Cell Signalling

<p>As agonists or antagonists depending on whether they enhance or inhibit a response. (C)</p> Signup and view all the answers

<p>They provide a means for cells to communicate effectively. (A)</p> Signup and view all the answers

<p>β-adrenoceptor agonist (B)</p> Signup and view all the answers

<p>Ca2+ Channel blocker (B)</p> Signup and view all the answers

<p>Lignocaine (B)</p> Signup and view all the answers

<p>Contraction of muscle, hormone secretion, and transmitter release (B)</p> Signup and view all the answers

<p>Histamine antagonist (B)</p> Signup and view all the answers

<p>It serves as a muscle relaxant (C)</p> Signup and view all the answers

<p>Treatment of hypertension (B)</p> Signup and view all the answers

<p>Nicorandil (B)</p> Signup and view all the answers

<p>Inhibits cyclic GMP breakdown (C)</p> Signup and view all the answers

<p>Digitoxin (A)</p> Signup and view all the answers

<p>Affinity (A)</p> Signup and view all the answers

<p>Tetrodotoxin (C)</p> Signup and view all the answers

<p>Salbutamol (D)</p> Signup and view all the answers

<p>To sense and respond to external environmental signals (A)</p> Signup and view all the answers

<p>RNA molecules (C)</p> Signup and view all the answers

<p>To display GTPase activity and undergo a conformational change (A)</p> Signup and view all the answers

<p>9 (B)</p> Signup and view all the answers

<p>The initiation of two potential signaling components (B)</p> Signup and view all the answers

<p>Hydrolysis of GTP into GDP (A)</p> Signup and view all the answers

<p>One Gα, one Gβ, and one Gγ subunit (D)</p> Signup and view all the answers

<p>Neuropeptides and small biogenic amines (C)</p> Signup and view all the answers

<p>To phosphorylate tyrosine amino acids (A)</p> Signup and view all the answers

<p>Serine, Threonine, Tyrosine (C)</p> Signup and view all the answers

<p>To catalyze the removal of phosphate groups from proteins (A)</p> Signup and view all the answers

<p>By cyclic-AMP (cAMP) (C)</p> Signup and view all the answers

<p>Release of inorganic phosphate (Pi) (B)</p> Signup and view all the answers

<p>ATP (D)</p> Signup and view all the answers

<p>Action of protein phosphatases (D)</p> Signup and view all the answers

<p>Protein kinases and phosphatases both help in signal amplification. (A)</p> Signup and view all the answers

<p>It binds to a receptor, initiating the signal relay. (A)</p> Signup and view all the answers

<p>They change concentration in response to extracellular hormone binding. (D)</p> Signup and view all the answers

<p>It means that each activated protein can activate more target proteins. (A)</p> Signup and view all the answers

<p>It prevents all cells from responding to the same hormone. (A)</p> Signup and view all the answers

<p>cAMP, cGMP, DAG, IP3, and Ca2+ (D)</p> Signup and view all the answers

<p>They amplify the signal by activating effector proteins. (C)</p> Signup and view all the answers

<p>Inaccurate cell responses and impaired functions (C)</p> Signup and view all the answers

<p>It leads to changes in protein synthesis or enzyme activity. (A)</p> Signup and view all the answers

<p>Inhibits glycogen synthesis and stimulates breakdown. (C)</p> Signup and view all the answers

<p>It phosphorylates glycogen synthase and inactivates it. (B)</p> Signup and view all the answers

<p>Phosphodiesterase (A)</p> Signup and view all the answers

<p>It acts as a co-activator for gene expression regulation. (A)</p> Signup and view all the answers

<p>β1 receptor via Gs protein (C)</p> Signup and view all the answers

<p>Decreased cAMP levels leading to reduced heart rate (B)</p> Signup and view all the answers

<p>Promotion of glycogen breakdown. (A)</p> Signup and view all the answers

<p>Inhibits ion channels to slow heart conduction. (C)</p> Signup and view all the answers

<p>It releases the Gβγ complex. (A)</p> Signup and view all the answers

<p>It synthesizes cAMP from ATP. (A)</p> Signup and view all the answers

<p>cAMP mediates cellular responses primarily through PKA. (B)</p> Signup and view all the answers

