35.1 Neurons and Glial Cells
3 min read•june 14, 2024
Neurons are the building blocks of our nervous system, transmitting signals that control our thoughts and actions. These specialized cells have unique structures like dendrites and axons, allowing them to communicate with each other through chemical and electrical signals.
Glial cells support and protect neurons, playing crucial roles in brain function. From astrocytes providing nutrients to insulating axons, these cells are essential for maintaining a healthy nervous system and facilitating efficient neural communication.
Neuron Structure and Function
Components and functions of neurons
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- Cell body () contains the nucleus and other organelles responsible for protein synthesis and cellular metabolism
- Dendrites are branched extensions that receive signals from other neurons and increase the surface area for receiving input
- is a long, thin extension that transmits electrical signals away from the cell body and is covered by a in some neurons for faster signal transmission
- is the end of the axon that forms with other neurons or target cells and contains synaptic vesicles that store and release (, )
- is the junction between the axon terminal of one and the or cell body of another neuron that allows for communication between neurons through chemical or electrical signaling ()
- are located on the postsynaptic membrane and bind to specific neurotransmitters, initiating a response in the target cell
Types of neurons
- Sensory neurons (afferent neurons) transmit sensory information from receptors to the central nervous system and usually have long dendrites and short axons (dorsal root ganglion neurons)
- Motor neurons (efferent neurons) transmit signals from the central nervous system to muscles or glands and usually have short dendrites and long axons (spinal motor neurons)
- Interneurons are found within the central nervous system, relay signals between sensory and motor neurons or other interneurons, and vary in structure depending on their specific function (Purkinje cells in the cerebellum)
- Multipolar neurons are the most common type of neuron, have one axon and multiple dendrites extending from the cell body, and are found in the brain, spinal cord, and autonomic nervous system (pyramidal cells in the cerebral cortex)
Glial Cells and Their Functions
Roles of glial cells
- Astrocytes provide structural support and nutrients to neurons, regulate the concentration of ions and neurotransmitters in the synaptic cleft ( uptake), and contribute to the formation and maintenance of the
- Oligodendrocytes (in the central nervous system) produce sheath that insulates axons and facilitate rapid and efficient transmission of electrical signals along axons
- Schwann cells (in the peripheral nervous system) produce myelin sheath that insulates axons and aid in the regeneration of damaged peripheral nerve fibers
- act as the immune cells of the central nervous system, phagocytose debris, dead cells, and pathogens, and secrete cytokines and other signaling molecules to regulate immune responses (, )
- cells line the ventricles of the brain and the central canal of the spinal cord, produce and circulate cerebrospinal fluid, and contribute to the formation of the blood-cerebrospinal fluid barrier
Neuronal Dynamics and Plasticity
- is the electrical potential difference across a neuron's membrane when it is not actively transmitting signals
- refers to the brain's ability to change and reorganize its structure and function in response to experience, learning, or injury
- is the process of generating new neurons, which occurs throughout life in specific regions of the brain and contributes to learning, memory, and adaptation
Key Terms to Review (55)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a crucial role in transmitting signals between nerve cells and muscle cells. It is essential for muscle contraction and is involved in various functions within the nervous system, including memory and learning processes. Acetylcholine is synthesized in neurons and released at synapses, where it binds to receptors on target cells to propagate signals.
Action potential: An action potential is a rapid, temporary change in the membrane potential of a neuron that allows it to transmit signals along its length. This electrical impulse occurs when a neuron becomes depolarized and then repolarized, resulting in the propagation of the signal to communicate with other neurons or muscles. The mechanism involves specific ion channels and plays a crucial role in the functioning of both neurons and glial cells, facilitating communication within the nervous system.
Afferent neuron: An afferent neuron is a type of nerve cell responsible for transmitting sensory information from the peripheral nervous system to the central nervous system. These neurons play a crucial role in processing sensory stimuli, allowing the body to respond appropriately to various environmental changes. By relaying information such as touch, temperature, and pain, afferent neurons enable the brain to interpret sensations and initiate necessary responses.
