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.

• Special Senses: Vision, hearing, balance, smell, and taste.

• Homeostatic Imbalances: Disorders affecting the nervous system and special senses.

Organization of the Nervous System

Structural Classification

The nervous system is divided into two main subdivisions:

• 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

The PNS is further divided into:

• Sensory (Afferent) Division: Carries impulses from sensory receptors to the CNS.

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

The motor division is subdivided into:

• Somatic Nervous System: Voluntary control of skeletal muscles.

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

The ANS is 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

Division	Main Components	Function
CNS	Brain, Spinal Cord	Integration, command center
PNS	Cranial & Spinal Nerves	Communication between CNS and body
Sensory (Afferent)	Sensory Receptors	Transmit signals to CNS
Motor (Efferent)	Effectors (muscles, glands)	Transmit signals from CNS
Somatic	Skeletal Muscles	Voluntary movement
Autonomic	Cardiac & Smooth Muscle, Glands	Involuntary control
Sympathetic	Various organs	"Fight or flight" response
Parasympathetic	Various organs	"Rest and digest" response

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), and Schwann cells, satellite cells (PNS).

• Neurons: Specialized cells that transmit nerve impulses. Each neuron has a cell body (with nucleus), dendrites (receive signals), and a single axon (sends signals).

Structural Classification of Neurons:

• Multipolar: Many dendrites, one axon (most common in CNS).

• Bipolar: One dendrite, one axon (found in special senses).

• Unipolar: Single process that splits into two branches (sensory neurons in PNS).

Functional Classification of Neurons:

• Sensory (Afferent) Neurons: Carry impulses toward CNS.

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

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

Key Learning Objectives

• Describe the functions and organization of the nervous system.

• Explain the structure and function 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.

Example: Nerve Impulse Generation

A nerve impulse is generated when a neuron responds to a stimulus strong enough to cause depolarization. This leads to an action potential, which is the electrical signal transmitted along the axon.

• Formula:

$V = IR$

Where V is voltage, I is current, and R is resistance. This formula describes the relationship between electrical properties in neurons.

Special Senses and Homeostatic Imbalances

Special Senses

• Vision: Anatomy of the eye, physiology of sight.

• Hearing and Balance: Structure and function of the ear.

• Smell and Taste: Chemoreceptors in the nose and tongue.

Homeostatic Imbalances

• Multiple Sclerosis: Autoimmune destruction of myelin in CNS.

• Hydrocephalus: Accumulation of cerebrospinal fluid in the brain.

• Concussion: Temporary brain dysfunction due to trauma.

• Cerebrovascular Accidents (Stroke): Disruption of blood flow to the brain.

• Paralysis: Loss of muscle function due to nervous system injury.

• Cerebral Palsy: Motor impairment from brain damage.

• Spina Bifida: Incomplete formation of vertebral arches.

• Special Senses Disorders: Conjunctivitis, night blindness, color blindness, glaucoma, otitis media, deafness, Meniere's syndrome, strabismus, presbyopia.

Study Strategies

• Read textbook chapters and take notes on vocabulary and key concepts.

• Complete practice quizzes and lab exercises to reinforce learning.

• Use flashcards for definitions and classifications.

Additional info: The syllabus emphasizes the importance of self-assessment, active note-taking, and using publisher resources for mastery of Anatomy & Physiology concepts.