3.2 Synaptic transmission and neurotransmitters
3 min read•august 7, 2024
Synaptic transmission is the cornerstone of neural communication. Neurotransmitters, released from synaptic vesicles, cross the to bind with receptors on the postsynaptic membrane, triggering responses in the receiving cell.
The balance of excitatory and inhibitory postsynaptic potentials shapes neural activity. Various neurotransmitters, like , , , and , play crucial roles in regulating diverse physiological functions and behaviors.
Synaptic Structure and Function
Components of a Synapse
Top images from around the web for Components of a Synapse
Communication Between Neurons · Anatomy and Physiology View original
Is this image relevant?
Chemical and Electrical Synapses | Biology for Majors II View original
Is this image relevant?
7.3 – Synapses – Introductory Animal Physiology View original
Is this image relevant?
Communication Between Neurons · Anatomy and Physiology View original
Is this image relevant?
Chemical and Electrical Synapses | Biology for Majors II View original
Is this image relevant?
1 of 3
Top images from around the web for Components of a Synapse
Communication Between Neurons · Anatomy and Physiology View original
Is this image relevant?
Chemical and Electrical Synapses | Biology for Majors II View original
Is this image relevant?
7.3 – Synapses – Introductory Animal Physiology View original
Is this image relevant?
Communication Between Neurons · Anatomy and Physiology View original
Is this image relevant?
Chemical and Electrical Synapses | Biology for Majors II View original
Is this image relevant?
1 of 3
- Synapse enables communication between neurons or between a neuron and another cell type (muscle cell or gland cell)
- Synaptic vesicle stores neurotransmitters in the presynaptic neuron's axon terminal
- Neurotransmitters are chemical messengers released into the synaptic cleft to transmit signals
- Synaptic cleft separates the presynaptic and postsynaptic membranes, providing a space for neurotransmitters to diffuse across
- Typically 20-40 nanometers wide
- Receptor proteins on the postsynaptic membrane bind to specific neurotransmitters, initiating a response in the postsynaptic cell
- Receptors can be ionotropic (directly open ion channels) or metabotropic (activate second messenger systems)
Neurotransmitter Reuptake and Recycling
- Neurotransmitter removes excess neurotransmitters from the synaptic cleft after signal transmission
- Prevents prolonged or excessive stimulation of the postsynaptic cell
- Reuptake is performed by transporter proteins on the presynaptic membrane or by glial cells surrounding the synapse
- Neurotransmitters are recycled and repackaged into synaptic vesicles for future release
- Some medications (SSRIs) target reuptake mechanisms to modulate neurotransmitter levels and treat conditions like or anxiety
Postsynaptic Potentials
Excitatory Postsynaptic Potential (EPSP)
- EPSP occurs when the binding of neurotransmitters to receptors causes the postsynaptic membrane to depolarize
- brings the membrane potential closer to the threshold for generating an
- Multiple EPSPs can summate spatially (from different synapses) or temporally (from repeated stimulation) to reach the threshold
- Spatial summation example: simultaneous activation of several synapses on a single postsynaptic neuron
- Temporal summation example: rapid, repeated stimulation of a single synapse
Inhibitory Postsynaptic Potential (IPSP)
- IPSP occurs when the binding of neurotransmitters to receptors causes the postsynaptic membrane to hyperpolarize
- moves the membrane potential further away from the threshold, making it harder to generate an action potential
- IPSPs can counteract the effects of EPSPs, modulating the overall excitability of the postsynaptic neuron
- Example: simultaneous activation of excitatory and inhibitory synapses on a single postsynaptic neuron
- The balance between EPSPs and IPSPs determines whether the postsynaptic neuron will fire an action potential
Types of Neurotransmitters
Acetylcholine
- Acetylcholine is a neurotransmitter involved in motor control, learning, and memory
- Released by motor neurons to stimulate muscle contraction at the neuromuscular junction
- Example: acetylcholine release at the synapse between a motor neuron and a skeletal muscle fiber
- Also plays a role in the autonomic nervous system, regulating heart rate, digestion, and other involuntary functions
Monoamines: Dopamine and Serotonin
- Dopamine is involved in reward-seeking behavior, motivation, and motor control
- Dysregulation of dopamine is associated with conditions like and addiction
- Example: dopamine release in the mesolimbic pathway during pleasurable experiences or in anticipation of rewards
- Serotonin regulates mood, sleep, appetite, and pain perception
- Imbalances in serotonin levels are linked to depression, anxiety, and other mood disorders
