*Week 2: Review Package

Chapter 12: Nervous Tissue

Central Nervous System (CNS)

  • Functions:

    • Sensory Input: The process of receiving information from sensory receptors.

    • Motor Output: The response generated by the CNS through motor neurons.

Peripheral Nervous System (PNS)

  • Divisions:

    • Sensory Division: Transmits sensory information to the CNS.

      • Somatic Senses: Senses such as touch, temperature, and pain.

      • Special Senses: Vision, hearing, taste, smell.

    • Motor Division: Conveys commands from the CNS to effectors.

      • Somatic Nervous System: Controls skeletal muscle movements.

      • Autonomic Nervous System: Controls involuntary functions.

        • Sympathetic Nervous System: Prepares body for stress response (fight or flight).

        • Parasympathetic Nervous System: Returns body to resting state (rest and digest).

        • Enteric Nervous System: Manages functions of the gastrointestinal tract.

Anatomy of a Neuron

  • Key Structures:

    • Cell Membrane: Protective barrier of the neuron.

    • Dendrites: Receive signals from other neurons.

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

    • Axon: Conducts impulses away from the cell body.

    • Oligodendrocyte: Cells that form the myelin sheath in the CNS.

    • Node of Ranvier: Gaps in the myelin sheath that facilitate rapid impulse transmission.

    • Myelin Sheath: Insulating layer that enhances signal conduction.

    • Synapse: Junction where communication occurs between neurons.

Neuroglia

  • Definition: Non-excitable support cells of the nervous system.

  • Types in CNS:

    • Astrocytes: Support neurons, regulate chemical environment, and facilitate nutrient exchange.

    • Microglial Cells: Phagocytic cells that remove debris and protect against pathogens.

    • Oligodendrocytes: Myelinate axons in the CNS.

    • Ependymal Cells: Produce cerebrospinal fluid.

  • Types in PNS:

    • Satellite Cells: Support ganglia in the PNS.

    • Schwann Cells: Myelinate axons in the PNS.

Graded Potentials

  • Overview: Changes in membrane potential that vary in magnitude.

  • Mechanism:

    • Increased stimulus strength leads to slight depolarization of the membrane and stronger graded potentials.

Action Potential

  • Definition: A rapid, irreversible change in membrane potential occurring when the threshold voltage is reached.

  • Phases:

    1. Depolarizing Phase: Voltage-gated Na+ channels open, leading to an influx of sodium ions, resulting in membrane potential becoming positive.

    2. Repolarizing Phase: Na+ channels close and K+ channels open, allowing potassium ions to exit, restoring negative membrane potential.

    3. After-Hyperpolarizing Phase: Membrane potential temporarily becomes more negative than resting potential due to prolonged opening of K+ channels.

  • Key Voltage Levels:

    • Resting: -70 mV

    • Threshold: -55 mV

    • Peak: +30 mV

Temporal and Spatial Summation

  • Temporal Summation: Rapid firing of one or more presynaptic neurons leads to cumulative depolarization in the postsynaptic neuron.

  • Spatial Summation: Simultaneous stimulation from multiple presynaptic terminals leading to overall depolarization.

Excitatory vs. Inhibitory Postsynaptic Potentials

  • Excitatory Postsynaptic Potentials (EPSPs):

    • Cause depolarization of the postsynaptic membrane.

    • Allow Na+ and K+ influx/efflux, potentially triggering an action potential if above threshold.

    • Examples include Glutamate and Acetylcholine (ACh).

  • Inhibitory Postsynaptic Potentials (IPSPs):

    • Increase permeability of the membrane to K+ or Cl–, leading to hyperpolarization.

    • Slow down the generation of action potentials.

    • Examples include GABA and serotonin.