Neurobiology: Neuron Structure and Function

Terminal Boutons

• Terminal boutons are small swellings at the axon's terminal end.
• They facilitate synapses with dendrites or perikaryon of other neurons.
• Commonly found in sensory ganglia of the dorsal root and certain cranial nerve ganglia.

Support Cells

• Oligodendrocytes

  • Responsible for forming myelin sheaths in the central nervous system (CNS).
  • One oligodendrocyte can myelinate up to 50 axons.
  • Predominantly present in white matter.
  • Often described as resembling a "sunny side up egg."

• Astrocytes

  • Highly branched cells filling spaces between neurons and oligodendrocytes.

Types of Neurons

• Multipolar Neurons
  • Characterized by numerous dendrites projecting from the cell body.
  • Typical pattern in various neural structures, including the cerebellum.

Cerebellar Layers

• Molecular Layer

  • The outer layer contains few neurons and many unmyelinated fibers.
  • Rich in both axons and dendrites, with very few stellate cells.

• Purkinje Layer

  • Composed of a single layer of Purkinje cells with large cell bodies.
  • Distinguished by fine axons and extensive dendritic branching in the molecular layer.

• Granular Layer

  • The inner layer packed with small neurons having unmyelinated axons.
  • Neurons extend outward to synapse with Purkinje cell dendrites in the molecular layer.

Spinal Cord

• The spinal cord comprises white matter and cell bodies of second-order neurons.
• Dorsal Columns
  • Transmit fibers responsible for vibration, proprioception, and fine touch.
  • Located in the cervical region's fasciculus gracilis (lower limbs) and fasciculus cuneatus (upper limbs).

Special Senses: Gustation

• Taste Buds
  • The human tongue hosts approximately 3,000 taste buds.
  • Primarily situated in the epithelium of the circumvallate papillae.

Eye Anatomy

• Photosensitive Layers

  • Receives light and terminates at the ora serrata behind the ciliary body.

• Fovea

  • Depression in the retina with maximum visual acuity surrounded by the macula lutea.

• Optic Nerve

  • Formed by afferent nerve fibers from the retina converging to exit through the lamina cribrosa of the sclera.

Visual Processing

• Rod Cells

  • Have a spherical process for interactions, less accommodating than cone cells.

• Cone Cells

  • Approximately 6 million in the eye, responsible for high-light vision and color perception.
  • Mainly located in the fovea for high spatial acuity.

• Integrating Neurons

  • Located in the inner nuclear layer, these neurons integrate signals from multiple rod and cone cells using bipolar cells.

• Different Types of Integrating Neurons

  • Bipolar Cells: Most numerous, connecting photoreceptors with optic tract neurons.
  • Horizontal Cells: Facilitate connections between adjacent rods and cones, also synapsing with bipolar cells.