Introduction to Cells

Cells are the basic building blocks of all living things. They are the smallest units of life that can function independently and perform all the necessary functions of life. Each cell has a specific role, and they come together to form tissues and organs.

What is a Neuron?

A neuron is a specialised type of cell in the nervous system that transmits information through electrical and chemical signals. Neurons are the brain's messengers, responsible for receiving sensory input (sight, smell, sound), sending motor commands (like walk over there or move hand), and carrying out complex processes (like thinking and remembering).

Cell Body (Soma)

The cell body, also known as the soma, is the main part of the neuron that contains the nucleus and most of the cell's organelles. It plays a critical role in integrating incoming signals from the dendrites and generating outgoing signals that travel down the axon. The soma is responsible for maintaining the neuron's overall health and function by housing the machinery necessary for protein synthesis and energy production.

Nucleus (of a neuron)

The nucleus is the control center of the neuron, located within the cell body. It contains the neuron's DNA and regulates all its activities, including growth, metabolism, and reproduction.

Within the neuron are several important structures that play crucial roles in its function:

Dendrites

Dendrites are the branch-like extensions of neurons that receive messages from other neurons. They act like antennas, picking up signals from surrounding cells and conveying this information to the neuron's cell body.

Axon

An axon is a long, slender projection of a neuron that carries electrical impulses away from the neuron's cell body. Imagine it as a highway for electrical signals, transmitting information over long distances within the body.

Axon Hillock

The axon hillock is a special part of the neuron's cell body where the axon starts. It is crucial for starting electrical impulses (action potentials). This area has many sodium channels that help generate and send these impulses. The axon hillock acts as a decision point, deciding if the incoming signals are strong enough to trigger an action potential.

Initial Segment

The initial segment is the first part of the axon just beyond the axon hillock. It is the site where action potentials are generated. This segment is rich in voltage-gated ion channels that respond to changes in membrane potential, facilitating the rapid depolarisation necessary to propagate the electrical signal along the axon. In other words, this area has special channels that open and close in response to electrical changes, allowing the signal to travel quickly down the axon.

Axon Terminals

Axon terminals are the endpoints of an axon. They make synaptic connections with other neurons or muscle cells, allowing the neuron to pass along its message. These terminals release neurotransmitters, which are chemicals that transmit signals across the synapse to other neurons.

Synapse

A synapse is the junction between two neurons, where one neuron can pass a signal to another. It's like a tiny gap where the magic of communication happens, allowing for the transfer of information from one neuron to the next.

Synaptic Cleft

The synaptic cleft is the small space between the presynaptic neuron (sending the signal) and the postsynaptic neuron (receiving the signal). Neurotransmitters released from the axon terminals cross this gap to transmit the signal.

Synaptic Vesicles

Synaptic vesicles are small sacs in the axon terminals that store neurotransmitters. When an electrical signal reaches the axon terminal, these vesicles release their neurotransmitter contents into the synaptic cleft, allowing the signal to be passed on.

Receptors (on the postsynaptic neuron)

Receptors are specialised protein molecules located on the surface of the postsynaptic neuron. These receptors bind to neurotransmitters released into the synaptic cleft, allowing the postsynaptic neuron to receive the signal and respond accordingly.

Microtubules

Microtubules are structural components within neurons that help maintain the cell's shape and facilitate the transport of materials within the cell. They are part of the cytoskeleton and provide a network along which organelles and vesicles can move. This transportation is vital for the distribution of nutrients, neurotransmitters, and other essential molecules throughout the neuron, especially over the long distances of axons.

Glial Cells

Glial cells are the support cells of the nervous system. They do not transmit signals like neurons, but they play crucial roles in maintaining the health and functionality of the nervous system. Glial cells provide support, protection, and nourishment to neurons.

Astrocytes

Astrocytes are star-shaped glial cells that provide structural and metabolic support to neurons. They maintain the blood-brain barrier, regulate blood flow, and help repair and scavenge damaged cells.

Oligodendrocytes

Oligodendrocytes are glial cells responsible for producing the myelin sheath in the central nervous system. The myelin sheath insulates axons, allowing for faster transmission of electrical signals.

Microglia

Microglia are the immune cells of the nervous system. They act as the first line of defense against infections and help clean up debris and dead cells through a process called phagocytosis.

