Module 11.2: Nervous System - Neurons and Neuroglial Cells

Module 11.2 Nervous System Study Guide

Structure and Function of Neuron Components

The neuron is the fundamental unit of the nervous system, specialized for transmitting electrical and chemical signals. Each component of the neuron plays a distinct role in its function.

• Cell Body (Soma): Contains the nucleus and most organelles; responsible for metabolic activities and integration of signals.

• Dendrites: Branched extensions that receive incoming signals from other neurons and convey them toward the cell body.

• Axon: A long, slender projection that transmits electrical impulses (action potentials) away from the cell body to other neurons or effectors.

• Axon Terminals: Endings of the axon where neurotransmitters are released to communicate with other cells.

• Myelin Sheath: Insulating layer (formed by neuroglial cells) that increases the speed of impulse transmission.

• Nodes of Ranvier: Gaps in the myelin sheath that facilitate rapid signal conduction via saltatory conduction.

Example: The myelin sheath allows for faster transmission of action potentials, which is essential for rapid reflexes.

Types of Neurons: Structure and Function

Neurons are classified based on their structure and function, each adapted to specific roles in the nervous system.

• Multipolar Neurons: Have multiple dendrites and a single axon; most common in the CNS; function as motor neurons and interneurons.

• Bipolar Neurons: Have one dendrite and one axon; found in sensory organs such as the retina; specialized for sensory transmission.

• Unipolar (Pseudounipolar) Neurons: Have a single process that splits into two branches; common in the PNS; function as sensory neurons.

Example: Bipolar neurons in the retina transmit visual information from photoreceptors to the brain.

Structure-Function Relationship in Neuron Types

The structural differences among neuron types support their specific functions in the nervous system.

• Multipolar Neurons: Multiple dendrites allow integration of information from many sources, ideal for motor and interneuron functions.

• Bipolar Neurons: Streamlined structure enables efficient transmission of sensory signals in specialized pathways.

• Unipolar Neurons: Single process allows rapid relay of sensory information from the periphery to the CNS.

Example: Unipolar neurons are well-suited for transmitting touch and pain signals quickly from the skin to the spinal cord.

Neuroglial Cells: Structure and Function

Neuroglial cells (glia) provide support, protection, and nutrition to neurons. There are four types in the CNS and two types in the PNS.

• CNS Neuroglial Cells:

  • Astrocytes: Star-shaped cells that maintain the blood-brain barrier, regulate ion balance, and provide structural support.

  • Oligodendrocytes: Form myelin sheaths around CNS axons, increasing signal transmission speed.

  • Microglia: Act as immune cells, removing debris and pathogens via phagocytosis.

  • Ependymal Cells: Line ventricles and produce cerebrospinal fluid (CSF).

• PNS Neuroglial Cells:

  • Schwann Cells: Form myelin sheaths around PNS axons, aiding in regeneration and fast signal transmission.

  • Satellite Cells: Surround neuron cell bodies in ganglia, regulating the environment and providing support.

Example: Oligodendrocytes myelinate multiple CNS axons, while Schwann cells myelinate a single PNS axon.

Structure-Function Relationship in Neuroglial Cells

The unique structures of neuroglial cells enable them to fulfill their specialized functions in the nervous system.

• Astrocytes: Extensive processes allow interaction with blood vessels and neurons, supporting nutrient transfer and homeostasis.

• Oligodendrocytes: Multiple extensions enable myelination of several axons simultaneously in the CNS.

• Microglia: Small size and mobility facilitate rapid response to injury or infection.

• Ependymal Cells: Ciliated surfaces help circulate CSF.

• Schwann Cells: Wrap around axons to form myelin, promoting regeneration after injury.

• Satellite Cells: Enclose cell bodies, maintaining a stable environment for neuronal function.

Example: Schwann cells' ability to regenerate myelin is crucial for recovery from peripheral nerve injuries.