- Example: serotonin release in the raphe nuclei projecting to various brain regions to modulate emotional states
GABA (Gamma-Aminobutyric Acid)
- GABA is the primary inhibitory neurotransmitter in the central nervous system
- Binding of GABA to its receptors leads to the opening of chloride channels, causing hyperpolarization and reducing neuronal excitability
- Example: GABA release by interneurons in the cerebral cortex to regulate the activity of pyramidal neurons
- Medications that enhance GABA signaling (benzodiazepines) are used to treat anxiety, seizures, and insomnia
Key Terms to Review (21)
Acetylcholine: Acetylcholine is a neurotransmitter that plays a critical role in the transmission of signals across synapses in the nervous system, particularly at the neuromuscular junction. It is essential for muscle contraction, acting by binding to receptors on muscle cells and triggering the opening of ion channels, which leads to depolarization and ultimately muscle contraction. Acetylcholine's function extends beyond motor control, as it also influences memory and attention in the central nervous system.
Action Potential: An action potential is a rapid and transient electrical signal that travels along the membrane of a neuron or muscle cell, allowing for the transmission of information and communication between cells. This process involves a series of changes in membrane potential due to the movement of ions across the membrane, which is essential for various physiological processes including muscle contraction and synaptic transmission.
Agonist: An agonist is a substance that binds to a receptor and activates it, leading to a biological response. In the context of synaptic transmission and neurotransmitters, agonists mimic the action of naturally occurring substances, such as neurotransmitters or hormones, by promoting the same physiological effects in target cells. This means that agonists can enhance or facilitate the signaling pathways that are crucial for communication between neurons and other cells in the body.
Antagonist: An antagonist is a substance that binds to a receptor and inhibits or blocks the action of another substance, typically a neurotransmitter. This blocking action can reduce or negate the physiological effects normally produced by the neurotransmitter, playing a critical role in modulating synaptic transmission and influencing various neural pathways. Antagonists are essential for understanding how different neurotransmitters interact with their receptors and can be used therapeutically to treat various conditions.
Chemical Synapse: A chemical synapse is a specialized junction where neurons communicate with each other through the release and reception of neurotransmitters. This process involves the conversion of an electrical signal into a chemical signal, allowing for precise transmission of information between nerve cells. The chemical synapse is essential for various functions in the nervous system, including reflexes, memory, and learning.
Depolarization: Depolarization is a process during which the membrane potential of a cell becomes less negative, moving towards a more positive value. This change in charge across the cell membrane is crucial for the initiation and propagation of action potentials in neurons and muscle cells, including cardiac myocytes. It plays a key role in various physiological functions, such as transmitting signals between neurons and coordinating heartbeats.
Depression: Depression, in the context of synaptic transmission and neurotransmitters, refers to a mental health disorder characterized by persistent feelings of sadness, hopelessness, and a lack of interest or pleasure in daily activities. It is associated with imbalances in neurotransmitters like serotonin, norepinephrine, and dopamine, which play crucial roles in regulating mood and emotional responses. Understanding depression involves recognizing how these neurotransmitter systems interact and affect neural communication within the brain.
Dopamine: Dopamine is a neurotransmitter that plays a key role in the brain's reward system and is involved in regulating mood, motivation, and motor control. It facilitates communication between neurons at synapses and is crucial for processing information and integrating neural signals, affecting how we feel pleasure and reinforcement.
Electrical Synapse: An electrical synapse is a type of junction between neurons that allows for direct electrical communication through gap junctions. In this mechanism, ions and small molecules pass directly from one neuron to another, enabling rapid transmission of signals, which is crucial for synchronizing activity in neural networks. Electrical synapses are particularly important in processes requiring speed and coordination, such as reflexes and certain brain functions.
