Neurons are the building blocks of our nervous system, enabling communication within our brain and body. These specialized cells have distinct parts like dendrites and axons, working together to transmit electrical and chemical signals that control our thoughts and actions.
Our nervous system is a complex network of neurons organized into the central and peripheral nervous systems. It's incredibly adaptable, with the ability to form new connections throughout our lives. This neuroplasticity allows us to learn, grow, and recover from injuries.
Structure and Function of Neurons
Components of neurons
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- Cell body (soma)
- Contains nucleus and other organelles maintains neuron's life processes
- Dendrites
- Branched extensions of neuron receive signals from other neurons
- Axon
- Long thin fiber extends from cell body conducts electrical impulses away from cell body
- Axon terminals
- Branched endings of axon contain synaptic vesicles that store neurotransmitters (dopamine, serotonin)
- Myelin sheath
- Insulating layer surrounding axon formed by Schwann cells in PNS and oligodendrocytes in CNS speeds up conduction of electrical impulses along axon
Process of neural communication
- Resting potential
- Electrical charge difference across neuron's membrane when not actively transmitting signal typically around -70 mV
- Action potential
- Brief reversal of electrical charge across neuron's membrane occurs when neuron stimulated and reaches threshold potential propagates along axon as electrical impulse
- Synaptic transmission
- Process by which signal transmitted from one neuron to another at synapse
- Steps in synaptic transmission:
- Action potential reaches axon terminal
- Voltage-gated calcium channels open allowing calcium ions to enter axon terminal
- Calcium influx triggers release of neurotransmitters from synaptic vesicles into synaptic cleft
- Neurotransmitters bind to neurotransmitter receptors on postsynaptic neuron's membrane
- Binding of neurotransmitters causes postsynaptic neuron to either depolarize (EPSP) or hyperpolarize (IPSP)
- Neurotransmitter reuptake and degradation
- Neurotransmitters removed from synaptic cleft by reuptake into presynaptic neuron or degradation by enzymes in synaptic cleft ensures postsynaptic neuron not continuously stimulated
Psychoactive Substances and Neurotransmitter Systems
Psychoactive substances and neurotransmitters
- Agonists
- Substances bind to and activate neurotransmitter receptors mimic effects of endogenous neurotransmitter (nicotine, morphine)
- Antagonists
- Substances bind to neurotransmitter receptors but do not activate them block effects of endogenous neurotransmitter (naloxone, flumazenil)
- Reuptake inhibitors
- Substances block reuptake of neurotransmitters from synaptic cleft increase duration and intensity of neurotransmitter action (SSRIs like fluoxetine, TCAs like amitriptyline)
- Neurotransmitter synthesis and degradation modulators
- Substances affect production or breakdown of neurotransmitters (levodopa precursor to dopamine used in Parkinson's disease treatment, MAOIs prevent breakdown of monoamine neurotransmitters like serotonin and norepinephrine)
Organization of the Nervous System
Major divisions
- Central nervous system (CNS)
- Consists of the brain and spinal cord, processes and integrates information
- Peripheral nervous system (PNS)
- Network of nerves that connects the CNS to the rest of the body, transmits signals between the CNS and organs, muscles, and glands
Neuroplasticity
- The brain's ability to reorganize itself by forming new neural connections throughout life
- Allows the nervous system to adapt to changes in the environment, learn new information, and recover from brain injuries
Key Terms to Review (36)
Neurotransmitters: Neurotransmitters are chemical messengers that facilitate communication between neurons in the nervous system. They are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, triggering a response that can either excite or inhibit the target cell. Neurotransmitters play a crucial role in various psychological processes and behaviors, including cognition, emotion, and motor function.
Serotonin: Serotonin is a neurotransmitter that plays a crucial role in regulating various physiological and psychological processes in the human body. It is often referred to as the 'feel-good' chemical due to its association with mood, sleep, appetite, and other important functions.
Dopamine: Dopamine is a neurotransmitter that plays a crucial role in various physiological and psychological processes within the human body. It is often referred to as the 'feel-good' chemical due to its association with pleasure, reward, and motivation. Dopamine is integral to the understanding of contemporary psychology, the functioning of the nervous system, substance use and abuse, sexual behavior and gender identity, personality, mood disorders, and childhood disorders.
