Neurological Winter 2026

Nervous System Overview

  • Functionality: Receives and reacts to environmental stimuli on both physiologic and cognitive levels.
  • Main Components:
    • Central Nervous System (CNS): Composed of the brain and spinal cord.
    • Peripheral Nervous System (PNS): Composed of nerves that extend from the CNS.

Central Nervous System

  • Protective Structures:
    • Skull: Houses and protects the brain.
    • Vertebral Column: Houses and protects the spinal cord.
  • Meninges: Membranes encasing the CNS, consisting of:
    • Dura Mater: Outer tough layer.
    • Arachnoid Layer: Middle layer with a spider web-like vascular structure.
    • Pia Mater: Innermost layer.
  • Cerebrospinal Fluid (CSF): Plasma-like liquid between arachnoid and pia mater, providing cushioning and support. It fills interconnected ventricles in the brain where it is produced, flows, and fills.
  • Neurons: Billions present in the brain.
  • Neuroglia Cells: Supportive cells that:
    • Scaffold neural tissue.
    • Protect neuron membranes.
    • Regulate interstitial fluid.
    • Defend against pathogens.
    • Assist with neural repair.

Neurons

  • Functionality: Generate and transmit bioelectrical impulses.
  • Dividing Capacity: Cannot divide; losses due to aging or injuries are irreversible.
  • Oxygen and Glucose Dependence: Require a constant supply, making them vulnerable to hypoxia and hypoglycemia.

Neuron Structure and Components

  • Axons: Transmit impulses away from the cell body.
  • Dendrites: Transmit impulses toward the cell body.
  • Myelin Sheath: Surrounds some axons, enhancing transmission speed.
  • Schwann Cells: Produce myelin sheath.
  • Nodes of Ranvier: Gaps where myelin is absent, allowing nutrient exchange.
  • White Matter: Comprises myelinated axon bundles.
  • Synapses: Gaps between neurons, including:
    • Presynaptic Terminal: End structure releasing neurotransmitters.
    • Synaptic Cleft: Space between pre- and postsynaptic neurons.
    • Postsynaptic Cell Membrane: Absorbs the neurotransmitters to propagate the signal.

Electrical Impulses

Generation of Neural Impulses

  • Ion Changes: Small ionic changes generate action potentials, characterized by resting potential.
  • Resting Potential: The plasma side of neuron's membrane has a slight charge due to sodium ions outside the cell.

Steps of Electrical Impulses

  1. Depolarization: Protein gates open, allowing sodium to enter the cell, raising the charge.
  2. Repolarization: Rapid potassium outflow returns the charge to resting potential.
  3. Impulse Transmission: Electrical impulses travel down the nerve, leading to neurotransmitter release from presynaptic terminals.
  4. Neurotransmitter Action: Crosses synaptic cleft unidirectionally, stimulating electrical reactions in adjacent neurons.
  5. Cycle Continuation: Process repeats at the next synapse upon neurotransmitter release.
  6. Neurotransmitter Fate: May be destroyed by enzymes or reabsorbed by postsynaptic membrane.
  7. Inhibition of Action Potential: Certain neurotransmitters inhibit action potentials.

Cranial Nerves

  • Definition: Brain functions through twelve pairs of cranial nerves originating from the base of the brain.
  • Functionality:
    • Carry sensory and/or motor fibers.
    • Each nerve travels from the brain through openings (foramina) to target destinations.

Major Regions of the Brain

Cerebrum

  • Size and Function: Largest brain region controlling higher thought processes.
  • Cerebral Cortex: Thin layer of gray matter surrounding the cerebrum.
  • White Matter: Beneath gray matter contains myelinated axon bundles facilitating communication.
  • Hemispheres: Divided into right and left sections, featuring gyri (folds) and sulci (grooves).
  • Lobes of the Cerebrum:
    • Frontal Lobe: Voluntary motor activity and personality traits.
    • Parietal Lobe: Sensory input interpretation, excluding smell, hearing, and vision.
    • Occipital Lobe: Visual information processing.
    • Temporal Lobe: Critical for hearing and memory.

Diencephalon

  • Thalamus: Relays most sensory input, influences mood, and initiates body movements.
  • Subthalamus: Participation in motor activities.
  • Hypothalamus: Regulates multiple bodily