Ependymal Cells

Ependymal cells line the ventricles of the brain and the central canal of the spinal cord. They produce and circulate cerebrospinal fluid (CSF), which cushions the brain and spinal cord.

Schwann Cells

Schwann cells are glial cells in the peripheral nervous system that produce the myelin sheath for peripheral nerves. They play a key role in nerve regeneration and repair.

Myelin Sheath

The myelin sheath is a fatty layer that wraps around the axons of neurons. It insulates the axons and allows electrical impulses to travel more quickly and efficiently.

Nodes of Ranvier

The Nodes of Ranvier are small gaps in the myelin sheath along the axon. These gaps allow the electrical signal to jump from one node to the next, speeding up signal transmission.

Amyloid Plaques

Amyloid plaques are clumps of protein fragments that accumulate between neurons. They are commonly associated with Alzheimer's disease. and are thought to disrupt cell communication and trigger inflammation.

Tau Tangles

Tau tangles are twisted fibers of tau protein found inside neurons. These tangles disrupt the transport system within the neuron and are also associated with Alzheimer's disease.

Neurofibrillary Tangles

Neurofibrillary tangles are another term for tau tangles, found in various neurodegenerative diseases. They interfere with the cell's transport system, leading to cell death.

Lewy Bodies

Lewy bodies are abnormal protein aggregates found inside neurons. They are associated with Parkinson's disease and Lewy body dementia and can disrupt normal cell function.

Pick Bodies

Pick bodies are abnormal inclusions found in neurons, composed of tau protein. They are associated with Pick's disease, a type of frontotemporal dementia.

Neurotransmitter Reuptake Transporters

Neurotransmitter reuptake transporters are proteins located on the surface of neurons. They help clear neurotransmitters from the synaptic cleft by transporting them back into the presynaptic neuron. This process ensures that neurotransmitters are recycled and reused, maintaining balance and efficient communication between neurons.

Vesicular Transporters

Vesicular transporters are proteins that move neurotransmitters into synaptic vesicles within the neuron. These vesicles store neurotransmitters until they are released into the synaptic cleft during signal transmission. Vesicular transporters ensure that neurotransmitters are available for release when needed.

Ion Channels

Ion channels are proteins in the neuron's cell membrane that allow ions to pass in and out of the cell. These channels open and close in response to electrical signals, playing a crucial role in generating and propagating action potentials. They help maintain the neuron's electrical balance and enable rapid signal transmission.

Neurofilaments

Neurofilaments are structural proteins within neurons that provide support and maintain the shape of the cell. They are part of the neuron's cytoskeleton, contributing to its strength and stability. Neurofilaments are particularly important in large axons, where they help maintain the axon's diameter and facilitate efficient signal transmission.

Microtubules

Microtubules are structural components within neurons that help maintain the cell's shape and facilitate the transport of materials within the cell. They are part of the cytoskeleton and provide a network along which organelles and vesicles can move. This transportation is vital for the distribution of nutrients, neurotransmitters, and other essential molecules throughout the neuron, especially over the long distances of axons.

Blood-Brain Barrier

The blood-brain barrier is a protective shield that separates the brain's blood vessels from the brain tissue. It regulates the passage of substances from the bloodstream into the brain, protecting it from harmful chemicals and pathogens while allowing essential nutrients to pass through.

Meninges

The meninges are three layers of protective tissue that cover the brain and spinal cord. These layers, called the dura mater, arachnoid mater, and pia mater, provide a protective barrier and support to the central nervous system, cushioning it from injury.

Cerebrospinal Fluid (CSF)

Cerebrospinal fluid (CSF) is a clear, colorless liquid that surrounds the brain and spinal cord. It acts as a cushion, absorbing shocks and protecting the brain and spinal cord from injury. CSF also helps transport nutrients and remove waste products from the brain.

Skull

The skull is a bony structure that encases and protects the brain. It provides a hard, protective shell to shield the brain from physical damage and injury.

Vertebral Column (for spinal cord protection)

The vertebral column, or spine, is a bony structure that encases and protects the spinal cord. It consists of individual vertebrae stacked on top of each other, providing a strong, flexible support system that safeguards the spinal cord while allowing for movement and flexibility.