Neurotransmitters: Biology of Synaptic Transmission PDF

Neurotransmitters  Neurotransmitters These are chemical messengers that transmit signals across synapses, which are junctions between neurons. These molecules play a crucial role in communication within the nervous system, allowing neurons to send signals to other ne...

Neurotransmitters  Neurotransmitters These are chemical messengers that transmit signals across synapses, which are junctions between neurons. These molecules play a crucial role in communication within the nervous system, allowing neurons to send signals to other neurons, muscles, or glands.  Acetylcholine Serotonin Dopamine Monoamines Catecholamines Serotonin Norepinephrine Glutamate GABA Amino acids Glycine  Acetylcholine Acetylcholine (ACh) is a neurotransmitter that plays a role in memory, learning, Serotonin attention, arousal especially involuntary/voluntary muscle movement. Dopamine All muscular movement is accomplished by the release of acetylcholine Serotonin Usually found in Motor Neurons, In Basal Ganglia, Neuromuscular junction. Norepinephrine Neuromuscular Junctions: In the PNS, acetylcholine is the neurotransmitter responsible for transmitting signals from motor neurons to muscle cells at the neuromuscular Glutamate junction. GABA Excitatory in nature, But can also be inhibitory (For example, in the basal ganglia, which is involved in motor control, acetylcholine acts in opposition to dopamine, Glycine providing an inhibitory influence)  Acetylcholine Serotonin Dopamine Serotonin Norepinephrine Glutamate GABA Glycine  Acetylcholine Receptors Serotonin Ionotropic – Nicotinic receptors, Excitatory Metabotropic – Muscarinic receptors, Excitatory or inhibitory Dopamine Serotonin Norepinephrine Glutamate GABA Glycine  Acetylcholine Deficiency of Acetylcholine in certain brain regions is linked Serotonin to Alzheimer’s Disease/ Dementia. An excessive amount of Acetylcholine will result to Dopamine the following: Excessive Stimulation of Muscles In the neuromuscular junction, excessive acetylcholine Serotonin release can lead to prolonged stimulation of muscles, potentially resulting in muscle twitching, cramps, or spasms. Norepinephrine Bradycardia (Slow Heart Rate) This is because acetylcholine can inhibit the activity of the sinoatrial (SA) node, which regulates heart rate. Glutamate In the central nervous system, excessive acetylcholine GABA activity can lead to symptoms such as confusion, hallucinations, and seizures. Glycine  Acetylcholine Serotonin Dopamine Used in treatment of: Serotonin Alzheimer’s Disease Norepinephrine Dementia Glutamate GABA Glycine  Acetylcholine Serotonin (5-HT) Serotonin Serotonin is one of the natural body chemicals that controls your mood. Dopamine It works with melatonin to help control when you sleep and wake up, as well as how you feel pain, Norepinephrine wellbeing and sexual desire. Usually found in Pineal Gland, Raphe in Pons, Limbic System. Glutamate Receptors GABA Ionotropic – 5-HT3 , Excitatory Metabotropic – 5-HT1-7 Excitatory or inhibitory Glycine  Acetylcholine Serotonin Lack of serotonin Dopamine It is thought to play a role in depression, anxiety, mania and other health conditions. Most of the serotonin found in your body is in your gut (intestines). Norepinephrine About 90% of serotonin is found in the cells lining your gastrointestinal tract. Glutamate Used in treatment for: GABA Depression Sleep Regulation Glycine  Acetylcholine Dopamine Serotonin Dopamine acts on areas of the brain to give you feelings of pleasure, satisfaction and motivation and Dopamine the reinforcing effects of drugs that people tend to abuse. Usually found in the substantia nigra and Norepinephrine Hypothalamus Receptors Glutamate All metabotropic – D1 - Excitatory D2 - Inhibitory GABA Glycine  Acetylcholine Serotonin Reward and Reinforcement: Dopamine is released in response to pleasurable stimuli, such as food, sex, Dopamine and social interactions. This release of dopamine reinforces the behavior that led to the pleasurable Norepinephrine experience, encouraging the individual to seek similar rewards in the future. Glutamate Motivation: Dopamine is involved in the motivation to pursue goals and engage in rewarding activities. It GABA plays a role in the anticipation of pleasure, prompting individuals to take action to achieve desirable Glycine outcomes.  Acetylcholine Serotonin Addiction: Substance abuse and certain behaviors associated with addiction can significantly impact the Dopamine dopamine system. Drugs of abuse, for example, often lead to a surge in dopamine levels, contributing to the Norepinephrine reinforcing effects of these substances and the development of addictive behaviors. Glutamate Mood and Well-Being: Dopamine also influences mood, and alterations in dopamine levels may be GABA associated with mood disorders. For example, conditions such as depression and bipolar disorder Glycine are thought to involve dysregulation in the dopamine system.  