UNIVERSITY CLASS NOTES | BIOLOGY & NEUROSCIENCE | THE NERVOUS SYSTEM
The Nervous System
Structure, Function, Communication & Disorders
First Year Biology — Neuroscience Module
Academic Year 2025/2026
Figure 1: Hierarchical Organization of the Human Nervous System
First Year Biology — The Nervous SystemPage 1
,UNIVERSITY CLASS NOTES | BIOLOGY & NEUROSCIENCE | THE NERVOUS SYSTEM
1. Introduction
The nervous system is one of the most complex and fascinating organ systems in the human body.
It serves as the primary communication network of the body, receiving, processing, and transmitting
information that coordinates virtually every bodily function — from the beating of the heart and
regulation of breathing, to conscious thought, emotion, memory, and voluntary movement.
Without the nervous system, no organ, tissue, or cell could function in a coordinated manner. It is
the body's master control and communication system, working in concert with the endocrine system
to maintain homeostasis and allow the organism to interact meaningfully with its environment.
1.1 Why Study the Nervous System?
Understanding the nervous system is essential for anyone entering the health sciences, biology, or
related fields. Neurological disorders are among the leading causes of disability worldwide.
Knowledge of how the nervous system is organized, how it functions at the cellular level, and how it
can fail provides the foundation for clinical diagnosis, pharmacological treatment, and emerging
therapies.
🎯 Learning Objectives
By the end of this chapter, students should be able to: (1) Describe the overall organization of
the nervous system and its two main divisions. (2) Identify the structure and function of neurons
and glial cells. (3) Explain how neurons communicate via electrical signals and chemical
synapses. (4) Outline the anatomy and function of the central nervous system. (5) Describe the
subdivisions of the peripheral nervous system. (6) Identify common nervous system disorders
and their neurological basis.
1.2 Historical Overview
Ancient scholars believed the heart was the seat of intelligence and sensation. It was not until the
17th and 18th centuries that scientists such as René Descartes, Luigi Galvani, and later Santiago
Ramón y Cajal began to unravel the true role of the nervous system. Cajal's neuron doctrine — the
principle that the nervous system is made up of discrete, individual cells — revolutionized
neuroscience and earned him the Nobel Prize in 1906. Modern neuroscience continues to build
upon these foundations using tools such as MRI, electrophysiology, optogenetics, and
computational modeling.
First Year Biology — The Nervous SystemPage 2
, UNIVERSITY CLASS NOTES | BIOLOGY & NEUROSCIENCE | THE NERVOUS SYSTEM
2. The Central Nervous System (CNS)
The Central Nervous System (CNS) consists of the brain and the spinal cord. Encased in protective
bone — the cranium and vertebral column respectively — and surrounded by three membranous
layers called the meninges, the CNS serves as the processing and integration centre for all sensory
input and motor output in the body.
Figure 2: Major Regions of the Brain and Their Functions
2.1 The Brain
The brain is the most complex organ in the known universe. In an adult human, it weighs
approximately 1.3–1.4 kg and contains roughly 86 billion neurons and an equal number of glial
cells. The brain is divided into three major regions: the cerebrum (forebrain), the cerebellum, and
the brainstem.
A. The Cerebrum
The cerebrum is the largest part of the brain and is responsible for higher cognitive functions such
as thought, voluntary movement, language, reasoning, perception, and emotion. It is divided into
two cerebral hemispheres — left and right — connected by a thick band of nerve fibres called the
corpus callosum.
Each hemisphere is further divided into four lobes:
• Frontal Lobe — Located at the front of the brain. Responsible for voluntary movement (via
the motor cortex), executive function, decision-making, planning, working memory,
personality, and speech production (Broca's area).
• Parietal Lobe — Located behind the frontal lobe. Processes sensory information such as
touch, temperature, pain, and spatial awareness (via the somatosensory cortex).
First Year Biology — The Nervous SystemPage 3
The Nervous System
Structure, Function, Communication & Disorders
First Year Biology — Neuroscience Module
Academic Year 2025/2026
Figure 1: Hierarchical Organization of the Human Nervous System
First Year Biology — The Nervous SystemPage 1
,UNIVERSITY CLASS NOTES | BIOLOGY & NEUROSCIENCE | THE NERVOUS SYSTEM
1. Introduction
The nervous system is one of the most complex and fascinating organ systems in the human body.
It serves as the primary communication network of the body, receiving, processing, and transmitting
information that coordinates virtually every bodily function — from the beating of the heart and
regulation of breathing, to conscious thought, emotion, memory, and voluntary movement.
Without the nervous system, no organ, tissue, or cell could function in a coordinated manner. It is
the body's master control and communication system, working in concert with the endocrine system
to maintain homeostasis and allow the organism to interact meaningfully with its environment.
1.1 Why Study the Nervous System?
Understanding the nervous system is essential for anyone entering the health sciences, biology, or
related fields. Neurological disorders are among the leading causes of disability worldwide.
Knowledge of how the nervous system is organized, how it functions at the cellular level, and how it
can fail provides the foundation for clinical diagnosis, pharmacological treatment, and emerging
therapies.
🎯 Learning Objectives
By the end of this chapter, students should be able to: (1) Describe the overall organization of
the nervous system and its two main divisions. (2) Identify the structure and function of neurons
and glial cells. (3) Explain how neurons communicate via electrical signals and chemical
synapses. (4) Outline the anatomy and function of the central nervous system. (5) Describe the
subdivisions of the peripheral nervous system. (6) Identify common nervous system disorders
and their neurological basis.
1.2 Historical Overview
Ancient scholars believed the heart was the seat of intelligence and sensation. It was not until the
17th and 18th centuries that scientists such as René Descartes, Luigi Galvani, and later Santiago
Ramón y Cajal began to unravel the true role of the nervous system. Cajal's neuron doctrine — the
principle that the nervous system is made up of discrete, individual cells — revolutionized
neuroscience and earned him the Nobel Prize in 1906. Modern neuroscience continues to build
upon these foundations using tools such as MRI, electrophysiology, optogenetics, and
computational modeling.
First Year Biology — The Nervous SystemPage 2
, UNIVERSITY CLASS NOTES | BIOLOGY & NEUROSCIENCE | THE NERVOUS SYSTEM
2. The Central Nervous System (CNS)
The Central Nervous System (CNS) consists of the brain and the spinal cord. Encased in protective
bone — the cranium and vertebral column respectively — and surrounded by three membranous
layers called the meninges, the CNS serves as the processing and integration centre for all sensory
input and motor output in the body.
Figure 2: Major Regions of the Brain and Their Functions
2.1 The Brain
The brain is the most complex organ in the known universe. In an adult human, it weighs
approximately 1.3–1.4 kg and contains roughly 86 billion neurons and an equal number of glial
cells. The brain is divided into three major regions: the cerebrum (forebrain), the cerebellum, and
the brainstem.
A. The Cerebrum
The cerebrum is the largest part of the brain and is responsible for higher cognitive functions such
as thought, voluntary movement, language, reasoning, perception, and emotion. It is divided into
two cerebral hemispheres — left and right — connected by a thick band of nerve fibres called the
corpus callosum.
Each hemisphere is further divided into four lobes:
• Frontal Lobe — Located at the front of the brain. Responsible for voluntary movement (via
the motor cortex), executive function, decision-making, planning, working memory,
personality, and speech production (Broca's area).
• Parietal Lobe — Located behind the frontal lobe. Processes sensory information such as
touch, temperature, pain, and spatial awareness (via the somatosensory cortex).
First Year Biology — The Nervous SystemPage 3
