Skeletal Muscle Tissue

Ch. 10-2 notes

Connective Tissue Components

• Fascia (fash-ee-a) – a sheet or broad band of C. T. that supports and surrounds muscles and other organs of the body

• 2 types– Superficial and deep

• deep has 3 layers– Epimysium (most superficial)– Perimysium– Endomysium (most deep)

Anatomy of Muscle Fiber

• Epimysium – outermost

• Perimysium – surrounds bundles of muscle fibers

• Endomysium – separates muscle fibers from each other

Microscopic Anatomy of a Muscle Fiber

• Muscles form from the fusion of myoblasts• Once fusion occurs, the fiber can no longer

divide• Number of muscle fibers is set before birth• The size of the muscle fibers is what changes

over time

Components of a Muscle Fiber

• Sarcolemma – covering of muscle fiber that contains the nuclei

• Transverse (T) tubules – tunnel from surface toward center of fiber; carry action potential

• Sarcoplasm – cytoplasm of muscle fiber– Contains myoglobin (binds oxygen to diffuse into

muscle fibers)

Components

Components

• Myofibrils – contractile organelles of muscle fiber, little fibers stuffed into sarcoplasm– Contain filaments• Thin and thick

• Sarcoplasmic reticulum (SR) – fluid-filled system of sacs, surround each myofibril, stores Ca2+ for muscle contraction

Components

• Filaments – small structures within myofibrils– Thin– Thick

• 2 thins for every 1 thick• Arranged in sarcomeres• Sarcomeres are separated by Z discs

Components

• Thin and thick filaments overlap• Sarcomere can be divided into zones and bands• A band – darker middle part of sarcomere• Zone of overlap – where thick and thin filaments

overlap• I band – lighter, less dense area with thin filaments; Z

disc passes through• H zone – center of A bad with thick filaments• M line – proteins hold the thick filaments together at

the center of the H zone

Components

Muscle Proteins

• Myofibrils are built from 3 proteins– Contractile – generate force during contraction– Regulatory – help switch contraction process on

and off– Structural• Keep thick and thin filaments in proper alignment• Give myofibril elasticity and extensibility• Link myofibrils to sarcolemma

Muscle Proteins

• Contractile proteins– Myosin and actin

• Myosin– Form thick filaments– Functions as a motor protein – push or pull structures

to achieve movement– 300 myosin form a single thick filament

• Actin– Form thin filaments– Each actin has a myosin-binding site

Muscle Proteins

Muscle Proteins

• Regulatory proteins– Tropomyosin and troponin– Part of the thin filament

• tropomyosin– Covers the myosin-binding sites during the relaxed

state• Troponin– Hold tropomyosin in place