Neurons: Cellular and Network Properties – Study Notes

Neurons: Cellular and Network Properties

Organization of the Nervous System

The nervous system is a complex network responsible for coordinating body functions and enabling communication between different body parts. It is divided into central and peripheral components, each with specialized roles.

• Central Nervous System (CNS): Consists of the brain and spinal cord. It acts as the main control center for processing information and directing responses.

• Peripheral Nervous System (PNS): Composed of all neural tissue outside the CNS. It connects the CNS to limbs and organs.

  • Sensory (Afferent) Neurons: Transmit sensory information from receptors to the CNS.

  • Efferent Neurons: Carry commands from the CNS to effectors (muscles and glands). Subdivided into:

    • Somatic Motor Division: Controls voluntary movements by innervating skeletal muscles.

    • Autonomic Division: Regulates involuntary functions. Further divided into:

      • Sympathetic Branch: Prepares the body for 'fight or flight' responses.

      • Parasympathetic Branch: Promotes 'rest and digest' activities.

• Enteric Nervous System: A network of neurons in the digestive tract walls. While controlled by the autonomic nervous system, it can function independently to regulate digestive processes.

Emergent Properties: The nervous system exhibits properties that arise from the complex interactions of its components, such as consciousness and cognition.

Cells of the Nervous System

The nervous system is composed of two main cell types: neurons and glial cells. Neurons are specialized for electrical signaling, while glial cells provide support and protection.

• Neurons: The functional units of the nervous system, responsible for transmitting electrical signals.

  • Neuron Classification by Structure:

    • Multipolar Neurons: Have multiple dendrites and a single axon; most common in the CNS.

    • Pseudounipolar Neurons: Have a single process that splits into two branches; typical of sensory neurons.

    • Bipolar Neurons: Have one dendrite and one axon; found in sensory organs like the retina.

    • Anaxonic Neurons: Lack a distinct axon; found in the brain and retina.

  • Neuron Classification by Function:

    • Sensory (Afferent) Neurons: Carry information toward the CNS.

    • Efferent Neurons: Transmit signals away from the CNS to effectors.

    • Interneurons: Connect neurons within the CNS and integrate information.

  • Neuron Structure:

    • Cell Body (Soma): Contains the nucleus and organelles; metabolic center.

    • Dendrites: Receive incoming signals; may have specialized structures called dendritic spines to increase surface area.

    • Axon: Conducts electrical impulses away from the cell body; originates at the axon hillock.

    • Collaterals: Branches of the axon that allow communication with multiple targets.

    • Axon Terminals: Swellings at the end of axons where neurotransmitters are released.

    • Varicosities: Enlarged regions along the axon where neurotransmitter release can also occur.

• Nerves: Bundles of axons in the PNS, surrounded by connective tissue. Types include:

  • Sensory Nerves: Carry only sensory fibers.

  • Motor Nerves: Carry only motor fibers.

  • Mixed Nerves: Contain both sensory and motor fibers.

Example: The sciatic nerve is a mixed nerve containing both sensory and motor axons.

Additional info:

• Glial cells, though not detailed in these slides, are essential for neuron function, providing structural support, insulation, and metabolic assistance.

• Emergent properties refer to complex behaviors and functions that arise from the collective activity of neural networks, not predictable from individual neuron properties alone.