Alzheimer's disease: Alzheimer's disease is a progressive neurological disorder that primarily affects memory, thinking, and behavior, leading to severe cognitive decline over time. It is the most common cause of dementia, characterized by the accumulation of amyloid plaques and tau tangles in the brain, which disrupt neuron function and communication. This degeneration of neurons and the role of glial cells in supporting neuronal health are crucial to understanding the pathophysiology of this devastating disorder.
Astrocyte: Astrocytes are star-shaped glial cells in the brain and spinal cord that play a crucial role in supporting neurons. They are involved in maintaining the blood-brain barrier, regulating blood flow, and providing nutrients to neurons, while also helping to repair the nervous system after injury. Their various functions highlight their importance in both homeostasis and neuroprotection within the central nervous system.
Axon: An axon is a long, slender projection of a neuron that conducts electrical impulses away from the cell body toward other neurons or muscles. This structure is crucial for the transmission of signals in the nervous system, as it allows for communication over long distances within the body. The axon can be covered by a myelin sheath, which enhances the speed of impulse conduction through a process called saltatory conduction.
Axon hillock: The axon hillock is the specialized region of a neuron where the cell body transitions into the axon. It plays a critical role in initiating and propagating action potentials.
Axon terminal: The axon terminal is the endpoint of an axon, where signals are transmitted to other neurons or target cells. It plays a crucial role in the communication process of the nervous system, as it is responsible for releasing neurotransmitters into the synaptic cleft, facilitating the transfer of information between neurons. These terminals contain synaptic vesicles filled with neurotransmitters, which are key for synaptic transmission and overall neural signaling.
Axon terminals: Axon terminals are the distal endings of an axon where neurotransmitters are released. They play a crucial role in transmitting signals to other neurons or effector cells across synapses.
Blood-brain barrier: The blood-brain barrier (BBB) is a selective permeability barrier that separates the circulating blood from the brain and central nervous system (CNS), serving to protect the brain from potentially harmful substances while allowing essential nutrients to pass through. This unique feature is critical for maintaining the brain's stable environment and is formed by endothelial cells that are tightly packed together, along with supporting glial cells, particularly astrocytes. The BBB plays a key role in the function and health of neurons, as well as influencing various nervous system disorders.
Dendrite: Dendrites are branched projections of a neuron that receive electrical signals from other neurons. These structures play a crucial role in the communication between neurons, as they act as the primary sites for synaptic transmission, collecting information and transmitting it to the neuron's cell body for processing.
Dopamine: Dopamine is a neurotransmitter that plays several important roles in the brain and body, including the regulation of mood, motivation, reward, and motor control. This chemical messenger is crucial for communication between neurons and is involved in both the central and peripheral nervous systems, influencing behavior and physical functions.
Dorsal Root Ganglion Neuron: A dorsal root ganglion neuron is a type of sensory neuron located in the dorsal root ganglia of the spinal cord, responsible for transmitting sensory information from the peripheral nervous system to the central nervous system. These neurons play a crucial role in processing sensory stimuli such as touch, pain, and temperature, by relaying signals from sensory receptors to the spinal cord.
Efferent neuron: An efferent neuron is a type of nerve cell that carries signals away from the central nervous system to muscles or glands, initiating a response in the body. These neurons play a crucial role in motor control, allowing the brain and spinal cord to communicate with the peripheral body parts to execute movement or secretions. Efferent neurons are essential for the function of the nervous system, facilitating the body's ability to react to stimuli.
Ependymal: Ependymal cells are a type of glial cell that lines the ventricles in the brain and the central canal of the spinal cord. They play a crucial role in the production and circulation of cerebrospinal fluid (CSF).
Ependymal cell: Ependymal cells are specialized glial cells that line the ventricles of the brain and the central canal of the spinal cord. They play a crucial role in the production and circulation of cerebrospinal fluid (CSF), which cushions and protects the brain and spinal cord while also maintaining homeostasis in the central nervous system.
