The Nervous System: Structure, Function, and Special Senses

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.

• Electrical Impulses: Used for rapid communication between cells.

• Stimuli: Changes detected by sensory receptors.

• Response: Activation of effector organs (muscles/glands).

Organization of the Nervous System

Structural Classification

The nervous system is divided into two main subdivisions based on structure:

• Central Nervous System (CNS): Consists of the brain and spinal cord. Responsible for integration and command.

• Peripheral Nervous System (PNS): Includes all neural elements outside the CNS (cranial and spinal nerves). Connects the CNS to limbs and organs.

Functional Classification

Functionally, the nervous system is divided into sensory and motor 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. 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 'fight or flight' responses.

    • Parasympathetic Division: Promotes 'rest and digest' activities.

Flowchart: Organization of the Nervous System

Division	Main Components	Function
CNS	Brain, Spinal Cord	Integration, command center
PNS	Cranial & Spinal Nerves	Communication between CNS and body
Sensory (Afferent)	Sensory organs, receptors	Transmit information to CNS
Motor (Efferent)	Somatic & Autonomic Systems	Transmit commands from CNS
Somatic	Skeletal muscles	Voluntary movement
Autonomic	Cardiac & smooth muscle, glands	Involuntary regulation
Sympathetic	Various organs	Fight or flight
Parasympathetic	Various organs	Rest and digest

Nervous Tissue

Neuroglia and Neurons

Nervous tissue consists of two main cell types: neuroglia and neurons.

• Neuroglia (Glial Cells): Support, protect, and insulate neurons. Types include astrocytes, microglia, oligodendrocytes (CNS), Schwann cells, and satellite cells (PNS).

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

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

Structure and Function of Neurons

• Neurons (Nerve Cells): Specialized for transmitting electrical impulses.

• Cell Body: Contains the nucleus and most organelles.

• Processes (Fibers): Extensions from the cell body; include dendrites and axons.

• Dendrites: Carry impulses toward the cell body.

• Axons: Carry impulses away from the cell body; arise from the axon hillock.

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

Classification of Neurons

Type	Direction of Impulse	Function
Sensory (Afferent)	Toward CNS	Transmit sensory information
Motor (Efferent)	Away from CNS	Transmit motor commands
Interneurons (Association)	Within CNS	Connect sensory and motor neurons

Course Objectives and Key Topics

Learning Outcomes

By the end of this lesson, students should be able to:

1. Describe the functions and organization of the nervous system.

2. Explain the roles of neuroglia and neurons.

3. Classify neurons structurally and functionally.

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

5. Describe types of reflexes and elements of a reflex arc.

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

7. Identify cranial and spinal nerves.

8. Describe the structure of a nerve and the autonomic nervous system.

9. Distinguish between sympathetic and parasympathetic divisions.

10. Describe homeostatic imbalances of the nervous system and special senses.

Additional Info

• Recommended Readings: Chapters 7 and 8 of the textbook cover the nervous system and special senses.

• Assignments: Lab exercises and quizzes are designed to reinforce these concepts.

• Study Tips: Take notes on vocabulary and definitions, and use self-assessment activities to prepare for exams.