Acetylcholine Serotonin Used in treatment for: Dopamine Schizophrenia Parkinson’s Disease Norepinephrine Glutamate GABA Glycine  Acetylcholine Norepinephrine Serotonin also known as noradrenaline, is a neurotransmitter Dopamine and a hormone that plays a crucial role in the sympathetic nervous system, which is responsible for Norepinephrine the body's "fight or flight" response. It is produced by the adrenal glands and certain neurons in the central nervous system. Glutamate Usually located in the ANS: Sympathetic Nervous GABA System and Brain. Glycine  Acetylcholine Norepinephrine is a key player in the sympathetic Serotonin nervous system. When the body perceives a threat, such as in a "fight or flight" situation, norepinephrine is Dopamine released into the bloodstream. This leads to increased heart rate, elevated blood pressure, and the redirection of blood flow to vital organs, preparing the body to Norepinephrine respond to the perceived danger. Glutamate Receptors: All metabotropic: α1 and β1 – Excitatory GABA : α2 and β2 – Inhibitory Glycine  Acetylcholine Used in treatment for: Serotonin ADHD Dopamine Anxiety Cardiac Failure Norepinephrine Glutamate GABA Glycine  Acetylcholine Serotonin Glutamate Dopamine Glutamate is the most abundant excitatory neurotransmitter in the central nervous system and plays a crucial role in various physiological Norepinephrine processes. It is involved in the transmission of signals between nerve cells (neurons) and is essential for Glutamate normal brain function. Found everywhere in the Central Nervous System. GABA Receptors Glycine All Ionotropic NMDA AMPA Kinate receptor  Acetylcholine Used in treatment for Serotonin Amyotrophic lateral sclerosis (ALS)/Lou Gehrig’s Dopamine Disease - Excites motor, sensory, and cognitive neurons. Norepinephrine Glutamate GABA Glycine  Acetylcholine Serotonin Gamma-Aminobutyric Acid (GABA) Dopamine neurotransmitter that plays a crucial role in the central nervous system. It is the primary inhibitory neurotransmitter in the brain, meaning it reduces the Norepinephrine activity of nerve cells (neurons). Glutamate Found everywhere in the central nervous system. Receptor (all inhibitory) GABA Ionotropic GABAA receptor -> Cl channel Glycine Metabotropic GABAB receptor -> K channels  Acetylcholine Used in Treatment of: Serotonin Anxiety Dopamine It inhibits motor, sensory, and cognitive neurons Norepinephrine Glutamate GABA Glycine  Acetylcholine Glycine Serotonin Glycine serves as an inhibitory neurotransmitter in the Dopamine central nervous system. Norepinephrine Inhibits spinal chord interneurons Receptors: Glutamate Ionotropic Cl- Channels GABA Glycine Biology of Synaptic Transmission Synaptic Structure A. Axodendritic synapses can occur on the smooth surface of a dendrite B. or on dendritic spines C. Axosomatic synapses occur on somatic membrane D. Axoaxonic synapses consist of synapses between two terminal buttons  Presynaptic Neuron Post Synaptic Neuron Key features of Synaptic Transmission Initiation of Action Potential: Stimulation triggers the opening of voltage-gated sodium channels, allowing sodium ions (Na⁺) to enter the neuron. This causes depolarization, reversing the membrane potential to become more positive inside the neuron. The depolarization wave (action potential) propagates along the axon toward the axon terminals (terminal buttons). Arrival at the Terminal Buttons: When the action potential reaches the axon terminals, it causes voltage-gated calcium (Ca²⁺) channels to open. Calcium ions flow into the presynaptic terminal due to their higher concentration outside the cell. Role of Calcium Ions: The influx of calcium ions binds to synaptotagmin, a protein on synaptic vesicles. This triggers the vesicles to move toward and dock with the presynaptic membrane. The vesicles fuse with the membrane through the action of SNARE proteins (e.g., synaptobrevin, syntaxin, and SNAP-25). Neurotransmitter Release: The fusion of synaptic vesicles with the presynaptic membrane releases neurotransmitters into the synaptic cleft via exocytosis. These neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic membrane, initiating a response. Cross section of Synapse The photograph from an electron microscope shows a cross section of a synapse. The omega-shaped figures are synaptic vesicles fusing with the presynaptic membranes of terminal buttons that form synapses with frog muscle.  Once neurotransmitters are released, they bind to ligand-gated ion channels on the postsynaptic membrane. Binding of the neurotransmitter opens these channels, allowing sodium ions to flow into the postsynaptic cell. The influx of sodium ions causes depolarization, generating an excitatory postsynaptic potential (EPSP). If the combined EPSPs are strong enough to reach the threshold, an action potential is triggered in the postsynaptic neuron. Note that receptors can be Ionotropic and Metabotropic Recycling of the Synaptic vesicles. Synaptic vesicles are being recycled through"Kiss and Run" Process: The vesicle fuses with the presynaptic membrane temporarily. Neurotransmitter is released into the synaptic cleft. The vesicle reseals and leaves the docking site. It gets refilled with neurotransmitter. The vesicle mixes with other vesicles in the terminal button. Not All Neurotransmitters Bind to Receptors: Not all neurotransmitter molecules released into the synaptic cleft will bind to ligand-gated ion channels (receptors). Fate of Neurotransmitters: Diffusion: Some neurotransmitters diffuse out of the synaptic cleft and are lost. Enzymatic Breakdown: Some neurotransmitters are degraded by enzymes in the synaptic cleft (e.g., acetylcholine is broken down by acetylcholinesterase). Reuptake: Most neurotransmitters are reabsorbed into the presynaptic neuron via transport proteins in a process called reuptake, where they are often recycled and reused. Recycling: After reuptake, neurotransmitters can be stored again in synaptic vesicles or broken down for components.