Nerve Impulses and the Nervous System

Overview of the Nervous System

The nervous system is the master control and communication system of the body, utilizing electrical impulses to regulate bodily functions. It is responsible for receiving sensory input, integrating information, and producing motor output.

• Sensory Input: Gathering information by monitoring changes (stimuli) both inside and outside the body.

• Integration: Processing and interpreting sensory input to determine if action is needed.

• Motor Output: Sending a response (effect) to the integrated stimuli, activating muscles or glands.

Example: Seeing a glass of water (sensory input), the brain processes the information (integration), and the arm muscles contract to pick up the glass (motor output).

Organization of the Nervous System

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It serves as the integration and command center of the body.

• Organs: Brain, spinal cord

• Functions:

  • Interpret incoming sensory information

  • Issue outgoing instructions

  • Integration and command center

Peripheral Nervous System (PNS)

The PNS includes all nerves extending from the brain and spinal cord. It connects the CNS to limbs and organs.

• Function:

  • Communication among sensory organs, the brain and spinal cord, and glands or muscles

  • Links all parts of the body

Neuroglia (Glial Cells): Support Cells of the Nervous System

Neuroglia, or glial cells, are non-neuronal cells that provide support, insulation, and protection for neurons. They do not conduct nerve impulses but are essential for the proper functioning of the nervous system.

• General Functions: Support, insulation, and protection of neurons

• Types: Four types in the CNS, two types in the PNS

Types of Neuroglia in the CNS

• Astrocytes:

  • Abundant, star-shaped cells

  • Make up nearly half of neural tissue

  • Brace and anchor neurons to capillaries

  • Form the blood-brain barrier, maintaining a controlled extracellular environment in brain tissue

• Microglia:

  • Spider-like phagocytes

  • Dispose of debris, such as dead brain cells and bacteria

• Ependymal Cells:

  • Line the central cavities of the brain and spinal cord

  • Cilia assist with the circulation of cerebrospinal fluid

• Oligodendrocytes:

  • Extensions wrap around nerve fibers in the CNS

  • Produce myelin sheaths—fatty insulating coverings

Additional info: Neuroglia can undergo cell division, unlike neurons. Most brain tumors (gliomas) arise from glial cells.

Types of Neuroglia in the PNS

• Schwann Cells: Form myelin sheaths around nerve fibers in the PNS

• Satellite Cells: Protect neuron cell bodies

Structure of Neurons

Neurons are specialized cells that transmit nerve impulses. They have distinct structural regions that facilitate the conduction of electrical signals.

• Cell Body: Contains the nucleus; metabolic center of the cell

• Dendrites: Conduct impulses toward the cell body; neurons may have hundreds of dendrites

• Axon: Conducts impulses away from the cell body; each neuron has only one axon (may have axon collaterals)

• Axon Hillock: The cone-shaped region of the cell body where the axon originates

• Axon Terminals: Endings of the axon that contain neurotransmitters in synaptic vesicles

• Synapse: The junction where an impulse is transmitted from one neuron to another or to an effector cell (e.g., muscle)

Summary Table: Types of Neuroglia

Key Terms and Definitions

• Neuron: A nerve cell specialized to transmit electrical impulses

• Neuroglia (Glial Cells): Non-neuronal cells that support, insulate, and protect neurons

• Myelin Sheath: Fatty insulating layer around axons that increases the speed of nerve impulse conduction

• Synapse: The site of communication between two neurons or between a neuron and an effector cell

• Axon Hillock: The region where the axon originates from the cell body

Additional info:

• Myelinated axons conduct impulses faster than unmyelinated axons due to saltatory conduction.

• Neurons are generally amitotic (do not divide), while neuroglia retain the ability to divide.