Central Nervous System: Structure and Function

Central Nervous System (CNS)

Overview of the CNS

The Central Nervous System (CNS) is the primary control center of the body, consisting of the brain and spinal cord. It is responsible for integrating sensory information and responding accordingly.

• Cephalization: Refers to the evolutionary trend of increasing complexity and concentration of nervous tissue in the anterior (head) region. The human brain represents the highest level of cephalization.

• Components: The CNS is composed of the brain (cerebral hemispheres, cerebellum, brain stem) and the spinal cord.

Basic Pattern of the CNS

Brain and Spinal Cord Organization

The CNS exhibits a distinct pattern of gray and white matter, which is essential for its function.

• Brain: Composed of wrinkled, pinkish-gray tissue. The surface anatomy includes the cerebral hemispheres, cerebellum, and brain stem.

• Gray Matter: Contains neuron cell bodies and unmyelinated fibers. In the brain, gray matter is found in the cortex and nuclei.

• White Matter: Composed of myelinated axons (fiber tracts) that connect different parts of the CNS.

• Spinal Cord: Has a central canal surrounded by a gray matter core, with an external region of white matter.

Lobes and Sulci of the Cerebrum

Major Lobes and Surface Features

The cerebrum is divided into distinct lobes and features grooves (sulci) and ridges (gyri) that increase its surface area.

• Lobes: Frontal, Parietal, Temporal, and Occipital lobes, each associated with specific functions.

• Sulci: Shallow grooves that separate the gyri. Major sulci include the central sulcus, lateral sulcus, and parieto-occipital sulcus.

• Fissures: Deeper grooves, such as the longitudinal fissure (separates hemispheres) and transverse cerebral fissure (separates cerebrum from cerebellum).

• Gyri: Elevated ridges of tissue between sulci.

Example: The precentral gyrus (anterior to the central sulcus) is the primary motor cortex, while the postcentral gyrus (posterior to the central sulcus) is the primary somatosensory cortex.

Gray and White Matter

Distribution and Function

Gray and white matter are distributed differently in the brain and spinal cord, reflecting their functional roles.

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons. Responsible for processing and integration of information.

• White Matter: Consists of myelinated axons that transmit signals between different CNS regions.

• Brain: Gray matter forms the cortex and deep nuclei; white matter lies beneath the cortex.

• Spinal Cord: Central gray matter core surrounded by white matter tracts.

Cerebral Cortex

Structure and General Functions

The cerebral cortex is the outermost layer of the cerebrum, composed of gray matter. It is the site of conscious mind activities.

• Accounts for about 40% of the brain's mass.

• Enables sensation, communication, memory, understanding, and voluntary movements.

• Each hemisphere controls the opposite side of the body (contralateral control).

• Hemispheres are not functionally identical.

• Conscious behavior involves the entire cortex; no area acts alone.

Functional Areas of the Cerebral Cortex

Classification of Functional Areas

The cerebral cortex is divided into three main types of functional areas, each with specialized roles.

• Motor Areas: Control voluntary movement.

• Sensory Areas: Responsible for conscious awareness of sensation.

• Association Areas: Integrate diverse information for purposeful action.

Example: The primary motor cortex (in the precentral gyrus) initiates voluntary movements, while the primary somatosensory cortex (in the postcentral gyrus) processes sensory input from the body.

Additional info:

• The organization of the cortex into functional areas underlies complex behaviors such as language, reasoning, and perception.

• Damage to specific areas can result in characteristic deficits (e.g., Broca's area and speech production).