<p>Receptor binding of a ligand. (D)</p> Signup and view all the answers

<p>They can couple with specific targets for downstream signaling. (A)</p> Signup and view all the answers

<p>By the dissociation of Gα-GTP from Gβγ. (B)</p> Signup and view all the answers

<p>cAMP. (D)</p> Signup and view all the answers

<p>cAMP. (B)</p> Signup and view all the answers

<p>Phosphorylating specific tyrosine residues (A)</p> Signup and view all the answers

<p>They phosphorylate each other (A)</p> Signup and view all the answers

<p>Inhibition of RNA polymerase (D)</p> Signup and view all the answers

<p>They phosphorylate multiple target proteins (A)</p> Signup and view all the answers

<p>Receptor internalization (C)</p> Signup and view all the answers

<p>ATP (D)</p> Signup and view all the answers

<p>It enhances receptor phosphorylation (B)</p> Signup and view all the answers

<p>It can alter enzyme activity and gene expression (B)</p> Signup and view all the answers

<p>To release Ca2+ from the endoplasmic reticulum (A)</p> Signup and view all the answers

<p>Binding of DAG and Ca2+ (B)</p> Signup and view all the answers

<p>Ca2+ binds non-covalently, causing structural changes in target proteins. (A)</p> Signup and view all the answers

<p>By facilitating the release of Ca2+ from specific receptors in the endoplasmic reticulum. (D)</p> Signup and view all the answers

<p>IP3 hydrolysis to form IP4 (D)</p> Signup and view all the answers

<p>PKC is dependent on DAG and Ca2+ for activation and is found in the membrane. (D)</p> Signup and view all the answers

<p>Activation of certain ion channels in the plasma membrane (B)</p> Signup and view all the answers

<p>IP3 (A), DAG (B)</p> Signup and view all the answers

<p>Prolonged activation of phosphorylated proteins by inhibition of phosphatases (D)</p> Signup and view all the answers

<p>Gα binds to PLC after exchanging GDP for GTP. (A)</p> Signup and view all the answers

<p>By releasing Ca2+ from the endoplasmic reticulum. (C)</p> Signup and view all the answers

<p>It phosphorylates cellular proteins, altering their activity. (B)</p> Signup and view all the answers

<p>It leads to the hydrolysis of PIP2. (C)</p> Signup and view all the answers

<p>Gq protein (C)</p> Signup and view all the answers

<p>Gα dissociates from both β and γ subunits. (D)</p> Signup and view all the answers

<p>IP3 and DAG (B)</p> Signup and view all the answers

<p>A substance that binds and activates the receptor to produce a maximum response (B)</p> Signup and view all the answers

<p>It binds to receptors but never elicits a maximum response (C)</p> Signup and view all the answers

<p>Studies where tissue is isolated and tested outside of a living organism (D)</p> Signup and view all the answers

<p>Measuring drug binding to receptors or physiological responses (D)</p> Signup and view all the answers

<p>Activation of the receptor leading to a cellular response (A)</p> Signup and view all the answers

<p>It occupies the receptor and reduces its activity below baseline levels (C)</p> Signup and view all the answers

<p>Drugs applied to the entire living organism (C)</p> Signup and view all the answers

<p>Both agonist and antagonist compete for the same binding site. (B)</p> Signup and view all the answers

<p>Interaction between distribution, metabolism, and different systems (C)</p> Signup and view all the answers

<p>It blocks the response by inhibiting the agonist at a different site. (D)</p> Signup and view all the answers

<p>It can reverse the effects of the antagonist. (B)</p> Signup and view all the answers

<p>Non-reversible antagonism (C)</p> Signup and view all the answers

<p>To inactivate the agonist through chemical reaction. (A)</p> Signup and view all the answers

<p>Antagonist binding permanently inhibits the agonist's effect. (D)</p> Signup and view all the answers

<p>Tetrodotoxin (D)</p> Signup and view all the answers

<p>Totally disables the receptor, making it unavailable. (C)</p> Signup and view all the answers

<p>L-arginine (D)</p> Signup and view all the answers

<p>iNOS (D)</p> Signup and view all the answers

<p>By activating NOS activity (B)</p> Signup and view all the answers

<p>To induce relaxation of vascular smooth muscle (D)</p> Signup and view all the answers

