain with oxygen and nutrients.
  • Continuously produced and recycled (not a static fluid).
• Choroid plexus are specialized structures found in all four ventricles that produce CSF.
• Tight junctions in ependymal cells control substance passage, ensuring that only selective substances enter the fluid.

Ventricles and Flow of CSF

• CSF flows from the lateral ventricles to the third ventricle, then to the fourth ventricle through three openings (one median and two lateral apertures).
• The flow can be illustrated in a flowchart format.
• The CSF plays a crucial role in cushioning the brain and maintaining intracranial pressure.

Blood-Brain Barrier

• The blood-brain barrier regulates which substances can pass from blood to the brain, allowing some substances (like glucose, oxygen) while blocking others (like potassium to prevent neuronal excitability).
• The hypothalamus and medulla oblongata have areas with a less complete blood-brain barrier to monitor blood composition.

Spinal Cord

• The spinal cord begins at the foramen magnum and usually ends at the L1-L2 vertebrae in adults (it is longer in childhood).
• Functions include:
  • Two-way communication between the brain and body (sensory up, motor down).
  • Spinal reflexes (quick, involuntary responses).
• The spinal cord is protected by vertebrae and has an epidural space filled with fat and blood vessels.

Anatomy of Spinal Cord

• The spinal cord has a central canal and ends in a cone-shaped structure called the conus medullaris.
• Below the conus medullaris, a collection of nerve roots known as the cauda equina extends down through the vertebral canal.

Dorsal and Ventral Roots

• Dorsal roots carry sensory information into the spinal cord, while ventral roots carry motor information out of the spinal cord.
• Dorsal horns contain sensory neuron cell bodies, whereas ventral horns contain motor neuron cell bodies.

Spinal Tracts

• Spinal tracts consist of collections of axons traveling in similar pathways, carrying either sensory information to the brain or motor information from the brain.
• Examples of important tracts:
  • Spinothalamic tract (pain and temperature sensations).
  • Corticospinal tract (motor control).
  • Spinocerebellar tract (proprioception for coordination).
• Each tract has a specific pathway and function in relaying information between the peripheral nervous system and the central nervous system.