Study Guide: Central Nervous System Structure and Function

9.1 Emergent Properties of Neural Networks

Neural Plasticity

Neural plasticity refers to the brain's ability to change and adapt as a result of experience. This property is fundamental for learning, memory, and recovery from brain injury.

• Plasticity: The capacity of neural networks in the brain to change through growth and reorganization.

• Significance: Enables learning, memory formation, and adaptation to new experiences or injuries.

• Example: After a stroke, undamaged parts of the brain can sometimes take over functions lost by damaged areas.

9.2 Evolution of Nervous Systems

Ganglia and Spinal Reflexes

As nervous systems evolved, specialized structures such as ganglia and reflex pathways developed to coordinate complex behaviors.

• Ganglion: A cluster of nerve cell bodies located outside the central nervous system (CNS).

• Spinal Reflex: An automatic response to a stimulus that is mediated by the spinal cord, bypassing the brain for rapid reaction (e.g., knee-jerk reflex).

9.3 Anatomy of the Central Nervous System

The CNS Develops from a Hollow Tube

The central nervous system (CNS) originates from a neural tube during embryonic development. This tube differentiates into major brain regions and the spinal cord.

• Development: The neural tube forms three primary brain vesicles: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain).

• Major Structures: These vesicles further differentiate into the cerebrum, diencephalon, brainstem, cerebellum, and spinal cord.

Gray Matter and White Matter

The CNS is organized into gray matter and white matter, each with distinct functions and locations.

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; involved in processing and integration.

• White Matter: Composed mainly of myelinated axons; responsible for transmitting signals between different CNS regions.

• Comparison: Gray matter is found on the surface of the brain (cortex) and in central regions (nuclei), while white matter lies beneath the cortex.

Bone and Connective Tissue Support the CNS

The brain and spinal cord are protected by bones and connective tissue layers called meninges.

• Bones: The skull protects the brain; the vertebral column protects the spinal cord.

• Meninges: Three layers of connective tissue that cover the CNS:

  • Dura mater: Outermost, tough layer next to the bone.

  • Arachnoid mater: Middle, web-like layer.

  • Pia mater: Innermost, delicate layer adhering to neural tissue.

The Brain Floats in Cerebrospinal Fluid (CSF)

Cerebrospinal fluid cushions the brain and spinal cord, providing mechanical and chemical protection.

• CSF Composition: Similar to plasma but with lower protein and different ion concentrations.

• Functions: Buoyancy, protection, waste removal, and nutrient delivery.

• Clinical Application: CSF samples are obtained via lumbar puncture for diagnostic purposes.

• CSF Circulation: Produced by choroid plexus, circulates through ventricles, subarachnoid space, and is reabsorbed into venous blood.

The Blood-Brain Barrier Protects the Brain

The blood-brain barrier (BBB) is a selective barrier formed by endothelial cells of brain capillaries, restricting passage of substances from blood to brain tissue.

• Properties: Tight junctions make brain capillaries less leaky than others.

• Permitted Molecules: Lipid-soluble substances and some small molecules can cross; most proteins and pathogens are blocked.

• Functional Areas: Some brain regions lack a BBB to allow hormone and nutrient exchange (e.g., hypothalamus, vomiting center).

Neural Tissue Has Special Metabolic Requirements

The CNS has high metabolic demands, requiring continuous oxygen and glucose supply.

• Oxygen: Required for ATP production; deprivation leads to rapid cell death.

• Glucose: Main energy source; hypoglycemia impairs brain function.

9.4 The Spinal Cord

Spinal Cord Regions and Structure

The spinal cord is divided into four regions: cervical, thoracic, lumbar, and sacral. It contains both gray and white matter, organized into horns and tracts.

• Regions: Cervical, thoracic, lumbar, sacral.

• Gray Matter: Central, butterfly-shaped area containing neuron cell bodies.

• White Matter: Surrounds gray matter; contains ascending (sensory) and descending (motor) tracts.

• Reflexes: Spinal reflexes are mediated by circuits within the spinal cord.

9.5 The Brain

Major Divisions of the Brain

The brain is divided into several major regions, each with specialized functions.

• Cerebrum: Largest part, responsible for higher brain functions.

• Diencephalon: Includes thalamus and hypothalamus; involved in sensory relay and homeostasis.

• Brainstem: Includes midbrain, pons, and medulla oblongata; controls basic life functions.

• Cerebellum: Coordinates movement and balance.

The Brain Stem

The brain stem is the oldest part of the brain, controlling vital functions and serving as a conduit for information between the brain and spinal cord.

