Central Nervous System: Brain Structure, White and Gray Matter, and Functional Areas

Central Nervous System (CNS): Brain and Spinal Cord

White and Gray Matter: Location and Function

The brain and spinal cord are composed of two main types of tissue: white matter and gray matter. Their locations and functions differ between the brain and spinal cord.

• White Matter

  • Definition: Consists mainly of myelinated axons (nerve fibers).

  • Function: Transmits electrical signals rapidly; sends and receives action potentials.

  • Location:

    • Brain: White matter is found deep within the brain, beneath the gray matter cortex.

    • Spinal Cord: White matter is located superficially, surrounding the gray matter.

• Gray Matter

  • Definition: Contains cell bodies (especially neuron somas), dendrites, and unmyelinated axons.

  • Function: Processes and integrates information; site of synapses.

  • Location:

    • Brain: Gray matter forms the superficial cerebral cortex and deeper nuclei.

    • Spinal Cord: Gray matter is central, shaped like an 'H' or butterfly.

Region	White Matter Location	Gray Matter Location
Brain	Deep (subcortical)	Superficial (cortex) and deep nuclei
Spinal Cord	Superficial	Central (H-shaped)

Brain Structure: Cerebrum, Diencephalon, Cerebellum, Brainstem

Cerebrum: Lobes and Major Features

The cerebrum is the largest part of the brain, responsible for higher mental functions, voluntary movement, and sensory perception. It is divided into two hemispheres and several lobes.

• Lobes of the Cerebrum:

  • Frontal lobe: Controls voluntary movement, reasoning, planning, and problem-solving.

  • Parietal lobe: Processes sensory information such as touch, temperature, and pain.

  • Temporal lobe: Involved in auditory processing and memory.

  • Occipital lobe: Responsible for visual processing.

• Hemispheres: The cerebrum is divided into right and left hemispheres, each controlling opposite sides of the body.

• Fissures:

  • Longitudinal fissure: Separates the right and left cerebral hemispheres.

  • Transverse fissure: Separates the cerebrum from the cerebellum.

  • Lateral fissure (Sylvian): Separates the temporal lobe from the frontal and parietal lobes.

• Sulci: Shallow grooves on the surface of the cerebrum; increase surface area for cortical neurons.

  • Central sulcus: Separates the frontal and parietal lobes.

  • Parieto-occipital sulcus: Separates the parietal and occipital lobes.

• Gyri: Elevated ridges between sulci; increase surface area of the brain.

Functional Areas of the Cerebral Cortex

Motor Cortices and Upper/Lower Motor Neurons

The motor cortices are located in the frontal lobes and are responsible for voluntary movement. Motor neurons transmit signals from the brain to muscles.

• Primary Motor Cortex (Precentral Gyrus):

  • Controls voluntary movement of skeletal muscles.

  • Receives information from association areas and executes movement.

• Premotor Cortex:

  • Plans, guides, coordinates, and executes complex movements.

  • Sends information to the primary motor cortex.

• Frontal Eye Fields:

  • Control voluntary eye movements (back and forth).

• Upper and Lower Motor Neurons:

  • Upper motor neurons originate in the motor cortex and synapse with lower motor neurons in the spinal cord.

  • Lower motor neurons directly innervate skeletal muscles.

Sensory Cortices

The sensory cortices are primarily located in the parietal, occipital, and temporal lobes. They process sensory information from the body and environment.

• Somatosensory Areas:

  • Primary Somatosensory Cortex (Postcentral Gyrus):

    • Receives and interprets sensory input: touch, pain, temperature, pressure, stretch, and joint position.

    • Example: Feeling an object in your arm.

  • Somatosensory Association Cortex:

    • Integrates and interprets sensory information; allows recognition of objects by touch.

    • Example: Recognizing a key by touch without seeing it.

• Visual Areas:

  • Primary Visual Cortex: Located in the occipital lobe; receives and processes visual input.

  • Visual Association Areas: Interpret color, movement, depth, and visual meaning.

• Auditory Areas:

  • Primary Auditory Cortex: Located in the temporal lobe; receives and processes auditory input.

Additional info:

• The notes reference the flow and function of cerebrospinal fluid (CSF), which is produced in the ventricles, circulates through the CNS, and provides protection and nutrient transport.

• Other referenced structures (e.g., diencephalon, cerebellum, brainstem) are part of the CNS and have specialized functions in coordination, autonomic control, and sensory relay.