Nervous system functions & Axons

Nervous System Overview

Outline Overview

  • The system is divided into parts:

    • Part One: Nervous Tissue

    • Basic structure and function of the nervous system

    • Part Two: Major Organs

    • Function of organs will be discussed

Main Divisions of the Nervous System

  • Central Nervous System (CNS)

    • Composed of two major organs:

    • Brain

    • Spinal Cord

  • Peripheral Nervous System (PNS)

    • Composed of nerves (bundles of neurons)

    • Defined as organs (two or more types of tissues)

Overall Functions of the Nervous System

  • Sensations: Detecting sensory input from the environment (external and internal)

  • Motor: Sending commands to muscles and glands

  • Integration: Interpretation of sensory information, decision-making, and memory formation

Detailed Functions Explained

  1. Sensational Detection

    • Examples include:

      • Feeling temperature (hot or cold, bumpy textures)

      • Awareness of body position (Is my arm raised?)

      • Digestive states (Full or empty stomach)

      • Pain perception

      • Visual and taste perceptions

  2. Motor Commands

    • Involves the following muscle types:

      • Smooth Muscle

      • Skeletal Muscle

      • Cardiac Muscle

    • Also commands glands to secrete substances (e.g., sweat, saliva)

  3. Integration and Interpretation

    • Enables higher functions:

      • Memories formation

      • Personality traits

      • Analytical thinking

  • Example of Integration:

    • Analyzing time on a traditional clock in a classroom setting:

    • Initial perception of time may create different emotional responses based on context (e.g., feeling of time pressure)

  1. Response Variations

    • Reactions to sensory input may differ based on:

      • Context (Classroom, home, driving)

      • Time of day or life phase (adult vs. child perspective on stop signs)

Neurons – Structural Elements and Functions

  • Neurons:

    • Large cell body (soma) with a prominent nucleus

    • Processes:

      • Dendrites: Receive information from other neurons

      • Axon: Transmits action potentials away from the soma

      • Axon Hillock: Region at the beginning of the axon where action potential originates

Neurofibrils and Matter Types

  • Neurofibrils: Provide structural support for axons and dendrites

  • Gray Matter: Containing cell bodies; appears darker due to the presence of nuclei and Nissl bodies (clusters of ribosomes and rough endoplasmic reticulum)

  • White Matter: Composed of myelinated axons

Myelination of Axons

  • Myelinated Axons:

    • Myelination speeds up impulse transmission.

    • Formed by:

      • Schwann Cells (in PNS)

      • Oligodendrocytes (in CNS)

  • Function of Myelin:

    • Acts as an insulator, allowing for faster transmission by enabling saltatory conduction (jumping from node to node)

    • Nodes of Ranvier: Gaps between Schwann cells where impulses are transmitted rapidly

  • Clinical Application:

    • Multiple Sclerosis:

      • An autoimmune disease that attacks myelination in CNS

      • Results in slower impulse transmission due to demyelination

Unmyelinated Axons and Neurolemma

  • In the peripheral nervous system, there exist unmyelinated axons that still have a protective layer from Schwann cells called neurolemma.

    • This layer can help regrow and guide axons if they become damaged.

Summary of Key Points

  • Functions of Axon:

    • To transmit impulses (NOT to receive, that is dendrites)

  • Myelination Impacts Transmission:

    • Loss of myelin results in slower impulse transmission.

  • Identification of Cell Types:

    • Schwann Cells: Myelinate in PNS

    • Oligodendrocytes: Myelinate in CNS

Practice Questions Recap

  1. Functions of nervous system: Motor, Integration, Sensations

  2. True or False: The function of the axon is to receive incoming information? False

  3. Function of myelination: Speed up the transmission of electrical impulses

  4. Result of myelin loss: Slowed electrical impulse transmission

  5. Autoimmune disease impacting myelin: Multiple Sclerosis

  6. Myelination creators in PNS and CNS: Schwann cells for PNS, Oligodendrocytes for CNS.

Next Steps

  • Upcoming discussions will focus on classification of neurons based on structure and function.