12.2 Nervous Tissue
4 min read•june 18, 2024
Neurons and neuroglia are the building blocks of the nervous system. Neurons transmit electrical signals, while support and protect them. Together, they form a complex network that enables our bodies to sense, think, and respond to stimuli.
Understanding the structure and function of neurons and neuroglia is crucial for grasping how the nervous system works. From the specialized parts of neurons to the diverse roles of glial cells, these components work in harmony to maintain brain health and function.
Neurons and Neuroglia
Structure and components of neurons
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- Cell body () contains the nucleus and organelles such as (rough endoplasmic reticulum) that synthesize proteins needed for function
- Dendrites are branching extensions covered in that receive signals from other neurons and transmit them towards the cell body
- is a long, thin projection that transmits electrical signals away from the cell body to other neurons
- is the where action potentials are generated (trigger zone)
- are the end of the axon that forms synapses with other neurons to release
- is an insulating layer around the axon formed by (PNS) or oligodendrocytes (CNS) that increases the speed of signal transmission
- Nodes of Ranvier are gaps in the that allow for , enabling faster signal propagation along the axon
Types of neurons by polarity and function
- Unipolar neurons have a single process extending from the cell body and are primarily sensory neurons in the ()
- Bipolar neurons have two processes extending from the cell body and are specialized sensory neurons (retinal cells, olfactory neurons)
- Multipolar neurons are the most common type in the nervous system with multiple dendrites and a single axon, including motor neurons and interneurons
- Sensory (afferent) neurons transmit sensory information from receptors (touch, pain) to the for processing
- Motor (efferent) neurons transmit signals from the central nervous system to effectors (muscles, glands) to initiate a response
- Interneurons connect sensory and motor neurons within the central nervous system to process, integrate, and modulate information
Roles of glial cells in nervous systems
- Astrocytes (CNS) provide structural support, maintain the , and regulate neurotransmitter levels and ion concentrations in the
- Oligodendrocytes (CNS) form the myelin sheath around axons in the central nervous system to facilitate rapid signal transmission
- (CNS) are the immune cells of the central nervous system that phagocytose debris and pathogens to protect neurons
- (CNS) line the ventricles and central canal of the and produce and circulate
- Schwann cells (PNS) form the myelin sheath around axons in the peripheral nervous system to facilitate rapid signal transmission
- (PNS) surround and support neuron cell bodies in ganglia to maintain the local environment
- Glial cells play a crucial role in supporting by regulating the extracellular environment and promoting synaptic remodeling
Neuroglia in CNS vs PNS
- Central Nervous System (CNS)
- Astrocytes provide structural support, maintain the blood-brain barrier, and regulate neurotransmitters and ions
- Oligodendrocytes form the myelin sheath around axons
- are the immune cells that phagocytose debris and pathogens
- Ependymal cells line the ventricles and central canal and produce cerebrospinal fluid
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- Schwann cells form the myelin sheath around axons
- Satellite cells surround and support neuron cell bodies in ganglia
- Similarities between CNS and PNS neuroglia include cells that form myelin sheath (oligodendrocytes, Schwann cells) and cells that provide support and protection to neurons (astrocytes, satellite cells)
- Differences include the presence of microglia and ependymal cells in the CNS, which are not found in the PNS, and satellite cells in the PNS, which are not present in the CNS
Neuronal Communication
- Neurons communicate through chemical and electrical synapses, with chemical synapses being more common
- Synapses are specialized junctions where neurons transmit signals to target cells (neurons, muscle cells, or gland cells)
- Neurotransmitters are chemical messengers released from presynaptic neurons that bind to receptors on postsynaptic cells
- The of a neuron is the difference in electrical charge between the inside and outside of the cell, which is crucial for signal transmission
- , the formation of new neurons, occurs in specific regions of the adult brain and contributes to learning, memory, and brain repair
Key Terms to Review (73)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a crucial role in the communication between neurons, the activation of muscle fibers, and the regulation of various physiological processes in the body. It is a key player in the functioning of the nervous system, muscle tissues, and the autonomic nervous system.
Acetylcholine (ACh): Acetylcholine is a neurotransmitter in the nervous system that plays a crucial role in stimulating muscle contractions and is involved in various brain functions including memory and learning. In the context of skeletal muscle, it is essential for transmitting nerve signals to muscle cells, leading to muscle movement.
Action Potential: An action potential is a rapid, transient electrical signal that travels along the cell membrane of excitable cells, such as neurons and muscle cells. It is the fundamental unit of communication in the nervous system, enabling the transmission of information between different parts of the body.
