Chapt 10 A&P: Flashcards~

Chapter 10: Muscle Tissue Overview

Introduction

• Learning changes everything.

• Content based on Anatomy & Physiology: An Integrative Approach, Fourth Edition by McKinley, O’Loughlin, and Bidle.

Part 1: Skeletal Muscle

Functions of Skeletal Muscle

• Movement: Responsible for moving bones and enabling facial expressions, speaking, breathing, and swallowing.

• Posture Maintenance: Stabilizes joints and maintains body position.

• Protection and Support: Packages and holds internal organs in position.

• Regulates Material Elimination: Circular sphincters control passage at orifices.

• Heat Production: Assists in maintaining body temperature.

Characteristics of Skeletal Muscle Tissue

• Excitability: Responds to stimuli through changes in electrical potential.

• Conductivity: Electrical changes travel along the cell membrane.

• Contractility: Filaments slide past each other for muscle movement.

• Extensibility: Ability to stretch beyond resting length.

• Elasticity: Returns to original length post-contraction or extension.

Gross Anatomy of Skeletal Muscle

• A skeletal muscle is an organ comprising skeletal muscle fibers, connective tissue, blood vessels, and nerves.

• Fascicle Structure: Muscle fibers are bundled within fascicles; a muscle contains multiple fascicles while each fascicle contains many muscle fibers.

• Muscle Fiber: Refers to individual muscle cells.

Connective Tissue Components

• Epimysium: Dense irregular connective tissue surrounding the whole muscle.

• Perimysium: Wrapping around fascicles, housing blood vessels and nerves.

• Endomysium: Areolar connective tissue surrounding individual fibers, providing electrical insulation and support.

• Attachments: Muscles connect to bones or skin via tendons or aponeuroses.

• Deep Fascia: Surrounds individual muscles and compartments.

• Superficial Fascia: Separates muscles from skin, composed of areolar and adipose tissue.

Blood Vessels and Innervation

• Skeletal muscle is vascularized, receiving oxygen and nutrients through extensive blood vessels.

• Innervated by somatic motor neurons, allowing voluntary control of contractions.

Microscopic Anatomy of Skeletal Muscle

• Muscle Fiber Composition: Contains sarcoplasm with organelles and contractile proteins; multinucleated and enclosed by a sarcolemma.

• Sarcoplasmic Reticulum: Internal membrane complex analogous to smooth ER; calcium reservoirs crucial for muscle contraction.

Myofilaments and Sarcomeres

• Myofilaments: Contractile proteins divided into thick filaments (myosin) and thin filaments (actin).

• Sarcomere Structure: The functional unit of muscle fibers, organized into repeating units.

• I-Bands and A-Bands: I-bands are light regions with thin filaments; A-bands are dark regions containing thick filaments.

• Crossbridge Cycling: Key mechanism of muscle contraction regulated by calcium availability and ATP.

Clinical Views

• Muscular Dystrophy: A group of inherited diseases resulting in muscle degeneration, primarily Duchenne muscular dystrophy (DMD) caused by dystrophin abnormalities.

• Myasthenia Gravis: Autoimmune disorder affecting neuromuscular junction, causing muscle weakness.

Energy Supply for Skeletal Muscle Metabolism

• ATP Storage: Limited ATP stored, used within 5 seconds of intense exertion.

• Creatine Phosphate: Quickly regenerates ATP for short-duration energy needs.

• Glycolysis and Aerobic Respiration: Glycolysis provides energy without oxygen; aerobic respiration occurs in mitochondria yielding large amounts of ATP.

Classification of Skeletal Muscle Fibers

• Fiber Types: Classified based on contraction speed and ATP supply methods.

• Slow-Twitch vs. Fast-Twitch: Slow-twitch fibers are fatigue-resistant (endurance); fast-twitch are powerful but fatigue quickly (sprints).

Muscle Response to Stimuli

• Muscle Twitch: A single contraction following a stimulus, with defined periods (latent, contraction, relaxation).

• Motor Unit Recruitment: The number of units recruited varies based on required force. Higher intensity leads to more motor units being recruited.

Muscle Contractions

• Isometric Contraction: Muscle tension increases without length change.

• Isotonic Contraction: Muscle tension overcomes resistance leading to movement, subdivided into concentric (shortening) and eccentric (lengthening) contractions.

Muscle Fatigue and Recovery

• Fatigue results from decreased glycogen and ion imbalances; muscle tone and tension are maintained through involuntary stimulation.

• Hypertrophy: Increased muscle size from exercise, while atrophy occurs with disuse.

Chapter 10 Part 2: Cardiac and Smooth Muscle

Cardiac Muscle Characteristics

• Found in the heart; striated and involuntary.

• Includes intercalated discs for synchronized contractions.

Smooth Muscle Overview

• Features fusiform shape; located in organ systems like blood vessels and intestines.

• Uses different mechanisms and proteins for contraction compared to skeletal muscle.

The events of excitation-contraction coupling and muscle relaxation are not the same; they are distinct processes associated with muscle function.

• Excitation-Contraction Coupling refers to the process where an action potential (nerve impulse) leads to muscle contraction. It involves the release of calcium ions from the sarcoplasmic reticulum, which enables crossbridge cycling between actin and myosin filaments, ultimately causing the muscle to contract.

• Muscle Relaxation occurs after contraction. This process involves the re-uptake of calcium ions into the sarcoplasmic reticulum, resulting in the detachment of myosin from actin, allowing the muscle fiber to return to its resting state.

In summary, excitation-contraction coupling initiates muscle contraction, whereas muscle relaxation terminates it.

Exocytosis of acetylcholine (ACh) is a crucial process in neuromuscular transmission. It occurs at the neuromuscular junction where motor neurons communicate with skeletal muscle fibers. Here’s a brief overview of the process:

1. Action Potential Arrival: When an action potential reaches the axon terminal of the motor neuron, it triggers the opening of voltage-gated calcium channels.

2. Calcium Influx: Calcium ions (Ca²⁺) rush into the axon terminal due to a concentration gradient.

3. Vesicle Fusion: The influx of calcium stimulates synaptic vesicles containing acetylcholine to move toward and fuse with the presynaptic membrane.

4. Release of Acetylcholine: Exocytosis occurs where acetylcholine is released into the synaptic cleft (the gap between the neuron and muscle fiber).

5. Activation of Muscle Fiber: ACh binds to receptors on the postsynaptic membrane of the muscle fiber, leading to an influx of sodium ions and initiating an action potential in the muscle fiber, which ultimately leads to muscle contraction.