Untitled Quiz

Types of Muscles

• Skeletal muscles are attached to bones, are striated, and are voluntarily controlled
• Cardiac muscles are located in the heart, are striated, and are involuntarily controlled
• Smooth muscles are located in blood vessels and hollow organs, are non-striated, and are involuntarily controlled

Whole Skeletal Muscle Anatomy

• Skeletal muscle (striated muscle) comprises about 40% of body weight
• Many skeletal muscles attach to the skeletal system, or sometimes to skin or connective tissue
• Skeletal muscle is composed of muscle, nerve, and connective tissue

Connective Tissue Coverings

• Each skeletal muscle is encased in a connective tissue sheath called the epimysium
• Muscle bundles are called fascicles and are surrounded by the perimysium
• Individual muscle fibers (cells) are surrounded by endomysium
• The connective tissues blend to form tendons that attach muscles to bone

Skeletal Muscle Fiber Anatomy

• Skeletal muscle fibers range in size from 1 mm to 4 cm in length
• Muscle fibers have multiple nuclei located at their periphery
• Alternating light and dark bands give muscle fibers a striated appearance
• Muscles enlarge due to fiber size increases, not an increase in number of fibers

Electrical Component Structure

• The sarcolemma (cell membrane) contains transverse tubules (T tubules) that extend into the center of the muscle fiber
• T tubules are associated with enlarged portions of the smooth endoplasmic reticulum (sarcoplasmic reticulum), called terminal cisternae
• The terminal cisternae and associated T tubules form a triad
• The sarcoplasmic reticulum's high Ca2+ concentration plays a crucial role in muscle contraction

Mechanical Component Structure

• Myofibrils, bundles of actin and myosin myofilaments, make up skeletal muscle
• Actin (thin filaments), and myosin (thick filaments) are arranged in repeating units called sarcomeres
• Sarcomeres provide the mechanical basis for muscle contraction
• Z disks are protein fiber networks that anchor actin myofilaments and separate sarcomeres
• Actin and myosin myofilaments slide past each other which shortens the sarcomeres causing the muscle to contract

Neuromuscular Junction

• A motor neuron stimulates muscle cells at a neuromuscular junction, a synapse
• A synapse is a junction between a nerve cell (neuron) and another cell (muscle, gland)
• A motor unit is a group of muscle fibers stimulated by a single motor neuron
• The presynaptic terminal is the axon terminal end
• The postsynaptic membrane is the sarcolemma (muscle fiber membrane)
• Neurotransmitters stimulate/inhibit postsynaptic cells: acetylcholine stimulates skeletal muscles

Action Potentials

• Resting membrane potential is the resting state of a cell where the inside is negative compared to the outside
• Action potentials are rapid changes in membrane charge
• The entry of Na+ causes the inside of the cell to become more positive (depolarization)
• The exit of K+ returns the cell to its resting state (repolarization)
• An action potential triggers the release of acetylcholine at the neuromuscular junction, stimulating muscle contraction

Muscle Contraction

• Sliding filaments model: actin and myosin filaments slide past each other, shortening the sarcomere
• Muscle action potential triggered by acetylcholine released at neuromuscular junction,
• Ca++ released from sarcoplasmic reticulum bind to troponin to expose myosin-binding sites on actin
• ATP hydrolysis provides energy for myosin head power stroke and subsequent cross-bridge cycle

Muscle Relaxation

• Acetylcholine is no longer released at the neuromuscular junction
• Ca++ is actively transported back into the sarcoplasmic reticulum
• Tropomyosin blocks myosin-binding sites on actin
• The muscle relaxes

Muscle Twitch

• A muscle twitch is a single contraction in response to a stimulus
• Phases include latent phase, contraction phase, and relaxation phase

Types of Contractions

• Isometric contractions: tension increase, no length change
• Isotonic contractions: tension increase, length change (muscle shortens or lengthens)

Muscle Tone

• Muscle tone is a constant tension maintained by muscles over time, which is important for posture, stability, etc

Types of Skeletal Muscle Fibers

• Slow-twitch fibers are fatigue-resistant, use aerobic respiration, are dark in color, and used for endurance activities
• Fast-twitch fibers tire quickly, use anaerobic respiration, are light in color, used for quick bursts of activity

Muscle Fatigue

• Fatigue is a temporary state of reduced work capacity
• Mechanisms include acidosis, ATP depletion, oxidative stress, and local inflammation

Muscle Soreness

• Muscle soreness often follows intense exercise, lasting several days
• It's a result of inflammatory chemicals affecting muscle fibers

Muscle Exercises

• Exercise regimens are important in tissue repair
• Oxygen deficit occurs when the body starts exercising and breathes heavily
• Excess postexercise oxygen consumption (EPOC): the time required for breathing to return to a pre-exercise rate

Muscle Names:

• Muscles are named based on location, size, shape, orientation, origin, insertion, and function.
• Examples of muscle names and functions are given.

Muscles of Mastication

• Muscles involved in chewing: temporalis, masseter, and pterygoids

Thoracic Muscles

• External intercostals elevate ribs, important for breathing
• Internal intercostals depress ribs, crucial during forced breathing
• Diaphragm moves during breathing

Abdominal Wall Muscles

• Rectus abdominis, external abdominal oblique, and internal abdominal oblique compress the abdomen
• Important in posture and movement

Pelvic Diaphragm Muscles

• Located in the pelvic floor

Upper Scapular Muscles and Limbs

• Trapezius, pectoralis major, serratus anterior, and deltoid are muscles involved in shoulder and upper back movements.

Upper Limb Muscles

• Triceps brachii, biceps brachii, brachialis, latissimus dorsi

Muscles of the Hips and Thighs

• Iliopsoas, gluteus maximus, gluteus medius, and muscles of the upper leg (rectus femoris, vastus lateralis, vastus medialis)

Muscles of the Lower Leg

• Tibialis anterior, gastrocnemius, and soleus are lower leg muscles essential for movement and stability.

Muscle Excitation

• Details on muscle excitation and how energy from ATP powers this process are provided.