Central Nervous System: Structure, Function, and Neurophysiology Study Guide

Central Nervous System

Overview of the Central Nervous System (CNS)

The central nervous system (CNS) consists of the brain and spinal cord. It is responsible for integrating sensory information, coordinating bodily functions, and facilitating higher cognitive processes such as learning and memory.

• Major Components: Brain (cerebrum, cerebellum, brainstem), spinal cord

• Functions: Processing sensory data, generating motor commands, regulating homeostasis, and enabling cognition

• Protection: Enclosed by the skull and vertebral column, protected by meninges and cerebrospinal fluid (CSF)

Brain Anatomy and Major Regions

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

• Cerebrum: Largest part, responsible for voluntary actions, sensory perception, reasoning, and memory

• Cerebellum: Coordinates movement and balance

• Brainstem: Includes midbrain, pons, and medulla oblongata; controls vital functions such as breathing and heart rate

• White Matter vs. Gray Matter: White matter consists of myelinated axons; gray matter contains neuron cell bodies and dendrites

Neuroanatomical Structures

Key structures within the CNS include gyri, sulci, fissures, and various nuclei and tracts.

• Gyri: Elevated ridges on the brain surface

• Sulci: Shallow grooves separating gyri

• Fissures: Deep grooves dividing major brain regions

• Nuclei: Clusters of neuron cell bodies within the CNS

• Tracts: Bundles of axons within the CNS

Action Potentials and Ion Channels

Neurons communicate via action potentials, which are rapid changes in membrane potential due to the movement of ions across the neuronal membrane.

• Resting Membrane Potential: Typically around -70 mV, maintained by Na+/K+ pumps

• Depolarization: Voltage-gated Na+ channels open, allowing Na+ influx

• Repolarization: Voltage-gated K+ channels open, allowing K+ efflux

• Hyperpolarization: Membrane potential becomes more negative than resting potential

Key Equation:

$V_m = V_{in} - V_{out}$

where $V_m$ is the membrane potential.

Example: Ion Channel States During Action Potential

• During the rising phase (depolarization), voltage-gated Na+ channels are open, K+ channels are mostly closed.

• During repolarization, Na+ channels inactivate, K+ channels open.

Glial Cells and Their Functions

Glial cells support and protect neurons in the CNS.

• Astrocytes: Maintain blood-brain barrier, regulate ion balance

• Oligodendrocytes: Form myelin sheaths in the CNS

• Ependymal Cells: Line ventricles, produce cerebrospinal fluid (CSF)

• Microglia: Act as immune cells within the CNS

Cerebrospinal Fluid (CSF)

CSF is a clear fluid that cushions the brain and spinal cord, removes waste, and provides nutrients.

• Production: Produced by ependymal cells in the choroid plexus

• Circulation: Flows through ventricles, central canal, and subarachnoid space

• Absorption: Reabsorbed into the bloodstream via arachnoid granulations

Neural Pathways and Tracts

Neural pathways are collections of axons that transmit signals within the CNS.

• Tracts: Bundles of axons in the CNS (e.g., corticospinal tract)

• Nerves: Bundles of axons in the peripheral nervous system (PNS)

• Pathways: Specific routes taken by nerve impulses (e.g., sensory, motor pathways)

Motor and Sensory Pathways

Motor pathways transmit commands from the CNS to muscles, while sensory pathways carry information from sensory receptors to the CNS.

• Anterior Corticospinal Pathway: Controls proximal muscles

• Lateral Corticospinal Pathway: Controls distal muscles, such as those used for writing

• DCML Pathway: Dorsal column-medial lemniscus, transmits fine touch and proprioception

• Spinocerebellar Pathway: Transmits proprioceptive information to the cerebellum

Brain Development and Major Brain Vesicles

During embryonic development, the brain forms from three primary vesicles: prosencephalon, mesencephalon, and rhombencephalon.

• Prosencephalon (forebrain): Develops into the cerebrum

• Mesencephalon (midbrain): Remains as the midbrain

• Rhombencephalon (hindbrain): Develops into the pons, medulla oblongata, and cerebellum

Diseases of the Nervous System

Several diseases affect the CNS, each with distinct symptoms and underlying causes.

• Alzheimer's Disease: Progressive memory loss and cognitive decline

• Huntington's Disease: Progressive motor dysfunction and psychiatric symptoms due to genetic mutation

• Amyotrophic Lateral Sclerosis (ALS): Degeneration of motor neurons, leading to muscle weakness

• Hemorrhagic Stroke: Bleeding in the brain causing neurological deficits

Sample Table: Comparison of Glial Cells

Glial Cell Type	Main Function	Location
Astrocyte	Support neurons, maintain blood-brain barrier	CNS
Oligodendrocyte	Form myelin sheath	CNS
Ependymal Cell	Produce and circulate CSF	CNS (ventricles)
Microglia	Immune defense	CNS

Key Terms and Definitions

• Neuron: Nerve cell specialized for communication

• Axon: Long projection that transmits electrical impulses away from the cell body

• Dendrite: Branch-like structure that receives signals from other neurons

• Synapse: Junction between two neurons where communication occurs

• Action Potential: Rapid change in membrane potential that travels along the axon

Example: Action Potential Graph Interpretation

• During the rising phase (Area B), voltage-gated Na+ channels are open, K+ channels are mostly closed.

• During repolarization (Area C), Na+ channels inactivate, K+ channels open.

Summary Table: Brain Regions and Functions

Region	Function
Frontal Lobe	Motor control, decision making, speech production
Parietal Lobe	Sensory perception, spatial awareness
Temporal Lobe	Auditory processing, memory
Occipital Lobe	Visual processing
Cerebellum	Coordination, balance

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