Nervous Tissues and Neuronal Function

  • Nerve Tissue Overview

    • Composed of neurons and neuroglial cells.

    • Neurons produce and conduct electrochemical impulses.

    • Co-evolved with muscle and organ systems for control and regulation.

  • Neurons

    • Elongated cells with three main parts:

    • Cell Body: Contains the nucleus.

    • Dendrites: Highly branched extensions that receive stimulation.

    • Axon: Single cytoplasmic extension that conducts impulses away from the cell body, can be very long.

  • Neuroglial Cells

    • Do not conduct impulses but support, nourish, and protect neurons.

    • Regulate neurotransmission.

    • Types include Schwann cells and oligodendrocytes which produce myelin sheaths.

  • Communication and Integration

    • Nervous system detects internal and external stimuli (e.g., light, sound, touch).

    • Endocrine system complements by issuing chemical signals for regulation.

  • Musculoskeletal System

    • Composed of muscles and skeletons; enables movement.

    • Varied skeletal structures:

    • Internal skeletons in vertebrates.

    • External skeletons in insects.

    • Hydrostatic skeletons in earthworms.

  • Regulation and Maintenance

    • Engages in nutrient acquisition, waste disposal, material distribution, internal environment maintenance.

    • Digestive system, circulatory system, respiratory system play key roles.

  • Defense Mechanisms

    • Integumentary system provides first line of defense (skin).

    • Immune responses include antibody production and specialized cell action against invaders.

  • Reproductive System

    • Responsible for continuity of species through gamete development, fertilization and nurturance of embryos.

  • Sensory and Motor Integration

    • Sensory neurons (afferent) carry information to the CNS (brain and spinal cord).

    • Motor neurons (efferent) carry impulses from the CNS to muscles and glands.

    • Interneurons (association neurons) facilitate complex reflexes and higher functions.

  • Peripheral Nervous System (PNS)

    • Comprises sensory (information collection) and motor (action triggering) pathways.

    • Somatic nervous system controls voluntary movements; autonomic nervous system controls involuntary functions (sympathetic and parasympathetic divisions).

  • Neuron Structure and Function

    • Most neurons have similar architecture:

    • Cell body (nucleus), dendrites (information reception), axon (signal conduction).

    • Myelin sheaths produced by Schwann cells (PNS) and oligodendrocytes (CNS) increase conduction speed.

    • Nodes of Ranvier enable saltatory conduction by exposing sections of axon to the extracellular environment, facilitating faster impulse transmission.

  • Membrane Potentials

    • Resting potential around -70 mV due to differential ion concentrations (mainly K+ and Na+).

    • Sodium-potassium pumps maintain concentration gradients.

  • Action Potentials

    • Triggered when a neuron reaches threshold potential, leading to depolarization (Na+ rush in) and repolarization (K+ rush out).

    • Consists of:

    • Rising Phase: Depolarization peaks (+35 to +40 mV).

    • Falling Phase: Na+ channels close, K+ channels open, membrane repolarizes.

    • Undershoot Phase: Slight hyperpolarization as K+ channels remain open longer.

    • Action potentials are all-or-nothing events without summation.

  • Propagation of Action Potentials

    • Action potentials propagate along axons via depolarization of adjacent membrane segments.

    • Speed increases with axon diameter and myelination (saltatory conduction).

  • Myelination Effects

    • Myelinated axons conduct impulses faster than unmyelinated axons.

    • Larger diameter axons reduce resistance to current flow, facilitating rapid signal transmission.

    This structured outline provides a comprehensive understanding of the nervous system's fundamental components, functions, and mechanisms of communication and regulation.


  • Neurons and Ion Channels

    • Neurons are essential cells in the nervous system that produce and conduct electrochemical impulses.

    • To understand their function, review the structure and operation of ion channels and pumps.

    • Membrane Potential: Refers to the electric potential difference across a cell membrane, created by the distribution of ions inside and outside the neuron.

    • Resting Potential: Typically around -70 mV, maintained by potassium (K+) and sodium (Na+) gradients facilitated by sodium-potassium pumps.

  • Typical Neuron Structure

    • Draw a labeled diagram of a neuron highlighting key components:

    • Cell Body (soma): Contains the nucleus and is crucial for cellular processes.

    • Dendrites: Extensions that receive signals from other neurons.

    • Axon: Transmits impulses away from the cell body.

    • Myelin Sheath: Insulating layer covering the axon, produced by Schwann cells in the PNS and oligodendrocytes in the CNS.

  • Subdivisions of the Nervous System

    • Central Nervous System (CNS): Comprises the brain and spinal cord; responsible for processing and integrating information.

    • Peripheral Nervous System (PNS): Consists of sensory (afferent) and motor (efferent) pathways; connects the CNS to the rest of the body.

    • Somatic Nervous System: Controls voluntary movements.

    • Autonomic Nervous System: Regulates involuntary functions with sympathetic and parasympathetic divisions.

  • Types of Neurons

    • Sensory Neurons: Carry information from sensory receptors to the CNS.

    • Motor Neurons: Transmit impulses from the CNS to effector organs (muscles and glands).

    • Interneurons: Connect sensory and motor neurons and participate in processing information.

  • Functions of Neuroglial Cells

    • Support, nourish, and protect neurons.

    • Regulate neurotransmission.

    • Provide structural support and insulation for axons via myelin sheaths (Schwann cells and oligodendrocytes).

  • Membrane and Resting Potential

    • Resting potential is established primarily by the unequal distribution of ions across the membrane, mainly K+ and Na+.

    • The sodium-potassium pump plays a critical role in creating and maintaining these concentration gradients.

  • Diagram of Membrane Potential

    • Create a visual representation of a cell membrane labeled to show how resting potential is formed and maintained:

    • Include ion channels (Na+ and K+), the sodium-potassium pump, and differential concentrations of ions inside and outside the neuron.

This structured overview incorporates the key learning outcomes regarding neurons and resting potentials, emphasizing essential information on structure, functions, and mechanisms of the nervous system.