Cell Biology: Signal Transduction and Muscle Function

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Questions and Answers

What role does calcium play in muscle contraction?

It directly activates myosin heads to pull on actin.

It inhibits the contraction-relaxation cycle.

It binds to troponin to allow myosin to attach to actin. (correct)

It binds to tropomyosin to initiate contraction.

What happens to tropomyosin when calcium binds to troponin?

It promotes the sliding filament theory.

It prevents calcium from binding to actin.

It binds more tightly to myosin.

It is pulled away from the myosin-binding sites on actin. (correct)

What initiates the contraction-relaxation cycle in muscle fibers?

The re-binding of tropomyosin to actin.

The release of calcium from the sarcoplasmic reticulum. (correct)

The decrease of ATP in muscle cells.

The binding of myosin to actin.

How does the sliding filament theory explain muscle contraction?

Thin filaments slide past thick filaments in an energy-dependent manner. Signup and view all the answers

During the muscle contraction process, what causes the elastic elements to pull filaments back to their relaxed position?

The decrease in free cytosolic calcium. Signup and view all the answers

What happens to the A band during muscle contraction?

It remains constant. Signup and view all the answers

What is the primary role of titin in muscle contraction?

To provide elasticity and stabilize myosin. Signup and view all the answers

What is defined as the force created by the muscle?

Muscle tension. Signup and view all the answers

What initiates the muscle action potential at the neuromuscular junction?

Net entry of sodium through ACh receptor channels. Signup and view all the answers

What is the process called when muscle tension is released?

Relaxation. Signup and view all the answers

What does excitation-contraction coupling primarily convert?

ACh signals to muscle action potentials. Signup and view all the answers

Which component does nebulin primarily interact with?

Actin filaments. Signup and view all the answers

Which muscle-related term describes the weight or force opposing contraction?

Load. Signup and view all the answers

What is the primary function of lipophilic signal molecules?

Modify existing proteins or synthesize new proteins Signup and view all the answers

How do lipophobic signal molecules primarily interact with target cells?

By binding to receptors on the cell membrane Signup and view all the answers

What mechanism does ligand binding to a receptor-enzyme typically activate?

Activates an intracellular enzyme Signup and view all the answers

Which type of receptor is primarily associated with the rapid opening or closing of ion channels?

Chemically gated (ligand-gated) ion channels Signup and view all the answers

What role do integrin receptors play in cellular signaling?

They alter enzyme activity or the cytoskeleton Signup and view all the answers

Signal transduction primarily involves which of the following processes?

Using membrane proteins to relay messages across membranes Signup and view all the answers

Which category of receptor directly influences ion channel activity through ligand binding?

Chemically gated ion channels Signup and view all the answers

What distinguishes lipophobic signal molecules from lipophilic ones?

Lipophobic molecules bind to receptors on the cell membrane, while lipophilic can diffuse through membranes Signup and view all the answers

What percentage of nephrons are located in the outer cortex of the kidney?

80% Signup and view all the answers

What is the main function of Bowman's capsule?

It serves as the site for plasma filtration. Signup and view all the answers

Which structure follows the proximal tubule in the nephron?

Loop of Henle Signup and view all the answers

What does the juxtaglomerular apparatus connect?

Afferent and efferent arterioles Signup and view all the answers

What is the final structure that urine passes through before excretion?

Renal pelvis Signup and view all the answers

What is the term for the inside space of a tubular structure, like an artery?

Lumen Signup and view all the answers

How many arterioles are found in one nephron?

Two Signup and view all the answers

What is the primary role of the distal tubule in nephron function?

Fluid adjustment before collecting duct Signup and view all the answers

What does the clearance of a solute primarily measure?

The rate of elimination of the substance from the body Signup and view all the answers

Which substance is used to measure glomerular filtration rate (GFR) and is neither reabsorbed nor secreted?

Inulin Signup and view all the answers

What aspect of creatinine makes it useful in measuring renal function?

It is a breakdown product of phosphocreatine Signup and view all the answers

What is micturition primarily controlled by?

Two sphincters: internal and external Signup and view all the answers

Which statement about inulin in the nephron is correct?

