The Central Nervous System (CNS)

Overview of the CNS

The central nervous system (CNS) is composed of the brain and spinal cord. It is responsible for integrating sensory information, coordinating movement, maintaining homeostasis, and supporting higher mental functions such as thought and emotion.

• Brain: Located in the cranial cavity, it directly controls most body functions.

• Spinal Cord: Extends from the brain and serves as a conduit for information to and from the body.

Functions of the Nervous System

The nervous system's functions can be categorized into three main types:

• Motor Functions: Involve the stimulation of muscle contraction or gland secretion. These are primarily functions of the peripheral nervous system (PNS).

• Sensory Functions: Involve the detection of sensations both within and outside the body. These are also primarily functions of the PNS.

• Integrative Functions: Exclusive to the CNS, these include decision-making processes such as:

  • Interpretation of sensory information

  • Planning and monitoring movement

  • Maintenance of homeostasis

  • Higher mental functions (e.g., language, learning)

Basic Structure of the Brain and Spinal Cord

The Brain

The brain is a soft, whitish-gray organ that is continuous with the spinal cord. It is housed within the cranial cavity and is the control center for most bodily functions.

• Weighs between 1250 and 1450 grams

• Composed mostly of nervous tissue, but also contains epithelial and connective tissue

• Contains internal cavities called ventricles filled with cerebrospinal fluid (CSF)

• Receives about 20% of total blood flow at rest, reflecting its high demand for oxygen, glucose, and nutrients

Divisions of the Brain

The brain is divided into four main regions, each with distinct functions and connections:

• Cerebrum: Responsible for higher mental functions, sensation, and movement.

• Diencephalon: Processes, integrates, and relays information; involved in homeostatic functions and regulation of movement.

• Cerebellum: Coordinates and plans movement, especially complex activities.

• Brainstem: Connects the brain to the spinal cord and controls basic involuntary functions, reflexes, and information relay.

Example: The cerebrum is involved in activities such as problem-solving and voluntary movement, while the brainstem regulates breathing and heart rate.

Key Terms and Definitions

• Cranial Cavity: The space within the skull that houses the brain.

• Ventricles: Internal cavities in the brain filled with cerebrospinal fluid.

• Cerebrospinal Fluid (CSF): A clear fluid that cushions the brain and spinal cord, provides nutrients, and removes waste.

• Peripheral Nervous System (PNS): The part of the nervous system outside the brain and spinal cord, involved in sensory and motor functions.

Additional info:

• The brain's high metabolic demand makes it especially sensitive to interruptions in blood flow or oxygen supply.

• Each division of the brain contains specialized structures and nuclei that contribute to its unique functions.