B

Physiology module 2 Sync session B

Introduction

  • The session begins with a technical issue regarding the slides and accessing Mentimeter, a polling tool used to engage students.

Course Reminders and Tips

  • The instructor emphasizes the importance of asynchronous (async) video lectures for success in the program.

  • Optional content will not be tested, providing clarity for students.

Active vs. Passive Transport

  • An activity regarding the classification of transport types:

    • Active Transport:

    • Defined as requiring energy to move substances against their gradient.

    • Example: Potassium pump is active because it requires ATP.

    • Passive Transport:

    • Defined as movement along a concentration gradient without energy input.

Osmolarity and Cell Volume Changes

  • Given scenario: A cell with an osmolarity of 280 placed in a solution with osmolarity of 100.

    • The shape of the cell will increase in volume.

    • Explanation: Water will move into the cell to equalize concentration, hence increasing cell volume.

Action Potentials

  • The distinction is made between active and passive processes in relation to action potentials:

    • Active - Sodium-potassium pump actively maintains ionic gradients.

    • Passive - The flow of ions during an action potential occurs without the direct expenditure of ATP.

Sodium-Potassium Pump

  • Function:

    • Maintains proper gradients of sodium (Na⁺) and potassium (K⁺) ions inside and outside the cell.

    • Operates primarily between action potentials, slowing down during an action potential.

Test Overview

  • Upcoming test on modules 1 and 2 (excluding module 3).

  • Structure: 60 questions, primarily multiple-choice, to be completed in 90 minutes.

    • Encouragement to understand concepts rather than just memorize facts.

Study Tips

  • Suggests using the Cornell notes system to take more effective notes, incorporating highlights, notes, and questions.

  • Advises using resources like ChatGPT strategically for understanding concepts rather than just retrieving information.

Neuromuscular Junction

  • Definition:

    • The point where a motor neuron connects with a muscle fiber, transmitting signals for contraction.

  • Action potentials play a crucial role in neurotransmitter release at the junction.

  • The synaptic cleft is where neurotransmitters (e.g., acetylcholine) diffuse to stimulate muscle contraction.

Process of Muscle Contraction

Action Potential Initiation

  • Action potentials travel down motor neurons to release neurotransmitters.

    • Action potential causes synaptic vesicles to release acetylcholine at the presynaptic terminal.

    • Acetylcholine binds to receptors on the muscle cell, leading to depolarization and muscle contraction.

Calcium's Role in Contraction

  • Calcium is crucial in muscle contraction, released by action potentials stimulating the sarcoplasmic reticulum.

  • Calcium binds to troponin, causing a conformational change that exposes binding sites on actin filaments for myosin.

Crossbridge Cycle

  • Definition: The process whereby myosin heads attach to actin filaments, resulting in muscle contraction.

    • Steps:

    1. Myosin head attaches to actin (requires calcium).

    2. ADP and phosphate are released, causing a power stroke that pulls actin filaments closer together.

    3. ATP binds to myosin, causing it to detach from actin.

    4. ATP hydrolysis moves the myosin head back to the original position, ready for another cycle.

  • Without ATP: Myosin heads remain bound to actin, resulting in rigor mortis upon death.

Relaxation of Muscles

  • Calcium must be actively pumped back into the sarcoplasmic reticulum by the Ca²⁺ ATPase pump for muscle relaxation.

  • Absence of calcium leads to closing of binding sites on actin by tropomyosin, preventing further contraction.

Clinical Implications

  • Discussion about the role of medications that influence neurotransmitter dynamics at the neuromuscular junction, such as muscle relaxers, beta blockers, and seizure medications.

Summary

  • Importance of understanding the neuromuscular junction, action potentials, and the physiology of muscle contraction is emphasized.

  • Completion of the crossbridge cycle is essential for muscle function and illustrates biochemical processes underpinning movement.