Nervous System

Team Biology at
Created by: Team Biology at, Last Updated: April 27, 2024

Nervous System

Dive into the intricate world of the nervous system, the pivotal network that orchestrates every thought, action, and sensation. This comprehensive guide illuminates the complex mechanisms of the brain, spinal cord, and peripheral nerves, showcasing their roles in maintaining homeostasis, processing sensory information, and executing motor functions. Through vivid examples, discover how the nervous system enables the seamless interaction between our bodies and the environment, ensuring survival and adaptation. Unlock the secrets of neural pathways and their impact on behavior and cognition, making this an essential read for anyone fascinated by human biology.

What is Nervous System?

The nervous system is a sophisticated network of neurons and supporting cells that acts as the control and communication system of the body. It is divided into two main parts: the central nervous system (CNS), comprising the brain and spinal cord, and the peripheral nervous system (PNS), consisting of all other neural elements. This system is responsible for receiving sensory information from the external and internal environment, processing this data, and coordinating responses by triggering muscles and glands. It plays a crucial role in maintaining homeostasis, enabling perception, motor functions, cognitive abilities, and emotions, making it fundamental to every aspect of life.

Human Nervous System Diagram

Human Nervous System

Central Nervous System

Central Nervous System

The Central Nervous System (CNS) is a crucial component of the nervous system in humans and other vertebrates. It consists primarily of the brain and spinal cord. The CNS is responsible for receiving sensory information from the external and internal environment, processing this information, and coordinating voluntary and involuntary responses to these stimuli.


The brain is housed within the skull and is the command center of the body. It is responsible for processing sensory information, thinking, learning, consciousness, and regulating many bodily functions. The brain can be divided into several parts, each with specific functions:

  • Cerebrum: The largest part of the brain, responsible for higher brain functions such as thought, action, reasoning, and emotion. It’s divided into two hemispheres and further into lobes that specialize in different functions.
  • Cerebellum: Located under the cerebrum, its functions include coordination of voluntary movements, balance, and posture.
  • Brainstem: Acts as a relay center connecting the cerebrum and cerebellum to the spinal cord, and controls autonomic functions such as breathing, heart rate, and blood pressure.

Spinal Cord

The spinal cord extends from the base of the brain, down through the spine, to the lower back. It is a bundle of nerve fibers enclosed within the spinal column. The spinal cord transmits neural signals between the brain and the rest of the body and is also responsible for reflex actions. It is divided into segments where spinal nerves emerge.

Functions of the CNS

  1. Sensory Processing: Receives information from sensory organs and internal sensors.
  2. Motor Control: Sends signals to muscles and glands, initiating movements and responses.
  3. Cognitive Functions: Includes thoughts, learning, memory, and decision-making.
  4. Regulation of Homeostasis: Controls and regulates bodily functions to maintain internal equilibrium.
  5. Emotional Responses: Processes and regulates emotions.

Protection of the CNS

The CNS is well-protected by several structures:

  • Skull and Vertebral Column: Physically shield the brain and spinal cord.
  • Meninges: Three layers of protective tissues that surround both the brain and spinal cord.
  • Cerebrospinal Fluid (CSF): Fills the spaces within and around the CNS, cushioning it from impact.
  • Blood-Brain Barrier: A selective barrier that prevents certain substances in the blood from reaching the brain tissue.

Peripheral Nervous System

The Peripheral Nervous System (PNS) is a vital component of the nervous system outside of the brain and spinal cord (which make up the Central Nervous System, CNS). It consists of nerves and ganglia, serving as a communication relay between the CNS and the rest of the body. The PNS is instrumental in connecting the CNS to limbs and organs, essentially serving as a network that sends and receives information to and from the CNS to regulate bodily functions and respond to the environment.

Components of the PNS

  1. Nerves: Bundles of axons (nerve fibers) that transmit signals to and from the brain and spinal cord. These can be sensory nerves, motor nerves, or mixed nerves.
  2. Ganglia: Clusters of neuron cell bodies located outside the CNS, which act as relay points and processing centers for peripheral signals.

Divisions of the PNS

The PNS is divided into two main parts, each with distinct functions:

  1. Somatic Nervous System (SNS): This system controls voluntary movements of the body through control of skeletal muscles. It also mediates the reception of external sensory information, such as touch, temperature, and pain, conveying this information to the CNS.
  2. Autonomic Nervous System (ANS): This system regulates involuntary body functions, such as heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. The ANS is further divided into:
    • Sympathetic Nervous System: Prepares the body for “fight or flight” responses during stress or emergencies.
    • Parasympathetic Nervous System: Controls “rest and digest” activities, helping the body to conserve energy and maintain a state of calm.

Functions of the PNS

  • Transmission of Sensory Signals: Peripheral sensory receptors gather information from the environment and internal body conditions, transmitting this data to the CNS for processing.
  • Execution of Motor Commands: Based on information processed by the CNS, the PNS carries commands to the muscles and glands, initiating actions and responses.
  • Regulation of Autonomic Functions: The ANS automatically adjusts the functions of internal organs and systems to maintain homeostasis and respond to changes in the environment.

Protection and Repair

Unlike the CNS, nerves in the PNS have a limited capacity to regenerate or repair themselves after injury, thanks to the presence of Schwann cells that promote axon regrowth. However, the extent of recovery depends on the severity and location of the injury.

The PNS plays a crucial role in the overall functioning of the body and its ability to interact with the external world. It is essential for voluntary movements, sensory perception, and the regulation of automatic body functions, illustrating the complexity and adaptability of the human nervous.



