Central Nervous System organization and cell types
Neurons: there are several types of neurons - anaxonic neurons: small neurons where the dendrites and axons are indistinguishable.
- Bipolar neurons: small neurons with two distinct processes; a dendritic process and an axon extending from the cell body.
- Unipolar neurons: large neurons with the cell body lying to one side of the continuous dendritic process and axon.
- Multipolar neurons: large neurons with several dendrites and a single axon extending from the cell body.
Bipolar neurons: Biopolar neurons are CNS neurons specific for transmitting information from specialized sensory systems: sight, smell and hearing.
Grey and white matter: Grey matter consisting of unmyelinated neurons is the processing area of the CNS. White matter – located in the inner cortex and surrounding grey matter in the spinal cord - provide pathways of communication between grey matter.
CNS Glial Cell Types: there are 4 types of glial cells
- astrocytes - Regulates the chemical microenvironment surrounding neurons,
- Oligodendrocytes - Myelinate central nervous system axons,
- Microglia - Migrating phagocytic cells resembling immune cells that remove waste, debris, and pathogens and
- Ependymal cells - Columnar cells that line the ventricals of the brain and the spinal canal in the spinal cord.
Overview: The brain is the control center of the body.
Anatomy: the brain is divided into the following regions:
- The Cerebrum - controls voluntary movements and coordinates mental activity,
- The Cerebellum - coordinates voluntary movements, balance and posture,
- The Limbic System - control center for the autonomic nervous system, emotion and memory and
- The Brainstem - life support systems (e.g. breathing, swallowing).
Ventricles are the spaces in the brain and the spinal cord where cerebrospinal fluid is produced and circulated.
The Spinal Cord
The spinal cord is the portal connecting the brain to the rest of the body.
Overview: The spinal cord, in an adult, is approximately 45 cm long and 1.5 cm wide and extends only to L1 or L2. Spinal nerves are named according to the vertebra they are adjacent to.
Anatomy: The spinal cord is well protected inside vertebrae. The dura (hard) mater is the outermost layer protecting the spinal cord. The pia (delicate) mater is the innermost layer protecting the spinal cord.
Functions: The spinal cord has a butterfly-like pattern, which consists of the grey matter - mostly unmyelinated interneurons. Afferent signals from the periphery synapse on interneurons in the grey matter of the spinal cord. Signals are then sent via myelinated neurons for processing by the appropriate centers in the brain.