Introduction to Neurons and Glial Cells

Action Potential and Neuron Function

  • Focus on chemical aspects of neurons, particularly action potential generation and propagation.

  • Initiation occurs at the axon hillock and terminates at the axon terminal.

  • Nodes of Ranvier enhance signal conduction along myelinated neurons.

Categories of Neurons

  • Unipolar Neurons: Typically pseudo unipolar; one process serves as both dendrite and axon, mainly in sensory nerves.

  • Bipolar Neurons: Two processes (one dendrite, one axon); found in retina (vision) and olfactory epithelium (smell).

  • Multipolar Neurons: Many dendrites; classic neuron type; allows integration of signals from multiple sources.

  • Possible neuroplasticity in multipolar neurons where dendrites and axons can switch roles.

Glial Cells Overview

  • Astrocytes: Star-shaped; regulate ion concentration, uptake excess neurotransmitters, assist in neuronal repair, and maintain blood-brain barrier (BBB).

  • Oligodendrocytes: Produce myelin in CNS, insulating axons.

  • Microglia: Act as immune cells in the CNS, removing pathogens.

  • Ependymal Cells: Involved in creating cerebrospinal fluid (CSF).

  • Satellite Cells: Function similarly to astrocytes in the PNS; modulate ion concentrations and repair damaged neurons.

  • Schwann Cells: Myelinate axons in the PNS; wrap around segments of axons.

Myelin and Signal Conduction

  • Myelin: Rich in lipids, crucial for rapid signal transmission; reduces signal attenuation.

  • Demyelination diseases (e.g., multiple sclerosis, Guillain-Barre syndrome) disrupt normal electrical signaling, affecting motor control and sensation.

Nervous System Function Example

  • Example: Testing water temperature with sensory receptors (thermoreceptors) in hands.

  • Signals from thermoreceptors generate graded potentials leading to action potentials in sensory neurons.

  • Information relayed through spinal cord to thalamus and then cerebral cortex for conscious perception and response.

Action Potential Mechanism

  • Requires depolarization by sodium (Na+) influx through voltage-gated ion channels.

  • Sodium-potassium pump maintains resting membrane potential (~-60 to -70 mV).

  • Action potentials propagate by opening adjacent voltage-gated channels along the neuron membrane, allowing rapid signaling.