Alzheimer's Disease: Alzheimer's disease is a progressive neurodegenerative disorder that primarily affects the brain, leading to cognitive decline, memory loss, and impaired daily functioning. It is the most common form of dementia, characterized by the accumulation of abnormal proteins that disrupt normal brain cell function and communication.
Astrocyte: Astrocytes are star-shaped glial cells in the brain and spinal cord that play roles in supporting neurons, maintaining the blood-brain barrier, and regulating nutrient and ion concentrations. They are integral to the repair and scarring process of the central nervous system (CNS) following traumatic injuries.
Astrocyte: Astrocytes are a type of glial cell found in the central nervous system (CNS) that provide essential support and protection for neurons. They play a critical role in the function and maintenance of the nervous tissue.
Axon: The axon is a long, slender projection of a neuron that transmits electrical signals away from the cell body to other neurons, muscles, or glands. It is a critical component of the nervous system, responsible for the rapid and efficient communication between different parts of the body.
Axon hillock: The axon hillock is a specialized part of the cell body (soma) of a neuron that connects to the axon, where it plays a crucial role in initiating nerve signals. It acts as the decision point for generating action potentials, determining whether or not the neuron will fire.
Axon Hillock: The axon hillock is a specialized region at the base of the neuron's cell body, or soma, where the axon emerges. It is a critical structure that integrates incoming signals from the dendrites and cell body, and generates the action potential that propagates down the axon, transmitting information to other neurons or target cells.
Axon segment: An axon segment is a distinct portion of an axon, the long, slender projection of a neuron that conducts electrical impulses away from the neuron's cell body. Each segment is delimited by nodes of Ranvier, which are gaps in the myelin sheath that facilitate rapid signal transmission.
Axon terminal: The axon terminal, also known as the synaptic knob, is the extremity of an axon that facilitates the transmission of signals to another neuron or effector cell through the synapse. It contains neurotransmitters which are released into the synaptic cleft to propagate nerve impulses.
Axon Terminals: Axon terminals are the specialized ends of an axon, the long projection that extends from the cell body of a neuron. They are responsible for transmitting electrical signals to other cells, such as muscle fibers or other neurons, by releasing neurotransmitters into the synaptic cleft, the space between the axon terminal and the target cell.
Axoplasm: Axoplasm is the cytoplasm within the axon of a neuron, containing various organelles and structural proteins crucial for neuronal function. It is involved in the transport of molecules between the neuron's cell body and its synaptic terminals.
Bipolar Neuron: A bipolar neuron is a type of sensory neuron found in the retina, olfactory system, and some other sensory organs. It has two long processes extending from the cell body - one dendrite and one axon, giving it a distinct bipolar shape.
Blood-Brain Barrier: The blood-brain barrier is a highly selective semipermeable membrane that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). It acts as a gatekeeper, controlling the movement of substances between the bloodstream and the brain to maintain the optimal environment for neuronal function and protection.
Blood-brain barrier (BBB): The blood-brain barrier is a selective permeability barrier that separates the circulating blood from the brain and extracellular fluid in the central nervous system (CNS). It protects the brain from foreign substances in the blood that may injure the brain, regulates transport of nutrients and waste, and maintains a stable environment for the brain.
Central Nervous System: The central nervous system (CNS) is the primary control center of the body, consisting of the brain and spinal cord. It is responsible for integrating and coordinating information from the peripheral nervous system to regulate and maintain bodily functions.
Cerebral cortex: The cerebral cortex is the outer layer of neural tissue of the cerebrum in the brain, playing a key role in memory, attention, perception, cognition, awareness, thought, language, and consciousness. It consists primarily of gray matter and is responsible for processing and integrating sensory information and directing voluntary motor functions.
Cerebral Cortex: The cerebral cortex is the outermost layer of the cerebrum, the largest part of the brain. It is responsible for higher-order cognitive functions, such as information processing, decision-making, and conscious awareness. The cerebral cortex plays a crucial role in the central nervous system and is closely tied to the topics of nervous tissue, central nervous system function, central processing, central control, and mental status examination.
Cerebrospinal Fluid: Cerebrospinal fluid (CSF) is a clear, colorless fluid that circulates within the ventricles of the brain and the central canal of the spinal cord, providing cushioning and protection for the central nervous system. This fluid plays a crucial role in various aspects of nervous system function and development, as well as overall bodily homeostasis.
