12.2 Nervous System
The human nervous system is a complex network of nerve cells (neurones) responsible for coordinating and controlling body activities. It is divided into two primary subsystems: the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of cranial nerves and spinal nerves. Together, these systems detect stimuli, transmit electrical nerve impulses, process sensory information, and initiate appropriate responses to maintain internal stability and react to the external environment.
Learning Objectives
- Describe the organisation of the human nervous system into the central nervous system and peripheral nervous system.
- State the main components of the human brain (cerebrum, hypothalamus, cerebellum, medulla oblongata, and pituitary gland) and explain their respective functions.
- Describe the structure and cross-section of the spinal cord (white matter, grey matter, dorsal root, ventral root, and dorsal root ganglion) and state its functions.
- Differentiate between the functions of the somatic nervous system and the autonomic nervous system within the peripheral nervous system.
Organisation and Structure of the Central and Peripheral Nervous System
The nervous system is organised into the central nervous system and the peripheral nervous system. The brain and spinal cord form the CNS, while cranial and spinal nerves form the PNS.
Central Nervous System
Brain and spinal cord — the integration and processing centre.
Peripheral Nervous System
12 pairs of cranial nerves and 31 pairs of spinal nerves.
Somatic vs Autonomic
Somatic controls voluntary actions; autonomic controls involuntary actions.
Short Explanation
What is the nervous system?
The nervous system acts as the communication network of the human body. The central nervous system serves as the integration and processing centre: the brain handles complex sensory perception, memory, coordination, and vital autonomic life functions, while the spinal cord controls reflex pathways and relays signals between the brain and the rest of the body. Surrounding this core is the peripheral nervous system, which acts as the wiring. It collects environmental data through receptors and cranial or spinal nerves, shuttles impulses to the CNS, and carries out voluntary commands via somatic nerves or involuntary adjustments through autonomic nerves.
The Human Brain
The brain is made up of more than 100 billion neurones and acts as the coordination and control centre. Its main components are the cerebrum, hypothalamus, cerebellum, medulla oblongata, and pituitary gland.
The Spinal Cord
The spinal cord is located within the vertebral column and bathed in cerebrospinal fluid. Its cross-section shows grey matter shaped like a butterfly or the letter 'H', surrounded by white matter. Each spinal nerve has a dorsal root and a ventral root.
Try to Answer First
Answer in your mind, then press “Check Answer”.
Which part of the brain is responsible for maintaining body balance and coordinating muscle contractions?
What is the difference between the dorsal root and the ventral root of a spinal nerve?
Why is sneezing considered an involuntary action, and which brain structure regulates it?
Common Mistakes
- Confusing the cerebrum with the cerebellum: students often mistakenly credit the cerebrum with body balance or the cerebellum with higher intelligence and voluntary thought.
- Mixing up the functions of the dorsal root and ventral root: forgetting that sensory impulses enter through the dorsal root while motor commands leave through the ventral root.
- Assuming the autonomic nervous system controls voluntary actions instead of involuntary visceral activities such as heartbeat and peristalsis.
- Misidentifying the composition of grey matter and white matter: grey matter consists mostly of cell bodies, whereas white matter consists of myelin-coated axons.
Concept Misunderstandings
The brain directly touches the skull bones for protection.
The central nervous system structures (brain and spinal cord) are cushioned and protected by cerebrospinal fluid, which also provides essential nutrients.
Spinal nerves only carry motor signals to muscles.
Each spinal nerve is a mixed nerve formed by the union of the dorsal root (sensory) and ventral root (motor), allowing bidirectional transmission.
The hypothalamus only functions as an endocrine gland.
The hypothalamus is a vital brain component that integrates the nervous system and endocrine system while directly controlling homeostatic mechanisms like body temperature and blood pressure.
Summary
- The human nervous system comprises the Central Nervous System (brain and spinal cord) and the Peripheral Nervous System (12 pairs of cranial nerves and 31 pairs of spinal nerves).
- The cerebrum governs voluntary actions, intelligence, reasoning, and sensory processing.
- The cerebellum maintains equilibrium, balance, and fine muscle coordination.
- The hypothalamus maintains homeostasis (temperature, water balance, hunger, thirst) and links the nervous system to the pituitary gland.
- The medulla oblongata directs vital involuntary processes (breathing, heartbeat, blood pressure, peristalsis, sneezing).
- The spinal cord processes reflexes and relays information via dorsal roots (sensory neurones) and ventral roots (motor neurones).
- The somatic nervous system controls voluntary actions, whereas the autonomic nervous system regulates involuntary body processes.
Short Activity
Objective: identify the organisation of the nervous system, brain functions, spinal cord structure, and PNS divisions.
A. Objective Quiz
Which part of the brain controls vital involuntary actions such as heartbeat, breathing rate, and blood pressure?
How many pairs of cranial nerves and spinal nerves make up the human peripheral nervous system?
B. Fill in the Blanks
The sensory neurones' cell bodies are clustered together in a swelling called the .
In a cross section of the spinal cord, the matter consists mainly of neuronal cell bodies and is arranged in a shape resembling a butterfly or the letter 'H'.
C. Matching / Drag and Drop
Match each component of the nervous system to its correct function or structural description. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Component to Its Function
Write the correct component next to each function.
| Function / Description | Component |
|---|---|
| 1. Controls emotions, personality, higher mental abilities, and voluntary actions. | |
| 2. Regulates homeostasis, body temperature, water balance, hunger, and thirst. | |
| 3. Transmits motor nerve impulses from the spinal cord out to the effectors. | |
| 4. Subsystem of the peripheral nervous system that regulates all controlled actions. |
Answer choices: Cerebrum • Hypothalamus • Ventral root • Somatic nervous system
