IMS 1.4 - Cell signalling and movement

What are the four main types of chemical signalling between cells?

Endocrine (hormones via bloodstream), paracrine (local cell-to-cell), autocrine (self-targeting), and direct contact (gap junctions).

What types of molecules serve as chemical signals?

Neurotransmitters, neuropeptides, steroid hormones, amino acid-derived hormones, and peptide hormones.

How do steroid hormones interact with target cells?

They diffuse through the plasma membrane and bind intracellular receptors to affect gene transcription.

What is the role of G-protein-coupled receptors in cell signalling?

They transduce signals via GTP-bound G-proteins, activating second messengers and intracellular cascades.

What percentage of an adult’s body weight is water, and how is it distributed?

60%; approximately 23L intracellular fluid, 15L interstitial fluid, 3L plasma, and 1L transcellular fluid.

What is the major difference between osmolarity and tonicity?

Osmolarity measures total solute concentration; tonicity compares osmotic pressure between two solutions, determining water movement.

Which ions are primarily found in the intracellular and extracellular compartments?

Intracellular: High K+, low Na+; Extracellular: High Na+, low K+.

What maintains the resting membrane potential of a cell?

The Na+/K+ ATPase pump maintains ion gradients and generates a net negative charge inside the cell.

What is the typical resting membrane potential of a muscle cell?

Between -60 mV and -90 mV, with the interior being negative.

What is the Nernst equation used for?

Calculating the membrane potential based on the concentration of ions inside and outside the cell.

What is the primary function of chemical signalling in cells?

To enable communication between cells for coordination, homeostasis, and physiological responses.

What are the three fluid compartments in the human body?

Intracellular fluid, extracellular fluid (interstitial and plasma), and transcellular fluid.

Which chemical signals are used for local signalling between adjacent cells?

Paracrine signals.

What hormone types can cross the plasma membrane directly?

Lipid-soluble hormones such as steroid hormones.

What is the function of the Na+/K+ ATPase pump in maintaining membrane potential?

It actively transports 3 Na+ ions out and 2 K+ ions into the cell, maintaining ion gradients and a negative resting potential.

What causes the inside of a resting cell to be negatively charged?

The presence of negatively charged proteins and phosphates, and the non-equilibrium distribution of Na+ and K+ ions.

What is osmolarity?

The total concentration of solute particles in a solution, measured in Osmoles per liter.

What is tonicity?

A measure of the osmotic pressure gradient between two solutions separated by a semipermeable membrane.

What effect does a hypotonic solution have on red blood cells?

It causes water to enter the cells, leading to swelling and possible lysis.

What is Brownian motion?

Random movement of particles in a fluid due to collisions with other atoms or molecules.

How do water molecules typically move across a membrane?

Through osmosis driven by concentration gradients.

What is the approximate water content of an adult male?

Approximately 60% of body weight.

How does body water content differ between men and women?

Men have higher water content (~60%) than women (~55%) due to lower body fat.

Which ion is in highest concentration in extracellular fluid?

Sodium (Na+).

Which ion is in highest concentration in intracellular fluid?

Potassium (K+).

What is the typical osmolarity of intracellular and extracellular fluid?

Approximately 267 mOsm/L intracellularly and 263 mOsm/L extracellularly.

What role does oncotic pressure play in capillaries?

It draws water back into the capillaries due to proteins like albumin.

What causes edema?

An imbalance of hydrostatic and oncotic pressures leading to fluid accumulation in interstitial spaces.

How do gases like CO2 and O2 cross cell membranes?

By simple diffusion due to high membrane permeability.

What is the effect of aging on body water content?

It decreases with age, increasing the risk of dehydration.

What is the resting membrane potential of most muscle cells?

Between -60 mV and -90 mV.

What is the Nernst equation used for?

Calculating the equilibrium potential for a specific ion based on its concentration gradient.

What determines membrane permeability for different molecules?

Molecule size, charge, polarity, and lipid solubility.

How does dehydration affect serum sodium concentration?

It increases serum sodium (>145 mmol/L), leading to hypertonicity.

How do steroid hormones travel in the blood?

Bound to carrier proteins due to their low water solubility.

What is the main function of insulin?

It facilitates glucose uptake into cells and regulates blood glucose levels.

What are the two main types of acetylcholine receptors?

Nicotinic (ion channel) and muscarinic (G-protein coupled).

Where is acetylcholine released in muscle contraction?

At the neuromuscular junction by motor neuron synaptic vesicles.

What enzyme breaks down acetylcholine in the synaptic cleft?

Acetylcholinesterase.

What happens when acetylcholine binds to nicotinic receptors on muscle cells?

It opens ion channels allowing Na+ influx and depolarization.

What is the structure that stores calcium in muscle cells?

The sarcoplasmic reticulum.

What triggers the release of calcium from the sarcoplasmic reticulum?

Action potential activates voltage-sensitive receptors (DHP and RyR channels).

What protein binds calcium to initiate contraction?

Troponin.

What blocks myosin binding sites on actin in resting muscle?

Tropomyosin.

What protein helps re-sequester calcium during muscle relaxation?

