Human Body Systems: Nervous System and Neurons Explained

Posted on Jul 12, 2025 in Biology

The Body’s Interaction Process

The human body constantly interacts with its internal and external environments to maintain stability and function. This complex process involves several key objectives:

  • Adapting the body to changing conditions in both the internal and external environment.
  • Connecting and coordinating different parts of our body to ensure they work together seamlessly.

Homeostasis: Maintaining Body Stability

Homeostatic processes are crucial for maintaining the body’s internal stability despite changes in the environment. This dynamic equilibrium ensures optimal physiological functioning.

Organs and Systems in Interaction

The interaction process involves several vital organs and systems:

  • Sensory Organs: These organs receive information from the environment in the form of stimuli. This information is then transformed into nerve impulses and transmitted to the nervous system.
  • Nervous System: It processes the received information and formulates an appropriate response.
  • Effector Organs: These organs carry out the response dictated by the nervous system.

Key systems contributing to this interaction include:

  • The Skeletal and Muscular Systems: Together forming the locomotor system, they are responsible for body movement (bones and muscles, respectively).
  • The Endocrine System: This system regulates various body functions by producing and releasing hormones.

To clarify the flow of information:

  • Changes produced in our environment are called stimuli.
  • Information about these changes is captured by specialized organs known as sensory organs.
  • This information is transmitted to integrated and coordinated organs, primarily the nervous system, which processes it and generates a response.
  • The response is then transmitted to effector organs, which are responsible for acting upon the body’s movement (via the locomotor system) or other functions (regulated by the endocrine system’s hormones).

The Neuron and Electrical Signals

The neuron is the fundamental anatomical and physiological unit of the nervous system. The transmission of information between neurons occurs through electrical signals, known as nerve impulses.

Understanding the Neuron

A neuron is a specialized cell designed to transmit electrical and chemical signals. Its primary components include:

  • Cell Body (Soma): Contains the nucleus and other essential organelles, filled with cytoplasm.
  • Axon: A long extension, also made up of cytoplasm, that carries nerve impulses away from the cell body to another neuron or cell.
  • Dendrites: Short, branched extensions of the cell body that receive nerve impulses from other neurons.

Neuron Structure and Function

Neurons can be classified by their structure or function:

Structural Classification:

  • Unipolar: A single process extending from the cell body.
  • Bipolar: Two processes extending from the cell body.
  • Multipolar: Multiple processes extending from the cell body (one axon, many dendrites).

Functional Classification:

  • Sensory Neurons: Transmit information from receptors to the central nerve centers.
  • Motor Neurons: Transmit signals from the nerve centers to the effector organs.
  • Interneurons: Connect the sensory neurons and the motor neurons, facilitating communication within the nervous system.

Electrical Signals: Nerve Impulses

A nerve impulse is generated when a neuron is stimulated. This stimulation causes electrical changes to originate in the neuron’s membrane, transmitting electrical signals from the dendrites toward the axon.

Synapses: Neuronal Connections

Neurons are not isolated; they establish specialized connections called synapses. Synapses allow nerve impulses to cross from one neuron to another, typically occurring between the end of the axon of one neuron and a dendrite of an adjacent neuron.

It’s important to note that there is no physical contact between neurons at a synapse. Instead, there is always a small gap between them, known as the synaptic cleft.

At the axon terminal, very small vesicles contain a substance called neurotransmitters. When a nerve impulse reaches the axon terminal, these vesicles break open, releasing neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the dendrite membrane of the adjacent neuron, initiating a new nerve impulse in that neuron.

Types of Neural Pathways

Neural pathways describe how neurons connect and transmit information:

  • Divergent Pathways: Information from one neuron is transmitted to many different neurons, spreading the signal.
  • Convergent Pathways: Information from many different neurons converges onto a single neuron, integrating multiple signals.

The Nervous System

The nervous system is a complex network of nerves and cells that carry messages to and from the brain and spinal cord to various parts of the body. Its crucial functions include:

  • Receiving the information transmitted by the sensory organs.
  • Interpreting that information and preparing adequate responses.
  • Transferring the necessary signals to the effector organs.
  • Coordinating all organs so that they function correctly in our body.
  • Carrying out intellectual and mental functions, such as thought, memory, and learning.
  • Being responsible for our emotions and feelings.

The Central Nervous System (CNS)

The Central Nervous System (CNS) is comprised of nerve centers responsible for integrating received information, coordinating it, and preparing a response. The primary components of the CNS are the brain and the spinal cord.

The CNS is well-protected from potential injuries by:

  • Bony Structures: The skull protects the brain, and the spine (vertebral column) protects the spinal cord.
  • Meninges: Three protective membranes called meninges envelop the brain and spinal cord. These layers are:
    • Dura Mater: The outermost, tough layer.
    • Arachnoid Mater: The middle, web-like layer.
    • Pia Mater: The innermost, delicate layer that adheres to the brain and spinal cord surface.
  • Cerebrospinal Fluid (CSF): This fluid circulates between the meninges, providing cushioning and protection against the effects of blows to the nerve centers.

The CNS is composed of two main types of tissue:

  • Grey Matter: Primarily consists of neuron cell bodies and dendrites, responsible for processing information.
  • White Matter: Composed mainly of neuron extensions, generally axons, which transmit signals between different areas of the brain and spinal cord.

The Spinal Cord

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. Its key functions include:

  • Producing reflex actions: These are rapid, involuntary responses to a stimulus that occur without direct participation from the brain.
  • Carrying sensory nerve impulses from the body to the brain and motor commands from the brain to the body.

The Brain

The brain is the most complex organ in the human body, serving as the control center for the nervous system. Key parts include:

  • Medulla Oblongata (Spinal Bulb): This structure connects the brain to the spinal cord and carries information between them. It is a vital part of the autonomic nervous system, regulating several essential body functions such as heartbeat, blood pressure, and breathing.