Central Nervous System (CNS)

Overview of the Nervous System

• Organization of the Nervous System:
  • Composed of the Central Nervous System (CNS) and Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Components: Brain and spinal cord.
• Functions: Acts as the integrating center for processing sensory information and directing responses.

Peripheral Nervous System (PNS)

• Divisions:
  • Afferent Division: Sensory neurons that send information to the CNS.
  • Efferent Division:
  • Somatic Motor: Controls skeletal muscle.
  • Autonomic: Controls smooth and cardiac muscle, as well as glands.

Neurons and Glial Cells

• Neurons: Basic functional unit of the nervous system.
  • Structure: Consist of dendrites, an axon, and synaptic terminals.
  • Types of Neurons:
  • Presynaptic Neuron: Sends signals.
  • Postsynaptic Neuron: Receives signals.
• Glial Cells: Support neurons, outnumber them by 10-50 times.

Membrane Potential

• Resting Membrane Potential: Electrical potential difference across the membrane at rest.
• Key Ions:
  • Extracellular: High in Na+ and Cl-.
  • Intracellular: High in K+ and negatively charged proteins.
• Equilibrium Potential: Net flux of an ion across a membrane is zero, described by the Nernst equation.

Action Potentials and Graded Potentials

• Graded Potentials:
  • Changes in membrane potential that vary in size.
  • Subthreshold and Suprathreshold:
  • Subthreshold: Too weak to trigger an action potential.
  • Suprathreshold: Strong enough to initiate an action potential.
• Action Potentials:
  • All-or-nothing response when a stimulus reaches threshold.
  • Characteristics:
  • Frequency of action potentials reflects stimulus strength.
  • Conducted without loss of strength along the axon.

Myelination and Conduction

• Saltatory Conduction:
  • Occurs along myelinated axons, greatly increasing conduction speed.
  • Myelin Formation:
  • PNS: Schwann cells individually myelinate axons.
  • CNS: Oligodendrocytes myelinate multiple axons.
• White vs. Grey Matter:
  • White Matter: Myelinated axons.
  • Grey Matter: Neuron cell bodies and unmyelinated axons.

Protection of the CNS

• Physical Protection:
  • Bony Structures: Skull and vertebrae.
  • Meninges: Three protective membranes:
  • Dura Mater: Outer layer.
  • Arachnoid Membrane: Middle layer.
  • Pia Mater: Inner layer, adheres to the brain and spinal cord.
• Cerebrospinal Fluid (CSF): Provides cushioning and chemical stability.
• Blood-Brain Barrier: Selectively permeable barrier that protects the brain from harmful substances in the blood.

Regions of the Brain

• Cerebrum: Largest part of the brain, involved in higher brain functions.
• Cerebellum: Coordinates movement and maintains posture.
• Brainstem: Controls vital functions and pathways between the brain and spinal cord.
• Limbic System: Involved in emotion and memory.

Functional Areas of the Cerebral Cortex

• Frontal Lobe: Involved in executive functions and voluntary motor control.
• Parietal Lobe: Processes sensory information.
• Temporal Lobe: Involved in auditory information and memory.
• Occipital Lobe: Responsible for visual processing.

Spinal Cord Anatomy

• Ascending Tracts: Carry sensory information to the brain.
• Descending Tracts: Convey motor commands from the brain to the body.
• Dorsal/Ventral Roots: Dorsal roots carry sensory information, ventral roots carry motor signals.

Imaging Techniques

• Electroencephalography (EEG): Measures brain electrical activity.
• Positron Emission Tomography (PET): Measures brain metabolism using radioactive tracers.
• Functional Magnetic Resonance Imaging (fMRI): Measures brain activity by detecting changes in blood flow.

Learning Outcomes

• Understand the organization and protective mechanisms of the CNS.
• Describe the anatomy and function of different brain regions.
• Comprehend cellular mechanisms involved in neuronal signaling and communication.