Skeletal Muscle Anatomy & Physiology PDF

Musculoskeletal Module Second Skeletal Muscles Stage Structure, Morphology and Mechanism Assist. Lect. Rasha Hamza Behavioral goals By the end of this lecture the student is expected to be able to:  Define the skeletal muscle.  Illustrate the function of the skeletal mu...

Musculoskeletal Module Second Skeletal Muscles Stage Structure, Morphology and Mechanism Assist. Lect. Rasha Hamza Behavioral goals By the end of this lecture the student is expected to be able to:  Define the skeletal muscle.  Illustrate the function of the skeletal muscle.  Classify the skeletal muscle according to their shapes.  Apply different facts about skeletal muscles and link them with pathological conditions.  Distinguish the structure of skeletal muscle.  Outline the contraction mechanism of skeletal muscle.  Assemble energy sources and its consumption.  Discuss some muscle conditions (contracture, fatigue, and tone). Introduction Skeletal Muscles (SM) are  Attached to bones by tendons, produce all the movements of body parts in relation to each other.  voluntary, meaning you control how and when they work.  The majority of the muscles in the body are skeletal muscles.  Make up between 30 to 40% of the total body mass.  Each SM is consists of various integrated tissues. These tissues include the skeletal muscle fibers, blood vessels, nerve fibers, and connective tissue. Skeletal Muscle Shapes 1. Circular: circular in shape, are normally sphincter muscles that surround an opening e.g. the mouth surrounded by Orbicularis oris 2. Convergent: The origin (the attachment to a fixed bone) is wider than the point of insertion. e.g. is Pectoralis Major. 3. Parallel: have fibers that run parallel to each other e.g. Sartorius 4. Fusiform: spindle-shaped, with the muscle belly being wider than the origin and insertion like Biceps brachii Skeletal Muscle Shapes 5. Unipennate: their fibers arranged to insert in a diagonal direction onto the tendon, which allows great strength like Extensor digitorum longus 6. Bipennate: have two rows of muscle fibers, facing in opposite diagonal directions, with a central tendon, like a feather. i.g Rectus femoris 7. Multipennate: have multiple rows of diagonal fibers, with a central tendon that branches into two or more tendons like Deltoid Skeletal Muscle  Skeletal muscle structure Epimysium: connective tissue that is covering of skeletal muscle. Perimysium: it is another protective covering layer that are surrounded fascicles and allows nerve and blood vessels to make their way through the muscle. Endomysium: a third layer of connective tissue that insulate muscle fibers.  Skeletal muscle structure Fascicule: it is consist of a bundle of muscle fibers, which are located underneath epimysium. Sarcolemma: the membrane covering a muscle fibers. Sarcoplasm: the cytoplasm of skeletal muscles. Sarcomere: is the smallest unit of the skeletal muscle Skeletal muscle movement Muscles are arranged in groupings of muscles that produce and modulate movement. Prime Mover: muscle responsible for a particular movement in one direction Antagonist: muscle move in opposite direction Synergist: (i) assists prime mover (ii) stabilizes action of prime mover, (fixator) fixes non- moving joint when primer mover acting over two joints How Skeletal Muscles move? Sensory neuron: is a cell that detects stimuli from the external environment, converts it into a signal, and transmits it to the central nervous system. Motor neurons: are the nerve cell responsible for carrying signals away from the central nervous system towards muscles to cause movement. Neuromuscular junction: is a synaptic connection between the terminal end of a motor nerve and skeletal muscle fiber. It is the site for the transmission of action potential from nerve to the muscle. Skeletal Muscle Excitation: It triggered by:  Signaling from the nervous system at the neuromuscular junction.  ACh molecules diffuse across synaptic cleft  Ach bind to ACh receptors within the sarcolemma  Na+ ions enter the muscle fiber causing depolarizing the membrane.  Release of calcium ions (Ca++) from storage in the sarcoplasmic reticulum. Skeletal muscle Contraction (Cross Bridge) The Sliding Filament Model of Contraction When signaled by a motor neuron a skeletal muscle fiber contracts as the thin filaments (actin) are pulled and then slide past the thick filaments (myosin) within the fiber’s sarcomeres. Types of Skeletal Muscle Fibers Skeletal muscle fibers can be classified based on two criteria: 1.How fast do fibers contract relative to others. 2 How do fibers regenerate ATP Characteristic Type I Type IIA Type IIB Regenerate ATP Slow oxidative/much Fast oxidative/moderate Fast glycolytic/less ATP ATP ATP Metabolism Aerobic Aerobic Anaerobic Color Red /more Red / more mitochondria White / less Mitochondria mitochondria Fatigue resistance Highest High Low Example Erector spinae Gastrocnemius, quadriceps Relaxation of a Skeletal Muscle  motor neuron stops releasing its chemical signal, ACh, into the synapse at the NMJ.  The muscle fiber will repolarize  Closes the gates in the SR where Ca++ was being released.  Reshielding of the actin-binding sites on the thin filaments.  Loss the ability to form cross- bridges between the thin and thick filaments.  Muscle Tone - Skeletal muscles are seldom completely relaxed but maintain a slight, ongoing contraction even when not actively engaged in movement. - Muscle Tone, serves important physiological functions. It plays a critical role in stabilizing joints and sustaining posture, ensuring that our bodies remain upright and stable. Hypoton ea Hyperto nea Muscle Contracture: A state of continuous muscle contraction occurs when ATP is depleted and resulted in failure of detachment of the actin filaments from myosin heads. Writer''s cramps ? Rigor mortis?  Muscle fatigue Depletion of ATP or glycogen. Blood interruption. Reduce oxygen level. Impaired signaling from nerves to muscles. Intermittent Claudication  Summary  Skeletal muscle is usually attached to the skeleton.  Skeletal muscles have different functions according to their position in the human body.  Skeletal muscles have variable shapes.  The main component of skeletal muscle is muscle fiber.  The key factor of skeletal muscle contraction is Ca ion.  A chemical synapsis between a motor neuron and a muscle fiber called neuromuscular junction.  There are different sources of energy for skeletal muscles.  Physiological condition related to skeletal muscles like contracture, fatigue, and tone.