<p>Thromboxane A2 (TxA2) (C)</p> Signup and view all the answers

<p>Depolarization must exceed the threshold potential (D)</p> Signup and view all the answers

<p>To temporarily allow Na+ influx at the stimulation site (C)</p> Signup and view all the answers

<p>The generation of action potentials (A)</p> Signup and view all the answers

<p>It suffers from rapid signal attenuation with distance (C)</p> Signup and view all the answers

<p>Greater than 1 meter (A)</p> Signup and view all the answers

<p>Na+ channels opening (A)</p> Signup and view all the answers

<p>Ca2+ channel activation (C)</p> Signup and view all the answers

<p>Once generated, all action potentials are the same magnitude. (B)</p> Signup and view all the answers

<p>Inactivated and cannot reopen immediately (B)</p> Signup and view all the answers

<p>Membrane potential becomes more negative (B)</p> Signup and view all the answers

<p>It prevents successive action potentials from occurring too quickly. (A)</p> Signup and view all the answers

<p>They package and transport neurotransmitters to the presynaptic membrane. (B)</p> Signup and view all the answers

<p>Influx of Ca2+ ions (D)</p> Signup and view all the answers

<p>It separates pre and post synaptic cells. (C)</p> Signup and view all the answers

<p>Electrochemical gradient (D)</p> Signup and view all the answers

<p>The effects of drugs on the body (B)</p> Signup and view all the answers

<p>The time course of drug movement in the body (C)</p> Signup and view all the answers

<p>Endocytosis (B)</p> Signup and view all the answers

<p>It decreases drug absorption (C)</p> Signup and view all the answers

<p>Serving as a defense mechanism against foreign substances (C)</p> Signup and view all the answers

<p>The patient's age (A)</p> Signup and view all the answers

<p>Increases drug absorption? (D)</p> Signup and view all the answers

<p>To establish the optimal dosage regimen (D)</p> Signup and view all the answers

<p>Bioavailability (A)</p> Signup and view all the answers

<p>Patient's vitamin levels (B)</p> Signup and view all the answers

<p>They can be significantly higher. (D)</p> Signup and view all the answers

<p>Oedema (D)</p> Signup and view all the answers

<p>Biotransformation (D)</p> Signup and view all the answers

<p>Drugs are transformed into hydrophilic compounds. (B)</p> Signup and view all the answers

<p>Tetracycline (C)</p> Signup and view all the answers

<p>It decreases the amount that reaches systemic circulation. (D)</p> Signup and view all the answers

<p>Binding of ATP to myosin (C)</p> Signup and view all the answers

<p>Moving vesicles along microfilaments (D)</p> Signup and view all the answers

<p>Skeletal muscle (A)</p> Signup and view all the answers

<p>They bind to actin, preventing contraction (D)</p> Signup and view all the answers

<p>Transporting vesicles (B)</p> Signup and view all the answers

<p>The movement of troponin and tropomyosin to their original positions (B)</p> Signup and view all the answers

<p>By Ca2+ binding to calmodulin (C)</p> Signup and view all the answers

<p>They facilitate calcium-induced calcium release from the sarcoplasmic reticulum (B)</p> Signup and view all the answers

<p>To phosphorylate myosin light chains, enabling actin binding (C)</p> Signup and view all the answers

<p>Activation of the contraction cycle through binding to troponin (D)</p> Signup and view all the answers

<p>The actin is released as the myosin head undergoes a shape change. (B)</p> Signup and view all the answers

<p>Calcium ions and troponin (A)</p> Signup and view all the answers

<p>Attached state without ATP (B)</p> Signup and view all the answers

<p>It facilitates a shift of tropomyosin allowing actin-myosin interaction. (A)</p> Signup and view all the answers

<p>The myosin head regains its original shape while losing ADP. (C)</p> Signup and view all the answers

<p>They can modify calcium ion levels affecting contractile strength. (D)</p> Signup and view all the answers

<p>Skeletal muscles are striated and voluntary, while cardiac muscles are striated and involuntary. (B)</p> Signup and view all the answers

<p>To prevent myosin heads from binding to actin when Ca2+ is low. (A)</p> Signup and view all the answers

<p>Increase in intracellular calcium concentration (C)</p> Signup and view all the answers

