[Primary sensory neurons in the central nervous system]

Area of Science:

• Neuroscience
• Sensory Biology
• Comparative Anatomy

Context:

• The nervous system's sensory capabilities are traditionally understood through external stimuli reception.
• Internal sensory mechanisms within the central nervous system (CNS) remain less explored.
• Existing literature lacks a unified scheme for vertebrate intracerebral and intraspinal interoceptors.

Purpose:

• To summarize personal observations and literature data on exteroceptive and interoceptive neurons in the brain and spinal cord.
• To describe various sensory neurons, including light-sensitive, chemo-, and thermosensitive types.
• To formulate a hypothesis regarding the CNS's intrinsic sensory innervation.

Summary:

• This paper reviews data on exteroceptive and interoceptive neurons in the CNS, including specialized structures like Hesse's intraspinal ocelli and various sensory neurons.
• It details light-sensitive ganglion neurons in invertebrates and sensory unipolar neurons associated with specific nerve structures in vertebrates.
• A unified scheme of vertebrate interoceptors is presented, supporting the hypothesis of intrinsic CNS sensory innervation.

Impact:

• Proposes that the CNS possesses its own sensory innervation, analogous to other organs.
• Identifies local primary sensory neurons and their dendrites within the CNS as distinct interoceptive and exteroceptive groups.
• Provides a foundational framework for understanding the CNS's internal sensory processing capabilities.