Skeletal Muscles
Classification of Muscle Tissues
Cardiac Muscles: Found only in the heart; involuntary and distinct in appearance under a microscope.
Smooth Muscles: Located in organs like the stomach and intestines; involuntary and appear smooth under microscopic view.
Skeletal Muscles: Striated and patterned in appearance; voluntary muscles controlled by nervous system signals.
Organizational Structure of Skeletal Muscle
Muscle Fiber: The term for a single skeletal muscle cell.
Fascicle: A group or bundle of multiple muscle fibers.
Ethymesium: The outermost layer of the skeletal muscle.
Paramecium: The middle layer that encases a fascicle.
Endomesium: The innermost layer of the skeletal muscle.
Fascia: A protective connective tissue capsule that prevents muscles from overstretching.
Microanatomy of the Muscle Fiber
Sarcoglyma: The outer membrane of the muscle cell.
Sarcoplasm: The jelly-like fluid or cytoplasm within the muscle fiber.
Myofibrils: Structures within the muscle cell that store glucose and oxygen.
Myofilaments: Protein fibers within myofibrils that enable contraction; consisting of thick myosin and thin actin.
Mitochondria: Organelles that produce energy in the form of ATP; cells with high activity levels contain many mitochondria.
Physiology of Muscle Contraction
Sarcomere: The specific functional area within the myofibril where contraction occurs.
Acetylcholine (ACH): The chemical neurotransmitter from the nervous system that initiates the contraction sequence.
Calcium: The electrolyte released within the muscle fiber that triggers myosin to grip actin, facilitating the sliding phenomenon.
Acetylcholine esterase: The enzyme that cleans up acetylcholine to allow the muscle to relax.
Contraction Mechanism: Muscles shrink or contract when fibers slide together and elongate during relaxation.
Contraction Responses and Terminology
Threshold: The minimum voltage required to trigger a muscle contraction.
Twitch: A single, brief contraction following a stimulus.
Trepe: The staircase phenomenon where sequential contractions become stronger due to increased calcium release.
Tetany: A continuous, sustained contraction without a period of relaxation.
Incomplete tetany: The state of partial contraction most skeletal muscles maintain to support posture.
Rigor mortis: Muscle rigidity after death caused by myosin and actin staying attached; it peaks at 12 hours and fades over the following 48 hours.
Static and Dynamic Contractions
Isotonic Contraction: The muscle changes length to move a load while tension remains constant (e.g., lifting a 10 pound dumbbell).
Isometric Contraction: Muscle tension increases while the length remains unchanged (e.g., holding a heavy textbook stationary).
Energy Metabolism and Respiration
Initial Phase: Muscles use ATP and creatine phosphate for brief bursts like sprinting; energy is produced via anaerobic respiration (without oxygen) using glucose.
Lactic Acid: A byproduct of anaerobic respiration that causes muscle soreness.
Prolonged Exercise: After approximately 10 minutes of moderate activity, the body switches to aerobic respiration (with oxygen).
Resting State: At rest, muscles obtain most of their energy by metabolizing fatty acids.
Functional Roles and Movement Terminology
Origin: The stationary end of a muscle attached to bone.
Insertion: The more mobile, movable end of a muscle.
Hypertrophy: The enlargement of muscles due to exercise.
Atrophy: The deterioration or shrinking of muscle tissue from lack of use.
Prime Mover: The muscle primarily responsible for triggering a movement.
Synergists: Muscles that assist or intensify the action of the prime mover.
Antagonist: The muscle that opposes or reverses a specific movement.
Naming Conventions of Major Muscles
Size: Includes terms like maximus (largest), minimus (smallest), major, minor, long, and short.
Shape: Includes deltoid (triangular shape) and trapezius (trapezoidal shape).
Location: Examples include radialis (near the radius), brachio (upper arm), and sterno pleatomastoid.
Origins: Biceps (two origins) and triceps (three origins).
Muscle Naming Reference: Examples of muscle names and categories are provided on page 164.
Muscles of the Trunk and Extremities
Diaphragm: The major muscle of the respiratory system; it enlarges the thoracic cavity for inspiration.
Intercostal Muscles: External intercostals elevate ribs during inspiration, while internal intercostals depress them during forced exhalation.
Rectus abdominis: The longitudinal abdominal muscles that create a six-pack appearance.
Sterno pleatomastoid: A muscle traveling from the sternum to the mastoid area, often holding significant tension.
Deltoid: A shoulder muscle used for swinging the arms and as a site for IM injections.
Brachialis: The prime mover for flexing the forearm; opposed by the tricep (the antagonist).
Quadriceps: The most powerful muscle in the body.
Gastrocnemius: The large bulging portion of the calf muscle.
Achilles (Calcaneal) Tendon: The tendon attaching the calf muscle to the calcaneus (heel bone).
Questions & Discussion
Q: What is the major muscle responsible for respiration? A: The diaphragm.
Q: Do we have to tell the heart to beat? A: No, cardiac muscle is involuntary.
Q: Is troponin measured for heart damage? A: Yes, it is measured to assess heart damage or muscle issues, which is covered further in med surg.
Q: What is the term for when a muscle is stuck in a long continuous contraction? A: Tetany, such as lockjaw from stepping on a rusty nail.
Q: What did Megan mention regarding the DENS? A: Reference was made to a burger in relation to previous lecture topics.
Q: Is there a specific name for abdominal muscle separation during pregnancy? A: Yes, it is referred to as rectus diastasis (or rectostasis as discussed by the group), involving the separation of the connective tissue between the right and left sides.
Q: Which muscle is the prime mover for flexing the forearms? A: The brachialis.