<p>Smooth muscle (B)</p> Signup and view all the answers

<p>It contracts slowly and does not fatigue easily. (D)</p> Signup and view all the answers

<p>Sarcoplasmic reticulum (D)</p> Signup and view all the answers

<p>Single nucleus per cell (D)</p> Signup and view all the answers

<p>Dihydropyridine receptors (A)</p> Signup and view all the answers

<p>Myosin and actin (D)</p> Signup and view all the answers

<p>Regulate the interaction between actin and myosin (D)</p> Signup and view all the answers

<p>Phosphorylation of myosin light chains (B)</p> Signup and view all the answers

<p>Cardiac muscle fibers contain intercalated discs for synchronized contraction. (D)</p> Signup and view all the answers

<p>It reverses the phosphorylation of myosin light chains, promoting relaxation. (A)</p> Signup and view all the answers

<p>They allow direct electrical and metabolic communication between cells for synchronized contraction. (B)</p> Signup and view all the answers

<p>Calcium binding to calmodulin. (C)</p> Signup and view all the answers

<p>Fast-twitch fibers have a lower myoglobin content than slow-twitch fibers. (D)</p> Signup and view all the answers

<p>To facilitate synchronized contraction through gap junctions. (B)</p> Signup and view all the answers

<p>Causes contraction by phosphorylating myosin light chains. (D)</p> Signup and view all the answers

<p>By activating guanylate cyclase, leading to cGMP production (C)</p> Signup and view all the answers

<p>Providing structural support and protection for neurons (A)</p> Signup and view all the answers

<p>Cardiac muscle exhibits involuntary contractions (B)</p> Signup and view all the answers

<p>It activates myosin light chain kinase in response to calcium (B)</p> Signup and view all the answers

<p>Directly promoting platelet aggregation (C)</p> Signup and view all the answers

<p>Epithelial tissue (B)</p> Signup and view all the answers

<p>It catalyzes the conversion of GTP to cGMP (A)</p> Signup and view all the answers

<p>To mediate relaxation by reducing calcium levels (D)</p> Signup and view all the answers

Cells communicating with each other to control growth, differentiation, and metabolism.

Chemicals released by cells and recognized by receptors on target cells.

Proteins on target cells that bind specific signaling molecules.

Drugs affect cells by acting on specific sites and mechanisms.

The process of relaying signals within a cell to produce a response.

A beta-adrenoceptor agonist used in asthma treatment.

A calcium channel blocker used to treat hypertension.

A sodium channel blocker used as a local anaesthetic.

A drug's ability to bind to a specific receptor.

A drug's ability to modify cell activity.

The range of receptors a drug can bind to.

A drug that inhibits an enzyme involved in blood pressure regulation.

A common ACE inhibitor used to treat hypertension.

A histamine antagonist used to treat ulcers

A chemical involved in stomach acid production that contributes to ulcers.

Calcium ions that play a crucial role in various cellular processes like muscle contraction and hormone release.

A sodium channel blocker that blocks nerve impulses.

A potassium channel opener used to treat vasodilation.

A drug that inhibits an enzyme, increasing cyclic GMP levels for smooth muscle relaxation.

A drug that increases the force of cardiac contraction, used to treat congestive heart failure

An extracellular molecule (signal) that binds to a receptor, initiating a signaling cascade.

A protein that receives the signal from the activated receptor and passes it on to the next component in the pathway.

A protein that produces a secondary messenger, ultimately triggering a cellular response.

A cytoplasmic molecule that triggers metabolic or structural changes in the cell in response to the first messenger binding to the receptor.

A common secondary messenger, cyclic adenosine monophosphate, involved in various cellular processes.

A chain of molecular interactions that transmits signals within the cell, leading to specific responses.

The process of amplifying a signal by activating multiple proteins at each step of the pathway.

Different cells respond differently to the same signal depending on their unique receptor and protein kinase combinations.

An enzyme that adds a phosphate group to a protein. It uses ATP as the phosphate source.

A type of protein kinase that specifically adds a phosphate group to tyrosine amino acids on target proteins.

An enzyme that removes a phosphate group from a protein. It reverses the action of a protein kinase.

The process of adding a phosphate group to a protein by a protein kinase.

The process of removing a phosphate group from a protein by a protein phosphatase.

