Central Nervous System

Overall Structure of the Brain

The brain is the central organ of the nervous system, responsible for processing sensory information, coordinating movement, and higher cognitive functions. It is divided into several major regions, each with specialized roles.

• Cerebral Hemispheres: The largest part of the brain, divided into left and right hemispheres.

• Diencephalon: Includes the thalamus, hypothalamus, and epithalamus.

• Brain Stem: Composed of the midbrain, pons, and medulla oblongata.

• Cerebellum: Located under the cerebral hemispheres, involved in coordination and balance.

The cerebral hemispheres contain:

• Outer "bark" or cortex of gray matter (neuron cell bodies)

• Middle region of white matter (myelinated axons)

• Inner gray matter of nuclei deep within the white matter

Ventricles of the Brain

The brain contains interconnected cavities called ventricles, filled with cerebrospinal fluid (CSF) and lined by ependymal cells. These ventricles cushion the brain and help circulate nutrients and remove waste.

• Lateral Ventricles: Paired, located within each cerebral hemisphere.

• Third Ventricle: Located in the diencephalon, connects to the lateral ventricles via the interventricular foramen.

• Fourth Ventricle: Located between the pons and cerebellum, connects to the third ventricle via the cerebral aqueduct.

Gyri, Sulci, and Fissures

The surface of the cerebral hemispheres is marked by ridges (gyri), shallow grooves (sulci), and deep grooves (fissures). These features increase the surface area and separate different functional regions.

• Gyri: Elevated ridges.

• Sulci: Shallow grooves.

• Fissures: Deep grooves, such as the longitudinal fissure separating the two hemispheres.

Functional Areas of the Cerebral Cortex

The cerebral cortex is responsible for higher brain functions, including perception, voluntary movement, and cognition. It is divided into three main types of areas:

• Motor areas: Control voluntary movement.

• Sensory areas: Conscious awareness of sensation.

• Association areas: Integrate diverse information for purposeful action.

Each hemisphere is concerned with the sensory and motor functions of the opposite side of the body.

Motor Areas

• Primary Motor Cortex: Located in the precentral gyrus of the frontal lobe; controls voluntary movements.

• Premotor Cortex: Plans and coordinates learned motor skills.

• Broca's Area: Controls muscles involved in speech production.

• Frontal Eye Field: Controls voluntary eye movements.

Sensory Areas

• Primary Somatosensory Cortex: Receives information from sensory receptors in skin and muscles.

• Somatosensory Association Area: Integrates sensory input for understanding.

• Visual Areas: Process visual information.

• Auditory Areas: Process sound information.

• Olfactory, Gustatory, and Vestibular Areas: Process smell, taste, and equilibrium, respectively.

Association Areas

• Anterior Association Area: Involved in intellect, cognition, personality, and memory.

• Posterior Association Area: Recognizes patterns and faces, localizes us in space.

• Limbic Association Area: Provides emotional impact.

Left and Right Hemisphere Functions

The two cerebral hemispheres have specialized functions, a phenomenon known as "cerebral lateralization."

• Left Hemisphere: Language abilities, math, logic.

• Right Hemisphere: Visual-spatial skills, intuition, emotion, appreciation of art and music.

Most individuals are left hemisphere dominant for language and right-handed.

Cerebral White Matter and Basal Nuclei

Cerebral white matter consists mainly of myelinated fibers that connect different brain regions and the spinal cord.

• Commissures: Connect corresponding areas of the two hemispheres (e.g., corpus callosum).

• Association fibers: Connect different parts of the same hemisphere.

• Projection fibers: Connect the cortex with lower brain areas and the spinal cord.

Basal Nuclei: Groups of cell bodies deep within the white matter, involved in regulating movement.

Diencephalon Components

The diencephalon includes the thalamus, hypothalamus, and epithalamus, each with distinct functions.

• Thalamus: Relay station for sensory information; involved in motor activities, emotion, arousal, and memory.

• Hypothalamus: Controls autonomic functions, emotional responses, body temperature, hunger, thirst, and endocrine system via the pituitary gland.

• Epithalamus: Contains the pineal gland, which secretes melatonin and regulates sleep-wake cycles.

Chief Homeostatic Roles of the Hypothalamus:

• Autonomic control center

• Center for emotional response and behavior

• Body temperature regulation

• Regulation of food intake

• Regulation of water balance and thirst

• Regulation of sleep-wake cycles

• Control of endocrine system functioning

Brain Stem Structure and Function

The brain stem connects the brain to the spinal cord and controls vital functions. It consists of the midbrain, pons, and medulla oblongata.

• Midbrain: Contains visual and auditory reflex centers, motor tracts, and nuclei for cranial nerves.

• Pons: Relays information between the cerebrum and cerebellum; involved in respiration.

• Medulla Oblongata: Controls autonomic functions such as heart rate, blood pressure, and respiration; contains nuclei for cranial nerves.

Decussation of the Pyramids: Most fibers cross to the opposite side, so each hemisphere controls the opposite side of the body.

Cerebellum Structure and Function

The cerebellum coordinates voluntary movements, balance, and posture. It receives input from the cerebral cortex, sensory pathways, and body proprioceptors.

• Processes information to produce smooth, coordinated movements.

• Regulates timing and patterns of muscle contraction.

Functional Brain Systems

Functional brain systems are networks of neurons that work together across different regions.

• Limbic System: Involved in emotion, motivation, and memory; includes the hippocampus, amygdala, and cingulate gyrus.

• Reticular Formation: Maintains alertness and consciousness; filters sensory input.

Meninges of the Brain

The meninges are three connective tissue membranes that protect the brain and spinal cord.

Key Terms and Definitions

• Gray Matter: Regions of the brain and spinal cord containing neuron cell bodies.

• White Matter: Regions containing myelinated axons.

• Cerebrospinal Fluid (CSF): Fluid that cushions the brain and spinal cord.

• Decussation: Crossing over of nerve fibers from one side to the other.

Important Equations

• Surface Area of the Cerebral Cortex (approximate):

Summary Table: Major Brain Regions and Functions

Additional info: Some explanations and definitions have been expanded for clarity and completeness.