The Central Nervous System

Brain Regions and Organization

The brain is organized into distinct regions, each with specialized functions. Understanding the structure and organization of the brain is essential for grasping its role in controlling bodily functions and higher mental processes.

• Gray matter: Consists mainly of neuron cell bodies and nonmyelinated fibers. It forms the outer layer (cortex) of the brain and is involved in processing and integration.

• White matter: Composed primarily of myelinated axons, facilitating communication between different brain regions.

• Basic pattern: In the CNS, central cavities are surrounded by gray matter, which is itself enclosed by white matter.

• Major brain regions: Cerebral hemispheres, diencephalon, brain stem, and cerebellum.

Example: The cerebral cortex is the site of conscious thought and voluntary action.

Cerebral Hemispheres

12.2 Cerebral Hemispheres

The cerebral hemispheres are divided into left and right halves, each responsible for different functions and controlling opposite sides of the body.

• Lobes of the brain: Frontal, parietal, temporal, occipital, and insula.

• Contralateral control: Each hemisphere controls the opposite side of the body.

• Lateralization: Some functions are specialized to one hemisphere (e.g., language is typically left-dominant).

Example: The left hemisphere is usually dominant for language and analytical tasks.

Cerebral Cortex

Structure and Function

The cerebral cortex is the 'executive suite' of the brain, responsible for conscious thought, awareness, sensory perception, and voluntary motor initiation.

• Composition: Contains neuron cell bodies, dendrites, glial cells, and blood vessels, but no axon bundles.

• Surface area: Highly folded to increase area for processing.

• Functional areas: Motor, sensory, and association areas.

• Accounts for: 40% of total brain mass.

Example: The prefrontal cortex is involved in decision-making and personality.

Functional Neuroimaging

Modern imaging techniques, such as diffusion tensor MRI, reveal fiber tracts and connectivity within the brain and spinal cord.

• Application: Used to study brain organization and diagnose neurological disorders.

Major Functional Areas of the Cerebral Cortex

Primary Somatosensory Cortex

Receives general sensory information from skin and proprioceptors of skeletal muscles, joints, and tendons.

• Spatial discrimination: Ability to identify the body region being stimulated.

• Somatosensory homunculus: Map showing which cortical areas correspond to specific body regions.

Primary Visual Cortex

Located in the occipital lobe, it receives visual information from the retina.

• Visual association area: Interprets visual stimuli (color, form, movement).

Primary Auditory Cortex

Located in the temporal lobe, it interprets information from inner ear as pitch, loudness, and location.

• Auditory association area: Permits perception of sound stimulus.

Cerebellum

Structure and Function

The cerebellum accounts for 11% of brain mass and is crucial for motor coordination, balance, and fine-tuning voluntary movements.

• Receives input: From cortex, brain stem, and sensory receptors.

• Function: Coordinates movement and maintains posture and equilibrium.

Example: Professional ballet dancers have particularly efficient cerebellar function.

Higher Mental Functions

Analysis of Higher Mental Functions

Higher mental functions include language, memory, brain waves, consciousness, and sleep-wake cycles.

• Language: Involves association cortex of left hemisphere; includes Broca's area (speech production) and Wernicke's area (language comprehension).

• Memory: Storage and retrieval of information; includes short-term and long-term memory.

• Brain waves: Electrical activity measured by EEG; different patterns correspond to different states of consciousness.

• Consciousness: Awareness of self and environment.

• Sleep-wake cycles: Regulated by brainstem and hypothalamus.

Memory

Memory involves encoding, storage, and retrieval of information. It is classified into short-term and long-term memory.

• Short-term memory (STM): Limited capacity, temporary storage.

• Long-term memory (LTM): Unlimited capacity, more permanent storage.

• Factors affecting memory: Emotional state, rehearsal, association, and automatic memory.

Brain Wave Patterns and the EEG

EEG (electroencephalogram) records electrical activity of the brain, useful for diagnosing brain disorders and studying sleep.

• Types of brain waves: Alpha, beta, theta, delta.

• Clinical uses: Detects epilepsy, tumors, infections, and sleep disorders.

Sleep and Sleep-Wake Cycles

Types and Stages of Sleep

Sleep consists of cycles between non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.

• NREM: Four stages, progressively deeper sleep.

• REM: Dreaming occurs, vital for memory consolidation.

• Typical sleep cycle: Lasts about 90 minutes, alternating between NREM and REM.

Importance of Sleep

• Restorative function: NREM stages 3 and 4 are most restorative.

• REM sleep: Important for memory consolidation and emotional stability.

• Sleep deprivation: Impairs cognitive function and health.

Blood Brain Barrier

Structure and Function

The blood brain barrier (BBB) maintains a stable environment for the brain by restricting passage of substances from the blood.

• Structure: Formed by tight junctions between endothelial cells of capillaries, supported by astrocytes.

• Function: Protects brain from toxins and pathogens, allows passage of essential nutrients.

• Selective permeability: Some substances (e.g., glucose, amino acids) pass through; others (e.g., most drugs, toxins) are blocked.

Example: The BBB prevents harmful substances from entering the brain, but can be a barrier to drug delivery for neurological diseases.

Summary Table: Major Brain Regions and Functions

Key Equations and Concepts

• EEG Frequency: , where is frequency and is period of the wave.

• Contralateral control: Each hemisphere controls the opposite side of the body.

Additional info: Some details about the blood brain barrier and sleep stages were expanded for academic completeness.