Protein kinases and phosphatases are themselves regulated by other signaling pathways. For example, some protein kinases are activated by calcium ions bound to calmodulin, and protein kinase A is activated by cyclic AMP.

Protein kinases and phosphatases play a crucial role in signal transduction by controlling the activity of proteins, which can lead to a cellular response.

Phosphorylation is reversible because protein phosphatases can remove phosphate groups added by protein kinases. This allows for dynamic regulation of protein activity.

G-protein coupled receptors (GPCRs) are the largest class of cell surface receptors. They are responsible for sensing and responding to the external environment.

GPCRs are activated by a wide range of extracellular signals, including small biogenic amines (like adrenaline), large protein hormones, neuropeptides, chemokines, and more.

GPCRs are transmembrane proteins with a unique structure: seven transmembrane domains (7-TM), a variable ligand-binding region, and cytoplasmic loops.

G-proteins are composed of three subunits: α, β, and γ. In their inactive state, they bind GDP, but upon activation, they exchange GDP for GTP.

When a G-protein is activated, it separates into two components: α and βγ. Both can then interact with different targets, triggering downstream signaling events.

GPCR activation triggers a cascade: Ligand binds, G-protein is activated, α-subunit dissociates, activating membrane enzyme or ion channel.

The activation of the G-protein is terminated by the hydrolysis of GTP back to GDP, causing the α-subunit to re-associate with βγ.

GPCRs are a highly important class of drug targets. Over 20% of the top 200 best-selling prescription drugs interact with GPCRs.

An enzyme that is activated by cAMP and phosphorylates other proteins, leading to various cellular responses.

A specific DNA sequence that is recognized by the CREB protein, allowing for the regulation of gene expression.

A transcription factor that binds to the cAMP responsive element (CRE) in DNA, regulating gene expression.

cAMP signaling is often activated by hormones that bind to G-protein coupled receptors (GPCRs), ultimately leading to the production of cAMP by adenylate cyclase.

cAMP signaling can either strengthen or weaken heart contraction depending on the receptor involved. β1 receptors linked to Gs protein increase cAMP, leading to stronger contraction, while acetylcholine receptors linked to Gi protein decrease cAMP, resulting in weaker contraction.

Adrenaline stimulates glycogen breakdown and inhibits glycogen synthesis by activating cAMP signaling, leading to increased glucose availability in muscle cells.

A type of cell surface receptor that activates G proteins, which are involved in signal transduction pathways. GPCRs are characterized by seven transmembrane domains and a variable ligand-binding region.

A protein complex involved in signal transduction pathways that binds GDP in its inactive state and GTP in its active state. They consist of three subunits: α, β, and γ.

When a ligand binds to a GPCR, it undergoes a conformational change, activating the G protein. This causes the α subunit to release GDP and bind GTP, becoming active.

The activated G protein (specifically the α subunit) separates from the βγ complex and can then bind to and activate target proteins, such as adenylate cyclase.

A membrane-associated enzyme that converts ATP to cAMP, a secondary messenger involved in various cellular processes. It is activated by the activated α subunit of certain G proteins (Gs) and inhibited by others (Gi).

cAMP signaling eventually ends through the breakdown of cAMP by phosphodiesterase. The α subunit also inactivates by hydrolyzing GTP back to GDP, leading to the reassociation with βγ complex, returning the G protein to its inactive state.

IP3 (inositol triphosphate) increases the concentration of calcium ions (Ca2+) inside the cell by releasing them from the endoplasmic reticulum (ER).

The concentration of calcium ions inside a cell is significantly lower (about 0.1 µM) compared to the concentration outside (about 2 mM).

Calcium binding to proteins causes structural changes, directly activating enzymes, ion channels, and cytoskeletal proteins.

Calmodulin (CaM) is a calcium-binding protein that acts as a messenger, activating protein kinases and influencing cellular processes.

Diacylglycerol (DAG) and calcium ions together activate protein kinase C (PKC), which then phosphorylates proteins on serine and threonine residues.

Protein kinase C (PKC) is important for cell growth and division. It is activated by DAG and calcium, and translocates to the cell membrane.

Okadaic acid, found in some shellfish, inhibits serine/threonine phosphatases, leading to prolonged phosphorylation of proteins and disrupting cellular processes.