A neuron, also known as a nerve cell, is the fundamental unit of the nervous system. Neurons are specialized to transmit information throughout the body, making them essential for all bodily functions, including movement, sensation, and cognition. The structure and function of neurons enable them to process and transmit neural signals, both within the nervous system and between the nervous system and other body parts.

Structure of a Neuron

A typical neuron consists of three main parts: the cell body (soma), dendrites, and an axon.

  • Cell Body (Soma): Contains the nucleus and cytoplasm, where most of the neuron’s metabolic and synthetic activities occur. It is the control center of the neuron.
  • Dendrites: Branch-like structures that extend from the cell body. Dendrites receive signals from other neurons or from sensory receptors and convey these signals toward the cell body.
  • Axon: A long, thin fiber that transmits signals away from the cell body to other neurons or to muscles or glands. Axons can vary in length, from a fraction of an inch to several feet.

Neurons are further classified into three types based on their function:

  1. Sensory Neurons (Afferent Neurons): Transmit signals from sensory receptors toward the central nervous system.
  2. Motor Neurons (Efferent Neurons): Carry signals from the central nervous system to effector cells in muscles or glands, initiating an action.
  3. Interneurons: Located entirely within the central nervous system, interneurons connect sensory and motor neurons, playing critical roles in reflexes, neuronal circuits, and the processing of information.

Neuronal Function

The basic function of a neuron is to receive, process, and transmit information through electrical and chemical signals. This process involves several steps:

  1. Signal Reception: Dendrites receive incoming signals from other neurons or sensory cells.
  2. Signal Integration: The cell body integrates the incoming signals to determine if the neuron should generate an output signal.
  3. Signal Transmission: If the integrated signals exceed a certain threshold, the neuron generates an action potential (electrical signal) that travels along the axon to its end.
  4. Signal Transfer: At the axon terminals, the action potential causes the release of neurotransmitters, chemicals that cross the synapse (the gap between neurons) to transmit the signal to the next neuron or to an effector cell.


Nerves are critical components of the nervous system, functioning as the communication pathways that relay signals between the brain and spinal cord (central nervous system, or CNS) and various parts of the body (peripheral nervous system, or PNS). These signals include both motor information, which commands muscle movements, and sensory information, which conveys sensations such as touch, pain, temperature, and position.

Structure of Nerves

Structure of Nerves

Nerves are comprised of numerous nerve fibers, which are long, slender projections of neurons. These nerve fibers are bundled together and are often surrounded by connective tissue sheaths that provide protection and support. The basic structural components of a nerve include:

  • Axons: The long, thin extensions of neurons that transmit electrical impulses.
  • Myelin Sheath: Some axons are covered by this fatty layer, which acts as insulation and significantly increases the speed of signal transmission.
  • Endoneurium: A delicate layer of connective tissue that encases individual nerve fibers.
  • Perineurium: A protective sheath that groups axons into bundles known as fascicles.
  • Epineurium: The tough outermost layer that encloses all the fascicles to form the nerve.

Types of Nerves

Nerves can be classified based on their direction of signal transmission:

  • Sensory (Afferent) Nerves: Carry sensory information from the sensory receptors toward the CNS.
  • Motor (Efferent) Nerves: Transmit motor signals from the CNS to muscles or glands, initiating action.
  • Mixed Nerves: Contain both sensory and motor fibers and can transmit signals in both directions.

Function of Nerves

Nerves facilitate the transmission of electrical impulses throughout the body, enabling the CNS to communicate with limbs, organs, and tissues. This communication network is essential for coordinating a wide range of functions, including:

  • Motor Control: Nerves transmit signals from the brain and spinal cord to muscles, controlling voluntary movements as well as reflexes.
  • Sensory Information Processing: Sensory nerves convey information about the external and internal environments to the CNS, allowing the body to respond appropriately.
  • Regulation of Bodily Functions: Autonomic nerves, part of the PNS, regulate involuntary functions such as heart rate, digestion, and respiratory rate.


What are the two divisions of the nervous system?

The nervous system, an intricate network, orchestrates the body’s myriad functions, distinguishing between the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS, encompassing the brain and spinal cord, processes sensory data, formulates responses, and governs intelligence, emotions, and memory. In contrast, the PNS connects the CNS to limbs and organs, facilitating voluntary and involuntary actions through its somatic and autonomic divisions. This remarkable system enables sensory perception, motor coordination, and the regulation of physiological processes, ensuring survival and adaptation in a changing environment. Its complexity and efficiency underscore the marvel of human biology.

What are nerves and neurons?

Nerves and neurons are fundamental components of the nervous system, facilitating communication throughout the body. Neurons, the basic units, transmit signals via electrical and chemical means. Each neuron consists of a cell body, dendrites for receiving signals, and an axon for sending signals. Nerves, composed of bundled neurons, act as communication cables, connecting the central nervous system to various body parts. They carry sensory information from external and internal environments to the brain and relay commands from the brain to muscles and organs. This intricate network enables sensory perception, movement, and the regulation of bodily functions, showcasing the complexity of biological communication systems.

What are the 7 organs of the nervous system?

The nervous system, an intricate network pivotal to the human body, comprises the brain, spinal cord, nerves, sensory organs, ganglia, cerebellum, and hypothalamus. It orchestrates a symphony of bodily functions, from basic survival instincts to complex thought processes. Through electrical and chemical signals, it communicates between various body parts, ensuring coordinated movements, sensory processing, and the maintenance of homeostasis. The brain, the command center, interprets sensory information, while the spinal cord acts as a communication conduit. Nerves, extending like cables, carry messages to and from the body, enabling our interaction with the environment and the nuanced control of our internal landscape.

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