The Nervous System: Structure, Function, and Disorders

The Nervous System

Introduction

The nervous system is a complex network of nerves and specialized cells called neurons that transmit signals throughout the body. It acts as the body's electrical wiring, coordinating voluntary and involuntary actions and facilitating communication between different body regions.

• Central Nervous System (CNS): Composed of the brain and spinal cord, the CNS processes information and directs responses.

• Peripheral Nervous System (PNS): Connects the CNS to limbs and organs, serving as a communication relay between the brain/spinal cord and the rest of the body.

Structural Divisions of the Nervous System

• CNS: Includes the brain, spinal cord, and associated nerves. Responsible for integrating sensory information and responding accordingly.

• PNS: Consists of sensory neurons, ganglia (clusters of neurons), and nerves. It links the CNS to sensory organs, muscles, and glands.

Functional Divisions of the Peripheral Nervous System

The PNS is divided into two main components:

• Somatic Nervous System: Controls voluntary movements of skeletal muscles and transmits sensory information to the CNS. It enables conscious activities such as moving limbs and perceiving touch, pain, and temperature.

• Autonomic Nervous System: Regulates involuntary body functions, including heart rate, digestion, respiratory rate, and hormone secretion. It operates without conscious control.

Subdivisions of the Autonomic Nervous System

• Sympathetic Nervous System: Prepares the body for stress-related activities ("fight or flight" response). Increases heart rate, dilates pupils, and inhibits digestion.

• Parasympathetic Nervous System: Promotes routine, restful activities ("rest and digest" response). Slows heart rate, stimulates digestion, and conserves energy.

The sympathetic and parasympathetic systems work together to maintain homeostasis—the body's internal balance.

Table: Comparison of Sympathetic and Parasympathetic Effects

Function	Sympathetic	Parasympathetic
Pupil	Dilates	Constricts
Salivation	Inhibits	Stimulates
Heart Rate	Increases	Slows
Bronchi	Dilates	Constriction
Digestion	Inhibits	Stimulates
Bladder	Relaxes	Contracts
Additional info:	Prepares for action	Promotes rest

Neurons in the Somatic Nervous System

• Motor Neurons: Carry instructions from the CNS to muscles, enabling movement.

• Sensory Neurons: Transmit sensory information from the body to the CNS.

Diseases of the Nervous System (Neurological Disorders)

Overview

Disorders of the nervous system can affect movement, speech, swallowing, breathing, learning, memory, senses, and mood. These disorders may result from degeneration, trauma, infection, genetic defects, cancer, or developmental abnormalities.

Degenerative Conditions

• Parkinson's Disease: Caused by the death of dopamine-producing neurons in the brain region controlling movement. Leads to difficulty initiating movement.

• Alzheimer's Disease: Characterized by the accumulation of abnormal proteins in and around neurons in the neocortex and hippocampus, impairing memory and daily functioning.

Genetic Disorders

• Huntington's Disease: An inherited disorder causing degeneration of nerve cells in the brain due to excess glutamate production. Affects movement and cognitive function.

Trauma and Injury

• Brain Injury/Stroke: Can kill neurons directly or deprive them of oxygen and nutrients, leading to loss of function.

• Spinal Cord Injury: Disrupts communication between the brain and muscles, potentially resulting in paralysis below the injury site.

Other Disorders

• Infections: Such as meningitis, which can damage nervous tissue.

• Cancer: Brain tumors can disrupt normal nervous system function.

• Structural Disorders: Developmental problems like spina bifida affect the formation and function of the nervous system.

Summary Table: Major Diseases of the Nervous System

Disease	Cause	Main Effect
Parkinson's Disease	Degeneration of dopamine neurons	Movement difficulties
Alzheimer's Disease	Protein buildup in brain	Memory loss, cognitive decline
Huntington's Disease	Genetic mutation, excess glutamate	Movement and cognitive impairment
Stroke/Brain Injury	Trauma or blood flow loss	Loss of function, neuron death
Meningitis	Infection	Inflammation, neurological damage
Brain Tumor	Uncontrolled cell growth	Disrupted brain function
Spina Bifida	Developmental defect	Impaired nervous system development

Key Terms

• Neuron: A specialized cell transmitting nerve impulses.

• Homeostasis: The body's ability to maintain stable internal conditions.

• Neurotransmitter: Chemical messenger that transmits signals across synapses between neurons.

Example Application

When you touch a hot object, sensory neurons in your skin send a signal through the PNS to the CNS, which processes the information and sends a response via motor neurons to move your hand away. If the spinal cord is injured, this communication may be disrupted, leading to loss of sensation or movement below the injury site.

Additional info: The nervous system is fundamental to all psychological processes, including sensation, perception, cognition, emotion, and behavior, making its study central to psychology.