SERCA (Sarcoplasmic/Endoplasmic Reticulum Ca2+ ATPase).

What is the function of calsequestrin?

It binds and stores calcium in the sarcoplasmic reticulum.

What is the role of T-tubules in muscle cells?

They conduct action potentials into the cell interior to trigger calcium release.

What are the structural units of muscle contraction?

Sarcomeres.

Which proteins make up the thick filament in sarcomeres?

Myosin.

Which proteins make up the thin filament in sarcomeres?

Actin, troponin, and tropomyosin.

What does the sliding filament theory describe?

The mechanism by which myosin heads pull actin filaments to shorten the sarcomere.

What are the three connective tissue layers in skeletal muscle?

Epimysium, perimysium, and endomysium.

What is a fascicle?

A bundle of skeletal muscle fibers wrapped in perimysium.

What is the smallest contractile unit in skeletal muscle?

The sarcomere.

What causes the striated appearance of skeletal muscle?

Alternating A-bands and I-bands in sarcomeres.

How does myosin generate force?

By forming cross-bridges and undergoing a power stroke using ATP hydrolysis.

What is the Lymn-Taylor model?

A model describing the cyclic interaction of myosin and actin powered by ATP.

What is the function of titin?

It stabilizes sarcomere structure and provides elasticity.

What is the function of nebulin?

It helps anchor and regulate the length of thin filaments.

What distinguishes skeletal muscle from cardiac and smooth muscle?

Long, multinucleated, voluntary, and striated.

What distinguishes cardiac muscle from other types?

Branched, involuntary, striated, with intercalated discs.

What distinguishes smooth muscle?

Non-striated, involuntary, spindle-shaped cells found in hollow organs.

What is a motor unit?

A single motor neuron and all the muscle fibers it innervates.

How does muscle force generation relate to sarcomere length?

There is an optimal sarcomere length for maximum force generation.

What is isometric contraction?

Muscle generates force without changing length.

What causes calcium to stop releasing during relaxation?

Cessation of neural stimulation and closure of RyR channels.

What type of transport allows glucose entry into cells via insulin?

Facilitated diffusion using GLUT4 transporters.

What happens to actin and myosin filaments during contraction?

They slide past each other; filament length stays constant.

Which neurotransmitters are derived from tyrosine?

Adrenaline, noradrenaline, and dopamine.

What condition results from acetylcholinesterase inhibition?

Paralysis due to prolonged muscle contraction (e.g., in nerve gas poisoning).

What disease involves failure of synaptic transmission at the NMJ?

Myasthenia gravis.

What is the function of mitochondria in muscle fibers?

ATP production for muscle contraction.

What is a major contributor to intracellular negativity?

Non-diffusible anions like proteins and phosphates.

What determines whether a signal causes excitation or inhibition?

The receptor type and ion channel affected.

What are gap junctions used for in cardiac muscle?

They allow electrical coupling between cells for coordinated contraction.

What is meant by "signal amplification" in cell signalling?

A small stimulus triggers a large intracellular response.

What is a second messenger in cell signalling?

An intracellular molecule activated by a receptor to propagate a signal (e.g., cAMP, IP3).

What is the purpose of a G-protein in signalling pathways?

It transduces signals from membrane receptors to effectors inside the cell.

What are ionotropic receptors?

Ion channel-linked receptors that open in response to ligand binding.

What are metabotropic receptors?

G-protein-coupled receptors that activate second messengers.

What protein kinase is commonly involved in signalling cascades?

Protein kinase A (PKA).

What hormone stimulates glycogen breakdown in muscle?

Adrenaline.

What is the neuromuscular junction also called?

Motor end plate.

What happens to membrane potential when Na+ rushes into a cell?

It depolarizes.

How do skeletal muscles vary contraction strength?

By recruiting more motor units or increasing firing frequency.

What is the functional role of synaptic vesicles?

Store and release neurotransmitters like acetylcholine.

What causes repolarization of the sarcolemma after an AP?

Outflow of K+ and activity of the Na+/K+ pump.

What is the role of phosphocreatine in muscle?

Provides rapid ATP regeneration during intense contraction.

What are examples of peptide hormones?

Insulin, ADH, glucagon.

What is a common result of dysfunction in intracellular trafficking?

Disease due to protein mislocalization or accumulation.

What are examples of diseases from vesicular trafficking defects?

Cystic fibrosis, some forms of Alzheimer’s disease.

How does intracellular calcium concentration affect contraction?

Increased Ca2+ promotes cross-bridge formation and contraction.

What does SERCA use to transport calcium?

ATP hydrolysis.

What happens if SERCA is inhibited?

Delayed calcium reuptake, resulting in prolonged contraction.

What is the function of the troponin complex?

It binds calcium and regulates actin-myosin interaction.

What is required for the myosin head to detach from actin?

Binding of a new ATP molecule.

What prevents overstretching of sarcomeres?

Titin's elastic properties.

Which structure connects muscle fibers electrically in cardiac tissue?

Intercalated discs.

What is the primary energy source in long-duration muscle activity?

Aerobic metabolism using glucose and fatty acids.

Which muscle type can maintain contraction the longest?

Smooth muscle.