Ch8A Neurons: Cell and Network Properties – Organization and Anatomy of the Nervous System

Neurons: Cell and Network Properties

Introduction

This study guide summarizes the organization and cellular anatomy of the nervous system, focusing on neuron structure, types, and functional categories. Understanding these foundational concepts is essential for exploring how electrical signals are generated and transmitted in the human body.

Organization of the Nervous System

Main Divisions

• Central Nervous System (CNS): Composed of the brain and spinal cord. Responsible for integrating sensory information and coordinating body responses.

• Peripheral Nervous System (PNS): Consists of all neural tissue outside the CNS. Divided into somatic (voluntary control) and autonomic (involuntary control) nervous systems.

Functional Subdivisions

• Somatic Nervous System: Controls voluntary movements via skeletal muscles.

• Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion) and is further divided into sympathetic and parasympathetic branches.

Diagram: Organization of the Nervous System

The nervous system is organized into the CNS and PNS, with the PNS further divided into sensory (afferent) and motor (efferent) divisions. The motor division includes the somatic and autonomic systems, which control different target tissues and organs.

Structure of the Neuron and Other Cells

Basic Neuron Anatomy

• Dendrites: Branch-like extensions that receive incoming signals from other neurons.

• Cell Body (Soma): Contains the nucleus and integrates incoming signals.

• Axon: Long, slender projection that transmits electrical impulses away from the cell body.

• Axon Hillock: Region where action potentials are initiated.

• Myelin Sheath: Insulating layer formed by glial cells (Schwann cells in PNS, oligodendrocytes in CNS) that increases signal conduction speed.

• Schwann Cells: Glial cells in the PNS that wrap around axons to form myelin.

Types of Neurons

• Multipolar Neurons: Have multiple dendrites and a single axon; most common type in the CNS.

• Bipolar Neurons: Possess one dendrite and one axon; found in sensory organs (e.g., retina).

• Anaxonic Neurons: Lack a distinct axon; found in the brain and sense organs.

Functional Categories of Neurons

• Sensory Neurons (Afferent): Transmit information from sensory receptors to the CNS.

• Efferent Neurons: Carry signals from the CNS to effectors (muscles or glands).

• Interneurons: Connect neurons within the CNS, facilitating communication between sensory and motor pathways.

Structural Categories of Neurons

Type	Description	Example
Pseudounipolar	Single process called the axon; dendrite fused with axon during development.	Somatic sensory neurons
Bipolar	Two relatively equal fibers extending off the central cell body.	Neurons for smell and vision

Example: Neuron Signal Transmission

• Input signal is received by dendrites.

• Integration occurs in the cell body and axon hillock.

• Output signal is transmitted along the axon to the synaptic terminal.

• Signal crosses the synaptic cleft to the postsynaptic neuron.

Additional info: The myelin sheath is critical for rapid signal transmission; its loss leads to neurological diseases such as multiple sclerosis.