Cerebrospinal fluid (CSF): Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in the brain and spinal cord that acts as a cushion for the brain's cortex, providing basic mechanical and immunological protection to the central nervous system. It circulates nutrients and chemicals filtered from the blood and removes waste products from the brain.
Choroid plexus: The choroid plexus is a network of cells and blood vessels located in the ventricles of the brain that produces cerebrospinal fluid (CSF). This fluid plays a crucial role in protecting the brain and spinal cord by providing cushioning and maintaining a stable environment.
Circulation and the Central Nervous System: Circulation in the context of the central nervous system (CNS) refers to the blood flow necessary for delivering oxygen and nutrients to neural tissues and removing waste products. Proper circulation is crucial for maintaining the health and functionality of the brain and spinal cord.
Dendrite: Dendrites are the branched extensions of a neuron that receive signals from other neurons and transmit them toward the cell body. They play a crucial role in integrating neural information received from multiple sources.
Dendrite: A dendrite is a branched projection of a neuron that receives signals from other neurons and transmits them to the cell body. Dendrites are a crucial component of the nervous system, playing a vital role in the perception and response to stimuli, the function of nervous tissue, and the generation of action potentials.
Dendritic Spines: Dendritic spines are small, specialized protrusions found on the dendrites of neurons in the central nervous system. They serve as the primary sites for excitatory synaptic connections, playing a crucial role in neuronal communication and information processing.
Dopamine: Dopamine is a neurotransmitter that plays a crucial role in the nervous system, influencing perception, motor function, motivation, reward, and various other physiological processes. It is a key component in understanding the function of nervous tissue, the central nervous system, and the autonomic system, as well as the effects of certain drugs on the body.
Dorsal Root Ganglia: The dorsal root ganglia are collections of nerve cell bodies located just outside the spinal cord, along the dorsal (posterior) roots of the spinal nerves. They play a crucial role in the peripheral nervous system by transmitting sensory information from the body to the central nervous system.
Electrical synapse: An electrical synapse is a type of neural connection where electrical signals are directly passed from one neuron to another through gap junctions, allowing for rapid and synchronized communication among neurons. These junctions facilitate the direct flow of ions and small molecules, enabling faster signal transmission compared to chemical synapses.
Ependymal cell: Ependymal cells are a type of glial cell that lines the ventricles in the brain and the central canal of the spinal cord, playing a crucial role in producing and circulating cerebrospinal fluid (CSF). These cells create a barrier between the CSF and nervous tissue, while also facilitating the movement of CSF.
Ependymal Cells: Ependymal cells are a type of glial cell found lining the ventricles of the brain and the central canal of the spinal cord. They play a crucial role in the circulation and protection of cerebrospinal fluid, which surrounds and cushions the central nervous system.
GABA Receptor: The GABA receptor is a type of receptor found in the nervous system that binds to the neurotransmitter gamma-aminobutyric acid (GABA). These receptors play a crucial role in regulating neuronal excitability and inhibiting the transmission of nerve impulses, thereby maintaining the balance between excitation and inhibition in the brain.
Ganglionic neuron: A ganglionic neuron is a type of nerve cell located in the autonomic ganglia, responsible for transmitting signals from the central nervous system to various targets in the body such as organs, blood vessels, and glands. These neurons play a crucial role in the autonomic nervous system by mediating involuntary functions like heart rate, digestion, and respiratory rate.
Glial Cells: Glial cells are non-neuronal cells in the central nervous system and peripheral nervous system that provide support and protection for neurons. They are essential for the proper functioning and maintenance of the nervous system.
Initial segment: The initial segment is the part of a neuron where the axon originates from the axon hillock and is crucial for initiating nerve signals. It plays a pivotal role in determining whether or not the neuron will fire an action potential based on the summation of inhibitory and excitatory signals received.
Ion Channels: Ion channels are pore-forming proteins embedded within the cell membrane that selectively allow the passage of specific ions, such as sodium, potassium, calcium, and chloride, across the membrane. These channels play a crucial role in regulating the movement of ions, which is essential for various physiological processes, including nerve impulse transmission, muscle contraction, and maintaining the appropriate balance of fluids and electrolytes within the body.
Membrane Potential: Membrane potential refers to the electrical charge difference across a cell's plasma membrane, which is crucial for various cellular processes. It arises due to the uneven distribution of charged ions, primarily sodium (Na+) and potassium (K+), across the membrane.
Microglia: Microglia are specialized cells within the central nervous system (CNS) that act as the primary immune defense mechanism, playing key roles in inflammation and tissue repair. They constantly survey the CNS, identifying and eliminating pathogens and damaged neurons.
