Chapter 14: Nervous Tissue

Introduction

• Overview of the nervous system: structural (anatomy) and functional aspects.
• Importance of understanding terms and concepts for future lectures on the brain and senses.
• Study guide recommended for organizing thoughts.

Components of the Nervous System

• Neurons and Glial Cells: Key players in nervous tissue.
  • Neuron Type: Identification of neurolemocyte (type of glial cell).
  • Neurons: Typically multipolar; communicate via synapses.
  • Function: Interpretation and response to stimuli.
  • Receptors: Detect stimuli (e.g., tactile receptors for touch).
  • Effectors: Muscles and glands responding to stimuli.

Nervous System Structure

• Central Nervous System (CNS):
  • Comprised of the brain and spinal cord.
• Peripheral Nervous System (PNS):
  • Includes nerves and ganglia.
  • Nerves: Bundles of axons (outside CNS).
  • Ganglia: Bundles of soma in the PNS.

Nervous System Function

• Functions:
  1. Collecting information: Sensory input via receptors.
  2. Processing and evaluating information: Within CNS.
  3. Responding to information: Motor output to effectors (muscles/glands).

Functional Divisions

• Sensory Division (Afferent):

  • Collects and sends sensory information from PNS to CNS.
  • Types:
    • Somatic Sensory: Conscious (e.g., proprioception, touch, sight).
    • Visceral Sensory: Unconscious (e.g., heart rate, gas levels).

• Motor Division (Efferent):

  • Sends motor commands from CNS to PNS.
  • Types:
    • Somatic Motor: Voluntary control (skeletal muscle).
    • Autonomic Motor: Involuntary control (cardiac/smooth muscle, glands).
    • Subdivisions:
      • Parasympathetic: Rest and digest.
      • Sympathetic: Fight or flight.

Neuron Structure and Classification

• Neurons: High metabolic rate; non-mitotic; long-lived.

• Structure:

  • Soma: Cell body containing organelles, Nissl bodies.
  • Dendrites: Receive signals.
  • Axon: Transmits action potentials.
  • Axon Hillock: Initiates action potential.

• Classification:

  • Structural: Multipolar (most common), unipolar, bipolar.
  • Functional: Sensory (afferent), motor (efferent), interneurons.

Glial Cells

• CNS Glial Cells:

  • Astrocytes: Blood-brain barrier, repair, and development.
  • Ependymal Cells: Produce cerebrospinal fluid.
  • Microglial Cells: Phagocytic, immune defense.
  • Oligodendrocytes: Form myelin sheath in CNS.

• PNS Glial Cells:

  • Satellite Cells: Support and separate neuron soma.
  • Neurolemmocytes (Schwann cells): Myelinate axons in PNS.

Nerve Structure

• Connective Tissue Layers:
  • Endoneurium: Around individual axons (areolar tissue).
  • Perineurium: Around fascicles (dense irregular connective tissue).
  • Epineurium: Around entire nerve (dense irregular connective tissue).

Synapses

• Mechanism: Transmission of nerve impulses via neurotransmitters (chemical).
• Components: Presynaptic and postsynaptic neurons; synaptic cleft.
• Process: Electrical signal within neuron; chemical signal between neurons.

Conclusion

• Understanding of nervous tissue essential for later topics on brain and senses.
• Future focus: action potentials and further details on nervous system functions.