Glia: Glia, also known as glial cells, are non-neuronal cells in the nervous system that provide support and protection for neurons. They play crucial roles in maintaining homeostasis, forming myelin, and participating in signal transmission.
Glial cell: Glial cells, also known as neuroglia, are non-neuronal cells in the nervous system that support and protect neurons. They play critical roles in maintaining homeostasis, forming myelin, and providing support and protection for neurons, which are the primary signaling cells of the nervous system.
Glutamate: Glutamate is an amino acid that serves as the primary excitatory neurotransmitter in the brain, playing a crucial role in synaptic transmission and plasticity. It is vital for processes such as learning and memory, influencing neuronal communication and overall brain function.
IL-1: Interleukin-1 (IL-1) is a pro-inflammatory cytokine that plays a crucial role in the immune response and is produced mainly by activated macrophages. This cytokine is essential for initiating and regulating inflammation, influencing the behavior of various immune cells, and stimulating the production of other cytokines, thereby impacting neuronal function and glial cell activity. IL-1 is a key player in neuroinflammation, which can affect neuronal health and contribute to various neurological disorders.
Interneuron: An interneuron is a type of neuron that acts as a connector within the central nervous system, facilitating communication between sensory and motor neurons. These neurons play a crucial role in reflexes and neural processing by integrating information from multiple sources before transmitting signals to other neurons. Interneurons can be excitatory or inhibitory, influencing the overall output of neural circuits.
Ion channels: Ion channels are protein structures embedded in cell membranes that allow specific ions to pass in and out of the cell. These channels play a crucial role in regulating various cellular processes, including the generation of electrical signals in neurons, maintaining ion gradients across membranes, and contributing to homeostasis. Their selective permeability to ions such as sodium, potassium, calcium, and chloride is essential for numerous physiological functions.
Microglia: Microglia are specialized glial cells in the central nervous system that act as the primary immune defense. They detect and respond to damage or infection by clearing debris and dead neurons.
Microglia: Microglia are the primary immune cells of the central nervous system (CNS) and play a crucial role in maintaining homeostasis, responding to injury, and protecting the brain from pathogens. They are specialized glial cells that act as the first line of defense in the CNS, constantly surveying the environment for signs of damage or infection. These cells also participate in neurodevelopmental processes and modulate neuronal activity, making them essential for both brain health and disease.
Multiple sclerosis: Multiple sclerosis (MS) is a chronic autoimmune disease that affects the central nervous system, where the immune system mistakenly attacks the protective myelin sheath covering nerve fibers. This damage disrupts communication between the brain and the rest of the body, leading to a variety of neurological symptoms and impairments. The role of neurons and glial cells is crucial in understanding how MS affects nerve signaling, while immune responses and antibody production are key to its pathogenesis and progression.
Multipolar neuron: A multipolar neuron is a type of nerve cell characterized by having multiple dendrites and a single axon, allowing for the integration of a large amount of information from various sources. This structure makes multipolar neurons particularly effective in processing and transmitting signals within the nervous system, especially in complex functions such as motor control and cognition.
Myelin: Myelin is a fatty substance that forms an insulating sheath around the axons of many neurons. It increases the speed at which electrical impulses propagate along the nerve cells.
Myelin sheath: The myelin sheath is a protective layer of fatty material that surrounds the axons of neurons, enhancing the speed and efficiency of electrical signal transmission. This sheath is crucial for the proper functioning of the nervous system, as it allows for quicker communication between nerve cells by insulating axons and facilitating saltatory conduction, where action potentials jump between nodes of Ranvier.
Neurogenesis: Neurogenesis is the process by which new neurons are generated in the brain, primarily occurring during development but also continuing into adulthood. This vital process plays a key role in brain plasticity, learning, memory, and overall brain health. Neurogenesis highlights the dynamic nature of the nervous system, showing that it is not a fixed structure but can adapt and change based on experiences and environmental factors.