Shellfish poisoning is caused by okadaic acid, which disrupts cellular processes by prolonging protein phosphorylation, particularly affecting sodium channels in intestinal cells.

A cell surface receptor that uses G proteins to relay signals inside a cell.

An enzyme activated by G proteins that breaks down PIP2, creating IP3 and DAG, both important second messengers.

A second messenger that triggers calcium release from the endoplasmic reticulum.

A second messenger that activates protein kinase C (PKC), mediating various cellular responses.

When a ligand binds to its GPCR, it activates a G protein, leading to the activation of PLC. PLC cleaves PIP2 into IP3 and DAG, which trigger calcium release and activate PKC, respectively.

IP3 releases calcium from the endoplasmic reticulum, while DAG activates PKC, both contributing to various cellular responses.

Receptors that span the cell membrane once and possess intrinsic enzyme activity. They respond only to protein stimuli, such as cytokines and mitogenic growth factors.

Kinases add a phosphate group (Pi) to proteins, while phosphatases remove them. This process alters protein shape and function, affecting enzyme activity, transport, and gene expression.

Platelet-derived growth factor (PDGF) binds to its receptors, causing them to dimerize and phosphorylate each other. This activates Ras, leading to the phosphorylation of MAPKs, which stimulate cell growth and development.

A mechanism to regulate receptor activity after prolonged exposure to a ligand. It involves receptor phosphorylation, internalization, and degradation, reducing sensitivity to the signal.

Proteins that bind to phosphorylated receptors, blocking their signaling activity and promoting their internalization. They help regulate receptor sensitivity and desensitization.

A decrease in the number of receptors on a cell surface, reducing its sensitivity to a specific ligand. This is an example of negative feedback.

The process where receptors are taken inside the cell after they bind to a ligand. This can lead to their degradation or recycling back to the cell surface.

A drug that binds to a receptor, preventing agonist binding and blocking its biological effect.

Both agonist and antagonist compete for the same receptor binding site.

Increasing agonist concentration can overcome the antagonist's effect.

Increasing agonist concentration doesn't reverse the antagonist's effect because it binds permanently.

Antagonist affects the response by inhibiting somewhere other than the agonist's receptor.

Antagonist directly inactivates the agonist through a chemical reaction.

Antagonist alters the absorption, distribution, metabolism, or excretion of the agonist.

Antagonist produces an opposite effect to the agonist, acting on a different receptor.

A chemical substance that binds to a receptor and activates it, causing a cellular response.

A type of agonist that can produce the maximum response at a given receptor.

An agonist that can bind to a receptor but cannot elicit a maximum response, even when all receptors are occupied.

An agonist that binds to a receptor and produces the opposite effect of a typical agonist.

The process by which a drug binds to a specific receptor on a cell, triggering a biological response.

The study of drug effects on isolated tissue or cells, conducted in a controlled laboratory setting.

The study of drug effects on whole living organisms, taking into account factors like absorption, distribution, and metabolism.

A neurotransmitter that plays a crucial role in muscle contraction, nerve signaling, and other bodily functions.

An enzyme responsible for producing nitric oxide (NO) from L-arginine. There are three main forms: iNOS, eNOS, and nNOS.

Inducible Nitric Oxide Synthase (iNOS) is found in various cell types, including vascular smooth muscle, endothelial cells, fibroblasts, and macrophages. It produces significantly more NO than eNOS or nNOS.

Endothelial Nitric Oxide Synthase (eNOS) is mainly found in the endothelium (lining of blood vessels) but also in cardiac myocytes, platelets, and osteoclasts. It plays a key role in regulating vascular tone.

Neuronal Nitric Oxide Synthase (nNOS) is found in neurons and is involved in neuronal signaling and communication.

The endothelium, the lining of blood vessels, plays a key role in regulating vascular tone. It releases vasoactive substances, like Nitric Oxide (NO) which causes relaxation, and Endothelin-1 (ET-1) which causes contraction.

A neuron is a specialized cell that receives, conducts, and transmits signals in the nervous system. It's the basic building block of the brain, spinal cord, and peripheral nerves.

Action potentials are electrical impulses that travel along the axon of a neuron. They're made possible by the presence of voltage-gated ion channels, which open and close in response to changes in membrane potential.

