muscle tissues 3/26

Severe Weather Preparedness

• Statewide Tornado Drill: Scheduled for 10:00 AM.

• Safety Protocols: Ensure students know where to take shelter if necessary.

• Designated Shelter: Room adjacent to the classroom, enclosed with no windows.

Muscle Structure Overview

• Discussing muscle structure across multiple organization levels:

  • Organ Level: Example - Biceps Brachii, a skeletal muscle.

  • Tissue Level: Comprised of skeletal muscle tissue.

  • Cellular Level: Individual muscle cells known as fibers.

Skeletal Muscle Tissue

• Definition of an Organ: Composed of more than one type of tissue, in this case, skeletal muscle tissue.

• Muscle Fibers: Each muscle tissue contains fibers, akin to individual cells.

Muscle Anatomy Details

• Fascia: Dense connective tissue covering the muscle; separates it from surrounding tissues.

• Epimysium: Layer of connective tissue surrounding the entire muscle.

• Fascicles: Bundles of muscle fibers; surrounded by perimysium.

• Endomysium: Connective tissue surrounding individual muscle fibers.

Muscle Fiber Structure

• Skeletal Muscle Fiber Components:

  • Sarcolemma: Plasma membrane of a muscle fiber.

  • Sarcoplasm: Cytoplasm within the muscle cell.

  • Sarcoplasmic Reticulum (SR): Endoplasmic reticulum of muscle cells, stores calcium.

  • Myofibrils: Cylindrical structures within fibers, organizing sarcomeres.

Myofibril Arrangement

• Myofilaments: Two types present in myofibrils:

  • Thick Myofilaments: Primarily made of myosin.

  • Thin Myofilaments: Primarily made of actin.

• Striation Pattern: Alternating A Bands (dark) and I Bands (light).

  • A Band: Contains thick filaments and overlapping thin filaments.

  • I Band: Region containing thin filaments only.

  • H Zone: Central region of the A Band containing only thick filaments.

  • Z Line: Boundary between neighboring sarcomeres, attachment site for thin filaments.

• Sarcomere: Functional contractile unit, extends from one Z Line to the next, becoming shorter during contraction.

Muscle Contraction Mechanism

• Involves interaction and overlap of thick and thin myofilaments.

• Contraction occurs when the Z Lines are pulled closer together as fibers shorten.

Nerve Impulses and Muscle Impulses

• Neurons: Transmit impulses via the axon to skeletal muscle fibers.

• Neuromuscular Junction (NMJ): Contact region between a motor neuron and a muscle fiber.

  • Presynaptic Membrane: Neuron's membrane at the NMJ.

  • Postsynaptic Membrane: Muscle fiber’s membrane (sacrolemma) at the NMJ, specifically the motor end plate.

• Synaptic Cleft: Gap between the presynaptic and postsynaptic membranes.

Neurotransmitter Action

• Acetylcholine (ACH): The neurotransmitter released into the synaptic cleft during impulse transmission.

  • Triggers muscle impulse after binding to receptors on the muscle fiber.

• Exocytosis: Process by which synaptic vesicles release ACH into the synaptic cleft.

Motor Units

• Definition: A motor unit consists of a motor neuron and the muscle fibers it controls.

• Control of Muscle Contraction: The size of a motor unit impacts the precision of muscle contractions; smaller units allow for finer control (e.g., eye muscles), while larger units allow for greater strength without precise control (e.g., hamstrings).

Ion Distributions in Neurons and Muscles

• Membrane Potential: Charge difference across the plasma membrane.

  • Outside Cell: More sodium ions (Na+), resulting in a net positive charge.

  • Inside Cell: More potassium ions (K+) and negatively charged proteins, resulting in net negative charge.

• Ion Polarization: The membrane is polarized due to differing concentrations of ions across the membrane, which is crucial for creating nerve and muscle impulses.

Upcoming Assessments

• Quiz Topic: Muscle structure at various levels is scheduled for Friday.