Neuromuscular junction: The neuromuscular junction is a specialized synapse where a motor neuron communicates with a muscle fiber, facilitating the contraction of muscles. This junction is critical for voluntary movement, as it transmits signals from the nervous system to muscle tissues, allowing for coordination and locomotion. Understanding its function involves exploring how neurons transmit signals, the role of various cell types, and the intricate relationship between the nervous and muscular systems.
Neuron: A neuron is a specialized cell that transmits nerve impulses throughout the nervous system, serving as the fundamental unit of communication in the brain and body. Neurons are critical for processing and transmitting information, playing key roles in reflexes, sensation, and cognitive functions. They communicate with each other via synapses, using neurotransmitters to relay signals across gaps between cells.
Neuroplasticity: Neuroplasticity is the ability of the nervous system to adapt and reorganize itself by forming new neural connections throughout life. This process is crucial for learning, memory, and recovery from injuries, showing how the brain can change in response to experience and environmental factors. It highlights the dynamic nature of neurons and glial cells, which play essential roles in supporting these adaptations.
Neurotransmitter: A neurotransmitter is a chemical messenger that transmits signals across synapses from one neuron to another, playing a crucial role in the communication between nerve cells. These molecules are released from the axon terminals of a neuron and bind to specific receptors on the target neuron, influencing various physiological processes and behaviors. The precise action of neurotransmitters helps modulate everything from muscle contraction to mood regulation.
Neurotransmitter receptors: Neurotransmitter receptors are specialized proteins located on the surface of neurons that bind to neurotransmitters, facilitating communication between nerve cells. These receptors play a crucial role in how signals are transmitted in the nervous system, impacting various physiological processes and behaviors by determining the response of a neuron to the presence of specific neurotransmitters.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals across synapses from one neuron to another. They play a crucial role in regulating various bodily functions and processes, including mood, sleep, and cognition.
NMDA receptor: The NMDA receptor is a specialized type of glutamate receptor in the brain that plays a crucial role in synaptic plasticity and memory function. It is unique because it requires both ligand binding and membrane depolarization to activate, which makes it important for learning processes and the strengthening of synapses.
Nodes of Ranvier: Nodes of Ranvier are small gaps in the myelin sheath of a neuron where the axon membrane is exposed, playing a critical role in the conduction of electrical signals along the nerve fibers. These nodes allow for saltatory conduction, which significantly speeds up the transmission of action potentials by enabling impulses to jump from one node to the next. This unique feature is essential for efficient communication within the nervous system.
Oligodendrocyte: An oligodendrocyte is a type of glial cell in the central nervous system that provides support and insulation to axons by forming myelin sheaths. These specialized cells play a crucial role in the conduction of electrical signals in neurons, enhancing the speed and efficiency of neural communication. Oligodendrocytes are essential for maintaining the health and function of neurons, contributing to processes such as signal transmission and neural repair.
Oligodendrocytes: Oligodendrocytes are a type of glial cell found in the central nervous system. They produce myelin, which insulates axons to facilitate rapid transmission of electrical signals.
Purkinje cell: Purkinje cells are large, multipolar neurons located in the cerebellar cortex that play a critical role in motor control and coordination. They are characterized by their extensive dendritic arborization and their unique ability to integrate input from various sources, making them vital for the fine-tuning of movements. Their output influences a variety of functions related to balance and motor learning.
Pyramidal cell: A pyramidal cell is a type of excitatory neuron characterized by its pyramid-shaped cell body and long apical dendrite, primarily found in the cerebral cortex and hippocampus. These cells play a crucial role in the processing and transmission of information within the brain, contributing to various cognitive functions such as learning and memory.
Radial glia: Radial glia are specialized glial cells that serve as scaffolding for neuronal migration during brain development. They also have stem cell properties, giving rise to neurons and other glial cells.
