Overview of Nervous System

• The nervous system is the body’s master controlling system.
• The nevous system performs our thoughts and actions.
• • Basic components of the nervous system:
  • brain
  • spinal cord
  • neuron
• Two major divisions:

  The central nervous system (CNS) and The peripheral nervous system (PNS)
• The central nervous system (CNS) is composed of the brain and spinal cord which act as integrating command centers.
• • The peripheral nervous system (PNS) consists of the neurons that link the body organs to the CNS.
• • Neurons (nerve cells or nerves) are the basic units of the nervous system. 
• Neurons are highly specialized cells that transmit nerve impulses or electrical messages from one body part to another.
• two common features of neurons

  • a cell body; and 
  • its neural processes or extensions.
• Parts of a neuron:

  Cell body (soma)

  Arm-like neural processes

  Dendrites

  Axons

  Axon terminal

  Synapse

  Myelin sheath
• The cell body (soma) is the center of a neuron as it contains the nucleus.
• The arm-like neural processes serve as passageways of signals.
• Dendrites transmit electrical signals toward the cell body.
• Axons generate impulses away from the cell body.
• The axons branch out into hundreds of axon terminals
• Axon terminals - the small vessels that contain the neurotransmitters or chemical messengers of signals.
• • Synapse is the extracellular gap that links the neurons together.
• • Myelin sheath is a fatty material that insulates the neural processes.
• Neurons may be classified based on their functions and structure. Classification of Neurons

  • functional classification
  • structural classification
• • Functional classification of neurons is based on the direction through which the nerve impulses travel relative to the CNS. 
• Neurons under Functional classification:

  • sensory neurons
  • motor neurons
  • interneurons
• Sensory neurons carry impulses from sensory receptors to the CNS.
• Sensory neurons - They are also referred to as afferent neurons, which literally means “to go toward.”
• • Motor neurons carry impulses from the CNS to the muscles and glands of our body.
• Motor neuron - They are referred to as efferent neurons which means “away from.”
• • Interneurons link the sensory and motor neurons to keep the flow of impulses between neurons.
• Interneurons - They are also called as association neurons.
• • Structural classification of neurons is based on the number of neural processes that extend from the cell body.
• Neurons under structural classification:

  • multipolar neuron
  • bipolar neuron
  • unipolar neuron
• A multipolar neuron has several dendrites and an axon.
• All motor neurons and interneurons have this kind of neural structure. TRUE
• All motor neurons are multipolar. TRUE
• • Bipolar neurons are those that have one axon and one dendrite.
• Bipolar neuron - They are only found in sensory organs, like the ears and eyes, where they act as sensory receptors.
• • Unipolar neurons consist of a single neural process that extends from the cell body in the form of an axon. 
• Unipolar neurons conducts nerve impulses both towards and away from the cell body
• Unipolar neurons act as sensory neurons
• Neuroglia (“nerve glue”) are supporting cells that lump together to support and protect the nerve cells.
• Neuroglia - cannot transmit impulses
• Neuroglia of the CNS:

  Astrocytes

  Microglia

  Ependymal cells

  Oligodendrocytes

  Schwann cells

  Satellite cells