I. Overview of the Nervous System

A. Divisions of the Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

• CNS: Consists of the brain and spinal cord. It is responsible for integrating, processing, and coordinating sensory data and motor commands.

• PNS: Includes all neural tissue outside the CNS, such as cranial and spinal nerves. It is subdivided into the somatic and autonomic nervous systems.

II. Introduction to the Central Nervous System (CNS)

A. Functions of the Brain

The brain is responsible for a wide range of functions, from basic life-sustaining activities to complex mental processes.

• Maintains internal environment through control of the ANS and endocrine system.

• Processes sensory information, initiates motor output, and is the center for higher functions such as reasoning, memory, and emotion.

B. Major Parts of the Brain

• Cerebrum: Largest part, divided into two hemispheres, responsible for higher brain functions.

• Diencephalon: Includes the thalamus and hypothalamus, involved in sensory and autonomic functions.

• Cerebellum: Coordinates balance and movement.

• Brain Stem: Includes the midbrain, pons, and medulla oblongata; controls vital functions.

C. Gray Matter and White Matter

• Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons. Forms the cortex (outer layer) of the cerebrum and cerebellum, and deeper nuclei.

• White Matter: Composed of myelinated axons, giving it a lighter appearance. Lies beneath the cortex in the brain, but is superficial in the spinal cord.

III. Brain Organization, Protection, and Blood Supply

A. Protective Coverings of the Brain

The brain is protected by the skull and three connective tissue membranes called meninges:

• Dura Mater: Tough, outermost layer, closely applied to the skull but not attached except at certain points. Contains dural sinuses for venous blood drainage.

• Arachnoid Mater: Middle, web-like membrane. The subarachnoid space beneath it contains cerebrospinal fluid (CSF).

• Pia Mater: Thin, delicate membrane that follows all contours of the brain and spinal cord.

Major Dural Folds:

• Falx Cerebri: Separates the two cerebral hemispheres along the longitudinal fissure.

• Tentorium Cerebelli: Separates the cerebellum from the cerebrum.

• Falx Cerebelli: Partially separates the right and left halves of the cerebellum.

B. Cranial Meninges and Spaces

• Subdural Space: Potential space between dura and arachnoid mater.

• Subarachnoid Space: Real space between arachnoid and pia mater, filled with CSF.

IV. Cerebrospinal Fluid, Ventricles, and Cerebral Blood Flow

A. Ventricles of the Brain

The brain contains four interconnected chambers called ventricles that are filled with cerebrospinal fluid (CSF):

• Lateral Ventricles (2): Located in each cerebral hemisphere; largest ventricles.

• Third Ventricle: Located in the diencephalon; connected to lateral ventricles by interventricular foramina.

• Fourth Ventricle: Located between the pons and cerebellum; connected to third ventricle by the cerebral aqueduct.

B. Formation and Circulation of CSF

• CSF is produced by the choroid plexus (specialized capillaries lined with ependymal cells) in each ventricle.

• CSF flows from the lateral ventricles → third ventricle → fourth ventricle → subarachnoid space → dural sinuses.

• CSF is reabsorbed into the venous blood via arachnoid villi (especially into the superior sagittal sinus).

C. Functions of Cerebrospinal Fluid (CSF)

• Buoyancy: Reduces the effective weight of the brain, preventing it from being crushed by its own mass.

• Protection: Cushions the brain from trauma (e.g., sudden movements, impacts).

• Chemical Stability: Removes metabolic wastes and helps maintain a stable environment for neurons.

Normal CSF volume: ~120 mL; produced at a rate of 20 mL/hour.

D. Blood Supply and the Blood-Brain Barrier (BBB)

• The brain receives about 15% of the body's blood supply and consumes 20% of its oxygen and 50% of its glucose at rest.

• Neurons depend on a constant supply of glucose and oxygen; interruption can cause rapid and irreversible damage.

• Blood-Brain Barrier: Formed by tight junctions between endothelial cells of brain capillaries and astrocyte processes. It restricts passage of harmful substances, while allowing essential nutrients to pass.

Key facts:

• 10-second interruption of blood flow: loss of consciousness.

• 1-2 minutes: impaired function.

• 4 minutes: irreversible brain damage.

E. Brain Injuries and Disorders

• Traumatic brain injuries: Concussion, contusion, subdural/subarachnoid hemorrhage.

• Stroke: Caused by decreased blood supply (ischemia) or bleeding (hemorrhage).

V. The Cerebrum

A. Structure and Function

The cerebrum is the largest part of the brain and the center of intelligence, personality, and conscious thought. It contains about 75% of all neurons in the nervous system.

• Divided into two hemispheres (right and left), separated by the longitudinal fissure and connected by the corpus callosum.

• Each hemisphere has folds called gyri and grooves called sulci.

• The outer layer is the cerebral cortex (gray matter), beneath which lies the medulla (white matter) and basal nuclei (deep gray matter).

• The cortex is the location of the conscious mind, allowing us to communicate, remember, and understand.

B. Lobes of the Cerebrum

• Frontal Lobe: Voluntary movement, planning, reasoning, problem-solving.

• Parietal Lobe: Sensory perception, spatial awareness.

• Temporal Lobe: Auditory processing, memory, language.

• Occipital Lobe: Visual processing.

• Insula: Deep within the lateral sulcus; involved in taste, visceral sensation, and emotion.

C. Communication Between Hemispheres

• Occurs via the corpus callosum, a large bundle of transverse white fibers.

D. Hemispheric Lateralization

• The two hemispheres are structurally similar but functionally specialized.

• Left hemisphere: Language, analytical, and mathematical skills.

• Right hemisphere: Spatial abilities, face recognition, visual imagery, and music.

• Lateralization is more pronounced in some individuals (e.g., left-handed people).

E. Functional Areas of the Cerebral Cortex

• Primary Motor Cortex: Controls voluntary movements.

• Primary Somatosensory Cortex: Receives sensory input from the body.

• Association Areas: Integrate information for higher functions such as learning, memory, and reasoning.

VI. Summary Table: Protective Structures of the CNS

VII. Key Equations and Definitions

• Cerebrospinal Fluid Production Rate:

• Buoyancy Principle: The brain and CSF have similar densities, so the brain "floats" in CSF, reducing its effective weight.

VIII. Clinical Correlations

• Concussion: Temporary loss of brain function due to trauma.

• Contusion: Bruising of brain tissue.

• Stroke: Disruption of blood supply to the brain, leading to tissue death.

• Blood-Brain Barrier Disruption: Can allow harmful substances to enter the brain, leading to infection or toxicity.

Additional info: Some explanations and definitions have been expanded for clarity and completeness based on standard academic sources in anatomy and physiology.