A neuron's threshold potential is the minimum level of depolarization needed to trigger an action potential. If the membrane potential reaches this threshold, a chain reaction of ion channel openings occurs, resulting in a rapid electrical impulse.

Sodium ions (Na+) rush into the neuron when voltage-gated sodium channels open during depolarization. This influx of positive charge contributes to the rapid rise in membrane potential, creating the action potential.

Action potentials allow neurons to transmit information quickly and reliably over long distances, enabling rapid communication throughout the nervous system. This is essential for everything from reflexes to thought processes.

A cycle where depolarization opens more sodium channels, leading to further depolarization and increased sodium influx. This continues until the membrane reaches its peak potential.

After the peak, sodium channels become inactive, preventing further sodium influx and allowing potassium channels to open, leading to repolarization.

Depolarization of the membrane, but the threshold for activation is higher than for sodium channels.

Potassium flows out of the cell, down its electrochemical gradient, making the inside of the cell more negative and contributing to repolarization.

An action potential either occurs fully or not at all. Its magnitude and duration are constant, regardless of the stimulus strength above the threshold.

Depolarization at one point triggers depolarization in the adjacent region, causing a chain reaction along the axon.

The temporary inactivation of sodium channels creates a refractory period, preventing the action potential from traveling backward.

A junction between two neurons or a neuron and a target cell, where the signal is transmitted.

Neurotransmitters, stored in vesicles in the presynaptic neuron, are released into the synaptic cleft, carrying the signal to the postsynaptic cell.

Calcium influx into the presynaptic terminal triggers the fusion of vesicles with the plasma membrane, releasing neurotransmitters into the synaptic cleft.

The study of how drugs affect the body.

The study of how the body handles drugs over time; absorption, distribution, metabolism, and excretion.

The movement of a drug from the site of administration into the bloodstream.

The process of a drug moving from the bloodstream to different tissues and organs.

The process of breaking down drugs in the body, usually by enzymes in the liver.

The elimination of drugs and their metabolites from the body, usually through urine and/or feces.

Transmembrane proteins that pump substances back out of cells, reducing drug absorption.

Some drugs increase (induce) or decrease (inhibit) P-gp activity, affecting drug absorption.

The percentage of a drug that reaches the systemic circulation after administration.

The metabolism of a drug by the liver before it reaches systemic circulation, reducing its bioavailability.

The reversible transfer of a drug from the systemic circulation to other body fluids and tissues.

Properties of the drug itself that influence how well it distributes, including its ability to dissolve in fats and water, and its tendency to bind to proteins.

Characteristics of the patient that can affect how well a drug distributes, such as their body size, fluid levels, and health conditions.

The process of chemically altering drug molecules in the body, usually making them more water-soluble for easier removal.

A product of drug metabolism that still has pharmacological effects, either similar or different from the original drug.

The removal of drugs and their metabolites from the body, primarily through urine, feces, and breath.

A deep invagination of the sarcolemma (plasma membrane) in skeletal and cardiac muscle cells, allowing action potentials to rapidly spread throughout the muscle fiber.

Dihydropyridine receptor (DHPR) is a protein in T-tubules of skeletal muscle that senses the action potential and activates the ryanodine receptor, triggering calcium release from the sarcoplasmic reticulum.

Calcium ions enter the smooth muscle cell cytosol. They bind to calmodulin, forming a complex that activates myosin light chain kinase (MLCK). MLCK then phosphorylates myosin, allowing it to interact with actin and initiate contraction.

Skeletal muscle T-tubules have DHPRs, which are directly linked to the sarcoplasmic reticulum (SR). Cardiac muscle T-tubules have L-type calcium channels, which are not directly linked to the SR but trigger calcium release through a Ca2+-induced Ca2+ release mechanism.

Relaxation occurs when myosin phosphatase (MP) removes the phosphate group from myosin light chains (MLC), preventing myosin from interacting with actin. This is regulated by cAMP and cGMP.

Proteins that bind to actin monomers or filaments, regulating actin's function and maintaining a reserve pool of monomers.

A family of motor proteins that use ATP to move along actin filaments, always from the minus end to the plus end.

Myosin-I moves vesicles along microfilaments, while myosin-II slides actin filaments past each other, shortening the actin bundle.