Resting membrane potential: Resting membrane potential is the electrical charge difference across the plasma membrane of a neuron or other excitable cell when it is not actively transmitting signals. This potential is primarily determined by the distribution of ions, particularly sodium (Na+) and potassium (K+), across the membrane, which establishes a stable environment necessary for cellular functions like communication.
Saltatory conduction: Saltatory conduction is a process by which nerve impulses jump from one node of Ranvier to another along myelinated axons, significantly increasing the speed of signal transmission. This mechanism allows for rapid communication between neurons and is crucial for efficient nervous system functioning, connecting to the structure of nerve cells and their supporting cells.
Santiago Ramón y Cajal: Santiago Ramón y Cajal was a Spanish neuroscientist and pathologist, recognized as the father of modern neuroscience for his pioneering work on the structure of the nervous system. His groundbreaking studies utilized innovative staining techniques to reveal the complex structure of neurons and their connections, significantly enhancing the understanding of how the brain functions in relation to neurons and glial cells.
Satellite glia: Satellite glia are a type of glial cell found in the peripheral nervous system. They surround neuron cell bodies within ganglia, providing support and maintaining the microenvironment.
Schwann cell: A Schwann cell is a type of glial cell that forms the myelin sheath around the axons of peripheral neurons, crucial for efficient signal transmission in the nervous system. These cells not only provide insulation to the axons, enhancing the speed of nerve impulses, but they also play a role in the regeneration of damaged nerves, making them essential for proper neuronal function and repair.
Serotonin: Serotonin is a neurotransmitter that plays a crucial role in regulating mood, emotions, and various bodily functions such as sleep and appetite. It is primarily found in the brain, intestines, and blood platelets, acting as a chemical messenger between neurons. Its significance extends to both normal neurological functioning and the development of various nervous system disorders.
Soma: Soma refers to the cell body of a neuron, which contains the nucleus and organelles essential for the cell's metabolic activities. It plays a critical role in integrating signals received from dendrites and generating action potentials that are transmitted along the axon. The soma is crucial for maintaining the overall health and function of the neuron, as it houses key components necessary for protein synthesis and cellular maintenance.
Spinal motor neuron: A spinal motor neuron is a type of neuron located in the spinal cord that is responsible for transmitting signals from the central nervous system to skeletal muscles, facilitating voluntary movements. These neurons play a critical role in the motor pathways that connect the brain to muscles, ensuring coordinated and controlled muscle contractions necessary for movement and posture.
Synapse: A synapse is the junction between two neurons, where communication occurs through the release and reception of neurotransmitters. This crucial connection enables the transmission of electrical signals and the integration of information within the nervous system. Synapses can be either excitatory or inhibitory, influencing whether the receiving neuron will generate an action potential.
Synapses: Synapses are specialized junctions where neurons communicate with each other or with effector cells. They facilitate the transmission of electrical or chemical signals between cells.
Synaptic transmission: Synaptic transmission is the process by which neurons communicate with one another through specialized junctions called synapses. This process involves the release of neurotransmitters from the presynaptic neuron into the synaptic cleft, where they bind to receptors on the postsynaptic neuron, leading to a response that can either excite or inhibit neuronal activity. Understanding synaptic transmission is crucial for grasping how information is processed and relayed in the nervous system.
Synaptic Vesicle: A synaptic vesicle is a small, membrane-bound sac located in the presynaptic terminal of a neuron that stores neurotransmitters, which are chemical messengers used to transmit signals across a synapse. When an action potential reaches the presynaptic terminal, these vesicles fuse with the plasma membrane and release their contents into the synaptic cleft, enabling communication between neurons and influencing various neural processes.
TNF-α: TNF-α, or Tumor Necrosis Factor-alpha, is a cytokine produced primarily by activated macrophages that plays a crucial role in the inflammatory response and immune system regulation. It acts as a signaling molecule to promote inflammation, recruit immune cells, and induce apoptosis in certain cells. Its functions connect directly to neuronal health and the balance of the immune system, influencing both neuronal signaling and immune disruptions.