Central Nervous System: Structure, Cells, and Tissues

Central Nervous System (CNS)

Overview

The Central Nervous System (CNS) is a primary division of the nervous system, responsible for integrating sensory information and coordinating bodily functions. It consists of the brain and spinal cord.

• Brain: The control center for processing information, thought, memory, and emotion.

• Spinal Cord: Transmits signals between the brain and the rest of the body, and mediates reflexes.

Neurons and Glial Cells in the CNS

Neurons

The CNS contains approximately 86 billion neurons, which are specialized cells responsible for transmitting electrical and chemical signals throughout the body.

• Neurons: Fundamental units of the nervous system, involved in communication, processing, and response.

Glial Cells

Glial cells comprise about 80% of the CNS and provide structural and functional support to neurons. There are several types of glial cells, each with distinct roles:

• Astrocytes: Develop the blood-brain barrier, regulate the extracellular environment, and provide metabolic support.

• Microglia: Act as phagocytes, removing debris and pathogens from the CNS.

• Oligodendrocytes: Form myelin sheaths around axons in the CNS, which increase the speed of electrical signal transmission.

• Ependymal cells: Line the cavities of the brain and spinal cord, involved in the production and circulation of cerebrospinal fluid (CSF).

• Schwann cells: Located in the Peripheral Nervous System (PNS), also form myelin sheaths around axons.

Additional info: Myelin is a lipid-rich substance that insulates axons, allowing for rapid signal conduction.

Tissues of the CNS

Gray Matter vs. White Matter

The CNS is composed of two main types of tissue: gray matter and white matter. These regions are distinguishable by their cellular composition and function.

• Gray Matter: Contains unmyelinated nerve cell bodies, dendrites, and axon terminals. It is involved in processing and integration of information.

• White Matter: Composed primarily of myelinated axons with few cell bodies. It is responsible for the transmission of signals between different regions of the CNS.

Example: In a cross-sectional image of the brain, gray matter appears darker and is found on the outer layer (cortex), while white matter is lighter and located deeper within the brain.

Functional Significance

• Gray matter: Site of synaptic connections and neural processing.

• White matter: Facilitates communication between different brain regions and between the brain and spinal cord.

Additional info: Damage to white matter can disrupt signal transmission, while damage to gray matter can impair processing and integration of information.