A repeating cycle powered by ATP that enables muscle contraction. Myosin heads bind to actin, release, cock, generate force, and repeat.

Muscle contraction relies on the interaction between actin and myosin filaments. The actin-myosin cycle, driven by ATP, causes myosin heads to pull on actin, shortening the muscle fiber.

The stiffening of muscles after death, caused by the myosin head being locked to actin without ATP to detach.

ATP binds to the myosin head, causing it to detach from actin, allowing the head to move to a new binding site.

The force-generating shape change of the myosin head as it binds to a new site on actin, causing the filament to slide.

Tropomyosin blocks the binding sites on actin, preventing myosin from attaching and causing muscle contraction.

Troponin binds calcium ions, causing tropomyosin to shift position, allowing myosin to attach to actin and initiate muscle contraction.

The removal of calcium ions from the troponin complex causes tropomyosin to return to its blocking position, preventing further myosin binding and stopping muscle contraction.

Calcium ions bind to troponin, triggering a conformational change that allows myosin to bind to actin and initiate muscle contraction.

Three types of muscle tissue that all rely on the interaction of actin and myosin filaments for contraction, but differ in their structure, regulation, and function.

A tissue composed of cells specialized for contraction, enabling movement, posture maintenance, and internal organ function.

The mechanism by which muscle contraction occurs. Myosin filaments 'walk' along actin filaments, pulling them closer together, shortening the muscle fiber.

Long, cylindrical cells capable of contracting when stimulated by nerve impulses.

Attached to bones, allowing voluntary movement, characterized by striated appearance due to organized arrangements of myofibrils.

Found in internal organs, responsible for involuntary movements like digestion and blood vessel constriction.

Found in the heart, responsible for rhythmic contractions that pump blood throughout the body.

Invaginations of the sarcolemma (muscle cell membrane) that carry electrical impulses deep into the muscle fiber, ensuring synchronized contraction.

Calcium channels located on the sarcoplasmic reticulum (SR), releasing Ca2+ into the sarcoplasm upon depolarization, triggering muscle contraction.

Troponin is a protein that holds Tropomyosin in place. Tropomyosin normally blocks the interaction of Actin and Myosin but is moved out of the way by Ca2+ binding to Troponin.

MLCK is an enzyme that phosphorylates Myosin Light Chains (MLC) in smooth muscles. This phosphorylation allows Actin and Myosin to interact, leading to smooth muscle contraction.

Smooth muscle is non-striated, found in the walls of various hollow organs, and usually involuntary. It has a spindle-shaped structure and a single, centrally located nucleus.

Many smooth muscles, such as those in the gut, are connected by 'gap junctions'. These junctions enable the muscles to contract in synchrony.

Fast twitch fibers contract rapidly, rely on anaerobic metabolism for ATP production, and are used for powerful but short-duration activities. Slow twitch fibers contract slowly, use aerobic metabolism, and are essential for endurance activities.

Calcium ions (Ca2+) enter the smooth muscle cell and bind to Calmodulin. This complex activates Myosin Light Chain Kinase (MLCK), which phosphorylates Myosin Light Chains (MLC), leading to contraction.

Cardiac muscle is both striated, like skeletal muscle, and involuntary, like smooth muscle. It is found in the heart wall and is connected by intercalated discs, which are specialized areas that facilitate communication and coordinated contractions.

Smooth muscle relaxation occurs when Myosin Phosphatase (MP) removes the phosphate group from Myosin Light Chains (MLC), preventing the interaction of Actin and Myosin and leading to muscle relaxation.

Nitric oxide (NO) is released from cells, diffuses to smooth muscle cells, and relaxes them by increasing cGMP levels.

NO activates guanylate cyclase, which converts GTP to cGMP. cGMP activates protein kinase G, leading to smooth muscle relaxation.

Besides blood vessels, NO is involved in skeletal muscle, heart contraction, metabolism, insulin signaling, and neuronal function. It also acts as an antioxidant, antithrombotic, and anti-inflammatory.

A tissue is a group of similar cells working together to perform a specific function. They have a common structure and function.

The four main tissue types are connective, epithelial, muscle, and nervous. Each plays a vital role in the body.

Connective tissue fills spaces, provides support, transports materials, and stores energy (as fat).

Epithelial tissue covers surfaces, lines internal passageways, and forms glands.