Neuron: A neuron is the fundamental unit of the nervous system, responsible for the transmission of electrical signals throughout the body. Neurons are specialized cells that are capable of receiving, processing, and transmitting information, enabling the coordination of various bodily functions and the integration of sensory input with motor output.
Glial Cells: Glial cells are non-neuronal cells that provide support and protection for the neurons in the nervous system. They are essential for the proper functioning and maintenance of the brain and spinal cord.
Axon: An axon is a long, slender projection of a neuron that transmits electrical signals away from the neuron's cell body to other cells. It is a crucial component of the nervous system, responsible for the rapid communication of information throughout the body.
Synapse: A synapse is the specialized junction where a nerve impulse is transmitted from one neuron to another, or from a neuron to an effector cell, such as a muscle or gland. It is the critical site of communication between neurons in the nervous system.
Dendrite: A dendrite is a branched projection of a neuron that receives signals from other neurons and conducts them toward the cell body. Dendrites are a critical component of the nervous system, as they facilitate the communication and integration of information within the brain and throughout the body.
Oligodendrocytes: Oligodendrocytes are a type of glial cell found in the central nervous system (CNS) that are responsible for the production and maintenance of the myelin sheath, which insulates and supports the axons of neurons. They play a crucial role in the efficient transmission of electrical signals within the CNS.
Astrocytes: Astrocytes are a type of glial cell, which are non-neuronal cells in the central nervous system (CNS). They have a star-like shape and perform a variety of crucial functions to support and protect neurons, the primary functional cells of the brain and spinal cord.
Myelin Sheath: The myelin sheath is a protective fatty layer that surrounds the axons of certain nerve cells, known as myelinated neurons. It acts as an insulator, enhancing the speed and efficiency of electrical impulse transmission along the neuron.
Action Potential: An action potential is a rapid, transient electrical signal that travels along the membrane of a neuron or other excitable cell. It is the fundamental unit of communication in the nervous system, allowing neurons to transmit information and coordinate various physiological processes throughout the body.
Synaptic Transmission: Synaptic transmission is the process by which an electrical or chemical signal is transmitted from one neuron to another across the synapse, the junction between two neurons. This process is fundamental to the communication and functioning of the nervous system.
Voltage-Gated Calcium Channels: Voltage-gated calcium channels are specialized ion channels found in the cell membranes of many cell types, including neurons and muscle cells. These channels open and close in response to changes in the electrical potential across the cell membrane, allowing the controlled influx of calcium ions into the cell, which triggers important physiological processes.
EPSP: EPSP stands for Excitatory Postsynaptic Potential, which is a change in the electrical potential across the postsynaptic membrane of a neuron caused by the binding of excitatory neurotransmitters released from the presynaptic terminal. This depolarization of the postsynaptic membrane brings the neuron closer to the threshold for generating an action potential.
IPSP: IPSP, or Inhibitory Postsynaptic Potential, is a type of synaptic potential that occurs when an inhibitory neurotransmitter is released at a postsynaptic neuron, causing a decrease in the likelihood of that neuron generating an action potential. It is a crucial mechanism in the regulation of neuronal excitability and information processing within the nervous system.
Neurotransmitter Reuptake: Neurotransmitter reuptake is the process by which neurotransmitters are removed from the synaptic cleft and transported back into the presynaptic neuron or surrounding glial cells after they have been released and have interacted with postsynaptic receptors. This process is essential for regulating the concentration of neurotransmitters in the synaptic cleft and maintaining proper neuronal communication.
Agonists: Agonists are substances that bind to and activate specific receptors in the body, mimicking the effects of the natural ligand or neurotransmitter that normally binds to that receptor. They are a key component in the functioning of the nervous system, as they facilitate the transmission of signals between neurons and target cells.
Antagonists: Antagonists are molecules or cells that bind to and block the function of a receptor, inhibiting or counteracting the effects of an agonist. They play a crucial role in the regulation of the nervous system by modulating the activity of neurotransmitters and their receptors.
