Ch 11 The Neuron

Histology of the Nervous System

  • Major Cell Types
    • Neurons
    • Main functional units of the nervous system.
    • Billions in number within the brain, spinal cord, and nerves.
    • Neuroglia (Glial Cells)
    • Support cells for neurons.
    • Six different types of neuroglial cells with varied structures and functions.

Characteristics of Neurons

  • Longevity
    • Neurons have extreme longevity; established prenatally and can last a lifetime.
    • Unlike skin cells that have a 30-day life cycle, neurons maintain their presence until death.
  • Fragility
    • Neurons are fragile and mostly amitotic (do not undergo mitosis).
    • Loss of neurons over time can result from lifestyle choices (e.g., drugs, alcohol).
    • Aging is associated with neurological decline (slower reflexes, cognitive function decrease).
  • Metabolic Demands
    • Highly metabolic, requiring a constant supply of ATP, sourced from glucose in the bloodstream.
    • Necessary for neuronal function throughout life, even during sleep.
  • Electrical Excitability
    • Neurons are electrically excitable (older texts may use the term 'irritable').
    • Respond to stimuli and generate action potentials using ions/electrolytes.

Anatomy of Neurons

  • Soma (Cell Body)
    • Integrative and metabolic center of the neuron.
  • Dendrites
    • Branch-like structures that act as antennae, receiving signals.
    • Act as the receptive region for incoming information.
  • Axon
    • Tail-like structure that transmits action potentials.
    • Functions like a cable carrying electrical currents.
  • Axon Hillock
    • The junction between soma and axon where action potentials are generated.
  • Schwann Cells
    • Myelinating cells that produce myelin as an insulator around axons.
    • Help in efficient signal transmission.
  • Nodes of Ranvier
    • Exposed areas between Schwann cells important for electrical conduction.
  • Axon Terminals
    • Secretory end of the neuron where neurotransmitters are released.
    • Critical for signal transmission to target cells.

Neuronal Classification by Function

  • Sensory Neurons
    • Also known as afferent neurons.
    • Function: Detect and relay stimuli from the environment to the central nervous system (CNS).
  • Interneurons
    • Also called association neurons.
    • Function: Integration center within the CNS, processing and relaying information.
  • Motor Neurons
    • Also known as efferent neurons.
    • Function: Carry out responses from the CNS to peripheral targets, can be voluntary or involuntary in nature.

Functions of the Nervous System

  • Sensing

    • Perception and detection of stimuli.

  • Integration

    • Processing and making sense of sensory information.

  • Response

    • Executing actions based on processed information.

  • Note: Understanding the structure and function of neurons is crucial for recognizing their role in the nervous system's overall function and health.