Introduction to the Nervous System

Overview

The nervous system is the master control and communication system of the body. It regulates every thought, action, and emotion by using electrical impulses to communicate. This system is responsible for monitoring changes inside and outside the body, processing and interpreting sensory input, and causing responses by activating muscles and glands.

• Key Functions: Sensory input, integration, and motor output.

• Key Divisions: Central Nervous System (CNS) and Peripheral Nervous System (PNS).

Organization of the Nervous System

Structural Classification

The nervous system is structurally divided into two main parts:

• Central Nervous System (CNS): Consists of the brain and spinal cord. It is the main control center for processing information.

• Peripheral Nervous System (PNS): Includes all neural elements outside the CNS, such as cranial and spinal nerves. It connects the CNS to limbs and organs.

Functional Classification

The functional classification divides the PNS into sensory (afferent) and motor (efferent) divisions:

• Sensory (Afferent) Division: Transmits impulses from sensory receptors to the CNS. Keeps the CNS informed of changes.

• Motor (Efferent) Division: Transmits impulses from the CNS to effector organs (muscles and glands). Subdivided into:

  • Somatic Nervous System: Voluntary control of skeletal muscles.

  • Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands. Further divided into:

    • Sympathetic Division: Prepares the body for stress-related activities ("fight or flight").

    • Parasympathetic Division: Conserves energy and promotes "rest and digest" functions.

Flowchart: Organization of the Nervous System

Nervous Tissue

Neuroglia

Neuroglia are supporting cells in the nervous system that provide structural and metabolic support to neurons. Types include astrocytes, microglia, oligodendrocytes (CNS), and Schwann cells, satellite cells (PNS).

• Astrocytes: Support and anchor neurons, regulate the environment.

• Microglia: Act as phagocytes, cleaning up debris.

• Oligodendrocytes/Schwann Cells: Form myelin sheaths for insulation.

• Satellite Cells: Protect and cushion neuron cell bodies in the PNS.

Neurons

Neurons are highly specialized cells that transmit nerve impulses. Each neuron has a cell body (soma), dendrites, and an axon.

• Cell Body: Contains the nucleus and organelles.

• Dendrites: Receive signals and carry them toward the cell body.

• Axon: Conducts impulses away from the cell body; arises from the axon hillock.

• Axon Terminals: Branches at the end of the axon that form synapses with other cells.

Neurons are classified functionally as:

• Sensory (Afferent) Neurons: Carry impulses to the CNS.

• Motor (Efferent) Neurons: Carry impulses from the CNS to effectors.

• Interneurons (Association Neurons): Connect sensory and motor neurons within the CNS.

Key Learning Objectives

• Describe the functions and organization of the nervous system.

• Explain the roles of neuroglia and neurons.

• Classify neurons structurally and functionally.

• Outline the steps in generating and conducting a nerve impulse.

• Identify the anatomy and functions of the brain and spinal cord.

• Describe the structure of nerves and the autonomic nervous system.

• Distinguish between sympathetic and parasympathetic divisions.

• Recognize homeostatic imbalances of the nervous system and special senses.

Additional info:

• Students are encouraged to read Chapters 7 and 8 in the textbook for detailed coverage of the nervous system and special senses.

• Practice activities and lab exercises are recommended for mastery of the material.

• Key terms to track include: integration, sensory input, motor output, neuroglia, neuron, axon, dendrite, CNS, PNS, somatic, autonomic, sympathetic, parasympathetic.