Microglia: Microglia are the resident immune cells of the central nervous system (CNS), responsible for immune surveillance, tissue repair, and maintaining homeostasis. As the primary immune effectors in the brain and spinal cord, microglia play a critical role in the context of nervous tissue and its functions.
Multiple Sclerosis: Multiple sclerosis (MS) is a chronic, autoimmune disease that affects the central nervous system (CNS), including the brain, spinal cord, and optic nerves. In MS, the immune system mistakenly attacks the protective myelin sheath surrounding the nerve fibers, leading to disruption of nerve signal transmission and a wide range of neurological symptoms.
Multipolar Neuron: A multipolar neuron is a type of nerve cell that has multiple extensions, or processes, projecting from the cell body. These extensions include one axon and several dendrites, which allow the neuron to receive and transmit signals to and from various parts of the body.
Myelin sheath: The myelin sheath is a fatty layer that surrounds the axons of many nerve cells, serving as electrical insulation and increasing the speed at which nerve impulses are conducted. It is essential for the proper functioning of the nervous system by facilitating rapid signal transmission.
Myelin Sheath: The myelin sheath is a protective fatty layer that surrounds the axons of certain nerve cells, called myelinated neurons. It acts as an insulator, increasing the speed of electrical impulse transmission along the neuron.
Neurofilaments: Neurofilaments are specialized cytoskeletal structures found within the axons and dendrites of neurons. They provide structural support and contribute to the maintenance of the neuron's shape and size, which is essential for efficient signal transmission along the length of the neuron.
Neurogenesis: Neurogenesis is the process by which new neurons are formed in the brain. It is a critical component of nervous tissue development and function, as it allows for the continuous generation of neural cells to replace damaged or aging ones.
Neuron: A neuron is the fundamental unit of the nervous system responsible for receiving, processing, and transmitting information throughout the body. Neurons are the building blocks of neural networks that mediate perception, response, and communication within the nervous tissue.
Neuroplasticity: Neuroplasticity refers to the brain's remarkable ability to adapt, change, and rewire itself in response to experience, learning, and environmental demands. It is a fundamental property of the nervous system that allows for the modification of neural pathways and synaptic connections throughout an individual's lifespan.
Neurotransmitters: Neurotransmitters are chemical messengers that transmit signals between neurons, or nerve cells, in the body. They play a crucial role in the communication and function of the nervous system, including the brain, spinal cord, and peripheral nerves.
Nissl Bodies: Nissl bodies are granular structures found in the cytoplasm of neurons, composed of rough endoplasmic reticulum and free ribosomes. They play a crucial role in protein synthesis and are a key feature of the neuron's structure and function.
NMDA Receptor: The NMDA (N-methyl-D-aspartate) receptor is a type of ionotropic glutamate receptor that plays a crucial role in the functioning of the nervous system. It is a ligand-gated ion channel that allows the influx of calcium and other cations when activated, triggering a cascade of signaling events that are essential for various neurological processes.
Node of Ranvier: The Node of Ranvier is a small gap in the myelin sheath of a nerve fiber, allowing for the rapid conduction of nerve impulses. It plays a critical role in the propagation of action potentials along myelinated neurons.
Node of Ranvier: The node of Ranvier is a gap or interruption in the myelin sheath that surrounds the axon of a neuron. These regularly spaced gaps allow for the rapid transmission of electrical signals along the neuron, a process known as saltatory conduction.
Oligodendrocyte: Oligodendrocytes are a type of glial cell in the central nervous system that forms the myelin sheath around neurons. This sheathing process is crucial for increasing the speed and efficiency of electrical signal transmission along the neuron.
Oligodendrocyte: Oligodendrocytes are a type of glial cell in the central nervous system (CNS) that are responsible for producing the myelin sheath that insulates and enhances the transmission of electrical signals along the axons of neurons. These specialized cells play a crucial role in the nervous tissue's ability to mediate perception and response, as well as the overall function of the nervous system.
Peripheral Nervous System: The peripheral nervous system (PNS) is the part of the nervous system that is outside the central nervous system (CNS), which includes the brain and spinal cord. The PNS is responsible for transmitting information between the CNS and the rest of the body, allowing for communication and coordination of various bodily functions.
Peripheral nervous system (PNS): The Peripheral Nervous System (PNS) is a part of the nervous system that consists of nerves and ganglia outside of the brain and spinal cord. It connects the central nervous system (CNS) to limbs and organs, essentially serving as a communication relay back and forth between the brain and the extremities.
