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 is responsible for every thought, action, and emotion, utilizing electrical impulses to communicate. This system monitors changes inside and outside the body, processes and interprets sensory input, and effects responses by activating muscles and glands.

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

• Key Terms: Stimuli (changes detected), sensory input (gathered information), integration (processing and decision-making), effectors (muscles/glands activated).

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 cranial and spinal nerves. Connects the CNS to limbs and organs.

Functional Classification

Functionally, the nervous system is divided into:

• Sensory (Afferent) Division: Carries impulses from sensory receptors to the CNS. Keeps the CNS informed of events inside and outside the body.

• 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.

Example:

When you touch a hot surface, sensory neurons send a signal to the CNS, which processes the information and sends a motor command to withdraw your hand.

Nervous Tissue

Neuroglia

Neuroglia are supporting cells in the nervous system that provide structural and metabolic support to neurons. Types include:

• Astrocytes: Support and anchor neurons to blood vessels.

• Microglia: Act as phagocytes, cleaning up debris.

• Ependymal cells: Line cavities and help circulate cerebrospinal fluid.

• Oligodendrocytes: Form myelin sheaths in the CNS.

• Schwann cells: Form myelin sheaths in the PNS.

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

Neurons

Neurons are highly specialized cells that transmit nerve impulses. All neurons have:

• Cell body: Contains the nucleus and metabolic machinery.

• Processes (Fibers): Extensions from the cell body, including:

  • Dendrites: Carry impulses toward the cell body.

  • Axons: Carry impulses away from the cell body. Each neuron has one axon, which arises from the axon hillock and branches into axon terminals.

Classification of Neurons

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

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

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

Major Topics and 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 and function of nerves.

• Explain the autonomic nervous system and its divisions.

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

Table: Structural and Functional Classification of the Nervous System

Classification	Subdivision	Main Components	Function
Structural	Central Nervous System (CNS)	Brain, Spinal Cord	Integration, command center
Structural	Peripheral Nervous System (PNS)	Cranial nerves, Spinal nerves	Communication between CNS and body
Functional	Sensory (Afferent) Division	Sensory receptors, Afferent neurons	Transmit sensory input to CNS
Functional	Motor (Efferent) Division	Effector organs, Efferent neurons	Transmit motor output from CNS
Functional	Somatic Nervous System	Skeletal muscles	Voluntary control
Functional	Autonomic Nervous System	Cardiac muscle, Smooth muscle, Glands	Involuntary control
Functional	Sympathetic Division	Various organs	"Fight or flight" response
Functional	Parasympathetic Division	Various organs	"Rest and digest" response

Key Equations and Concepts

• Resting Membrane Potential: The difference in electrical charge across the neuron's membrane, typically $-70\ \text{mV}$.

• Action Potential: Rapid change in membrane potential that travels along the axon. Generated when the threshold is reached.

• Equation for Nerve Impulse Transmission:

$\text{Nerve Impulse} = \text{Depolarization} \rightarrow \text{Action Potential} \rightarrow \text{Repolarization}$

Study Tips

• Keep track of vocabulary words and their definitions.

• Take good notes and prepare for quizzes and exams by reviewing key concepts.

• Use flashcards for important terms and processes.

Additional info:

• This syllabus outlines the major topics and objectives for a college-level Anatomy & Physiology course focused on the nervous system and special senses.

• Students are expected to read textbook chapters, complete lab exercises, and self-assess using quizzes.