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Neurons and Other Cells

Case Presentation

  • 27-year-old female geologist, Milan, Italy.

  • Symptoms: progressive bilateral upper limb weakness and left eyelid drooping; worsens after physical activity, partially improves with rest.

Diagnosis and Condition

  • Condition: Myasthenia gravis (MG)

  • Description: Autoimmune disorder causing muscle weakness due to disrupted nerve-muscle communication.

  • Affects voluntary muscles: eyes, mouth, throat, and limbs.

Neuronal Communication

  • Neurons communicate with muscle cells via synapse at the neuromuscular junction.

  • Acetylcholine (ACh) is the neurotransmitter involved.

  • In MG, antibodies block ACh receptor sites, impairing communication.

Nervous System Divisions

  • Central Nervous System (CNS): Brain and spinal cord.

  • Peripheral Nervous System (PNS): Nerves and sensory organs, acting as a communication network.

Reflexes

  • Example: Pain withdrawal reflex triggers quick muscle response through sensory and motor neurons.

Types of Neural Cells

  • Neurons: Basic units of the nervous system, electrically active.

  • Neuroglia: Supportive roles; potential signaling functions under research.

Neuron Structure

  • Cell Body (Soma), Dendrites, and Axon.

  • Types of neurons: Afferent (sensory), Efferent (motor), Interneurons; classified functionally and structurally.

Action Potential

  • Rapid alterations in membrane potential (from -70mV to +30mV).

  • Depends on voltage-gated sodium (Na⁺) and potassium (K⁺) channels.

Membrane Potential

  • Resting Potential: -70 to -90 mV; primarily influenced by K⁺ ions.

  • Establishment through selective permeability and ion pumps.

Refractory Periods

  • Absolute Refractory: No second action potential during AP.

  • Relative Refractory: Possible second AP with stronger stimulus.

Key Concepts

  • All-or-None Behavior of action potentials: consistent magnitude regardless of stimulus strength.