Saltatory conduction: Saltatory conduction is the process by which nerve impulses jump between the nodes of Ranvier along myelinated axons, significantly speeding up electrical transmission. This method allows for faster communication between neurons without increasing the size of the axon.
Saltatory Conduction: Saltatory conduction is the rapid transmission of electrical impulses along the length of a nerve fiber by 'jumping' from one node of Ranvier to the next, rather than propagating continuously. This specialized form of signal transmission is a key feature of the nervous system and plays a crucial role in the function of nervous tissue.
Satellite Cells: Satellite cells are a population of stem cells found in skeletal muscle tissue that play a crucial role in the development, growth, and regeneration of muscle fibers. They are essential for maintaining and repairing muscle tissue throughout an individual's lifetime.
Schwann Cells: Schwann cells are a type of glial cell found in the peripheral nervous system. They are responsible for forming the myelin sheath around the axons of neurons, which enhances the speed of electrical signal transmission. Schwann cells are essential for the proper function and maintenance of the peripheral nervous system.
Serotonin: Serotonin is a neurotransmitter that plays a crucial role in the nervous system, regulating various physiological and psychological processes. It is involved in the perception and response of the nervous tissue, the function of nervous tissue, and the activity of the pineal gland.
Soma: The soma, also known as the cell body, is the central part of a neuron that contains the nucleus and the majority of the cytoplasm. It is the core of the neuron and is responsible for maintaining the cell's essential functions.
Somatic nervous system (SNS): The somatic nervous system is a part of the peripheral nervous system that oversees voluntary movements and the transmission of sensory information to the central nervous system. It consists of nerve fibers that send sensory information to the central nervous system and motor nerve fibers that project to skeletal muscle.
Spinal cord: The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the brainstem down the back and is encased within the vertebral column. It functions as a major conduit for information to travel between the brain and the rest of the body, enabling sensory data to be sent to the brain and motor commands to be dispatched to various body parts.
Spinal Cord: The spinal cord is a long, cylindrical structure that extends from the base of the brain, known as the medulla oblongata, to the lower back region. It serves as the main communication pathway between the brain and the rest of the body, transmitting sensory information to the brain and motor commands from the brain to the muscles. The spinal cord is a crucial component of the central nervous system and plays a vital role in the structural organization of the human body, the function of various tissues, the vertebral column, and the processing of motor and sensory information.
Synapse: A synapse is the specialized junction between two neurons or between a neuron and another cell, where information is transmitted from one to the other through the release of neurotransmitters. It is a critical component in the nervous system's ability to perceive and respond to stimuli, as well as facilitate communication between neurons.
Synaptic cleft: The synaptic cleft is a tiny gap between the axon terminal of one neuron and the dendrite or cell body of another neuron or muscle cell. It facilitates the transfer of chemical signals across neurons or between neurons and muscle cells.
Synaptic Cleft: The synaptic cleft is the small gap or space between the presynaptic terminal of one neuron and the postsynaptic membrane of the next neuron. It is a crucial component in the process of communication between neurons, allowing for the transmission of electrical and chemical signals across the synapse.
Synaptic end bulb: A synaptic end bulb is a swelling at the end of an axon terminal of a neuron, where neurotransmitters are stored before being released into the synaptic cleft. It plays a crucial role in the transmission of nerve impulses from one neuron to another or to an effector cell.
Synaptic Transmission: Synaptic transmission is the process by which an electrical or chemical signal is transmitted from one neuron to another across the synaptic cleft, the small gap between the axon terminal of the presynaptic neuron and the dendrite or cell body of the postsynaptic neuron. This process is essential for the communication and coordination of the nervous system.
The Action Potential: An action potential is a rapid, temporary change in the electrical membrane potential of a neuron or muscle cell, allowing it to transmit a signal. It involves an influx of sodium ions into the cell followed by an efflux of potassium ions, restoring the original electrical condition.
Unipolar Neuron: A unipolar neuron is a type of nerve cell that has a single projection, or process, extending from the cell body. This projection serves as both the axon and the dendrite, carrying signals from the sensory receptors to the central nervous system.
Ventricle: In the context of heart anatomy, a ventricle is one of the two lower chambers of the heart that receive blood from the atria above them and pump it out to the body (left ventricle) or to the lungs (right ventricle). These muscular chambers are crucial for the circulatory system’s function, propelling oxygenated and deoxygenated blood to their respective destinations.