Neurons: Structure and Function

Neurons are the fundamental units of the nervous system, responsible for transmitting
information throughout the body. They are composed of the following parts:

 Soma (Cell Body): Contains the nucleus and organelles, managing cell function.
 Dendrites: Branch-like extensions that receive signals from other neurons.
 Axon: A long projection that transmits electrical signals away from the soma.
 Terminal Buttons: Found at the axon's end, these release neurotransmitters into the
synapse.

Central Nervous System (CNS) and Peripheral Nervous System (PNS)

 CNS: Includes the brain and spinal cord, acting as the control center for processing and
decision-making.
 PNS: Composed of nerves outside the CNS, connecting it to muscles, organs, and the
sensory system.

Types of Neurons

 Sensory Neurons: Transmit sensory information to the CNS.

 Motor Neurons: Carry commands from the CNS to muscles and glands.
 Interneurons: Connect sensory and motor neurons within the CNS for processing.

Neuronal Functions and Processes

 Axoplasmic Transport: The movement of materials within an axon.

o Anterograde Transport: Moves materials from the soma to the terminal buttons.
o Retrograde Transport: Moves materials from the axon terminals back to the
soma.
 Synaptic Connections: Neurons communicate through synapses, where
neurotransmitters are released to pass signals to other neurons.

Chromosomes, DNA, and RNA

 Chromosomes: Structures in the nucleus containing genetic information.

 DNA (Deoxyribonucleic Acid): The genetic blueprint for cellular functions.
 mRNA (Messenger Ribonucleic Acid): Transfers genetic instructions from DNA to
ribosomes for protein synthesis.

Cellular Components of Neurons

 Cytoplasm: The fluid inside cells, supporting organelles.

 Cytoskeleton: Maintains cell shape and structure, including microtubules that facilitate
transport.
 Nucleus: Stores DNA and coordinates activities like growth and reproduction.
 Enzymes: Catalyze chemical reactions.
  Endoplasmic Reticulum (ER):
o Rough ER: Involved in protein synthesis.
o Smooth ER: Synthesizes lipids and processes toxins.
 Golgi Apparatus: Packages proteins for transport or secretion.
 Exocytosis: Process of releasing substances from the cell.
 Lysosomes: Break down cellular waste.
 Mitochondria: Produce ATP (adenosine triphosphate), the energy currency of the cell.

Supporting Cells of the Nervous System

 Glial Cells: Provide support, protection, and nutrition to neurons.

CNS Glial Cells:

 Astrocytes: Regulate the blood-brain barrier, provide nutrients, and support synaptic
communication.
 Oligodendrocytes: Form the myelin sheath for axons in the CNS, speeding up signal
transmission.
 Microglia: Perform phagocytosis to remove debris and defend against pathogens.

PNS Supporting Cells:

 Schwann Cells: Form myelin sheaths for axons in the PNS.

 Myelin Sheath Formation: Insulates axons and speeds up electrical signals.
 Node of Ranvier: Gaps in the myelin sheath that facilitate rapid signal conduction.

Blood-Brain Barrier
The blood-brain barrier (BBB) protects the CNS by preventing harmful substances in the
bloodstream from entering the brain while allowing essential nutrients to pass.

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The nervous system is the body’s communication system that sends, receives, and processes
information to keep everything working smoothly. It is made up of two main parts: the Central
Nervous System (CNS) and the Peripheral Nervous System (PNS). The CNS includes the
brain and spinal cord, which act as the control center for decision-making and processing. For
example, if you accidentally touch a hot stove, the CNS quickly processes this information and
decides you need to move your hand. The PNS consists of nerves outside the CNS that connect it
to the rest of the body, like your muscles, organs, and sensory receptors.

Neurons, the building blocks of the nervous system, are specialized cells that send messages
throughout the body. A neuron has three main parts: the soma (cell body), dendrites, and axon.
The soma contains the nucleus, which controls the cell’s activities. The dendrites are branch-like
structures that receive signals from other neurons, while the axon is a long projection that sends
electrical signals to other cells. At the end of the axon are terminal buttons, which release
chemicals called neurotransmitters into the synapse (the tiny gap between neurons). For
instance, when you move your hand to pick up a cup, neurons send signals from your brain to
your hand muscles, allowing the movement.

There are three types of neurons based on their functions. Sensory neurons carry information
from your body to your brain, like when you feel heat or cold. Motor neurons carry commands
from your brain to your muscles or glands, like when you decide to wave at someone.
Interneurons are found in the brain and spinal cord and process information by connecting
sensory and motor neurons. For example, when you step on something sharp, sensory neurons
send the pain signal to your brain, interneurons process it, and motor neurons signal your foot to
pull away.

Inside neurons, materials are constantly being transported to keep them functioning. This
movement is called axoplasmic transport, which happens in two directions. Anterograde
transport moves materials from the soma to the terminal buttons, while retrograde transport
moves materials back to the soma for recycling.

Neurons rely on several cell parts to work efficiently. The nucleus stores genetic information in
the form of DNA (deoxyribonucleic acid), which acts as a blueprint for the cell. Instructions
from DNA are carried by mRNA (messenger ribonucleic acid) to produce proteins needed for
the cell’s function. The cytoplasm is the jelly-like substance inside the cell that holds the
cytoskeleton, a network of structures like microtubules that maintain the cell’s shape and help
transport materials. The endoplasmic reticulum (ER) helps produce proteins and lipids, while
the Golgi apparatus packages these materials for use or transport. Neurons also use
mitochondria to produce ATP (adenosine triphosphate), which provides the energy they need
to function. For example, mitochondria help neurons generate energy to send signals over long
distances.

Supporting cells play a vital role in helping neurons do their job. In the CNS, astrocytes provide
nutrients, remove waste, and maintain the blood-brain barrier, which protects the brain from
harmful substances while allowing nutrients to enter. Oligodendrocytes create the myelin
sheath, a protective layer that wraps around axons and speeds up signal transmission. Gaps in
the myelin sheath, called Nodes of Ranvier, help signals travel even faster. Microglia act as the
nervous system’s immune cells, cleaning up debris and fighting infections through a process
called phagocytosis.

In the PNS, Schwann cells create the myelin sheath for peripheral nerves, similar to how
oligodendrocytes function in the CNS. For example, the myelin sheath allows signals to travel
quickly from your brain to your hand when you want to grab an object.

Altogether, the nervous system relies on neurons, supporting cells, and many small processes to
keep the body functioning smoothly. Whether it’s pulling your hand away from danger or
processing a pleasant touch, every part works together in harmony to keep you safe and active.