Exocytosis: Exocytosis is a cellular process where substances are expelled from the cell through the fusion of vesicles with the plasma membrane, releasing their contents into the extracellular space. This mechanism is crucial for various physiological functions, including the secretion of hormones, neurotransmitters, and the transportation of proteins and lipids to the cell membrane, highlighting its importance in cellular communication and nutrient absorption.
GABA: GABA, or gamma-aminobutyric acid, is the primary inhibitory neurotransmitter in the central nervous system. It plays a crucial role in reducing neuronal excitability throughout the nervous system, helping to maintain a balance between excitation and inhibition. This balance is essential for normal brain function, affecting everything from muscle tone to anxiety levels.
GABA Receptors: GABA receptors are protein structures located in the brain and central nervous system that respond to the neurotransmitter gamma-aminobutyric acid (GABA). They play a crucial role in mediating inhibitory neurotransmission, which helps regulate neuronal excitability and maintain balance within neural circuits. This modulation is essential for processes like relaxation, anxiety control, and sleep regulation.
Hyperpolarization: Hyperpolarization is a change in a cell's membrane potential, making it more negative than the resting potential. This process typically occurs when potassium ions leave the cell or chloride ions enter, increasing the negativity inside the cell and moving it further away from the threshold needed to trigger an action potential. Hyperpolarization plays a crucial role in synaptic transmission by influencing the excitability of neurons and the overall signaling in the nervous system.
Immunohistochemistry: Immunohistochemistry is a technique used to detect specific proteins or antigens in tissues using antibodies that bind to those targets, allowing researchers to visualize their distribution and localization within the cells or tissues. This method is essential for understanding cellular functions, especially in the nervous system and in comparative immunological studies across different animal groups.
NMDA receptors: NMDA receptors are a type of glutamate receptor that play a critical role in synaptic transmission and plasticity in the brain. They are unique because they are both ligand-gated and voltage-dependent, which means they require the binding of glutamate and a change in membrane potential to open. This dual requirement allows NMDA receptors to act as coincidence detectors, important for processes like learning and memory.
Parkinson's Disease: Parkinson's disease is a neurodegenerative disorder that primarily affects movement, causing tremors, stiffness, and difficulty with balance and coordination. It is linked to the degeneration of dopamine-producing neurons in the substantia nigra, a critical area in the brain involved in motor control, highlighting the importance of synaptic transmission and neurotransmitter function in maintaining smooth movement.
Patch-clamp technique: The patch-clamp technique is a powerful electrophysiological method used to measure the ionic currents that flow through individual ion channels in cells. This technique provides insights into the properties and behaviors of ion channels, which are crucial for understanding synaptic transmission and neurotransmitter release in neurons. By isolating a small patch of membrane, researchers can study the activity of specific ion channels, allowing for a deeper understanding of how these channels contribute to neuronal signaling.
Presynaptic Terminal: The presynaptic terminal is the specialized structure at the end of a neuron that is responsible for releasing neurotransmitters into the synaptic cleft. It contains synaptic vesicles filled with neurotransmitters, which are essential for communication between neurons. This area plays a critical role in synaptic transmission, influencing how signals are transmitted across neurons and affecting various physiological processes.
Reuptake: Reuptake is the process by which neurotransmitters are reabsorbed by the presynaptic neuron after they have transmitted a signal across a synapse. This mechanism helps to terminate the action of neurotransmitters and resets the synapse for future signaling, ensuring that neuronal communication is regulated and efficient. It plays a crucial role in maintaining neurotransmitter balance and influences various physiological processes, including mood regulation and synaptic plasticity.
Serotonin: Serotonin is a neurotransmitter that plays a crucial role in regulating mood, behavior, and various physiological processes in the body. It is primarily found in the brain, intestines, and blood platelets and is known for its impact on feelings of happiness and well-being. This chemical messenger is essential for synaptic transmission, facilitating communication between neurons, and contributes to neural integration by modulating the flow of information in the nervous system.
Synaptic Cleft: The synaptic cleft is the small gap between the presynaptic neuron and the postsynaptic neuron, playing a crucial role in synaptic transmission. It serves as the site where neurotransmitters are released from the presynaptic neuron into this space, allowing them to bind to receptors on the postsynaptic membrane. This process is essential for communication between neurons and is foundational for motor control and overall nervous system function.