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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.