Reuptake Inhibitors: Reuptake inhibitors are a class of drugs that work by blocking the reabsorption or reuptake of certain neurotransmitters in the brain, leading to an increase in their availability and enhanced signaling between neurons. These inhibitors are commonly used to treat various neurological and psychiatric conditions.
SSRIs: SSRIs, or Selective Serotonin Reuptake Inhibitors, are a class of medications primarily used to treat depression and other mental health disorders. They work by inhibiting the reuptake or reabsorption of the neurotransmitter serotonin in the brain, leading to an increase in serotonin levels and improved mood and emotional regulation.
Tricyclic Antidepressants (TCAs): Tricyclic antidepressants (TCAs) are a class of medications primarily used to treat depression by inhibiting the reuptake of the neurotransmitters serotonin and norepinephrine in the brain. They are called 'tricyclic' due to their three-ring chemical structure.
MAOIs: MAOIs, or Monoamine Oxidase Inhibitors, are a class of medications primarily used to treat depression and certain other mental health conditions. They work by inhibiting the activity of the enzyme monoamine oxidase, which is responsible for breaking down neurotransmitters like serotonin, norepinephrine, and dopamine in the brain. By preventing this breakdown, MAOIs can increase the availability of these important chemicals, leading to improved mood and other therapeutic effects.
Nucleus: The nucleus is the central, membrane-enclosed organelle that contains the genetic material and controls the activities of a eukaryotic cell. It is the command center that directs the cell's functions and coordinates its various processes.
Peripheral Nervous System: The peripheral nervous system (PNS) is the part of the nervous system that is located outside the central nervous system (brain and spinal cord). It is responsible for transmitting information between the central nervous system and the rest of the body, including sensory information from the body to the brain and motor commands from the brain to the muscles.
Neuroplasticity: Neuroplasticity refers to the brain's ability to adapt, change, and reorganize 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.
Motor Neurons: Motor neurons are nerve cells in the central nervous system that transmit signals from the brain and spinal cord to the muscles, enabling voluntary movement and muscle contraction. They are a crucial component in the pathway of motor control and are essential for the execution of physical actions.
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 is crucial for the efficient transmission of electrical signals throughout the body.
Cell Body: The cell body, also known as the soma, is the central part of a neuron that contains the nucleus and is responsible for the neuron's metabolic activities. It is the main component of a neuron, providing the necessary support and resources for the axon and dendrites to function effectively.
Axon Terminals: Axon terminals are the specialized structures located at the end of an axon, the long, thin projection of a neuron that transmits electrical signals to other cells. These terminals are responsible for the release of neurotransmitters, the chemical messengers that enable communication between neurons and their target cells.
Soma: The soma, also known as the cell body, is the central part of a neuron that contains the nucleus and most of the cell's organelles. It is the main body of the neuron, responsible for receiving and integrating signals from other neurons, and generating action potentials that are transmitted through the axon to other cells.
Sensory Neurons: Sensory neurons, also known as afferent neurons, are specialized nerve cells that transmit information from sensory receptors in the body to the central nervous system. They play a crucial role in our ability to perceive and respond to various stimuli, such as touch, temperature, pain, and changes in the internal environment.
Synaptic Vesicles: Synaptic vesicles are small, membrane-enclosed structures found within the presynaptic terminals of neurons. They play a crucial role in the process of neurotransmitter release at chemical synapses, which is a fundamental mechanism of communication in the nervous system.
Central Nervous System: The central nervous system (CNS) is the primary information processing and control center of the body, consisting of the brain and spinal cord. It is responsible for integrating and coordinating the body's physiological processes, sensory inputs, and motor outputs.
Resting Potential: The resting potential is the difference in electrical charge between the inside and outside of a cell when the cell is not actively transmitting an electrical signal. This potential difference is crucial for the functioning of neurons and other excitable cells within the nervous system.
Neurotransmitter Receptors: Neurotransmitter receptors are specialized proteins located on the surface of neurons that bind to specific neurotransmitters, triggering a response within the cell. These receptors play a crucial role in the transmission of signals between neurons, allowing the nervous system to coordinate various physiological and behavioral processes.