It is excreted until no inulin is left in the nephron Signup and view all the answers

Study Notes

Signal Transduction

Transmission of info from one side of the cell membrane to the other, using membrane proteins

Lipophilic Signal Molecules

Diffuse through cell membranes
Bind to cytosolic receptors or nuclear receptors
Slow process

Lipophobic Signal Molecules

Bind to receptors on the cell membrane
Rapid process

Membrane Receptors

4 categories of membrane receptors
- Receptor Channels
- G-protein Coupled
- Receptor-Enzymes
- Integrin Receptors

Receptor Channels

Ligand binding opens or closes the channel

G-protein Coupled Receptors

Ligand binding opens an Ion channel or alters enzyme activity.

Receptor Enzymes

Ligand binding activates an intracellular enzyme.

Integrin Receptors

Ligand binding alters enzymes or the cytoskeleton.

Muscle Tension

Force created by muscle

Load

Weight or force opposing contraction

Contraction

Creation of tension in muscle

Relaxation

Release of tension

Major Steps Leading Up To Skeletal Muscle Contraction

Events at the neuromuscular junction
Excitation-Contraction (E-C) Coupling
Contraction-Relaxation Cycle

Events at the Neuromuscular Junction

Converts an ACh signal from a somatic motor neuron into an electrical signal in the muscle fiber.
Steps:
- Somatic motor neuron releases Ach at the neuromuscular junction
- Net entry of sodium through the Ach receptor channel initiates a muscle action potential
- Action potential in t-tubule alters the sarcoplasmic reticulum

Excitation Contraction Coupling

Muscle action potentials are translated into calcium signals
Calcium signals initiate a contraction-relaxation cycle
Explained by the sliding filament theory of contraction.

Contraction-Relaxation Cycle

The SR pumps calcium back into its lumen.
Decrease in free cytosolic calcium causes calcium to unbind from troponin
Tropomyosin re-covers the binding site
When myosin heads release, elastic elements pull filaments back to their relaxed position.

Sliding Filament Theory of Contraction

Overlapping actin and myosin myofibrils.
Thin filaments slide past thick filaments in an energy-dependent process
Results in muscle contraction.

Troponin

Controls the position of tropomyosin.
Binds reversibly to calcium.

Tropomyosin

Prevents myosin and actin from interacting by covering the myosin-binding site.

Contraction Steps

Calcium release, binds to troponin, troponin pulls tropomyosin from myosin-binding sites on actin.
Myosin binds tightly to and moves actin
Repeats as long as binding sites are uncovered and ATP and calcium are available.

Structure of the Kidney

Divided into an outer cortex (80% nephrons) and an inner medulla (20% nephrons)

Bowman's Capsule

Site of plasma filtration with the glomerulus.
Bowman's capsule combined with glomerulus is referred to as the renal corpuscle.

Proximal (Closeby) Tubule

Filtered fluid flows here.

Loop of Henle

Segment that dips toward the medulla and then back up.
"U" shaped.

Distal (Far Away) Tubule

Fluid passes, which drains into a single larger tube called the collecting duct

Collecting Ducts

Single larger tube towards the end after the distal tube.
Converges and drains into the renal pelvis.
Filtered and modified fluid (urine) flows into the ureter on its way to excretion.

Juxtaglomerular Apparatus

Area where the nephrons twist and fold back on itself.
Final part of the ascending limb of the loop passes between afferent/efferent arterioles.

Cortex (Upper Half)

All of Bowman's capsule, proximal and distal tubes.

Medulla (Lower Half)

Loop of Henle and collecting ducts.

Nephron

Two arterioles and two sets of capillaries that form a portal system.

Lumen

Inside space of a tubular structure, such as an artery or intestine.

Clearance

Movement from blood to lumen.
How much of a plasma that flowed through the glomerulus per unit of time was CLEARED of that substance.

Inulin and Creatinine

Inulin
- Neither reabsorbed or secreted, ONLY EXCRETED.
- Filter freely in the nephron, when no inulin is present it's considered cleared from inulin.
Creatinine
- Breakdown product of phosphocreatine.
- Small amount secreted, so it can be used to measure creatinine clearance.

Micturition (Urine)

Removal of urine from the body; voiding of the bladder.
Two sphincters control urine flow from the bladder (internal/smooth and external/skeletal sphincter).

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Description

This quiz covers key concepts in signal transduction and muscle physiology. It explores the mechanisms of lipophilic and lipophobic signal molecules, types of membrane receptors, and the basics of muscle tension and contraction. Test your understanding of these essential biological processes.