Animal and Human Neural Systems

Animal Neural Systems

• Animal nervous systems are composed of specialized cells called neurons that detect, receive, and transmit stimuli.
• Lower invertebrates have simple neural networks (e.g., Hydra).
• Insects have a more organized system with a brain, ganglia, and neural tissues.
• Vertebrates possess the most developed neural systems.

Human Neural System

• Divided into central nervous system (CNS) and peripheral nervous system (PNS).

• CNS: brain and spinal cord; responsible for information processing and control.

• PNS: all nerves connected to the CNS; contains afferent and efferent fibers.

  • Afferent fibers: transmit impulses from tissues/organs to the CNS.
  • Efferent fibers: transmit impulses from the CNS to peripheral tissues/organs.

• PNS also includes:

  • Somatic neural system: relays impulses to skeletal muscles.
  • Autonomic neural system: regulates involuntary organs/smooth muscles.
    • Sympathetic and parasympathetic systems: further subdivisions of the autonomic system.
  • Visceral nervous system: complex network involving nerves, fibers, ganglia, and plexuses for visceral impulse transmission.

Neuron Structure and Function

• Neurons are microscopic, structural and functional units of the nervous system.

  • Three main parts: cell body, dendrites, and axon.
  • Cell body: contains cytoplasm and Nissl's granules.
  • Dendrites: short, branching fibers extending from the cell body; receive impulses. Have Nissl's granules.
  • Axon: long fiber that transmits impulses away from the cell body; also has branches ending in synaptic knobs. Synaptic knobs contain synaptic vesicles with neurotransmitters.

• Neuron types based on axon and dendrite configuration:

  • Multipolar: one axon, multiple dendrites (e.g., cerebral cortex)
  • Bipolar: one axon, one dendrite (e.g., retina)
  • Unipolar: one axon, single projection that branches into separate afferent and efferent fibers.

• Axon types:

  • Myelinated: insulated by Schwann cells forming a myelin sheath; have gaps (nodes of Ranvier) between myelin segments.
    • Found in cranial and spinal nerves.
  • Unmyelinated: Schwann cell surrounds axon but doesn't create a myelin sheath.
    • Common in autonomic and somatic neural systems.

Nerve Impulse Generation and Conduction

• Neuron membranes are polarized.
• Ion channels allow selective ion permeability.
• At rest, axonal membranes are more permeable to potassium ions (K+) and less permeable to sodium ions (Na+). Inner membrane has high K+, negatively charged proteins, and low Na+, outer membrane is more positive.
• Ionic gradients maintained by active transport (sodium-potassium pump): 3 Na+ pumped out, 2 K+ pumped in.

Explore the complexities of neural systems in both animals and humans. This quiz covers the structure and functions of the nervous systems, including examples from invertebrates to vertebrates, as well as the central and peripheral nervous systems in humans. Test your knowledge on how these systems control and coordinate bodily functions.