• Cranial Nerves: Twelve pairs arise from the brainstem, controlling sensory and motor functions of the head and neck.

• Reticular Formation: Network of neurons involved in arousal and consciousness.

Medulla Oblongata

The medulla controls autonomic functions such as heart rate, breathing, and blood pressure. It contains nuclei for somatosensory and corticospinal tracts, and the pyramids where motor fibers cross.

Pons and Midbrain

• Pons: Located above the medulla; relays information between cerebrum and cerebellum, regulates breathing.

• Midbrain: Involved in visual and auditory processing, motor control.

Cerebellum

The cerebellum is located at the back of the brain and is essential for coordination, precision, and accurate timing of movements.

Diencephalon

• Thalamus: Relay station for sensory and motor signals to the cerebral cortex; can modulate information.

• Hypothalamus: Regulates homeostasis, endocrine functions, and autonomic nervous system.

Cerebrum

• Hemispheres: Two hemispheres connected by the corpus callosum.

• Lobes: Frontal, parietal, temporal, occipital.

• Surface Folding: Gyri and sulci increase surface area for higher cognitive functions.

Gray and White Matter in the Cerebrum

• Gray Matter: Cerebral cortex (outer layer), basal ganglia, limbic system.

• White Matter: Myelinated axons connecting different brain regions.

9.6 Brain Function

Motor Systems and Output

Motor output from the CNS is influenced by multiple systems, including the motor cortex, basal ganglia, and cerebellum.

• Descending Pathways: Carry motor commands from the brain to the body; cross at the pyramids in the medulla.

• Visceral and Neuroendocrine Coordination: Hypothalamus and brainstem coordinate autonomic and endocrine responses.

The Cerebral Cortex: Functional Areas

The cerebral cortex is organized into areas specialized for sensory perception, motor control, and association/integration.

• Primary Sensory Cortex: Receives and processes sensory input.

• Primary Motor Cortex: Directs voluntary movement.

• Association Areas: Integrate information and direct complex behaviors.

• Lateralization: Left hemisphere: language, logic; Right hemisphere: spatial, creative tasks.

Noninvasive Brain Imaging

• Techniques: MRI, fMRI, PET, EEG are used to study brain structure and function without surgery.

Sensory Information Processing

Sensory information is relayed to the brain, processed in specific cortical regions, and integrated into perception.

• Flow: Sensory receptors → spinal cord/brainstem → thalamus → primary sensory cortex.

• Special Senses: Vision (occipital lobe), hearing (temporal lobe), taste (insula), smell (olfactory cortex).

Perception

• Definition: The conscious interpretation of sensory stimuli.

Behavioral State System

The behavioral state system modulates motor output and consciousness, involving diffuse modulatory systems and the reticular activating system.

• Diffuse Modulatory Systems: Networks that regulate arousal, mood, and attention.

• Reticular Activating System: Maintains wakefulness and consciousness.

Sleep and Circadian Rhythms

• Sleep: An active state essential for health; includes REM and non-REM stages.

• Circadian Rhythms: Biological cycles regulated by the suprachiasmatic nucleus in the hypothalamus.

Emotion and Motivation

• Emotion: Generated by limbic system structures (e.g., amygdala).

• Motivation: Drives goal-directed behavior; involves reward pathways.

• Moods: Long-lasting emotional states; imbalances can lead to disorders like depression.

Learning and Memory

Learning involves changes in synaptic strength; memory is the retention and recall of information.

• Memory Traces: Physical changes in neural circuits.

• Hippocampus: Essential for forming new memories.

• Short-term vs. Long-term Memory: Short-term is temporary; long-term is stable and stored in the cortex.

• Memory Consolidation: The process of transferring information from short-term to long-term storage.

• Types: Reflexive (implicit) and declarative (explicit) memory.

Language

• Complex Behavior: Involves multiple brain regions for comprehension and production (e.g., Broca's and Wernicke's areas).

• Lateralization: Usually localized in the left hemisphere.

• Aphasia: Language impairment due to brain damage; Broca's aphasia affects speech production, Wernicke's affects comprehension.

Personality and Mental Disorders

• Personality: Shaped by both genetic inheritance and life experiences.

• Schizophrenia: A severe mental disorder characterized by distorted thinking; diagnosis involves clinical assessment, and treatment includes medication and therapy.

Structure	Function
Gray Matter	Processing, integration, cell bodies
White Matter	Signal transmission, myelinated axons
Dura Mater	Protection, outermost meninge
Arachnoid Mater	Cushioning, middle meninge
Pia Mater	Nourishment, innermost meninge

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.