ap muscle tissue basics notes

Muscle Tissues Basics

• Overview

  • Muscle cells have the unique ability to contract (shorten) based on the Sliding Filament Model.

  • There are three types of muscle cells: Skeletal, Smooth, and Cardiac.

• Types of Muscle Cells

  • Skeletal Muscle

    • Voluntary control.

    • Longest muscle cells (fibers), typically shaped like long, thin structures.

  • Smooth Muscle

    • Involuntary.

    • Present in "guts" and blood vessel walls.

    • Non-striated, lacks sarcomeres.

  • Cardiac Muscle

    • Involuntary.

    • Found only in the heart.

    • Striated and branched with intercalated discs.

Structural Characteristics

• Muscle Fibers

  • All muscle cells collectively referred to as muscle "fibers."

  • Skeletal and cardiac muscles are classified as striated due to visible stripes under a microscope.

  • Smooth muscle is non-striated.

• Skeletal Muscle Structure

  • Each skeletal muscle has associated arteries, nerves, and veins.

  • Comprised of bundles called fascicles.

  • Connective tissue (CT) wrappings include:

    • Epimysium: wraps entire muscle.

    • Perimysium: wraps each fascicle.

    • Endomysium: wraps individual muscle fibers within fascicles.

Muscle Attachments

• Attachment Types

  • Indirect Attachment: through tendons where all CTs merge.

  • Direct Attachment: directly onto the periosteum of bones.

• Muscle Terminology

  • Insertion: attachment site on the more movable bone.

  • Origin: attachment site on the less movable or fixed bone.

Contraction Mechanism

• Process of Skeletal Muscle Contraction

  • Achieved through motor neuron stimulation which sends an action potential.

  • Neuromuscular Junction: the site where the neuron communicates with muscle cells. Includes:

    • Axon terminals (boutons)

    • Synaptic cleft

    • Junctional folds on muscle fibers.

  • Acetylcholine (ACh): neurotransmitter that opens chemically-gated sodium-potassium channels, resulting in an influx of Na+ ions to initiate contraction.

Sliding Filament Model

• Mechanism of Contraction

  • Myofibrils are packed with sarcomeres that are the basic contractile units.

  • The contraction occurs by sliding thin actin filaments against thick myosin filaments.

  • Troponin and Tropomyosin function to regulate contraction by blocking or permitting interactions between actin and myosin in response to calcium ion release.

Energy for Contraction

• ATP Sources and Regeneration

  1. Creatine Phosphate: provides immediate energy (regenerates ATP).

  2. Aerobic Pathway: efficient ATP generation (30 ATPs per glucose) when oxygen is available.

  3. Anaerobic Pathway: less efficient (only 2 ATPs per glucose) without oxygen, leads to lactic acid production.

Muscle Fatigue

• Possible Causes

  • Results from low Ca2+ release, not related to ATP levels.

  • Critical Ions: Na+, K+, Ca2+, which play roles in nerve impulses and muscle contractions.

Muscle Contraction Types

• Types of Contractions

  1. Isometric Contraction: muscle tension cannot move the object (e.g., trying to lift a heavy weight without movement).

  2. Isotonic Contraction: muscle tension is great enough to move the object; can be concentric (shortening) or eccentric (lengthening).

Summary of Muscle Physiology

• Motor Units and Muscle Strength

  • Composed of one motor neuron and multiple muscle fibers.

  • Increased power is achieved through motor unit recruitment and wave summation.

• Muscle Cell Types Based on Contraction Speed

  1. Slow Oxidative Muscles: suited for endurance.

  2. Fast Oxidative Muscles: good for quick bursts.

  3. Fast Glycolytic Muscles: excellent for intense activities but fatigue quickly.

Recovery and Exercise Effects

• EPOC (Excess Postexercise Oxygen Consumption): Additional oxygen needed post-exercise for recovery, including replenishing myoglobin and glycogen levels.