Lecture on Nervous and Sensory Systems

Overview of Nervous Systems

• Nervous System Organization

  • Typical nervous systems have two major branches:
    • Central Nervous System (CNS):
      • Includes brain and spinal cord in humans, and brain and nerve cord in invertebrates.
      • Interneurons in CNS integrate information.
    • Peripheral Nervous System (PNS):
      • Includes sensory and motor neurons.
      • Divided into:
        • Somatic Nervous System: Controls voluntary muscles and sensory information.
        • Autonomic Nervous System (ANS): Involuntary actions; organized into:
          • Sympathetic ANS: "Fight or flight" response.
          • Parasympathetic ANS: "Rest and digest" functions.

• Nervous Systems in Different Animals

  • Bilateral animals have CNS with a brain and nerve cord.
  • Radially symmetric animals, like starfish and anemones, have different systems like neural rings and nerve nets.

Sensory Systems

• Function: To transduce environmental energies into neural signals (electrical and chemical).
• Types of Stimuli:
  • Mechanical: Example: touch, sound.
  • Electromagnetic: Example: visible light.
  • Chemical: Example: smell, taste.

Hearing

• Sound as a Mechanical Stimulus

  • Sound is vibrations of molecules, characterized by:
    • Frequency: Determines pitch; measured in Hertz (Hz).
    • Amplitude: Determines volume.
  • Human hearing range: 20 Hz to 20,000 Hz.

• Hearing Mechanism

  • Sound enters through external ear structures.
  • Tympanic Membrane (eardrum): Vibrates in response to sound.
  • Ossicles (ear bones): Malleus, incus, stapes focus vibrations onto the cochlea.
  • Cochlea: Fluid-filled organ where vibrations are transduced into neural signals.
    • Organ of Corti: Contains hair cells that transduce vibrations.
    • Basilar Membrane: Vibrates and helps differentiate sound frequencies via tonotopic map.

• Transduction Process

  • Hair cells in the cochlea have cilia that bend, opening ion channels.
  • Potassium (K+) influx changes membrane potential.
  • Voltage changes cause neurotransmitter release to nerve fibers.

• Cochlear Implants

  • Used to aid hearing in individuals with non-functioning hair cells.
  • Electrode arrays stimulate neurons directly based on sound frequency analysis.

Animal Hearing

• Most vertebrates have similar hearing structures.
• Insects have ear-like structures at various body sites, using membranes to detect sound vibrations.